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Logging damage and the subsequent dynamics of a dipterocarp forest in East Kalimantan (1990–1996)
Forest Ecology and Management 165 (2002) 85–103
Logging damage and the subsequent dynamics of a dipterocarp forest in East Kalimantan (1990–1996) Plinio Sista,*, Nicolas Nguyen-The´b,1 a
Conveˆnio Cirad-Foreˆt-Embrapa, Embrapa Amazonia Oriental, Trav. Dr. Enaes Pinneiro, CEP 66.095-100, Bele´m Para, Brazil b AFOCEL, Domaine de St Cle´ment, 34980 St Cle´ment de Rivie`re, France Received 18 September 2000; received in revised form 16 March 2001; accepted 31 May 2001
Abstract The effects of logging damage on forest dynamics processes were assessed in a lowland dipterocarp forest of East Kalimantan, Indonesia. From 1990 to 1991, twelve 4 ha plots (200 m 200 m) each divided into four 1 ha subplots were set up and all trees with dbh 10 cm measured and identified at least at the generic level. Logging was carried out from November 1991 to March 1992 in nine plots while three plots served as control. The 48 subplots were grouped according to the proportion of remaining basal area after harvesting, as follows: group 1 with more than 80% of the original basal area remaining, group 2 with 70–79%, group 3 with less than 70%, and group 4 as control plots. Remeasurements were carried out just after logging in 1992 and then every 2 years until 1996. Felling intensity varied from 1 to 17 stems ha1 (50–250 m3 ha1). In primary forest, mean annual mortality remained constant to 1.5% per year throughout the study period while mean annual mortality rate was significantly higher in logged-over forest (2.6% per year). This higher rate resulted from a higher mortality of injured trees (4.9% per year). Four years after logging, mortality rates in logged-over and primary forest were similar. Recruitment remained constant at 8 trees ha1 per year in primary forest and varied from 14 to 32 trees ha1 per year in logged-over stand in proportion with the amount of damage. In stands with the lowest remaining basal area, the establishment and growth of dipterocarps was strongly limited by the strong regeneration of pioneer species. This study suggests that total basal area removed by logging in primary forest (harvested trees and trees killed during felling and skidding) should not exceed 15% of the original one; reduced-impact logging (RIL) techniques applied with a maximum harvesting intensity of 8 trees ha1, can keep logging damage under this threshold. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Lowland mixed dipterocarp forest; East Kalimantan; Reduced-impact logging (RIL); Logging impact; Growth and yield; Forest dynamics; Silviculture; Dipterocarps; TPTI
1. Introduction In the Indonesian selective logging system (TPTI), all commercial trees, mainly dipterocarps, over 50 or *
Corresponding author. Tel.: þ33-4-67-59-37-66; fax: þ33-4-67-59-37-33. E-mail addresses: [email protected] (P. Sist), [email protected] (N. Nguyen-The´). 1 Tel.: (5591) 299 4593; fax: (5591) 276 98 45.
60 cm dbh, the diameter limit 50 or 60 cm depending on the type of forest, can be removed with a felling cycle of 35 years. In Borneo where primary lowland forests exhibit a high density of harvestable trees (23 ha1 > 50 cm dbh and 16 ha1 > 60 cm dbh, Sist and Saridan, 1999), logging operations, especially if uncontrolled, substantially affects forest structure, dynamics processes and productivity (Nicholson, 1979; Uhl and Vieira, 1989; Bertault and Sist, 1997; Pinard and Putz, 1996; Johns et al., 1996).
0378-1127/02/$ – see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 8 - 1 1 2 7 ( 0 1 ) 0 0 6 4 9 - 1
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Several studies carried out in East Borneo commonly report that uncontrolled logging damage more than 50% of the original stand (Nicholson, 1958; Kartawinata, 1978; Pinard and Putz, 1996; Bertault and Sist, 1997). These heavy cuts will result in a seriously depleted residual stand that is unlikely to recover an acceptable harvesting volume within the 35 cycles cutting set up by the Indonesian regulations (Favrichon and Young Cheol, 1998; Sist et al., 1998). Furthermore, the large canopy openings created during intensive, uncontrolled logging are prone to heavy vine invasion and are very vulnerable to fire, as was dramatically demonstrated in Indonesia during recent El Nin˜ o-related dropouts (Laumonier and Legg, 1998). Finally, the low economic value of logged forests makes them prone to conversion into agriculture lands. Reducing logging damage to both forest and soil is likely to shorten felling cycles by ensuring better natural regeneration and growth of the desired commercial species (Putz, 1994; Dykstra and Heinrich, 1996). Although minimising the deleterious effect of logging is a principal requirement for achieving sustainable forest management, it is also important to predict the post-logging yields as related to harvesting intensities and damage (Kleine and Heuveldop, 1993; Ong and Kleine, 1995). Unfortunately, in southeast Asia and particularly in Indonesia, there are still very few studies based on reliable growth and yield data on how logging damage intensity affects forest dynamics (Manokaran and Kochumen, 1987; Ong and Kleine, 1995). In this paper, we analyse the impact of different logging damage intensities on the dynamics (growth, mortality and recruitment) of a tropical lowland mixed dipterocarp forest of Borneo during the first 4 years after logging (Bertault and Kadir, 1998). We expect these results to be useful in defining acceptable logging damage threshold that does not compromise the regeneration and yield capability of the residual stand.
2. Study site and methods 2.1. Study site The study area was located in the Indonesian province of East Kalimantan (Borneo Island), in the district of Berau, near Tanjung Redeb (28N,
1178150 W), within a 500,000 ha forest concession (Bertault and Kadir, 1998). The climate is equatorial with a mean annual rainfall of about 2000 mm. August is the driest month with a mean of 90 mm rainfall and January the wettest with 242 mm (data for Tanjung Redeb over the period 1984–1993). The bedrock is primarily alluvial deposits (mudstone, siltstone, sandstone and gravel) dating from the Miocene and Pliocene. Soils are mainly Ultisols (87%), with some Entisols (11%) and Inceptisols (2%). The topography is gently undulating to hilly in the north, changing to steep slopes with elevations reaching 500 m a.s.l. in the south. 2.2. Methods 2.2.1. Plot establishment and logging treatments A 5% inventory of the 1000 ha zone scheduled for logging provided the database for sample plot selection (Bertault and Kadir, 1998). In 1990–1991, twelve 4 ha plots (200 m 200 m), each plot divided into four 1 ha subplots, were established in areas with similar harvestable volume and slopes. All trees with dbh 10 cm were measured (girth at 1.30 m or 20 cm above buttresses), numbered and mapped on a scale of 1/200. The topography of the area being very variable, Sumaryono (1998) ordered the 12 plots into five main groups: (1) flat areas with slope generally less than 10% (two plots); (2) slopping terrain with slopes ranged 10–20% (three plots); (3) undulating to moderately steep terrain with slopes in some places exceeding 30–50% (three plots); (4) steep and dissected terrain with slopes often exceeding 50% (two plots); (5) very steep and hilly configurations with slopes usually exceeding 50% (two plots). Logging was carried out from November 1991 to May 1992, in the 1000 ha annual coupe area including the permanent sample plots. Four different treatments were defined, each treatment being replicated three times. Treatments included two reduced-impact logging (RIL) techniques (2 3 plots), a conventional logging (CL) method (three plots) and, finally, an unlogged control treatment including three plots (Bertault and Sist, 1997). In conventional logging, skidtrails were not planned in advance and workers worked unsupervised. The two RIL treatments, RIL1 and RIL2, differed from the minimum diameter cutting limit set up at 50 and 60, respectively. In both RIL treatments, skidtrails were planned in the plots before
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harvesting according to the position of trees and the topography. Although directional felling was part of the RIL recommendations, this could not be successfully applied due to the poor technical skill of the fellers on these techniques. In both CL and RIL logs were extracted using tractor Komatsu D60E and D65E. Logs were transported by logging trucks to the Segah River at about 40 km from the site, where they were transferred by raft or barge to the mills (for more details see Sist and Bertault (1998)). Owing to market conditions and the Indonesian silvicultural system at the time of this study, harvesting was limited to the following dipterocarp species Anisoptera spp., Dipterocarpus spp., Dryobalanops beccarii, Hopea spp., Parashorea spp. and Shorea spp. Two years after logging (1994), in the logged plots, all seriously damaged trees, such as those leaning or with broken boles were cut (dbh 20 cm) or poisoned (dbh 20 cm). The basal area removed was proportional to the amount of damage caused by logging in the stand. It resulted that in heavily damaged plots, we removed in mean 1 m2 ha1 against 0.5 m2 ha1 in low to moderately disturbed plots. In mean, for the 36 logged subplots, we removed 19 trees ha1 (S:D: ¼ 9:8) or 0.70 m2 ha1 (S:D: ¼ 0:42). This was not taken into account for the calculation of ‘‘natural mortality’’ after logging. In control plots, all trees were identified to species from 1990 to 1993. In the other nine plots, logged in 1991–1992, tree identification was limited to the genus level for dipterocarps and to the family level for the other taxa (Sist and Saridan, 1999). 2.2.2. Tree damage assessment In all logged plots, trees damaged or killed with dbh 10 cm were recorded at the end of felling and again at the end of skidding in order to distinguish the felling damage from those of skidding. Six main classes of injuries or cause of death were defined as follows: (1) bark and wood damage; (2) leaning; (3) crown injury; (4) broken trunk still alive; (5) broken trunk and dead; (6) uprooted. Resprouting of broken trees was assessed 3 months after logging and then at each successive census periods (1994 and 1996). 2.2.3. Plot monitoring The first measurements were made before logging in 1990–1991, the second 3 months after logging
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(1992), and then successively every 2 years (1994 and 1996) during the same period (May–August). The time elapsed between the first and second measurement varied from 0.95 to 1.67 years (345–608 days) according to the date of plot establishment. The mean time interval between the second and third measurements (1992–1994) and between the third and fourth one (1994–1996) were not significantly different (740 days, S:D: ¼ 7:8 and 732 days, S:D: ¼ 26:0, respectively, t ¼ 1:01, d:f: ¼ 13, P ¼ 0:05). Post-logging measurement periods can be therefore considered equal thus avoiding the influence of the length of census period on mortality rates assessment (Sheil and May, 1996). The second measurement occurred 3 months after logging and it is therefore likely that data recorded during the first census period in the logged plots were not totally representative of the growth tree pattern before logging (i.e. primary forest). To avoid any bias, the control plots are here taken as references for the growth in primary forest for the period 1990–1992. At each census period, girth of all live individuals 10 cm dbh was measured to the nearest millimetre with a fibreglass tape at a level permanently marked on each tree with a strip painted on the bole. Mean annual diameter increment (MADI) were calculated only for trees with a regular bole shape excluding those with fluted and latticed boles. At each enumeration, new trees with dbh 10 cm were also measured and mapped. Presumed cause of mortality of each dead tree was recorded as follows: (1) natural death, standing tree; (1) standing dead tree injured by logging; (2) tree harvested; (3) tree killed during logging; (4) tree fall gap, natural death; (5) tree killed by the fall of another tree; (6) tree removed during clearing operations after logging; (7) tree poisoned during clearing operation after logging. During the entire 1990–1996 census period, 28,657 trees were monitored and recorded in the data base. 2.2.4. Subplots grouping and data analysis There was a positive and significant correlation between the proportion of stems damaged and basal area removed (R2 ¼ 0:62, P ¼ 0:01, n ¼ 36, Bertault and Sist, 1997). This result suggested that felling intensity was an important feature in the damage caused by logging regardless to the technique (RIL or CL, Sist et al., 1998). Two years after logging, there was a positive correlation between post-logging
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mortality and the proportion of the original basal area remaining after logging (R2 ¼ 0:43, Nguyen-The´ et al., 1998). To assess the effect of logging damage intensity on forest dynamics processes, regardless to the logging techniques, we ordered the 48 subplots according to the percentage of the original basal area remaining after logging, as follows—group 1 (G1): low damage with remaining basal area 80% of the original (n ¼ 11 subplots); group 2 (G2): moderate damage with 70–79% remaining basal area (n ¼ 14 subplots); group 3 (G3): high damage with remaining basal area <70% (n ¼ 11 subplots); group 4 (G4): control plots (n ¼ 12 subplots). These groups were defined so they were centred on the average remaining basal area of all the plots (74%) and to obtain a fair distribution of the 48 subsquares. Rates of mortality between two measurements were calculated using the following formula: m12 ¼
1 m2 100 t12 N1
where m1–2 is the mortality rate in percentage of trees per year, t1–2 the time between measurements 1 and 2 in years, m2 the number of trees recorded during measurement 1 and dead at measurement 2 and N1 is the number of trees at measurement 1. Three main groups of species were also distinguished as follows: (1) dipterocarps excluding Vatica spp. which are all understory species in contrast with all the other species of dipterocarps; (2) pioneers, following definition given in Swaine and Whitmore (1988), the most common species being Anthocephalus chinensis (Lam.) Rich., Duabanga moluccana Bl., Macaranga gigantea (Reichb. f. & Zoll.) Muell. Arg., M. hypoleuca (Reichb. f. & Zoll.) Muell. Arg., M. triloba Muell. Arg., Octomeles sumatrana Miq.; (3) others. Comparison of mortality, recruitment and growth rates were based on one-way analysis of variance (ANOVA) and t-test mean comparison using GLM and t-test Cochran procedures of SAS software (SAS, 1990). For mortality rates, ANOVAs were performed on stand half-lives estimation on the basis of the logarithmic model (¼log(0.5)/mortality rate, Lieberman et al., 1985). For the period 1994–1996, an extreme value of mortality rate was recorded (8.5%) due to a landslide in subsquare 1 of plot 4 which was therefore excluded from the data analysis.
3. Results 3.1. Description of the forest before logging Before logging, mean (S.D., n ¼ 48 subplots) tree density (dbh 10 cm), basal area and standing volume in the 12 plots were, respectively, 530 71:6 stems ha1, 31.5 m2 ha1 4:2 and 402:0 61:0 m3 ha1. The dipterocarps represented about 25% of the total tree density (135 stems ha1 in mean), 50% of the total basal area (15.9 m2 ha1) and 60.2% of the stand volume (242.5 m3 ha1, Sist and Saridan, 1999). In primary forest, 70% of the trees with dbh 50 cm were dipterocarps thereby dominating the main and upper canopy. Before logging mean basal areas and densities of the four groups of plots (G1, G2, G3 and G4), were not significantly different (ANOVA, F ¼ 1:31, P ¼ 0:28 for basal area, and F ¼ 2:59, P ¼ 0:06 for density, d:f: ¼ 47). 3.2. Logging intensity and damage in the three groups of damage intensity In the nine harvested plots, logging intensity ranged from 1 to 17 trees ha1 (9–247 m3 ha1) and averaged 9 trees ha1 (86.9 m3 ha1, Bertault and Sist, 1997). On average, logging damage affected 44% of the initial tree population with similar proportion of injured and dead trees (20.8 and 23.2%, respectively). Mean density of harvested trees varied from 6 trees ha1 in G1 to 14 trees ha1 in G3 and were significantly different in the three groups (ANOVA, F ¼ 22:71, P < 0:001, Table 1). 3.3. Mortality In the control plots, the mean annual mortality rates during the 1990–1992 and 1994–1996 successive census periods varied from 1.30 to 1.65% per year (Table 2). These variations were not significant (Table 2) and the mean annual mortality of 1.5% per year yields a population half-life estimated on the 1990–1996 period of about 46 years (Table 2). For the post-logging period of 1992–1994, mean half-life times in the four groups of damage intensity, including control plots, were significantly different (ANOVA, F ¼ 9:01, d:f: ¼ 46, P < 0:001). This resulted from a higher mortality rate in G2 and G3
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Table 1 Stand characteristics before and after logging in the four groups of plots (S.D.)a
Total number of subplots Subplots with RIL Subplots with conventional (CL) Mean felling intensity (harvested trees ha1) Mean percentage of injured trees Mean percentage of trees killed Mean percentage of basal area remaining in 1992 Mean density before logging (1990) Mean basal area before logging (1990) Mean density of dipterocarps before logging (1990) Mean basal area of dipterocarps in 1990 (m2 ha1) Mean density after logging in 1992 (trees ha1) Mean basal area after logging in 1992 (m2 ha1) Mean density of dipterocarps in 1992 (trees ha1) Mean basal area of dipterocarps in 1992 (m2 ha1) Mean density of all trees in 1996 (trees ha1) Mean basal area of all trees in 1996 (m2 ha1) Mean density of dipterocarps in 1996 (trees ha1) Mean basal area of dipterocarps in 1996 (m2 ha1) a
Low damage (G1)
Medium damage (G2)
High damage (G3)
Control (G4)
11 7 4 5.7 15.3 14.8 86.2 557.7 32.8 139.4 15.5 486.4 28.3 117.9 12.4 498.0 28.7 120.6 12.5
14 10 4 8.3 21.5 22.0 75.4 540.2 31.8 113.1 14.8 429.4 23.9 85.8 9.3 445.1 24.2 90.1 9.4
11 7 4 13.9 25.4 33.0 58.6 481.9 29.5 104.5 15.7 331.0 17.3 63.6 6.4 401.7 18.7 72.3 6.6
11 – – – – – – 527.9 56.9 30.7 3.1 109.3 23.0 14.5 2.9 524.1 54.7 30.7 3.2 108.1 23.0 14.5 3.1 528.4 59.3 30.9 3.5 108.7 22.2 14.4 3.3
2.2 5.6 4.6 4.6 71.9 4.9 43.0 3.6 80.3 4.9 34.9 3.3 67.5 3.9 36.8 2.8
3.3 6.0 4.9 19.7 80.3 5.5 35.1 3.6 65.4 3.6 26.1 2.2 56.2 3.5 25.3 2.3
3.0 5.5 6.7 7.7 55.6 1.7 28.1 3.1 64.2 2.7 20.8 2.3 53.7 2.0 22.6 2.3
Year 1990: before logging; 1992: after logging; 1996: 4 years after logging.
(2.5 and 3.7% per year, respectively, Table 2) than in undisturbed stand (ANOVA, F ¼ 11:67, d:f: ¼ 35, P < 0:01). However, trees in the less damaged plots (G1) suffered mortality rates similar to those observed in the control plots (t ¼ 1:49, d:f: ¼ 14:8, P ¼ 0:17). The mean annual mortality rate of the all logged plots together was 2.6% per year, which represents a significant reduction in half-life relative to that of trees in the control plots (28 versus 53 years, t ¼ 2:8, d:f: ¼ 11:5, P < 0:001). For the period 1992–1994, mean mortality rate of injured trees was 4.9% per year while those of undamaged trees was only 1.8% per year (t ¼ 7:87, d:f: ¼ 35, P < 0:001) and similar to the mortality recorded in primary forest (ANOVA, F ¼ 0:81, d:f: ¼ 46, P ¼ 0:49). For the period 1994–1996, mean half-life times in the four groups were similar (ANOVA, F ¼ 1:16, d:f: ¼ 46, P ¼ 0:36); mean annual mortality rates varying from 1.5 to 1.9% per year (Table 2). Four years after logging, annual mortality rate in logged forest was therefore similar to that recorded in undisturbed stand (1.7 versus 1.5% per year, Table 2). This decrease of mortality in comparison to that recorded 2 years after logging was likely to be the result of the removal of the most badly damaged stems, eliminating
by this way the most vulnerable trees in terms of survival. Mortality rates of dipterocarps followed the same pattern as the whole stand (Table 2). During the 2 years following logging operations, mortality of dipterocarps was higher in G2 and G3 than in control plots (ANOVA, F ¼ 4:62, d:f: ¼ 34, P < 0:001) while in G1 this was similar to that recorded in primary forest (t ¼ 0:55, d:f: ¼ 18, P ¼ 0:58, Table 2). During 1994–1996 half-lives of dipterocarps in logged forest were not statistically different from those of undisturbed plots (Table 2, ANOVA, F ¼ 1:19, d:f: ¼ 40, P ¼ 0:35). Possible links between mortality and initial diameter were tested in each group, by comparing the observed distribution of dead trees according to dbh classes with a theoretical population obtained by applying the mean annual mortality rates of each group for each period (see Table 2) to the initial living trees in each dbh classes. For the period 1992–1994, in the most damaged plots (group 3), the distribution of dead trees according to dbh classes was different from the theoretical one (w2 ¼ 59:82, d:f: ¼ 4, P < 0:01). In this group, trees belonging to the 10–19 cm dbh class showed the highest mortality (>4%, Fig. 1a). For the other groups, and for both census periods,
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Table 2 Mean annual mortality rates S:D: according to the four groups of logging damage intensity and the census periods (1990–1996)a 1990–1992
1992–1994
Low damage (G1) Percentage of all trees per year (density) Percentage of all trees per year (basal area) Percentage of dipterocarps per year (density) Percentage of dipterocarps per year (basal area)
– – – –
1.6 2.0 1.4 1.8
0.6 1.3 2.5 1.8
1.6 1.4 1.6 1.2
0.7 0.9 0.9 1.2
Medium damage (G2) Percentage of all trees per year (density) Percentage of all trees per year (basal area) Percentage of dipterocarps per year (density) Percentage of dipterocarps per year (basal area)
– – – –
2.5 2.0 2.5 1.2
1.0 1.1 1.6 1.7
1.9 2.2 2.3 2.7
0.7 1.5 1.4 3.5
High damage (G3) Percentage of all trees per year (density) Percentage of all trees per year (basal area) Percentage of dipterocarps per year (density) Percentage of dipterocarps per year (basal area)
– – – –
3.7 2.9 4.6 3.0
2.4 2.1 3.6 2.3
1.7 1.4 1.4 1.2
0.6 0.7 1.2 1.3
Logged-over forest (G1 þ G2 þ G3) Percentage of all trees per year (density) Percentage of all trees per year (basal area) Percentage of dipterocarps per year (density) Percentage of dipterocarps per year (basal area)
– – – –
2.6 2.3 2.8 1.9
1.6 1.5 2.6 2.0
1.7 1.7 1.9 1.8
0.7 1.2 2.7 2.4
Undisturbed (G4)b Percentage of all trees per year (density) Percentage of all trees per year (basal area) Percentage of dipterocarps per year (density) Percentage of dipterocarps per year (basal area)
1.6 1.6 1.8 1.8
1.3 1.3 1.4 1.4
0.5 1.1 0.8 1.9
1.5 1.6 1.2 1.4
0.8 1.5 1.2 2.3
0.5 1.2 0.8 2.6
1994–1996
a
Low damage: remaining basal area 80% of the original basal area before logging; medium damage ¼ 70–79%; high damage ¼ <70%. Results of paired t-test for the comparison of mean annual mortality rates in control plots between the successive census periods: 1990– 1992 and 1992–1994, and 1992–1994 and 1994–1996 are, respectively, t ¼ 1:59, P ¼ 0:14 and t ¼ 0:60, P ¼ 0:55, d:f: ¼ 11. b
variations in the proportions of dead trees according to dbh were not significant (Fig. 1a and b). For the period 1994–1996, variations in the proportions of dead trees according to dbh classes, in the four groups were not significant (Fig. 1b). 3.4. Recruitment For the period 1992–1996, the total number of trees newly recorded with dbh 10 cm was significantly different in the four groups of plots (ANOVA, F ¼ 23:9, d:f: ¼ 46, P < 0:001). In primary forest, density of recruitment remained at a constant rate of about 8 trees ha1 per year while, in contrast, in logged stands it varied from 14 trees ha1 per year in group 1 to 33 trees ha1 per year in group 3 (Table 3). For the entire post-logging census period
(1992–1996), recruitment in the three groups of logged plots was significantly different as density of recruitment increased with amount of damage (ANOVA, F ¼ 17:70, d:f: ¼ 35, P < 0:001, Table 3). In groups 1 and 2 the density of recruitment between the successive periods remained almost constant, while in contrast, in group 3, it increased drastically from 43 to 87 trees during 1992–1994 and 1994–1996, respectively (Table 3). For the 1992–1996 period, the proportions of trees in the three categories of species (dipterocarps, pioneers and others) were different in the three groups of logged plots (w2 ¼ 340:8, d:f: ¼ 4, P < 0:01). However, there was no significant difference between G1 and G2 (w2 ¼ 0:73, d:f: ¼ 2, P ¼ 0:69). The density of pioneer trees recruited during both census periods was significantly higher in group 3 than in the other two
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Fig. 1. Mean annual mortality rates according to the dbh classes during the two successive post-logging periods ((a) 1992–1994; (b) 1994– 1996; (from left to right) G1, G2, G3 and G4). (a) Results of w2 tests in the four groups for the period 1992–1994—G1: w2 ¼ 0:84, d:f: ¼ 3, P ¼ 0:84; G2: w2 ¼ 0:58, d:f: ¼ 4, P ¼ 0:96; G3: w2 ¼ 59:82, d:f: ¼ 4, P < 0:001; G4: w2 ¼ 2:5, d:f: ¼ 3, P ¼ 0:46. (b) Results of w2 tests in the four groups for the period 1994–1996—G1: w2 ¼ 0:93, d:f: ¼ 3, P ¼ 0:81; G2: w2 ¼ 0:94, d:f: ¼ 4, P ¼ 0:91; G3: w2 ¼ 0:34, d:f: ¼ 4, P ¼ 0:95; G4: w2 ¼ 0:225, d:f: ¼ 3, P ¼ 0:97.
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Table 3 Mean densities of recruitment for the two successive post-logging census periods and mean proportions of each species category (pioneers, dipterocarps and others) for the entire period 1992–1996 in the four groups of plots Mean density S.D. (1992–1994)
Mean density S.D. (1994–1996)
Mean density S.D. (1992–1996)
Mean % S.D. (1992–1996)
Group 1 Pioneers Dipterocarps Others Total
1.3 5.5 18.3 25.1
2.2 3 7 8.8
3.1 6.9 20.4 30.4
3.5 5.4 7.6 8.7
4.4 12.4 38.6 55.4
5 5.9 11 14.5
8 8.2 22.2 9.4 69.8 7 –
Group 2 Pioneers Dipterocarps Others Total
0.9 7.8 21.6 30.4
1.4 3.5 6.9 9.9
5.6 8.6 27.9 42.1
6.1 3.2 7.5 12.4
6.6 16.4 49.6 72.6
6.8 5.2 10.1 17.6
7.8 7.3 22.8 5.6 69.4 9.4 –
Group 3 Pioneers Dipterocarps Others Total
8.5 7.5 27.1 43.2
13.8 5.1 9.5 17.9
38.5 11.7 37.4 87.6
31.6 8.7 11.6 43.4
47.1 19.3 64.4 130.8
37.3 11.8 18 51.3
30.7 20 14.2 6.6 55.1 21.9 –
Group 4 Pioneers Dipterocarps Others Total
0.2 2.9 13.6 16.7
0.4 2.6 6.9 7.9
0.3 3.4 13.4 17.1
0.5 1.6 7.6 8.9
groups of logged plots (ANOVA, F ¼ 3:55 and F ¼ 13:81, d:f: ¼ 35, respectively, for mean densities in 1994 and 1996). For the period 1994–1996, in G3, mean pioneer density increased from 8.5 trees ha1 in 1994 to 38.5 trees ha1 in 1996, whereas in G1 and G2 it remained at a low and constant level (1–6 stems ha1, Table 3). In G3, for the 1992–1996 period, pioneers represented in mean 30% of the recruitment as compared to about 8% in G1 and G2 and 1% in control plots (Table 3). Recruitment of dipterocarps between 1992 and 1996 was significantly different in the four groups (ANOVA, F ¼ 6:85, d:f: ¼ 46, P < 0:001). Density of recruited dipterocarps was higher in logged-over stand than in control plots (16 stems ha1, S:D: ¼ 8:2, n ¼ 36 in logged forest versus 6 stems ha1, S:D: ¼ 3:4, n ¼ 11, t ¼ 5:68, d:f: ¼ 40:4, P < 0:01, Table 3). Dipterocarp recruitment was similar in the three groups of logged plots (ANOVA, F ¼ 1:19, d:f: ¼ 35, P ¼ 0:31 and F ¼ 1:83, d:f: ¼ 35, P ¼ 0:17 for 1994 and 1996, respectively).
0.5 0.7 6.4 18 27 11.6 33.9 13.1
1.2 1.8 19.4 8.8 79.4 9.1 –
3.5. Growth In the control plots, during the 1990–1992 and 1992– 1994 measurement periods, mean annual diameter (MADI) of all the stand was almost constant varying from 0.22 to 0.23 cm per year only (Tables 4 and 5). For these same periods, MADI of dipterocarps only was also constant but higher than that of all trees considered together (0.34 cm per year). In 1994–1996, MADI of the entire stand decreased to 0.18 cm per year and that of dipterocarps to 0.29 cm per year (Table 4). These growth rates were significantly lower than those recorded during the previous two periods (Table 5). In the control plots, for the three census periods, growth rates recorded in the six dbh classes were significantly different (Table 7). The distribution of MADI according to dbh suggested that growth increased with dbh (Fig. 2a). The significant growth decrease recorded in 1994–1996 was noticeable in all the dbh classes but was more pronounced for trees with dbh 30 cm (Fig. 3a).
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Table 4 Mean annual diameter increment (cm per year) in the four groups of plots during the census periodsa Groups
1990–1992
1992–1994
1994–1996
Low damage (G1) All trees Dipterocarps
0.25 (0.63, 5103) 0.35 (0.36, 1243)
0.33 (0.31, 4776) 0.47 (0.35, 1170)
0.34 (0.31, 4583) 0.49 (0.37, 1122)
Medium damage (G2) All trees Dipterocarps
0.22 (0.48, 5734) 0.32 (0.32, 1158)
0.38 (0.34, 5138) 0.53 (0.41, 1029)
0.38 (0.39, 4894) 0.51 (0.37, 961)
High damage (G3) All trees Dipterocarps
0.26 (0.32, 3463) 0.36 (0.35, 665)
0.51 (0.42, 2840) 0.73 (0.52, 542)
0.50 (0.41, 2720) 0.68 (0.52, 514)
Logged-over forest (G1 þ G2 þ G3) All trees Dipterocarps
0.24 (0.51, 14300) 0.34 (0.34, 3066)
0.39 (0.36, 12754) 0.54 (0.42, 2741)
0.39 (0.38, 12197) 0.54 (0.41, 2597)
Control plots (G4) All trees Dipterocarps
0.23 (0.41, 5545) 0.34 (0.75, 1156)
0.22 (0.25, 5423) 0.34 (0.32, 1120)
0.18 (0.21, 5264) 0.29 (0.27, 1090)
a
Values in parenthesis are given as (S.D., n).
Table 5 Comparison of mean diameter increments in primary forest (control plots) and logged-over forest (G1, G2 and G3)a Groups Undisturbed forest all stand Undisturbed forest dipterocarpsb Logged-over forest all stand Logged-over forest dipterocarpsb
T1 (d.f.) 0.80 0.22 43.92 25.04
(5378) (1117) (12658) (2726)
P1
T2 (d.f.)
0.42 0.82 0.0001 0.0001
15.07 7.09 0.46 0.20
P2 (5239) (1086) (12075) (2575)
0.0001 0.0001 0.64 0.41
a
Paired t-test: T1 ¼ t-value for the comparison of mean increment recorded for the period 1990–1992 vs. 1992–1994; T2 ¼ comparison for the period 1992–1994 vs. 1994–1996; P1 and P2 respective probabilities associated to T-values. b Except Vatica spp.
For both post-logging census periods (1992–1994 and 1994–1996), mean annual diameter increments in logged-over forest remained much higher than in primary forest (0.39 cm per year for all trees and 0.54 cm per year for dipterocarps, Table 5). During both post-logging periods, mean annual diameter increments for all trees considered together and for just dipterocarps were lower in groups 1 and 2 than in group 3 (Tables 4 and 6). In all the three groups of logged plots, and for the two measurement periods, growth rate varied significantly with dbh classes, except in G3 for the 1992– 1994 period only (Table 7). In G1 and G2, for both post-logging periods, small trees (10–19 cm dbh) showed the lowest mean increments, whereas those with dbh 50 cm the highest (Fig. 2b and c). In G3,
growth increments varied with both periods and dbh classes (Fig. 2d). For the 1994–1996 period, growth gains decreased substantially in all dbh classes and in all the three groups of logged plots (Fig. 3b–d). Table 6 Comparison (ANOVA) of the mean annual diameter increments in the three groups of damage intensity for each post-logging census period (1992–1994 and 1994–1996)a Periods
Stand
F (d.f.)
1992–1994 1992–1994 1994–1996 1994–1996
All trees Dipterocarps All trees Dipterocarps
252.5 (12753) 74.38 (2740) 154.5 (12196) 41.68 (2596)
a All tests showing a significant difference between groups with P < 0:001.
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However, in G1, growth gains between 1992–1994 and 1994–1996 were still positive in all dbh classes while most of the trees in G2 and G3 had a slightly lower or constant growth in 1994–1996 (Fig. 3b–d). In G3, in contrast with the other two groups, trees with dbh 50 cm showed the highest growth gain (Fig. 3d).
3.6. Effect of logging on forest structure In 1992, just after logging, mean densities were reduced to 87, 79.6 and 68.2% of the original, respectively, in G1, G2 and G3 (Table 1). By 1996, the mean densities had recovered to 89, 83 and 84% of the
Fig. 2. Growth rates according to dbh classes in the four group of plots ((a) control plots; (b) G1; (c) G2; (d) G3) for the three census periods ((black bars) 1989–1992; (dashed bars) 1992–1994; (empty bars) 1994–1996).
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95
Fig. 2. (Continued ).
original in G1, G2 and G3, respectively (Table 1). Tree density in G3 recovered rapidly, but 4 years after logging, basal area had reached only 63.2% of the original (Table 1). Commercial species (i.e. dipterocarps excluding Vatica spp.) showed the same pattern with an even higher contrast between density and basal
area recovery rates, naturally linked to the impact of harvesting of the biggest trees (Table 1). Under high logging intensity, as in plots of group 3, 4 years after logging, the basal area and density of dipterocarps were, respectively, 40 and 70% of the initial one before logging (Table 1).
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Fig. 3. Gain of growth (%) in the four groups of plots according to the dbh classes ((a) control plots; (b) G1; (c) G2; (d) G3). Gain between 1989–1992 and 1992–1994 periods (grey bars); gain between 1992–1994 and 1994–1996 periods (dotted bars). Gains were calculated as follows: {(MADI19921994 MADI1990–1992)/MADI1990–1992g 100.
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Fig. 3. (Continued ).
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Table 7 Comparison of the mean annual diameter increment of the six dbh classes within each group and for each period of measurementa F1990–1992 (d.f.) Low damage (G1) Medium damage (G2) High damage (G3) Control (G4)
– – – 20.54a (5544)b
P-value – – – <0.001c
F1992–1994 (d.f.) a
11.92 15.28 0.58 47.34
b
(4775) (5132) (2839) (5422)
P-value c
<0.001 <0.001 0.71 <0.001
F1994–1996 (d.f.)
P-value
19.17 13.56 2.60 54.38
<0.001 <0.001 0.02 <0.001
(4577) (4893) (2714) (5263)
a
ANOVA on six dbh classes (10–19, 20–29, 30–39, 40–49, 50–59, 60 cm) for the three census periods. Degree of freedom. c Probability associated with value of F. b
For the period 1992–1994, in the control plots, there was a positive change in basal area (0.35 m2 ha1, Fig. 4a) and a decrease in the three groups of logged plots which varied from 0.23 m2 ha1 in G1 and G2 to 0.58 m2 ha1 in G3 (Fig. 4b–d). Although mortality varied substantially among the groups, from 0.81 m2 ha1 in control plots to 1.8 m2 ha1 in G1, these variations were not statistically different (ANOVA, F ¼ 0:52, d:f: ¼ 46, P ¼ 0:68). For the period 1994–1996, basal area in primary forest decreased by 0.16 m2 ha1 mainly due to a drastic reduction of growth (0.59 m2 ha1 in 1994– 1996 versus 1.05 m2 ha1 in 1992–1994, Fig. 4a). In contrast with the previous period, basal area of the logged stands increased (Fig. 4b–d). The highest increase was in G3 (1.9 m2 ha1, ANOVA, F ¼ 8:67, d:f: ¼ 35, P < 0:001) while those of G1 and G2 (0.63 and 0.48 m2 ha1, respectively) were similar (t ¼ 0:32, d:f: ¼ 18, P ¼ 0:75). The high basal area increment recorded in G3 was the result of the combination of two factors: a relative low mortality, a high increment from recruitment (1.1 m2 ha1) and from growth (1.35 m2 ha1, Fig. 4d). The low increase of the basal area in G2 was mainly the result of a high mortality (Fig. 4c) though mortality rates in terms of density were similar in the three groups, which suggests a strong influence of tree size.
4. Conclusions and discussion 4.1. Mortality In unlogged forest, over the 6-year period of this study, mean annual mortality was 1.5% per year
(population half-life time of about 46 years) without significant variation between the three successive measurements. These values are very similar to those reported in other mixed dipterocarp forest of Asia (Wyatt-Smith, 1966; Primack et al., 1985; Manokaran and Kochumen, 1987; Pe´ lissier et al., 1998) as well as in tropical forests of America and Africa (Philips and Gentry, 1994). There was no evidence that mortality differed between dbh classes. This result is in accordance with others studies in tropical forest (Lieberman et al., 1985; Swaine et al., 1987; Manokaran and Kochumen, 1987; Sheil and May, 1996) but in opposition to several others (Uhl et al., 1988; Durrieu de Madron, 1994; Pe´ lissier et al., 1998) which reported higher mortality rates of small trees. For 2 years following logging, tree mortality in logged-over forest was twice higher than in primary forest (2.6 versus 1.3% per year, respectively). The most severely damaged stands also showed the highest mortality. Four years after logging, mortality in undisturbed and logged-over forests was similar but this is in part due to the post-logging treatment which removed the most badly damaged trees and consequently reduced significantly the proportion of trees with the lowest probability of survival. Several studies in tropical forest also reported a maximum mortality rates in logged-over forest during the first 2 years following logging and becoming similar to the virgin forest approximately 5–10 years after harvesting (Wan Razali, 1989; Durrieu de Madron, 1994; Silva et al., 1995). The higher mortality in logged-over forest resulted from a higher mortality of injured trees, while, in contrast, undamaged stems had the same mortality rate as those in unlogged forest. This suggests that reduction of tree damage during a logging operation would also result in a reduction of
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Fig. 4. Net basal area increment (m2 ha1) during the period 1992–1994 and 1994–1996 in the four groups of plots ((a) control plots; (b) G1; (c) G2; (d) G3): growth (black bars); mortality (grey bars); recruitment (dashed bars); post-logging treatment (dotted bars).
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Fig. 4. (Continued ).
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post-logging mortality. Previous analyses 2 years after logging in the plots of the study area showed that leaning and snapped-off trees were the two main important causes of post-logging mortality (NguyenThe´ et al., 1998). These damages are mainly caused by felling operations (Bertault and Sist, 1997) and research on the development of felling techniques able to reduce this type of damages should be developed. Finegan and Camacho (1999) also found that mortality increased with decreasing crown illumination and quality of crown form. Other injuries such as bark and wood damage may favour the entry of pathogen agents which are likely to reduce tree survival rate or cause bole distortions that will make the timber commercially unsuitable (Nicholson, 1958). 4.2. Recruitment and growth Both the abundant recruitment of pioneer trees in severely damaged stands (G3) and the low proportion of dipterocarps in comparison with the other two groups, confirmed that large canopy openings resulting from high felling intensity (14 trees ha1 felled in G3) promoted the regeneration of pioneer species. In contrast, the establishment or growth of seedlings and saplings of dipterocarps might be limited or even impeded by both competition from pioneer species and the extreme new microclimate conditions, such as light intensity and drought (Nussbaum et al., 1995; Kuusipalo et al., 1996; Tuomela et al., 1996; Van Gardingen et al., 1998; Clearwater et al., 1999). In undisturbed forest, growth rates over the period 1990–1996, were constant with mean annual diameter increment for the whole stand of 0.22 cm per year. For the same period, dipterocarps showed a significant higher mean annual diameter increment of 0.34 cm per year. These values are consistent with other studies in mixed dipterocarp forest of southeast Asia (Nicholson, 1965b; Primack et al., 1985, 1989; Manokaran and Kochumen, 1987). During the last period of measurement 1994–1996, however, mean annual diameter increment decreased to 0.18 cm per year for the whole stand and to 0.29 cm per year for dipterocarps. This significant growth decrease was observed in all dbh classes and was probably correlated to an unusually long dry period from June to September 1994 associated with the El Nin˜ o southern oscillation (ENSO) climate phenomenon. Late in 1994, most of the
101
dipterocarps in the study area produced flowers followed in mid-1995 by a mast fruiting production (Nguyen-The´ and Sist, 1998). According to Primack et al. (1989), years of low growth can often be correlated with years of flowering and fruiting suggesting that trees mainly allocated resources for reproduction rather than growth. The other alternative, according to the same authors, is that flowering and slow growth are both consequences of a dry period stimulating flowering and inhibiting growth. In logged-over forest, we did not observe a decrease of growth as in primary forest. In the absence of any previous data in logged-over forest in long periods and under normal climatic conditions, it is not possible to conclude about any negative effect of this drought on tree growth in logged-over forest. Canopy opening from logging stimulated tree growth during the 4 years after logging. The highest growth rates were recorded in the most severely damaged stands (G3) while those observed in the low and moderately damaged forest were lower. In G1 and G2 small trees (dbh 20 cm) clearly grew slower than bigger ones whereas in G3 this pattern was not significant or less marked. This suggests that small trees need more light to reach the same growth rate of big trees. 4.3. Implication for management Drastic reductions of basal area by logging involve important changes in both dynamics processes and floristic composition of the forest. Although dipterocarps are climax species (sensu Swaine and Whitmore, 1988), growth of seedlings and saplings are acknowledged to be stimulated by canopy opening (Nicholson, 1960, 1965a; Meijer, 1970; Fox, 1973; Turner, 1990; Ashton, 1998). However, even the most light-demanding dipterocarp species reach a maximum growth rates under the moderate light intensity, occurring in rather small gaps. In contrast, pioneers require much bigger canopy openings to germinate and grow (Clearwater et al., 1999). Based on these observations, several authors recommended that gaps created by logging should be limited to 500–650 m2 to favour dipterocarp advance regeneration growth and to limit pioneer invasion (Kuusipalo et al., 1996; Tuomela et al., 1996; Van Gardingen et al., 1998). Because gap size resulting from logging is mainly
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determined by the density of felled trees and their spatial distribution, it will be therefore necessary to limit logging intensity to an acceptable threshold (Bertault and Sist, 1997; Van Gardingen et al., 1998; Sist et al., 1998). Colonisation of gaps by pioneer species will also certainly delay dipterocarp regeneration and growth and consequently the length of the rotation cycle period. Forest dynamic processes in the low damaged logged-over stand (G1) suggested that basal area reduction rate by logging, which includes harvested trees and those killed during felling and skidding, should not exceed 15%. Under these conditions, postlogging mortality was similar to that of unlogged forest; pioneer species regeneration was limited to 1– 6 trees ha1 per year; dipterocarps represented more than 20% of the recruitment and canopy opening resulting from logging stimulated dipterocarp growth during at least the first 4 years following logging. In group 1, mean felling was only 6 trees ha1 and therefore lower than the 8 trees ha1 harvested on average in the area. Under such felling intensity, only RIL techniques can keep basal area removal below 15% (Bertault and Sist, 1997; Sist et al., 1998).
Acknowledgements This study was carried out in the framework of STREK project (1989–1996) in East Kalimantan, a research and development cooperation between Cirad-Foreˆ t, The Ministry of Forestry of Indonesia and INHUTANI I. We wish to thank D. Dykstra, R. Fimbel, S. Gourlet-Fleury, F. Houllier, and T.C. Whitmore for reviewing an earlier version of the manuscript, as well as the two reviewers for their very valuable comments.
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1995. Growth and yield of a tropical rain forest in Brazilian Amazon 13 years after logging. For. Ecol. Manage. 71, 267– 274. Sist, P., Bertault, J.-G., 1998. Reduced impact logging experiments: impact of harvesting intensities and logging techniques on stand damage. In: Bertault, J.-G., Kadir, K. (Eds.), Silvicultural Research in a Lowland Mixed Dipterocarp Forest of East Kalimantan. The Contribution of STREK Project. Cirad-Foreˆ t, FORDA, INHUTANI I, pp. 139–161. Sist, P., Saridan, A., 1999. Stand structure and floristic composition of a primary lowland dipterocarp forest in East Kalimantan. J. Trop. For. Sci. 11, 704–722. Sist, P., Nolan, T., Bertault, J.-G., Dykstra, D., 1998. Harvesting intensity versus sustainability in Indonesia. For. Ecol. Manage. 108, 251–260. Sumaryono, M.S., 1998. Bearu pedology. In: Bertault, J.-G., Kadir, K. (Eds.), Silvicultural Research in a Lowland Mixed Dipterocarp Forest of East Kalimantan. The Contribution of STREK Project. Cirad-Foreˆ t, FORDA, INHUTANI I, pp. 111– 126. Swaine, M.D., Whitmore, T.C., 1988. On the definition of ecological species groups in tropical forests. Vegetatio 75, 81–86. Swaine, M.D., Hall, J.B., Alexander, I.J., 1987. Tree population dynamics at Kade, Ghana (1968–1982). J. Trop. Ecol. 3, 331– 345. Tuomela, K., Kuusipalo, J., Vesa, L., Nuryanto, K., Sagal, A.P.S., Adjers, G., 1996. Growth of dipterocarps seedlings in artificial gaps: an experiment in a logged-over rainforest in South Kalimantan, Indonesia. For. Ecol. Manage. 81, 95–100. Turner, I.M., 1990. The seedlings survivorship and growth of three Shorea species in a Malaysian tropical rain forest. J. Trop. Ecol. 6, 469–478. Uhl, C., Vieira, I.C.G., 1989. Ecological impact of selective logging in the Brazilian Amazon: a case study from the Paragominas region of the state of Para. Biotropica 21, 98–106. Uhl, C., Clark, K., Maquirino, P., 1988. Vegetation dynamics in Amazonian treefall gaps. Ecology 69, 751–763. Van Gardingen, P.R., Clearwater, M.J., Nifinluri, T., Effendi, R., Ruswantoro, P.A., Ingleby, K., Munro, R.C., 1998. Impacts of logging on the regeneration of lowland dipterocarps forest in Indonesia. Commonwealth For. Rev. 77, 71–82. Wan Razali, W.M., 1989. Modelling tree mortality in mixed tropical forests of peninsular Malaysia. In: Wan Razali, W.M., Chan, H.T., Appanah, S. (Eds.), Proceedings of the Seminar on Growth and Yield in Tropical Mixed/Moist Forests, Kuala Lumpur, FRIM, Malaysia, 20–24 June 1988, pp. 96–102. Wyatt-Smith, J., 1966. Ecological studies on Malayan forests. Malayan Forestry Department Research Pamphlet no. 52, 81 pp.
Logging damage and the subsequent dynamics of a dipterocarp forest in East Kalimantan (1990–1996) Plinio Sista,*, Nicolas Nguyen-The´b,1 a
Conveˆnio Cirad-Foreˆt-Embrapa, Embrapa Amazonia Oriental, Trav. Dr. Enaes Pinneiro, CEP 66.095-100, Bele´m Para, Brazil b AFOCEL, Domaine de St Cle´ment, 34980 St Cle´ment de Rivie`re, France Received 18 September 2000; received in revised form 16 March 2001; accepted 31 May 2001
Abstract The effects of logging damage on forest dynamics processes were assessed in a lowland dipterocarp forest of East Kalimantan, Indonesia. From 1990 to 1991, twelve 4 ha plots (200 m 200 m) each divided into four 1 ha subplots were set up and all trees with dbh 10 cm measured and identified at least at the generic level. Logging was carried out from November 1991 to March 1992 in nine plots while three plots served as control. The 48 subplots were grouped according to the proportion of remaining basal area after harvesting, as follows: group 1 with more than 80% of the original basal area remaining, group 2 with 70–79%, group 3 with less than 70%, and group 4 as control plots. Remeasurements were carried out just after logging in 1992 and then every 2 years until 1996. Felling intensity varied from 1 to 17 stems ha1 (50–250 m3 ha1). In primary forest, mean annual mortality remained constant to 1.5% per year throughout the study period while mean annual mortality rate was significantly higher in logged-over forest (2.6% per year). This higher rate resulted from a higher mortality of injured trees (4.9% per year). Four years after logging, mortality rates in logged-over and primary forest were similar. Recruitment remained constant at 8 trees ha1 per year in primary forest and varied from 14 to 32 trees ha1 per year in logged-over stand in proportion with the amount of damage. In stands with the lowest remaining basal area, the establishment and growth of dipterocarps was strongly limited by the strong regeneration of pioneer species. This study suggests that total basal area removed by logging in primary forest (harvested trees and trees killed during felling and skidding) should not exceed 15% of the original one; reduced-impact logging (RIL) techniques applied with a maximum harvesting intensity of 8 trees ha1, can keep logging damage under this threshold. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Lowland mixed dipterocarp forest; East Kalimantan; Reduced-impact logging (RIL); Logging impact; Growth and yield; Forest dynamics; Silviculture; Dipterocarps; TPTI
1. Introduction In the Indonesian selective logging system (TPTI), all commercial trees, mainly dipterocarps, over 50 or *
Corresponding author. Tel.: þ33-4-67-59-37-66; fax: þ33-4-67-59-37-33. E-mail addresses: [email protected] (P. Sist), [email protected] (N. Nguyen-The´). 1 Tel.: (5591) 299 4593; fax: (5591) 276 98 45.
60 cm dbh, the diameter limit 50 or 60 cm depending on the type of forest, can be removed with a felling cycle of 35 years. In Borneo where primary lowland forests exhibit a high density of harvestable trees (23 ha1 > 50 cm dbh and 16 ha1 > 60 cm dbh, Sist and Saridan, 1999), logging operations, especially if uncontrolled, substantially affects forest structure, dynamics processes and productivity (Nicholson, 1979; Uhl and Vieira, 1989; Bertault and Sist, 1997; Pinard and Putz, 1996; Johns et al., 1996).
0378-1127/02/$ – see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 8 - 1 1 2 7 ( 0 1 ) 0 0 6 4 9 - 1
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Several studies carried out in East Borneo commonly report that uncontrolled logging damage more than 50% of the original stand (Nicholson, 1958; Kartawinata, 1978; Pinard and Putz, 1996; Bertault and Sist, 1997). These heavy cuts will result in a seriously depleted residual stand that is unlikely to recover an acceptable harvesting volume within the 35 cycles cutting set up by the Indonesian regulations (Favrichon and Young Cheol, 1998; Sist et al., 1998). Furthermore, the large canopy openings created during intensive, uncontrolled logging are prone to heavy vine invasion and are very vulnerable to fire, as was dramatically demonstrated in Indonesia during recent El Nin˜ o-related dropouts (Laumonier and Legg, 1998). Finally, the low economic value of logged forests makes them prone to conversion into agriculture lands. Reducing logging damage to both forest and soil is likely to shorten felling cycles by ensuring better natural regeneration and growth of the desired commercial species (Putz, 1994; Dykstra and Heinrich, 1996). Although minimising the deleterious effect of logging is a principal requirement for achieving sustainable forest management, it is also important to predict the post-logging yields as related to harvesting intensities and damage (Kleine and Heuveldop, 1993; Ong and Kleine, 1995). Unfortunately, in southeast Asia and particularly in Indonesia, there are still very few studies based on reliable growth and yield data on how logging damage intensity affects forest dynamics (Manokaran and Kochumen, 1987; Ong and Kleine, 1995). In this paper, we analyse the impact of different logging damage intensities on the dynamics (growth, mortality and recruitment) of a tropical lowland mixed dipterocarp forest of Borneo during the first 4 years after logging (Bertault and Kadir, 1998). We expect these results to be useful in defining acceptable logging damage threshold that does not compromise the regeneration and yield capability of the residual stand.
2. Study site and methods 2.1. Study site The study area was located in the Indonesian province of East Kalimantan (Borneo Island), in the district of Berau, near Tanjung Redeb (28N,
1178150 W), within a 500,000 ha forest concession (Bertault and Kadir, 1998). The climate is equatorial with a mean annual rainfall of about 2000 mm. August is the driest month with a mean of 90 mm rainfall and January the wettest with 242 mm (data for Tanjung Redeb over the period 1984–1993). The bedrock is primarily alluvial deposits (mudstone, siltstone, sandstone and gravel) dating from the Miocene and Pliocene. Soils are mainly Ultisols (87%), with some Entisols (11%) and Inceptisols (2%). The topography is gently undulating to hilly in the north, changing to steep slopes with elevations reaching 500 m a.s.l. in the south. 2.2. Methods 2.2.1. Plot establishment and logging treatments A 5% inventory of the 1000 ha zone scheduled for logging provided the database for sample plot selection (Bertault and Kadir, 1998). In 1990–1991, twelve 4 ha plots (200 m 200 m), each plot divided into four 1 ha subplots, were established in areas with similar harvestable volume and slopes. All trees with dbh 10 cm were measured (girth at 1.30 m or 20 cm above buttresses), numbered and mapped on a scale of 1/200. The topography of the area being very variable, Sumaryono (1998) ordered the 12 plots into five main groups: (1) flat areas with slope generally less than 10% (two plots); (2) slopping terrain with slopes ranged 10–20% (three plots); (3) undulating to moderately steep terrain with slopes in some places exceeding 30–50% (three plots); (4) steep and dissected terrain with slopes often exceeding 50% (two plots); (5) very steep and hilly configurations with slopes usually exceeding 50% (two plots). Logging was carried out from November 1991 to May 1992, in the 1000 ha annual coupe area including the permanent sample plots. Four different treatments were defined, each treatment being replicated three times. Treatments included two reduced-impact logging (RIL) techniques (2 3 plots), a conventional logging (CL) method (three plots) and, finally, an unlogged control treatment including three plots (Bertault and Sist, 1997). In conventional logging, skidtrails were not planned in advance and workers worked unsupervised. The two RIL treatments, RIL1 and RIL2, differed from the minimum diameter cutting limit set up at 50 and 60, respectively. In both RIL treatments, skidtrails were planned in the plots before
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harvesting according to the position of trees and the topography. Although directional felling was part of the RIL recommendations, this could not be successfully applied due to the poor technical skill of the fellers on these techniques. In both CL and RIL logs were extracted using tractor Komatsu D60E and D65E. Logs were transported by logging trucks to the Segah River at about 40 km from the site, where they were transferred by raft or barge to the mills (for more details see Sist and Bertault (1998)). Owing to market conditions and the Indonesian silvicultural system at the time of this study, harvesting was limited to the following dipterocarp species Anisoptera spp., Dipterocarpus spp., Dryobalanops beccarii, Hopea spp., Parashorea spp. and Shorea spp. Two years after logging (1994), in the logged plots, all seriously damaged trees, such as those leaning or with broken boles were cut (dbh 20 cm) or poisoned (dbh 20 cm). The basal area removed was proportional to the amount of damage caused by logging in the stand. It resulted that in heavily damaged plots, we removed in mean 1 m2 ha1 against 0.5 m2 ha1 in low to moderately disturbed plots. In mean, for the 36 logged subplots, we removed 19 trees ha1 (S:D: ¼ 9:8) or 0.70 m2 ha1 (S:D: ¼ 0:42). This was not taken into account for the calculation of ‘‘natural mortality’’ after logging. In control plots, all trees were identified to species from 1990 to 1993. In the other nine plots, logged in 1991–1992, tree identification was limited to the genus level for dipterocarps and to the family level for the other taxa (Sist and Saridan, 1999). 2.2.2. Tree damage assessment In all logged plots, trees damaged or killed with dbh 10 cm were recorded at the end of felling and again at the end of skidding in order to distinguish the felling damage from those of skidding. Six main classes of injuries or cause of death were defined as follows: (1) bark and wood damage; (2) leaning; (3) crown injury; (4) broken trunk still alive; (5) broken trunk and dead; (6) uprooted. Resprouting of broken trees was assessed 3 months after logging and then at each successive census periods (1994 and 1996). 2.2.3. Plot monitoring The first measurements were made before logging in 1990–1991, the second 3 months after logging
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(1992), and then successively every 2 years (1994 and 1996) during the same period (May–August). The time elapsed between the first and second measurement varied from 0.95 to 1.67 years (345–608 days) according to the date of plot establishment. The mean time interval between the second and third measurements (1992–1994) and between the third and fourth one (1994–1996) were not significantly different (740 days, S:D: ¼ 7:8 and 732 days, S:D: ¼ 26:0, respectively, t ¼ 1:01, d:f: ¼ 13, P ¼ 0:05). Post-logging measurement periods can be therefore considered equal thus avoiding the influence of the length of census period on mortality rates assessment (Sheil and May, 1996). The second measurement occurred 3 months after logging and it is therefore likely that data recorded during the first census period in the logged plots were not totally representative of the growth tree pattern before logging (i.e. primary forest). To avoid any bias, the control plots are here taken as references for the growth in primary forest for the period 1990–1992. At each census period, girth of all live individuals 10 cm dbh was measured to the nearest millimetre with a fibreglass tape at a level permanently marked on each tree with a strip painted on the bole. Mean annual diameter increment (MADI) were calculated only for trees with a regular bole shape excluding those with fluted and latticed boles. At each enumeration, new trees with dbh 10 cm were also measured and mapped. Presumed cause of mortality of each dead tree was recorded as follows: (1) natural death, standing tree; (1) standing dead tree injured by logging; (2) tree harvested; (3) tree killed during logging; (4) tree fall gap, natural death; (5) tree killed by the fall of another tree; (6) tree removed during clearing operations after logging; (7) tree poisoned during clearing operation after logging. During the entire 1990–1996 census period, 28,657 trees were monitored and recorded in the data base. 2.2.4. Subplots grouping and data analysis There was a positive and significant correlation between the proportion of stems damaged and basal area removed (R2 ¼ 0:62, P ¼ 0:01, n ¼ 36, Bertault and Sist, 1997). This result suggested that felling intensity was an important feature in the damage caused by logging regardless to the technique (RIL or CL, Sist et al., 1998). Two years after logging, there was a positive correlation between post-logging
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mortality and the proportion of the original basal area remaining after logging (R2 ¼ 0:43, Nguyen-The´ et al., 1998). To assess the effect of logging damage intensity on forest dynamics processes, regardless to the logging techniques, we ordered the 48 subplots according to the percentage of the original basal area remaining after logging, as follows—group 1 (G1): low damage with remaining basal area 80% of the original (n ¼ 11 subplots); group 2 (G2): moderate damage with 70–79% remaining basal area (n ¼ 14 subplots); group 3 (G3): high damage with remaining basal area <70% (n ¼ 11 subplots); group 4 (G4): control plots (n ¼ 12 subplots). These groups were defined so they were centred on the average remaining basal area of all the plots (74%) and to obtain a fair distribution of the 48 subsquares. Rates of mortality between two measurements were calculated using the following formula: m12 ¼
1 m2 100 t12 N1
where m1–2 is the mortality rate in percentage of trees per year, t1–2 the time between measurements 1 and 2 in years, m2 the number of trees recorded during measurement 1 and dead at measurement 2 and N1 is the number of trees at measurement 1. Three main groups of species were also distinguished as follows: (1) dipterocarps excluding Vatica spp. which are all understory species in contrast with all the other species of dipterocarps; (2) pioneers, following definition given in Swaine and Whitmore (1988), the most common species being Anthocephalus chinensis (Lam.) Rich., Duabanga moluccana Bl., Macaranga gigantea (Reichb. f. & Zoll.) Muell. Arg., M. hypoleuca (Reichb. f. & Zoll.) Muell. Arg., M. triloba Muell. Arg., Octomeles sumatrana Miq.; (3) others. Comparison of mortality, recruitment and growth rates were based on one-way analysis of variance (ANOVA) and t-test mean comparison using GLM and t-test Cochran procedures of SAS software (SAS, 1990). For mortality rates, ANOVAs were performed on stand half-lives estimation on the basis of the logarithmic model (¼log(0.5)/mortality rate, Lieberman et al., 1985). For the period 1994–1996, an extreme value of mortality rate was recorded (8.5%) due to a landslide in subsquare 1 of plot 4 which was therefore excluded from the data analysis.
3. Results 3.1. Description of the forest before logging Before logging, mean (S.D., n ¼ 48 subplots) tree density (dbh 10 cm), basal area and standing volume in the 12 plots were, respectively, 530 71:6 stems ha1, 31.5 m2 ha1 4:2 and 402:0 61:0 m3 ha1. The dipterocarps represented about 25% of the total tree density (135 stems ha1 in mean), 50% of the total basal area (15.9 m2 ha1) and 60.2% of the stand volume (242.5 m3 ha1, Sist and Saridan, 1999). In primary forest, 70% of the trees with dbh 50 cm were dipterocarps thereby dominating the main and upper canopy. Before logging mean basal areas and densities of the four groups of plots (G1, G2, G3 and G4), were not significantly different (ANOVA, F ¼ 1:31, P ¼ 0:28 for basal area, and F ¼ 2:59, P ¼ 0:06 for density, d:f: ¼ 47). 3.2. Logging intensity and damage in the three groups of damage intensity In the nine harvested plots, logging intensity ranged from 1 to 17 trees ha1 (9–247 m3 ha1) and averaged 9 trees ha1 (86.9 m3 ha1, Bertault and Sist, 1997). On average, logging damage affected 44% of the initial tree population with similar proportion of injured and dead trees (20.8 and 23.2%, respectively). Mean density of harvested trees varied from 6 trees ha1 in G1 to 14 trees ha1 in G3 and were significantly different in the three groups (ANOVA, F ¼ 22:71, P < 0:001, Table 1). 3.3. Mortality In the control plots, the mean annual mortality rates during the 1990–1992 and 1994–1996 successive census periods varied from 1.30 to 1.65% per year (Table 2). These variations were not significant (Table 2) and the mean annual mortality of 1.5% per year yields a population half-life estimated on the 1990–1996 period of about 46 years (Table 2). For the post-logging period of 1992–1994, mean half-life times in the four groups of damage intensity, including control plots, were significantly different (ANOVA, F ¼ 9:01, d:f: ¼ 46, P < 0:001). This resulted from a higher mortality rate in G2 and G3
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Table 1 Stand characteristics before and after logging in the four groups of plots (S.D.)a
Total number of subplots Subplots with RIL Subplots with conventional (CL) Mean felling intensity (harvested trees ha1) Mean percentage of injured trees Mean percentage of trees killed Mean percentage of basal area remaining in 1992 Mean density before logging (1990) Mean basal area before logging (1990) Mean density of dipterocarps before logging (1990) Mean basal area of dipterocarps in 1990 (m2 ha1) Mean density after logging in 1992 (trees ha1) Mean basal area after logging in 1992 (m2 ha1) Mean density of dipterocarps in 1992 (trees ha1) Mean basal area of dipterocarps in 1992 (m2 ha1) Mean density of all trees in 1996 (trees ha1) Mean basal area of all trees in 1996 (m2 ha1) Mean density of dipterocarps in 1996 (trees ha1) Mean basal area of dipterocarps in 1996 (m2 ha1) a
Low damage (G1)
Medium damage (G2)
High damage (G3)
Control (G4)
11 7 4 5.7 15.3 14.8 86.2 557.7 32.8 139.4 15.5 486.4 28.3 117.9 12.4 498.0 28.7 120.6 12.5
14 10 4 8.3 21.5 22.0 75.4 540.2 31.8 113.1 14.8 429.4 23.9 85.8 9.3 445.1 24.2 90.1 9.4
11 7 4 13.9 25.4 33.0 58.6 481.9 29.5 104.5 15.7 331.0 17.3 63.6 6.4 401.7 18.7 72.3 6.6
11 – – – – – – 527.9 56.9 30.7 3.1 109.3 23.0 14.5 2.9 524.1 54.7 30.7 3.2 108.1 23.0 14.5 3.1 528.4 59.3 30.9 3.5 108.7 22.2 14.4 3.3
2.2 5.6 4.6 4.6 71.9 4.9 43.0 3.6 80.3 4.9 34.9 3.3 67.5 3.9 36.8 2.8
3.3 6.0 4.9 19.7 80.3 5.5 35.1 3.6 65.4 3.6 26.1 2.2 56.2 3.5 25.3 2.3
3.0 5.5 6.7 7.7 55.6 1.7 28.1 3.1 64.2 2.7 20.8 2.3 53.7 2.0 22.6 2.3
Year 1990: before logging; 1992: after logging; 1996: 4 years after logging.
(2.5 and 3.7% per year, respectively, Table 2) than in undisturbed stand (ANOVA, F ¼ 11:67, d:f: ¼ 35, P < 0:01). However, trees in the less damaged plots (G1) suffered mortality rates similar to those observed in the control plots (t ¼ 1:49, d:f: ¼ 14:8, P ¼ 0:17). The mean annual mortality rate of the all logged plots together was 2.6% per year, which represents a significant reduction in half-life relative to that of trees in the control plots (28 versus 53 years, t ¼ 2:8, d:f: ¼ 11:5, P < 0:001). For the period 1992–1994, mean mortality rate of injured trees was 4.9% per year while those of undamaged trees was only 1.8% per year (t ¼ 7:87, d:f: ¼ 35, P < 0:001) and similar to the mortality recorded in primary forest (ANOVA, F ¼ 0:81, d:f: ¼ 46, P ¼ 0:49). For the period 1994–1996, mean half-life times in the four groups were similar (ANOVA, F ¼ 1:16, d:f: ¼ 46, P ¼ 0:36); mean annual mortality rates varying from 1.5 to 1.9% per year (Table 2). Four years after logging, annual mortality rate in logged forest was therefore similar to that recorded in undisturbed stand (1.7 versus 1.5% per year, Table 2). This decrease of mortality in comparison to that recorded 2 years after logging was likely to be the result of the removal of the most badly damaged stems, eliminating
by this way the most vulnerable trees in terms of survival. Mortality rates of dipterocarps followed the same pattern as the whole stand (Table 2). During the 2 years following logging operations, mortality of dipterocarps was higher in G2 and G3 than in control plots (ANOVA, F ¼ 4:62, d:f: ¼ 34, P < 0:001) while in G1 this was similar to that recorded in primary forest (t ¼ 0:55, d:f: ¼ 18, P ¼ 0:58, Table 2). During 1994–1996 half-lives of dipterocarps in logged forest were not statistically different from those of undisturbed plots (Table 2, ANOVA, F ¼ 1:19, d:f: ¼ 40, P ¼ 0:35). Possible links between mortality and initial diameter were tested in each group, by comparing the observed distribution of dead trees according to dbh classes with a theoretical population obtained by applying the mean annual mortality rates of each group for each period (see Table 2) to the initial living trees in each dbh classes. For the period 1992–1994, in the most damaged plots (group 3), the distribution of dead trees according to dbh classes was different from the theoretical one (w2 ¼ 59:82, d:f: ¼ 4, P < 0:01). In this group, trees belonging to the 10–19 cm dbh class showed the highest mortality (>4%, Fig. 1a). For the other groups, and for both census periods,
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Table 2 Mean annual mortality rates S:D: according to the four groups of logging damage intensity and the census periods (1990–1996)a 1990–1992
1992–1994
Low damage (G1) Percentage of all trees per year (density) Percentage of all trees per year (basal area) Percentage of dipterocarps per year (density) Percentage of dipterocarps per year (basal area)
– – – –
1.6 2.0 1.4 1.8
0.6 1.3 2.5 1.8
1.6 1.4 1.6 1.2
0.7 0.9 0.9 1.2
Medium damage (G2) Percentage of all trees per year (density) Percentage of all trees per year (basal area) Percentage of dipterocarps per year (density) Percentage of dipterocarps per year (basal area)
– – – –
2.5 2.0 2.5 1.2
1.0 1.1 1.6 1.7
1.9 2.2 2.3 2.7
0.7 1.5 1.4 3.5
High damage (G3) Percentage of all trees per year (density) Percentage of all trees per year (basal area) Percentage of dipterocarps per year (density) Percentage of dipterocarps per year (basal area)
– – – –
3.7 2.9 4.6 3.0
2.4 2.1 3.6 2.3
1.7 1.4 1.4 1.2
0.6 0.7 1.2 1.3
Logged-over forest (G1 þ G2 þ G3) Percentage of all trees per year (density) Percentage of all trees per year (basal area) Percentage of dipterocarps per year (density) Percentage of dipterocarps per year (basal area)
– – – –
2.6 2.3 2.8 1.9
1.6 1.5 2.6 2.0
1.7 1.7 1.9 1.8
0.7 1.2 2.7 2.4
Undisturbed (G4)b Percentage of all trees per year (density) Percentage of all trees per year (basal area) Percentage of dipterocarps per year (density) Percentage of dipterocarps per year (basal area)
1.6 1.6 1.8 1.8
1.3 1.3 1.4 1.4
0.5 1.1 0.8 1.9
1.5 1.6 1.2 1.4
0.8 1.5 1.2 2.3
0.5 1.2 0.8 2.6
1994–1996
a
Low damage: remaining basal area 80% of the original basal area before logging; medium damage ¼ 70–79%; high damage ¼ <70%. Results of paired t-test for the comparison of mean annual mortality rates in control plots between the successive census periods: 1990– 1992 and 1992–1994, and 1992–1994 and 1994–1996 are, respectively, t ¼ 1:59, P ¼ 0:14 and t ¼ 0:60, P ¼ 0:55, d:f: ¼ 11. b
variations in the proportions of dead trees according to dbh were not significant (Fig. 1a and b). For the period 1994–1996, variations in the proportions of dead trees according to dbh classes, in the four groups were not significant (Fig. 1b). 3.4. Recruitment For the period 1992–1996, the total number of trees newly recorded with dbh 10 cm was significantly different in the four groups of plots (ANOVA, F ¼ 23:9, d:f: ¼ 46, P < 0:001). In primary forest, density of recruitment remained at a constant rate of about 8 trees ha1 per year while, in contrast, in logged stands it varied from 14 trees ha1 per year in group 1 to 33 trees ha1 per year in group 3 (Table 3). For the entire post-logging census period
(1992–1996), recruitment in the three groups of logged plots was significantly different as density of recruitment increased with amount of damage (ANOVA, F ¼ 17:70, d:f: ¼ 35, P < 0:001, Table 3). In groups 1 and 2 the density of recruitment between the successive periods remained almost constant, while in contrast, in group 3, it increased drastically from 43 to 87 trees during 1992–1994 and 1994–1996, respectively (Table 3). For the 1992–1996 period, the proportions of trees in the three categories of species (dipterocarps, pioneers and others) were different in the three groups of logged plots (w2 ¼ 340:8, d:f: ¼ 4, P < 0:01). However, there was no significant difference between G1 and G2 (w2 ¼ 0:73, d:f: ¼ 2, P ¼ 0:69). The density of pioneer trees recruited during both census periods was significantly higher in group 3 than in the other two
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Fig. 1. Mean annual mortality rates according to the dbh classes during the two successive post-logging periods ((a) 1992–1994; (b) 1994– 1996; (from left to right) G1, G2, G3 and G4). (a) Results of w2 tests in the four groups for the period 1992–1994—G1: w2 ¼ 0:84, d:f: ¼ 3, P ¼ 0:84; G2: w2 ¼ 0:58, d:f: ¼ 4, P ¼ 0:96; G3: w2 ¼ 59:82, d:f: ¼ 4, P < 0:001; G4: w2 ¼ 2:5, d:f: ¼ 3, P ¼ 0:46. (b) Results of w2 tests in the four groups for the period 1994–1996—G1: w2 ¼ 0:93, d:f: ¼ 3, P ¼ 0:81; G2: w2 ¼ 0:94, d:f: ¼ 4, P ¼ 0:91; G3: w2 ¼ 0:34, d:f: ¼ 4, P ¼ 0:95; G4: w2 ¼ 0:225, d:f: ¼ 3, P ¼ 0:97.
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Table 3 Mean densities of recruitment for the two successive post-logging census periods and mean proportions of each species category (pioneers, dipterocarps and others) for the entire period 1992–1996 in the four groups of plots Mean density S.D. (1992–1994)
Mean density S.D. (1994–1996)
Mean density S.D. (1992–1996)
Mean % S.D. (1992–1996)
Group 1 Pioneers Dipterocarps Others Total
1.3 5.5 18.3 25.1
2.2 3 7 8.8
3.1 6.9 20.4 30.4
3.5 5.4 7.6 8.7
4.4 12.4 38.6 55.4
5 5.9 11 14.5
8 8.2 22.2 9.4 69.8 7 –
Group 2 Pioneers Dipterocarps Others Total
0.9 7.8 21.6 30.4
1.4 3.5 6.9 9.9
5.6 8.6 27.9 42.1
6.1 3.2 7.5 12.4
6.6 16.4 49.6 72.6
6.8 5.2 10.1 17.6
7.8 7.3 22.8 5.6 69.4 9.4 –
Group 3 Pioneers Dipterocarps Others Total
8.5 7.5 27.1 43.2
13.8 5.1 9.5 17.9
38.5 11.7 37.4 87.6
31.6 8.7 11.6 43.4
47.1 19.3 64.4 130.8
37.3 11.8 18 51.3
30.7 20 14.2 6.6 55.1 21.9 –
Group 4 Pioneers Dipterocarps Others Total
0.2 2.9 13.6 16.7
0.4 2.6 6.9 7.9
0.3 3.4 13.4 17.1
0.5 1.6 7.6 8.9
groups of logged plots (ANOVA, F ¼ 3:55 and F ¼ 13:81, d:f: ¼ 35, respectively, for mean densities in 1994 and 1996). For the period 1994–1996, in G3, mean pioneer density increased from 8.5 trees ha1 in 1994 to 38.5 trees ha1 in 1996, whereas in G1 and G2 it remained at a low and constant level (1–6 stems ha1, Table 3). In G3, for the 1992–1996 period, pioneers represented in mean 30% of the recruitment as compared to about 8% in G1 and G2 and 1% in control plots (Table 3). Recruitment of dipterocarps between 1992 and 1996 was significantly different in the four groups (ANOVA, F ¼ 6:85, d:f: ¼ 46, P < 0:001). Density of recruited dipterocarps was higher in logged-over stand than in control plots (16 stems ha1, S:D: ¼ 8:2, n ¼ 36 in logged forest versus 6 stems ha1, S:D: ¼ 3:4, n ¼ 11, t ¼ 5:68, d:f: ¼ 40:4, P < 0:01, Table 3). Dipterocarp recruitment was similar in the three groups of logged plots (ANOVA, F ¼ 1:19, d:f: ¼ 35, P ¼ 0:31 and F ¼ 1:83, d:f: ¼ 35, P ¼ 0:17 for 1994 and 1996, respectively).
0.5 0.7 6.4 18 27 11.6 33.9 13.1
1.2 1.8 19.4 8.8 79.4 9.1 –
3.5. Growth In the control plots, during the 1990–1992 and 1992– 1994 measurement periods, mean annual diameter (MADI) of all the stand was almost constant varying from 0.22 to 0.23 cm per year only (Tables 4 and 5). For these same periods, MADI of dipterocarps only was also constant but higher than that of all trees considered together (0.34 cm per year). In 1994–1996, MADI of the entire stand decreased to 0.18 cm per year and that of dipterocarps to 0.29 cm per year (Table 4). These growth rates were significantly lower than those recorded during the previous two periods (Table 5). In the control plots, for the three census periods, growth rates recorded in the six dbh classes were significantly different (Table 7). The distribution of MADI according to dbh suggested that growth increased with dbh (Fig. 2a). The significant growth decrease recorded in 1994–1996 was noticeable in all the dbh classes but was more pronounced for trees with dbh 30 cm (Fig. 3a).
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Table 4 Mean annual diameter increment (cm per year) in the four groups of plots during the census periodsa Groups
1990–1992
1992–1994
1994–1996
Low damage (G1) All trees Dipterocarps
0.25 (0.63, 5103) 0.35 (0.36, 1243)
0.33 (0.31, 4776) 0.47 (0.35, 1170)
0.34 (0.31, 4583) 0.49 (0.37, 1122)
Medium damage (G2) All trees Dipterocarps
0.22 (0.48, 5734) 0.32 (0.32, 1158)
0.38 (0.34, 5138) 0.53 (0.41, 1029)
0.38 (0.39, 4894) 0.51 (0.37, 961)
High damage (G3) All trees Dipterocarps
0.26 (0.32, 3463) 0.36 (0.35, 665)
0.51 (0.42, 2840) 0.73 (0.52, 542)
0.50 (0.41, 2720) 0.68 (0.52, 514)
Logged-over forest (G1 þ G2 þ G3) All trees Dipterocarps
0.24 (0.51, 14300) 0.34 (0.34, 3066)
0.39 (0.36, 12754) 0.54 (0.42, 2741)
0.39 (0.38, 12197) 0.54 (0.41, 2597)
Control plots (G4) All trees Dipterocarps
0.23 (0.41, 5545) 0.34 (0.75, 1156)
0.22 (0.25, 5423) 0.34 (0.32, 1120)
0.18 (0.21, 5264) 0.29 (0.27, 1090)
a
Values in parenthesis are given as (S.D., n).
Table 5 Comparison of mean diameter increments in primary forest (control plots) and logged-over forest (G1, G2 and G3)a Groups Undisturbed forest all stand Undisturbed forest dipterocarpsb Logged-over forest all stand Logged-over forest dipterocarpsb
T1 (d.f.) 0.80 0.22 43.92 25.04
(5378) (1117) (12658) (2726)
P1
T2 (d.f.)
0.42 0.82 0.0001 0.0001
15.07 7.09 0.46 0.20
P2 (5239) (1086) (12075) (2575)
0.0001 0.0001 0.64 0.41
a
Paired t-test: T1 ¼ t-value for the comparison of mean increment recorded for the period 1990–1992 vs. 1992–1994; T2 ¼ comparison for the period 1992–1994 vs. 1994–1996; P1 and P2 respective probabilities associated to T-values. b Except Vatica spp.
For both post-logging census periods (1992–1994 and 1994–1996), mean annual diameter increments in logged-over forest remained much higher than in primary forest (0.39 cm per year for all trees and 0.54 cm per year for dipterocarps, Table 5). During both post-logging periods, mean annual diameter increments for all trees considered together and for just dipterocarps were lower in groups 1 and 2 than in group 3 (Tables 4 and 6). In all the three groups of logged plots, and for the two measurement periods, growth rate varied significantly with dbh classes, except in G3 for the 1992– 1994 period only (Table 7). In G1 and G2, for both post-logging periods, small trees (10–19 cm dbh) showed the lowest mean increments, whereas those with dbh 50 cm the highest (Fig. 2b and c). In G3,
growth increments varied with both periods and dbh classes (Fig. 2d). For the 1994–1996 period, growth gains decreased substantially in all dbh classes and in all the three groups of logged plots (Fig. 3b–d). Table 6 Comparison (ANOVA) of the mean annual diameter increments in the three groups of damage intensity for each post-logging census period (1992–1994 and 1994–1996)a Periods
Stand
F (d.f.)
1992–1994 1992–1994 1994–1996 1994–1996
All trees Dipterocarps All trees Dipterocarps
252.5 (12753) 74.38 (2740) 154.5 (12196) 41.68 (2596)
a All tests showing a significant difference between groups with P < 0:001.
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However, in G1, growth gains between 1992–1994 and 1994–1996 were still positive in all dbh classes while most of the trees in G2 and G3 had a slightly lower or constant growth in 1994–1996 (Fig. 3b–d). In G3, in contrast with the other two groups, trees with dbh 50 cm showed the highest growth gain (Fig. 3d).
3.6. Effect of logging on forest structure In 1992, just after logging, mean densities were reduced to 87, 79.6 and 68.2% of the original, respectively, in G1, G2 and G3 (Table 1). By 1996, the mean densities had recovered to 89, 83 and 84% of the
Fig. 2. Growth rates according to dbh classes in the four group of plots ((a) control plots; (b) G1; (c) G2; (d) G3) for the three census periods ((black bars) 1989–1992; (dashed bars) 1992–1994; (empty bars) 1994–1996).
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95
Fig. 2. (Continued ).
original in G1, G2 and G3, respectively (Table 1). Tree density in G3 recovered rapidly, but 4 years after logging, basal area had reached only 63.2% of the original (Table 1). Commercial species (i.e. dipterocarps excluding Vatica spp.) showed the same pattern with an even higher contrast between density and basal
area recovery rates, naturally linked to the impact of harvesting of the biggest trees (Table 1). Under high logging intensity, as in plots of group 3, 4 years after logging, the basal area and density of dipterocarps were, respectively, 40 and 70% of the initial one before logging (Table 1).
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Fig. 3. Gain of growth (%) in the four groups of plots according to the dbh classes ((a) control plots; (b) G1; (c) G2; (d) G3). Gain between 1989–1992 and 1992–1994 periods (grey bars); gain between 1992–1994 and 1994–1996 periods (dotted bars). Gains were calculated as follows: {(MADI19921994 MADI1990–1992)/MADI1990–1992g 100.
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Fig. 3. (Continued ).
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Table 7 Comparison of the mean annual diameter increment of the six dbh classes within each group and for each period of measurementa F1990–1992 (d.f.) Low damage (G1) Medium damage (G2) High damage (G3) Control (G4)
– – – 20.54a (5544)b
P-value – – – <0.001c
F1992–1994 (d.f.) a
11.92 15.28 0.58 47.34
b
(4775) (5132) (2839) (5422)
P-value c
<0.001 <0.001 0.71 <0.001
F1994–1996 (d.f.)
P-value
19.17 13.56 2.60 54.38
<0.001 <0.001 0.02 <0.001
(4577) (4893) (2714) (5263)
a
ANOVA on six dbh classes (10–19, 20–29, 30–39, 40–49, 50–59, 60 cm) for the three census periods. Degree of freedom. c Probability associated with value of F. b
For the period 1992–1994, in the control plots, there was a positive change in basal area (0.35 m2 ha1, Fig. 4a) and a decrease in the three groups of logged plots which varied from 0.23 m2 ha1 in G1 and G2 to 0.58 m2 ha1 in G3 (Fig. 4b–d). Although mortality varied substantially among the groups, from 0.81 m2 ha1 in control plots to 1.8 m2 ha1 in G1, these variations were not statistically different (ANOVA, F ¼ 0:52, d:f: ¼ 46, P ¼ 0:68). For the period 1994–1996, basal area in primary forest decreased by 0.16 m2 ha1 mainly due to a drastic reduction of growth (0.59 m2 ha1 in 1994– 1996 versus 1.05 m2 ha1 in 1992–1994, Fig. 4a). In contrast with the previous period, basal area of the logged stands increased (Fig. 4b–d). The highest increase was in G3 (1.9 m2 ha1, ANOVA, F ¼ 8:67, d:f: ¼ 35, P < 0:001) while those of G1 and G2 (0.63 and 0.48 m2 ha1, respectively) were similar (t ¼ 0:32, d:f: ¼ 18, P ¼ 0:75). The high basal area increment recorded in G3 was the result of the combination of two factors: a relative low mortality, a high increment from recruitment (1.1 m2 ha1) and from growth (1.35 m2 ha1, Fig. 4d). The low increase of the basal area in G2 was mainly the result of a high mortality (Fig. 4c) though mortality rates in terms of density were similar in the three groups, which suggests a strong influence of tree size.
4. Conclusions and discussion 4.1. Mortality In unlogged forest, over the 6-year period of this study, mean annual mortality was 1.5% per year
(population half-life time of about 46 years) without significant variation between the three successive measurements. These values are very similar to those reported in other mixed dipterocarp forest of Asia (Wyatt-Smith, 1966; Primack et al., 1985; Manokaran and Kochumen, 1987; Pe´ lissier et al., 1998) as well as in tropical forests of America and Africa (Philips and Gentry, 1994). There was no evidence that mortality differed between dbh classes. This result is in accordance with others studies in tropical forest (Lieberman et al., 1985; Swaine et al., 1987; Manokaran and Kochumen, 1987; Sheil and May, 1996) but in opposition to several others (Uhl et al., 1988; Durrieu de Madron, 1994; Pe´ lissier et al., 1998) which reported higher mortality rates of small trees. For 2 years following logging, tree mortality in logged-over forest was twice higher than in primary forest (2.6 versus 1.3% per year, respectively). The most severely damaged stands also showed the highest mortality. Four years after logging, mortality in undisturbed and logged-over forests was similar but this is in part due to the post-logging treatment which removed the most badly damaged trees and consequently reduced significantly the proportion of trees with the lowest probability of survival. Several studies in tropical forest also reported a maximum mortality rates in logged-over forest during the first 2 years following logging and becoming similar to the virgin forest approximately 5–10 years after harvesting (Wan Razali, 1989; Durrieu de Madron, 1994; Silva et al., 1995). The higher mortality in logged-over forest resulted from a higher mortality of injured trees, while, in contrast, undamaged stems had the same mortality rate as those in unlogged forest. This suggests that reduction of tree damage during a logging operation would also result in a reduction of
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Fig. 4. Net basal area increment (m2 ha1) during the period 1992–1994 and 1994–1996 in the four groups of plots ((a) control plots; (b) G1; (c) G2; (d) G3): growth (black bars); mortality (grey bars); recruitment (dashed bars); post-logging treatment (dotted bars).
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Fig. 4. (Continued ).
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post-logging mortality. Previous analyses 2 years after logging in the plots of the study area showed that leaning and snapped-off trees were the two main important causes of post-logging mortality (NguyenThe´ et al., 1998). These damages are mainly caused by felling operations (Bertault and Sist, 1997) and research on the development of felling techniques able to reduce this type of damages should be developed. Finegan and Camacho (1999) also found that mortality increased with decreasing crown illumination and quality of crown form. Other injuries such as bark and wood damage may favour the entry of pathogen agents which are likely to reduce tree survival rate or cause bole distortions that will make the timber commercially unsuitable (Nicholson, 1958). 4.2. Recruitment and growth Both the abundant recruitment of pioneer trees in severely damaged stands (G3) and the low proportion of dipterocarps in comparison with the other two groups, confirmed that large canopy openings resulting from high felling intensity (14 trees ha1 felled in G3) promoted the regeneration of pioneer species. In contrast, the establishment or growth of seedlings and saplings of dipterocarps might be limited or even impeded by both competition from pioneer species and the extreme new microclimate conditions, such as light intensity and drought (Nussbaum et al., 1995; Kuusipalo et al., 1996; Tuomela et al., 1996; Van Gardingen et al., 1998; Clearwater et al., 1999). In undisturbed forest, growth rates over the period 1990–1996, were constant with mean annual diameter increment for the whole stand of 0.22 cm per year. For the same period, dipterocarps showed a significant higher mean annual diameter increment of 0.34 cm per year. These values are consistent with other studies in mixed dipterocarp forest of southeast Asia (Nicholson, 1965b; Primack et al., 1985, 1989; Manokaran and Kochumen, 1987). During the last period of measurement 1994–1996, however, mean annual diameter increment decreased to 0.18 cm per year for the whole stand and to 0.29 cm per year for dipterocarps. This significant growth decrease was observed in all dbh classes and was probably correlated to an unusually long dry period from June to September 1994 associated with the El Nin˜ o southern oscillation (ENSO) climate phenomenon. Late in 1994, most of the
101
dipterocarps in the study area produced flowers followed in mid-1995 by a mast fruiting production (Nguyen-The´ and Sist, 1998). According to Primack et al. (1989), years of low growth can often be correlated with years of flowering and fruiting suggesting that trees mainly allocated resources for reproduction rather than growth. The other alternative, according to the same authors, is that flowering and slow growth are both consequences of a dry period stimulating flowering and inhibiting growth. In logged-over forest, we did not observe a decrease of growth as in primary forest. In the absence of any previous data in logged-over forest in long periods and under normal climatic conditions, it is not possible to conclude about any negative effect of this drought on tree growth in logged-over forest. Canopy opening from logging stimulated tree growth during the 4 years after logging. The highest growth rates were recorded in the most severely damaged stands (G3) while those observed in the low and moderately damaged forest were lower. In G1 and G2 small trees (dbh 20 cm) clearly grew slower than bigger ones whereas in G3 this pattern was not significant or less marked. This suggests that small trees need more light to reach the same growth rate of big trees. 4.3. Implication for management Drastic reductions of basal area by logging involve important changes in both dynamics processes and floristic composition of the forest. Although dipterocarps are climax species (sensu Swaine and Whitmore, 1988), growth of seedlings and saplings are acknowledged to be stimulated by canopy opening (Nicholson, 1960, 1965a; Meijer, 1970; Fox, 1973; Turner, 1990; Ashton, 1998). However, even the most light-demanding dipterocarp species reach a maximum growth rates under the moderate light intensity, occurring in rather small gaps. In contrast, pioneers require much bigger canopy openings to germinate and grow (Clearwater et al., 1999). Based on these observations, several authors recommended that gaps created by logging should be limited to 500–650 m2 to favour dipterocarp advance regeneration growth and to limit pioneer invasion (Kuusipalo et al., 1996; Tuomela et al., 1996; Van Gardingen et al., 1998). Because gap size resulting from logging is mainly
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determined by the density of felled trees and their spatial distribution, it will be therefore necessary to limit logging intensity to an acceptable threshold (Bertault and Sist, 1997; Van Gardingen et al., 1998; Sist et al., 1998). Colonisation of gaps by pioneer species will also certainly delay dipterocarp regeneration and growth and consequently the length of the rotation cycle period. Forest dynamic processes in the low damaged logged-over stand (G1) suggested that basal area reduction rate by logging, which includes harvested trees and those killed during felling and skidding, should not exceed 15%. Under these conditions, postlogging mortality was similar to that of unlogged forest; pioneer species regeneration was limited to 1– 6 trees ha1 per year; dipterocarps represented more than 20% of the recruitment and canopy opening resulting from logging stimulated dipterocarp growth during at least the first 4 years following logging. In group 1, mean felling was only 6 trees ha1 and therefore lower than the 8 trees ha1 harvested on average in the area. Under such felling intensity, only RIL techniques can keep basal area removal below 15% (Bertault and Sist, 1997; Sist et al., 1998).
Acknowledgements This study was carried out in the framework of STREK project (1989–1996) in East Kalimantan, a research and development cooperation between Cirad-Foreˆ t, The Ministry of Forestry of Indonesia and INHUTANI I. We wish to thank D. Dykstra, R. Fimbel, S. Gourlet-Fleury, F. Houllier, and T.C. Whitmore for reviewing an earlier version of the manuscript, as well as the two reviewers for their very valuable comments.
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