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Composition and diversity of woody regeneration in a 37-year-old teak (Tectona grandis L.) plantation in Northern Thailand
Forest Ecology and Management 247 (2007) 246–254 www.elsevier.com/locate/foreco
Composition and diversity of woody regeneration in a 37-year-old teak (Tectona grandis L.) plantation in Northern Thailand Narong Koonkhunthod a,*, Katsutoshi Sakurai b, Sota Tanaka c a
United Graduate School of Agricultural Sciences, Ehime University, Matsuyama 790-8566, Japan b Faculty of Agriculture, Kochi University, Nankoku, Kochi 783-8502, Japan c Graduate School of Kuroshio Science, Kochi University, Nankoku, Kochi 783-8502, Japan Received 23 October 2006; received in revised form 27 April 2007; accepted 30 April 2007
Abstract Patterns of woody regeneration in terms of species composition and diversity were studied in a 37-year-old teak plantation established on degraded mixed deciduous forest (MDF) at Mae Yuak Plantation Station, Ngao District, Lampang Province, Northern Thailand. In order to assess the role of plantations in regeneration of woody tree species within the plantation, the understorey floristic structures and composition were evaluated fifteen 20 m 20 m plots at three sites differing in topographic position, stand structure and distance from natural forest. The average density and species richness of woody regeneration in the plantation was 556.7 stem ha1 and 9.6 species plot1, respectively. The Shannon– Wiener index was 2.47–2.68, and Sorensen’s index of similarity between plantation and the adjacent MDF was 0.38–0.55. A total of 334 woody regeneration individuals were found in 0.6 ha of teak plantation, representing 37 species, with Leguminosae the most common family. Pterocarpus macrocarpus Kurz (Leguminosae) showed the highest density of 73.3 stem ha1. The eight most dominant species were P. macrocarpus, Dalbergia oliveri Gamble, Croton roxburghii N.P. Balakr, Xylia xylocarpa (Roxb.) Tuab., D. cultrate Graham ex Benth., Wrightia arborea (Dennst.) Mabb., Schleichera oleosa (Lour.) Oken and Morinda tomentosa Heyne ex Roth. The proximity to the natural forest, seed dispersal characteristics and site qualities influenced woody regeneration. These results show teak plantations could be effective tools in rehabilitating degraded MDF in Northern Thailand. # 2007 Published by Elsevier B.V. Keywords: Teak; Plantation; Rehabilitation; Woody regeneration
1. Introduction Due to the rapid and extensive deforestation of tropical forests, the restoration and rehabilitation of degraded and secondary forest has become an important issue (Parrotta et al., 1997a). As primary forests have been increasingly kept as protected areas for environment and biodiversity conservation, the importance of the estimated 850 million ha of degraded and secondary forests has grown considerably in relation to their potential for wood production, environmental functions and support for the livelihood of local people (ITTO, 2002). Tree plantations can be effective tools for restoration or rehabilitation of degraded forest (Fang and Peng, 1997; Haggar et al., 1997; Loumeto and Huttel, 1997; Oberhauser, 1997; Zhuang, 1997). Plantations can support biodiversity conserva-
* Corresponding author at: Tel.: +81 88 864 5181; fax: +81 88 864 5181. E-mail address: [email protected] (N. Koonkhunthod). 0378-1127/$ – see front matter # 2007 Published by Elsevier B.V. doi:10.1016/j.foreco.2007.04.053
tion (Hartley, 2002), arrest site degradation (Lugo, 1997) and facilitate forest succession through modification of both physical and biological conditions (Parrotta et al., 1997a). Plantations promote understorey regeneration by shading out grasses and other light-demanding species, changing understorey microclimates, improving soil properties and increasing vegetation structural complexity. These changes lead to increased seed inputs by attracting seed dispersing wildlife (Lugo, 1997; Parrotta et al., 1997a). In addition, forest plantations reduce soil erosion and fire hazards (Cusack and Montagnini, 2004). In Thailand, coincident with population and rapid economic growth, forest resources have been severely depleted (ICEM, 2003). As a result, the forest area has decreased from 60% of the total land area in 1953 (ITTO, 2006) to approximately 33% in 2004 (Royal Forest Department, 2004). After the disastrous flash floods and immense landslide damage in Southern Thailand in 1988, logging in natural forests was banned in 1989 (ICEM, 2003). Thus, the focus of forestry policy moved clearly
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towards conservation and watershed protection, with the remaining natural forests reserved as protected areas (e.g. national parks, wildlife sanctuaries). The forest plantations owned by government were converted to conservation areas and silvicultural operations were no longer allowed in plantations over 10-year old. According to the Thai Forestry Sector Master Plan adopted in 1997, it was a goal to return the forest area to 40% (ITTO, 2006). To meet this goal and to make up for the timber production shortage, reforestation and afforestation were important strategies (Niskanen, 1998). Because of its favorable properties and wide range of uses, teak (Tectona grandis L., family Labiatae) is one of the world’s most versatile and outstanding timbers (Gyi and Tint, 2005). Teak occurs naturally in India, Laos, Myanmar and Thailand (White, 1991). Recently, teak has been planted in at least 36 tropical countries on about 5.7 million ha (Bhat and Ma, 2004). It develops best in a sub-tropical climate with mean monthly minimum and maximum temperatures of 9 and 41 8C, respectively, annual rainfall of 1300–3800 mm and a dry period of 3–5 months (White, 1991). Teak is a light-demanding species and able to resist fire. Under natural conditions, teak occurs throughout the Northern part of Thailand, lat 16–208N and long 97–1018E, and dominates the mixed deciduous forest (MDF) associated with Pterocarpus macrocarpus, Xylia kerii, Afzelia xylocarpa, Largerstroemia calyculata and bamboos (Kaosa-ard, 1992). Forest plantations in Thailand were mainly established by the Royal Forest Department (RFD) for the purpose of conservation. Plantations intended for wood production were undertaken by state enterprises, such as the Forest Industry Organization (FIO) and the Thai Plywood Factory, and the private sector (Thaiutsa et al., 1999). The total extent of planted forest in 2000 was estimated to be 2.81 million ha (excluding rubber and oil palm plantations), of which 30% (836 000 ha) was teak plantations (FAO, 2001). From both conservation and production standpoints, teak plays a major role in forest plantations in Thailand. The first teak plantation was begun in 1906 by the RFD, however, on an area less than 1 ha (Corvanich, 1992). Approximately 69% of teak plantation was owned by RFD, 27% by FIO, and 4% by others (Thaiutsa et al., 1999). Most researchers investigating teak plantations in Thailand have focused on silvicultural management and productivity (Petmark and Sahunalu, 1980; Srisuksai, 1991; Thaiutsa et al., 1999; Lakarnchua, 2004). There have been few studies on the understorey vegetation of teak plantations in Thailand (Neeranathpibul and Sangtongpraow, 2002; Kaewkrom et al., 2005) or other countries (Saha, 2001; Healey and Gara, 2003). The present study investigates the diversity and composition of woody regeneration in a teak plantation established on degraded MDF in Lampang Province, Northern Thailand in comparison with an adjacent natural MDF. The MDF can be regarded as the climax stage in local natural vegetation development. The varying characteristics of the teak plantation sites enabled exploration of physiographic factors that might impact on the amount and type of natural woody regeneration.
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2. Materials and methods 2.1. Study site The present study was conducted at Mae Yuak Plantation Station (MYPS; lat 188550 N, long 998560 E), managed by the RFD in Ngao District, Lampang Province, Northern Thailand (Fig. 1). Between 1951 and 2000 the mean annual precipitation was 1231 mm and the mean monthly rainfall was more than 150 mm May–September and lower than 50 mm November– March (Jutakorn et al., 2002). The mean annual temperature was 26.2 8C, with a mean maximum temperature of 37.1 8C in April and a mean minimum of 14.8 8C in December. The elevation in the study area is 400–600 m above mean sea level and topography is undulating terrain. In general, soils are Lithosols, Brown Forest Soils, Red-Brown Earths and ReddishBrown Lateritic Soils in the Thai soil classification system (Land Development Department, 1982), and parent materials are sandstone, shale and limestone (Boonkird et al., 1960). The first plantation for commercial teak timber production was established in 1968 on degraded MDF. As mentioned previously, due to disastrous floods, the purpose of plantations has been altered to rehabilitate degraded forests and ameliorate watershed areas (Neeranathpibul and Sangtongpraow, 2002). The system is as follows. One-year-old teak stumps are planted with an initial spacing of 2 m 2 m following the clearing and burning of the site. During the first 10 years, weeds are controlled annually using hand tools. The stand is thinned at 10 and 15 years old to 50 and 30% of the initial stem density, respectively. Since 1989, silvicultural operations are not allowed within the plantations. Fertilizer is not applied. The total plantation area established between 1968 and 1994 was 2792 ha. At present, illegal logging and conversion of forest to agriculture are the
Fig. 1. Location of Mae Yuak Plantation Station (MYPS) in Lampang Province, Northern Thailand.
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major causes of degradation of plantations and the MDF, although damage from forest fires can often occur in the dry season. The particular stand used for the present study was chosen as it was the oldest (37 years) and was similar to the adjacent natural MDF in general stand physiognomy, the height of trees in both were similar and there were non-teak trees forming part of the canopy in the plantation. The 160 ha stand was surrounded by MDF and an agricultural area. The study was conducted in November 2004 and July 2005. To assess the heterogeneity of the woody regeneration within the stand, three sites were selected for investigation on the basis of differences in topographic position, stand structure and distance from natural forest. Site 1 was on the upper part of a hill with an elevation 400–470 m, the canopy dominated by teak and regenerated vegetation, and was connected to the MDF. Site 2 was on the top and the ridge of another hill with an elevation 400–440 m, the canopy dominated by small teak and associated with bamboo, and was about 1000 m away from the MDF. Site 3 was by a small stream, on a foothill with an elevation of 400 m, and was dominated by large teak and connected to the MDF. The adjacent MDF was the reference site, with elevation 450–560 m, and dominated by various native tree species.
species number at each site, respectively. The density of a species was the number of trees of that species per hectare. The relative density of a species was calculated as its density divided by the total density of all species and multiplied by 100. The frequency of a species was the number of plots in which that species was found. The relative frequency of a species was calculated as the frequency of a species divided by the total number of sampling plots and multiplied by 100. The number of plots used for calculation of relative density and frequency was 15 for plantation and 5 for MDF. The importance value (IV) was calculated as the sum of the relative density and the relative frequency. The IV was used to evaluate the dominance of a species in the area (Parrotta et al., 1997b). A higher IV value indicates more dominance of that species at the site. Diversity of trees at each site was estimated by the Shannon–Wiener index (Shannon, 1948). Sorensen’s index of similarity (SI) was used to compare floristic composition of the plantation and the MDF (Sorenson, 1948). The differences in density, basal area and species richness among the four sites were statistically analyzed using one-way analysis of variance on the means of the five samples within each site. 3. Results
2.2. Vegetation survey 3.1. Planted teak At each of the four sites, five sample plots 20 m 20 m were established along a line transect at 100 m intervals (Fig. 1). Line transects were laid out in the direction that represented the characteristics of each site, including stand structure and topographic position, and allowed comparison of characteristics of woody regeneration. As much as possible, the transects were from upper to lower parts of the sites. The Site 1 transect began at the plantation-MDF boundary and extended east-to-west. The Site 2 transect began at the hilltop and proceeded along the ridge east-to-west. The Site 3 transect was parallel to the plantationMDF boundary, 50 m away on a flat area. The MDF transect began at the plantation-MDF boundary and extended west-toeast into the MDF, the starting point was 500 m north of the Site 1 transect starting point. In each plot, all trees with a diameter at breast height (DBH) 4.5 cm were measured for DBH and identified to species level. DBH 4.5 cm has been used as the general threshold of tree size in forest ecology in Thailand as at this size they are able to tolerate and survive abiotic and biotic hazards (e.g. soil-water stress, forest fire, herbivores and diseases; Bunyavejchewin, 1984; Dhanmanonda and Sahunalu, 1992). Woody species were also classified by their principal seed dispersal mode (i.e. wind, animals or gravity) based on observation and Gardner et al. (2000). The identification of trees was done in the field and confirmed at the Royal Forest Herbarium, Bangkok. The number of bamboo clumps was also counted. The nomenclature followed The Forest Herbarium (2001) and Gardner et al. (2000). 2.3. Data analysis The species richness and total species richness were calculated as the number of species per plot and the total
Planted and naturally regenerated teak could be identified by spacing differences. In the plantation the average density and basal area of teak was 316.7 stem ha1 and 9.4 m2 ha1 (n = 15), respectively (Table 1). The density of teak was not significantly different among sites (Fig. 2). In contrast, the basal area was highest in Site 3 and lowest in Site 2 (P < 0.05) (Fig. 3). Both average density and average basal area of teak were higher in the plantation than in the MDF (Table 1). 3.2. Composition of woody regeneration The most common family in the teak plantation understorey was Leguminosae which was composed of eight species (Table 2). P. macrocarpus Kurz (Leguminosae) had the highest density of 73.3 stem ha1. The six most common species ranked by density accounted for 53.0% of a total of 334 stems: P. macrocarpus, Croton roxburghii N.P. Balakr. (Euphorbiaceae), Dalbergia oliveri Gamble, Xylia xylocarpa (Roxb.) Tuab., D. cultrata Graham ex Benth. (Leguminosae), and Wrightia arborea (Dennst.) Mabb. (Apocynaceae). On the other hand, eight uncommon species (plotted on the right side of Fig. 4) were represented by only one stem each. According to woody regeneration IV ranking, the most dominant species was P. macrocarpus (IV = 21.5). Eight dominant species comprised 53.8% of the total IV: P. macrocarpus, D. oliveri, C. roxburghii, X. xylocarpa, D. cultrata, W. arborea, Schleichera oleosa (Lour.) Oken (Sapindaceae) and Morinda tomentosa Heyne ex Roth (Rubiaceae) (Table 2). In respect to heterogeneity, there were differences in woody regeneration composition among the three plantation sites (Table 2). Based on the IV (data not shown) the dominant
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Table 1 Characteristics of woody plant species which have DBH 4.5 cm in the teak plantation and the adjacent mixed deciduous forest (MDF) at Mae Yuak Plantation Stationa (mean S.E.; n = 5; plot size = 20 m 20 m) Teak plantationb Site 1 Total species richness Species richness (species plot1)
MDFc Site 2
Site 3
Average
19 9.8 1.1 a
25 10.8 1.1 a
19 8.2 1.0 a
21 9.6 0.6
27 10.8 1.6 a
Density (stem ha1) Woody regeneration Teak
555.0 86.4 a 335.0 67.8 b
615.0 109.7 a 335.0 54.5 b
500.0 70.3 a 280.0 24.2 b
556.7 49.8 316.7 28.7
345.0 64.9 a 40.0 17.0 a
Basal area (m2 ha1) Woody regeneration Teak
9.5 1.4 a 9.1 1.9 bc
7.4 1.6 a 6.2 1.0 b
5.4 0.8 a 12.9 1.2 c
7.4 0.8 9.4 1.0
19.7 2.9 b 1.9 0.9 a
Shannon–Wiener index (H0 )
2.47
2.68
a b c
2.49
2.55
3.00
The different letters within a row denote significant differences between means (P < 0.05). The values of total species richness, species richness and Shannon–Wiener index do not include planted teak. For the MDF, woody regeneration is woody species.
species at each site differed. Ranked by IV; Site 1 was dominated by P. macrocarpus, D. oliveri and S. oleosa; Site 2 by C. roxburghii, W. arborea and Symplocos racemosa Roxb. (Symplocaceae); Site 3 by D. oliveri, D. cultrata and X. xylocarpa. The occurrence of bamboo clumps was also markedly different among sites, the density was highest in Site 1 (mean S.E.; 685.0 109.7 clump ha1), lower in Site 2 (475.0 25.0 clump ha1) and lowest in Site 3 (100.0 41.1 clump ha1). The predominant form of seed dispersal of woody regenerations was by animals (Table 3). However, the proportion of wind-dispersed species (53.3%) was higher than animal-dispersed species (28.1%). Moreover, the dominant woody regenerations (P. macrocarpus, D. oliveri, D. cultrata and W. arborea) were wind-dispersed species (Table 2).
Fig. 3. Basal area of teak and woody plant species which have DBH 4.5 cm in the teak plantation (Sites 1–3) and in the adjacent natural mixed deciduous forest (MDF) at Mae Yuak Plantation Station.
The vegetation under the even-aged teak plantation was characterized by differences in DBH size classes and species composition (Figs. 5 and 6). Within the plantation, the understorey was dominated by woody regenerations with small DBH (Fig. 5). Site 2 had the highest number of stems in the 4.5– 11.5 and 11.5–18.5 cm DBH size classes (76 and 35 stems,
respectively). The highest number of stems in the 18.5–25.5 and >25.5 cm DBH size classes were in Site 1 (16 and 6 stems, respectively). The numbers of stems in the 4.5–11.5 and 11.5– 18.5 cm DBH size classes were higher in all plantation sites compared to the MDF, but lower in the 18.5–25.5 and >25.5 cm size. A total of 334 woody regeneration individuals were recorded in the three plantation sites (total area of 0.6 ha), representing 37 species (Table 2). Fifteen species were recorded both in the plantation and the adjacent MDF. It was noticed that naturally
Fig. 2. Density of teak and woody plant species which have DBH 4.5 cm in the teak plantation (Sites 1–3) and in the adjacent natural mixed deciduous forest (MDF) at Mae Yuak Plantation Station.
Fig. 4. Species rank–density curve of the woody regeneration which have DBH 4.5 cm in the understorey of the teak plantation and the woody plant species which have DBH 4.5 cm in the mixed deciduous forest (MDF), at Mae Yuak Plantation Station.
3.3. Density and species richness in woody regeneration
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Table 2 Woody plant species which have DBH 4.5 cm in the teak plantation and the adjacent mixed deciduous forest (MDF) at Mae Yuak Plantation Station Botanical name
Family
Importance value a
Number of stem Plantation Site 1
Lannea coromandelica (Houtt.) Merr. Spondias pinnata (L.f.) Kurz Cananga latifolia (Hook.f. & Thomson) Finet & Gagnep. Miliusa velutina (Dunal) Hook.f. & Thomson Polyalthia cerasoides (Roxb.) Benth. ex Bedd. Holarrhena pubescens Wall. ex G.Don Wrightia arborea (Dennst.) Mabb. Fernandoa adenophyllla (Wall. Ex G. Don) Steenis Oroxylum indicum (L.) Kurz Stereospermum neuranthum Kurz Garuga pinnata Roxb. Anogeissus acuminata (Roxb. ex DC.) Guill. & Perr. Terminalia alata Heyne ex Roth Dillenia obovata (Blume) Hoogland Shorea siamensis Miq. Diospyros mollis Griff. Croton roxburghii N.P.Balakr. Phyllanthus columnaris Mull.Arg. Phyllanthus emblica L. Irvingia malayana Oliv. Ex. A. W. Benn. Tectona grandis L.f.d Vitex glabrata R.Br. Vitex pinnata L. Careya sphaerica Roxb. Albizia lebbeck (L.) Benth. Dalbergia sp.1 Dalbergia cochinchinensis Pierre Dalbergia glomeriflora Kurz Dalbergia cana Graham ex Kurz Dalbergia oliveri Gamble Dalbergia cultrata Graham ex Benth. Erythrina subumbrans (Hassk.) Merr. Pterocarpus macrocarpus Kurz Xylia xylocarpa (Roxb.) Tuab. Lagerstroemia calyculata Kurz Artocarpus lachucha Roxb. Ficus hispida L.f. Gardenia philasteri Pierre ex Pit. Haldina cordifolia (Roxb.) Ridsdale Morinda tomentosa Heyne ex Roth Schleichera oleosa (Lour.) Oken Turpinia pomifera DC. Eriolaena candollei Wall. Sterculia sp.1 Strychnos nux-vomica L. Symplocos racemosa Roxb. Grewia eriocarpa Juss. Unidentified 3 Unidentified 5
Anacardiaceae Anacardiaceae Annonaceae Annonaceae Annonaceae Apocynaceae Apocynaceae Bignoniaceae Bignoniaceae Bignoniaceae Burseraceae Combretaceae Combretaceae Dilleniaceae Dipterocarpaceae Ebenaceae Euphorbiaceae Euphorbiaceae Euphorbiaceae Irvingiaceae Labiatae Labiatae Labiatae Lecythidaceae Leguminosae Leguminosae Leguminosae Leguminosae Leguminosae Leguminosae Leguminosae Leguminosae Leguminosae Leguminosae Lythraceae Moraceae Moraceae Rubiaceae Rubiaceae Rubiaceae Sapindaceae Staphyleaceae Sterculiaceae Sterculiaceae Strychnaceae Symplocaceae Tiliaceae Unidentified Unidentified
Total a b c d
3 3
MDF
Site 2 1 5 1 2 4 7 14 3
Plantationc
1 1 3 1
3 8
1.0 5.9 1.0 5.3 2.9 5.1 8.7 2.3
6
4
3.2 2.9
1 31
7 8
1 67 1
1 56
2
8 1
1 4
5 4 1 2
1 1 6 23 12 7 13
2 1 1 4 4 2 1
1 2 2 2 10 2
6
7 10 1
13 2
3 2 4
17.8 3.2 3.2 1.0 16.9 3.8 1.0 2.0
1
3 3 3
2 1 4 2 2 4
17.8 1.0 2.0 1.0 3.3
7.1 6.9 20.4 10.3 1.0 21.5 14.1 3.0 1.3 1.0 2.0 6.2 7.8 8.1 3.6 3.3
190
156
3.2
3.2 3.2 15.2 6.3 3.2 3.2 10.8 10.8 6.3 3.2
6.3 3.2 8.9 6.3 6.3 10.8
6.0 7.6
1 1 1
178
14.1
17.1
8 1 1
9 6 12 6 1 32 7 2
7.6
2.3 1
67
MDF
Site 3
3 1
Dispersal agentsb
77
3.2 3.2 200.0
A A A A A W W W W W A W W A W A G A A A W A A A W W W W W W W W W G W A A A W A A A W A A A A ? ?
200.0
Importance value were calculated as the sum of relative density and relative frequency. A = animal dispersal, W = wind dispersal, and G = gravity. Excluding planted teak. In plantation, teak was planted.
regenerated teak under the plantation also had stems with a DBH < 4.5 cm. The total species richness in the plantation was highest in Site 2; which was however lower than in the MDF (Table 1). The average density and species richness of woody
regeneration were 556.7 stem ha1 and 9.6 species plot1 (n = 15), respectively (Table 1). Among sites, both density and species richness tended to be higher in Site 2 than the other sites (Figs. 2 and 6). Average density of woody regeneration in
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the plantation was higher than in the MDF, but average species richness was lower (Table 1). Species diversity of woody regeneration, as evaluated by the Shannon–Wiener index, was 2.68 in Site 2, 2.49 in Site 3 and 2.47 in Site 1, which were lower compared to 3.00 in the MDF (Table 1). In comparing the similarity between plantation and MDF, the highest SI (0.55) was between Site 1 and the MDF, while the lowest SI (0.38) was between Site 2 and the MDF (Table 4). 4. Discussion Fig. 5. Stem number of woody regenerations which have DBH 4.5 cm in the teak plantation (Sites 1–3) and woody plant species which have DBH 4.5 cm in the adjacent natural mixed deciduous forest (MDF) at Mae Yuak Plantation Station according to the different DBH size class.
Fig. 6. Species richness of woody regeneration which have DBH 4.5 cm in the teak plantation (Sites 1–3) and woody plant species which have DBH 4.5 cm in the adjacent natural mixed deciduous forest (MDF) at Mae Yuak Plantation Station.
Table 3 Number of woody plant species which have DBH 4.5 cm according to seed dispersal modes in the teak plantation and the adjacent mixed deciduous forest (MDF) at Mae Yuak Plantation Station Dispersal mode
Plantation
MDF
Wind Animals Gravity Unidentified
15 20 2 0
15 9 1 2
Total
37
27
Table 4 Sorensen’s index of similarity of woody plant species which have DBH 4.5 cm in the teak plantation (Sites 1–3) and the adjacent mixed deciduous forest (MDF) at Mae Yuak Plantation Station
Site 2 Site 3 MDF
Site 1
Site 2
Site 3
0.52 0.50 0.55
0.57 0.38
0.43
In the present study, 37 species of naturally regenerated trees were recorded. This was somewhat smaller than those of previous reports, although the comparison may be affected by differences in sampling methodology, plantation age and other factors. In Phrae Province, Northern Thailand, 39–46 native tree species (DBH 4.5 cm) colonized 13–43-year-old teak plantations established on degraded MDF, with the dominant species belonging to family Leguminosae (Neeranathpibul and Sangtongpraow, 2002). In Lampang Province, Northern Thailand, 59 species of tree seedlings from native forest regenerated in a 12-year-old teak plantation, and the most common family was also Leguminosae (Kaewkrom et al., 2005). In India, Saha (2001) reported 46 regenerated tree species in a teak plantation. On the other hand, 27 species were recorded in the adjacent natural MDF. There have been other reports of larger numbers of species from other areas with natural MDF in Northern Thailand, from 41 species in Maehongson Province (Tangtham, 1971) to 68 species in Phrae Province (Bunyavejchewin, 1984). Although the general circumstances appear favorable for the MDF rehabilitation in this area, there were variations in planted teak and regenerating flora among sites. Understanding the factors influencing these variations will be useful in improving plantation design and management, to accelerate natural succession and the growth of planted trees. 4.1. Planted teak The density of teak was higher in the plantation than in the natural forest. This indicates the advantage of rehabilitation to restore teak numbers in the area. The average density of teak aged 30–42 years in Huay Tak Plantation Station, 30 km south of the MYPS, was found to be 375 stem ha1 (Chalermpongse, 1992). In the present study, the average density of teak was 317 stem ha1. However, based on the thinning practices mentioned earlier, the expected density should be 750 stem ha1 (assuming 100% survival). The estimated loss of planted teak, amounting to 57% (433 stem ha1) of the expected density, could be ascribed to illegal logging and natural thinning. In addition, Chuntanapapb (1969) reported the density of natural teak in the MDF in Northern Thailand was 410 stem ha1 in the absence of logging. This value was much higher than the density of natural teak in the MDF of the present study area (40 stem ha1), and indicates that logging has caused a severe reduction in teak in Northern Thailand.
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The DBH of planted teak varied markedly within the plantation. At Site 3 on the foothill, teak showed the greatest DBH; while at Site 2 on the hilltop, DBH was the lowest. This difference may be related to site quality. In Costa Rica, the variation of DBH and height of teak in plantations depended on rotation length and site quality (Pe´rez and Kanninen, 2005). However, further study on site quality is necessary. Although seedlings with DBH 4.5 cm were observed, the natural regeneration of teak with DBH 4.5 cm was not found in the plantation. This indicates that the planted teak suppressed the growth of teak saplings, probably due to low light intensity. In the natural stands, improvements in felling practices, removal of interior growing stock of all ages, and tending of the better elements of the stand, has increased the natural regeneration rate of teak (Chuntanapapb, 1969). Shade intolerant species usually fail to regenerate in species-rich understoreys (Lugo, 1997), and if a planted species is shortlived and light-demanding, they may eventually disappear from plantations (Parrotta et al., 1997a). In addition, forest fires probably damage teak seedlings, although it is reported that they can resist forest fires when taller than 2 m (Dhanmanonda and Sahunalu, 1992). 4.2. Woody regeneration Although the total number of woody species was higher in the plantation (37 species across three sites) than in the MDF (27 species), the average species richness of the plantation was lower (Table 1). This difference may be partially due to the difference in the number of sampling plots; 15 plots for the plantation and 5 plots for the MDF. However, since there were more stems of small size classes (Fig. 5), the difference could be due to younger age of the plantation compared to the MDF. When the forest community has developed over time, natural thinning from competition can occur. Thus, the tree density at maturity may be lower than at the initial stage, and therefore similar to the natural forest. The variation in species composition between the sites may be explained by the proximity to the natural forest, seed dispersal characteristics and site qualities. Seed dispersal into the plot is probably an important influence on abundance and diversity of the understorey vegetation, as found in other countries (Parrotta et al., 1997b). In the plantation, the dominant woody regeneration species, P. macrocarpus and D. oliveri (Table 2), are wind-dispersed; their fruits, known as samara, have a rigid wing around the entire seed and are 40– 70 and 70–90 mm in size, respectively (Gardner et al., 2000). When released from trees, the samara seeds flutter or spin through the air and, depending on the wind velocity and height, can be carried considerable distances. At Site 2, the dominant tree species W. arborea was also wind-dispersed (Table 2). The seeds of W. arborea have a crown of silky hairs arising directly from the top of the seed, with a total length of 15 mm (Gardner et al., 2000). After release from seedpods, the slightest gust of wind catches the crown and propels the seed into the air like a parachute, thus they can be dispersed long distances.
In contrast to small-seeded species, those with large seeds are more likely to be dispersed over shorter distances and are expected to have lower rates or likelihoods of colonizing far from the seed source (Parrotta et al., 1997a; Wunderle, 1997). The most dominant species in the MDF, Terminalia alata Heyne ex Roth (Combretaceae), was not found in the plantation (Table 2). The fruit of T. alata contains a heavy seed with five rigid wings, 30–60 mm in size (Gardner et al., 2000), although it is wind-dispersed, it only travels short distances. It is likely that trees with large seeds need more time to colonize within plantations. Seed dispersal by animals is also important in increasing the diversity of woody regeneration. In general, even-aged monocultures are less attractive to wildlife than plantations of mixed ages and species. Increased vegetation complexity increases attractiveness to more animal species, thereby improving the likelihood of seed dispersal by generalist or opportunistic frugivores (Wunderle, 1997). Although teak plantations are lacking in food resources to attract seeddispersing animals, there were some animal-dispersed species among the woody regeneration (Table 3). Successful establishment of planted trees shades out grasses and light-demanding species, and modification of site conditions contributes to the development of a woody understorey (Lugo, 1997; Ruiz-Jae´n and Aide, 2005). As a result, increasing structural complexity could attract seed-dispersing wildlife and thus increase seed inputs from neighboring native forest (Parrotta et al., 1997a). One of the important factors influencing colonization by forest plant species is soil fertility (de Keersmaeker et al., 2004). In the tropical rainforest of west Sumatra, the heterogeneity of soil fertility was the important influence on tree species diversity (Kubota et al., 2000); more tree species and higher population occurred on more infertile soil and where there was higher variation in soil properties. In contrast, a relatively low number of species suited to homogeneous environments were dominant on fertile soil. In the present study, soil fertility might be related to species diversity. However, specific study on the relation of site quality and species diversity within teak plantations is necessary to test this hypothesis. 4.3. Teak plantation as a tool for rehabilitating the MDF Although the original objective was timber production, the diversity and abundance of woody regeneration found in the plantation understorey indicated that teak plantations could be effective tools in restoring tree diversity. The recovery of native forest plant species is a measure of restoration success (Ruiz-Jae´n and Aide, 2005). In the reforestation of degraded pastures in the Atlantic lowlands of Costa Rica, 69 woody regeneration species were found in plantation understoreys, one-third of which commonly occurred in the primary forest (Haggar et al., 1997). In the present study, a total of 37 woody regeneration species were found in the plantation understorey, 15 of these species were also found in the adjacent forest. Thus teak plantations can enhance the recovery of the native forest tree species in degraded MDF. Regeneration under plantations has been suggested to restore forests on degraded and deforested lands in the tropics (Powers
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et al., 1997). The beneficial effects of tree plantations are probably due to suppression of grasses or other light-demanding species, improving microclimate conditions (i.e. shade, temperature and soil moisture) and attracting seed-dispersing wildlife (Parrotta et al., 1997a). Thus the teak plantation has been enriched by regeneration of the native tree species. Based on these results, there appear to be three possible management alternatives: (1) abandon the plantation and allow further successions to develop the understorey; (2) carefully thin the plantation to facilitate natural regeneration; (3) stratify sites into suitable or unsuitable classes, and apply intensive silviculture to improve productivity at suitable sites and less at unsuitable sites. The first alternative is the present situation of MYPS, where the manager can only protect the plantation from illegal logging and invasion by agriculture. However more protection and social intervention by the local people is needed to decrease the rate of illegal logging. The second alternative offers revenue from the thinning operation, which can be used to facilitate or introduce primary forest species through direct seeding or seedlings. The third alternative will depend on site quality and requires detailed analyses of the relationships between site quality and productivity. The success of rehabilitation programs and sustainable forest utilization depends on policy makers’ selection of plantation management alternatives. However, currently choice depends on the socio-economic situation rather than on the ecological and environmental circumstances. 5. Conclusion The results show that teak plantations can facilitate the development of native forest trees under their canopy in terms of species composition and diversity, and can be used to rehabilitate degraded MDF in Northern Thailand. In addition, mixed-species plantations could further accelerate the restoration process (Parrotta et al., 1997b; Tucker and Murphy, 1997; Hartley, 2002). Therefore, at the beginning of plantation establishment, teak should be mixed with other tree species, for example fruit-bearing native forest species (e.g. S. racemosa and Polyalthia cerasoides (Roxb.) Benth. ex Bedd.) to attract seed-dispersing animals. Large-seeded species (e.g. T. alata) should also be included since they are slow to disperse into the plantation sites. This will aid the recovery of species diversity to that seen in the primary forest. Acknowledgements We would like to thank the chief, Mr. Kasem Khumma, and the staff of Mae Yuak Plantation Station for supporting our fieldwork; Mr. Jedsada Wongprom, Mr. Rungarun Sumkaew and Mr. Sombat Kokgratiem for their assistance in the field and in preparing soil samples. References Bhat, K.M., Ma, H.O., 2004. Teak growers unite. ITTO Tropical Forest Update. http://itto.or.jp (accessed January 15, 2004).
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Boonkird, S., Dawson, M.D., Stone Jr., E.L., 1960. A preliminary study of teak soils and sites in Lampang Province, Thailand. J. Natl. Res. Council. 1, 27–75. Bunyavejchewin, S., 1984. Structure and growth in teak forest 10 years after logging. Thai. J. For. 3 (3), 197–211. (in Thai). Chalermpongse, A., 1992. Growth performance in different age-classes of Huay-Tak teak plantation. In: Royal Forest Department (Eds.), Proceedings of the Symposium on the 50 years of the Huay Tak Teak Plantation Station. Wiang Thong Hotel, Lampang, (in Thai), pp. 180–208.. Chuntanapapb, L., 1969. Effect of improvement felling on increment and natural regeneration of teak forest. For. Res. Bull. 7, 1–25. (in Thai). Corvanich, A., 1992. Teak in Thailand: past experience and future prospect. In: Royal Forest Department (Eds.), Proceedings of the Symposium on the 50 years of the Huay Tak Teak Plantation Station. Wiang Thong Hotel, Lampang, (in Thai), pp. 1–14.. Cusack, D., Montagnini, F., 2004. The role of native species plantations in recovery of understory woody diversity in degraded pasturelands of Costa Rica. For. Ecol. Manage. 188, 1–15. de Keersmaeker, L., Martens, L., Verheyen, K., Hermy, M., De Schrijver, A., Lust, N., 2004. Impact of soil fertility and insolation on diversity of herbaceous woodland species colonizing afforestations in Muizen forest (Belgium). For. Ecol. Manage. 188, 291–304. Dhanmanonda, P., Sahunalu, P., 1992. Research on natural forest. In: Royal Forest Department (Eds.),Proceedings of the Symposium on the 50 years of the Huay Tak Teak Plantation Station. Wiang Thong Hotel, Lampang, (in Thai), pp. 15–55.. Fang, W., Peng, S.L., 1997. Development of species diversity in the restoration process of establishing a tropical man-made forest ecosystem in China. For. Ecol. Manage. 99, 185–196. FAO, 2001. Global Forest Resources Assessment 2000. FAO Forestry Paper 140. FAO, Roam, Italy. Gardner, S., Sidisunthorn, P., Anusarnsunthorn, V., 2000. Field Guide to Forest Trees of Northern Thailand. Kobfai Publishing Project, Bangkok. Gyi, K.K., Tint, K., 2005. Management Status of Natural Teak Forests. http:// fao.org/DOCREP/005/AC773E/ac773e07.html (accessed January 24, 2005). Haggar, J., Wightman, K., Fisher, R., 1997. The potential of plantations to foster woody regeneration within a deforested landscape in lowland Costa Rica. For. Ecol. Manage. 99, 55–64. Hartley, M.J., 2002. Rationale and methods for conserving biodiversity in plantation forests. For. Ecol. Manage. 155, 81–95. Healey, S.P., Gara, R.I., 2003. The effect of a teak (Tectona grandis) plantation on the establishment of native species in an abandoned pasture in Costa Rica. For. Ecol. Manage. 176, 497–507. ICEM, 2003. Lessons Learned in Cambodia, Lao PDR, Thailand and Vietnam. Review of Protected Areas and Development in the Lower Mekong River Region. ICEM, Indooroopilly, Queensland, Australia. ITTO, 2002. ITTO guidelines for the restoration, management and rehabilitation of degraded and secondary tropical forests. ITTO Policy Development Series No. 13. ITTO, 2006. Status of Tropical Forest Management 2005. http://itto.or.jp (accessed June 10, 2006). Jutakorn, J., Kongboriruk, P., Kodsuk, C., 2002. Diagnosis of Temperature and Rainfall in Thailand from 1951–2000. Meteorological Department, Bangkok. Kaewkrom, P., Gajaseni, J., Jordan, C.F., Gajaseni, N., 2005. Floristic regeneration in five types of teak plantations in Thailand. For. Ecol. Manage. 210, 351–361. Kaosa-ard, A., 1992. Country report on teak in Thailand: teak in Asia. In: Wood, H. (Ed.), Proceedings of the CHAINA/ESCAP/FAO Regional Seminar on Research and Development of Teak, Guangzhou, China, pp. 79–86. Kubota, D., Masunaga, T., Hermansah, Hotta, M., Wakatsuki, T., 2000. Soil quality characterization in relation to tree species diversity in tropical rain forest, West Sumatra. Tropics 9 (2), 133–145. Lakarnchua, S., 2004. Log grading and merchantable volume of teak: a case study of Thong Pha Phum plantation, Amphoe Thong Pha Phum, Changwat Kanchanaburi. M.Sc. Thesis. Kasetsart University, Bangkok (In Thai). Land Development Department, 1982. Report of Soil Suitability Survey No. 315. Lampang Province, Bangkok (in Thai).
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Loumeto, J.J., Huttel, C., 1997. Understory vegetation in fast-growing tree plantations on savanna soils in Congo. For. Ecol. Manage. 99, 65–81. Lugo, A.E., 1997. The apparent paradox of reestablishing species richness on degraded lands with tree monocultures. For. Ecol. Manage. 99, 9–19. Neeranathpibul, J., Sangtongpraow, S., 2002. Plant species diversity and soil property changes in different-year old teak plots of Maehad plantation, Nongmuangkhai District, Phrae Province. Thai. J. For. 19–21, 136–145 (in Thai). Niskanen, A., 1998. Financial and economic profitability of reforestation in Thailand. For. Ecol. Manage. 104, 57–68. Oberhauser, U., 1997. Secondary forest regeneration beneath pine (Pinus kesiya) plantations in the northern Thai highlands: a chronosequence study. For. Ecol. Manage. 99, 171–183. Parrotta, J.A., Turnbull, J.W., Jones, N., 1997a. Catalyzing native forest regeneration on degraded tropical lands. For. Ecol. Manage. 99, 1–7. Parrotta, J.A., Knowles, O.H., Wunderle Jr., J.M., 1997b. Development of floristic diversity in 10-year-old restoration forests on a bauxite mined site in Amazonia. For. Ecol. Manage. 99, 21–24. Pe´rez, D., Kanninen, M., 2005. Stand growth scenarios for Tectona grandis plantations in Costa Rica. For. Ecol. Manage. 210, 425–441. Petmark, P., Sahunalu, P., 1980. Primary production of teak plantations. II. Net primary production of various age plantations of teak at Ngao Lampang. For. Res. Bull. 70, 1–35 (in Thai). Powers, J.S., Haggar, J.P., Fisher, R.F., 1997. The effect of overstory composition on understory woody regeneration and species richness in 7-year-old plantations in Costa Rica. For. Ecol. Manage. 99, 43–54. Royal Forest Department, 2004. Forestry Statistics of Thailand 2004. Data Center, Information Office. Royal Forest Department, Bangkok. Ruiz-Jae´n, M.C., Aide, T.M., 2005. Vegetation structure, species diversity, and ecosystem processes as measures of restoration success. For. Ecol. Manage. 218, 159–173.
Saha, S., 2001. Vegetation composition and structure of Tectona grandis (teak family Verbenaceae) plantations and dry deciduous forests in central India. For. Ecol. Manage. 148, 159–167. Shannon, C.E., 1948. Mathematical theory of communication. Bell Syst. Tech. J. 27, 379–423. Sorenson, T., 1948. A method of establishing groups of equal amplitude in a plant based on similarity of species content and its applications to analysis of vegetation on Danish commons. Biol. Skr. 5, 1–34. Srisuksai, B., 1991. Growth and yields of the 18-year-old plantation teak, forest industry organization. M.Sc. Thesis. Kasetsart University, Bangkok (in Thai). Tangtham, N., 1971. Structure and growth of once exploited teak forest. For. Res. Bull. 18, 1–81 (in Thai). Thaiutsa, B., Puangchit, L., Yarwudhi, C., Wacharinrat, C., Kobayashi, S., 1999. Coppicing ability of Teak (Tectona grandis) after thinning. In: Kobayashi, S., Turnbull, J.W., Toma, T., Mori, T., Majid, N.M.N.A. (Eds.), Proceedings of the Workshop on the Rehabilitation of Degraded Tropical Forest Ecosystems, Bogor, Indonesia, pp. 149– 156. The Forest Herbarium, 2001. Thai Plant Names: Tem Smitinand. Royal Forest Department, Bangkok. Tucker, N.I.J., Murphy, T.M., 1997. The effects of ecological rehabilitation on vegetation recruitment: some observations from the wet tropics of North Queensland. For. Ecol. Manage. 99, 133–152. White, K.J., 1991. Teak: Some Aspects of Research and Development, RAPA Publication 1991/17. FAO, Bangkok. Wunderle Jr., J.M., 1997. The role of animal seed dispersal in accelerating native forest regeneration on degraded tropical lands. For. Ecol. Manage. 99, 223–235. Zhuang, X., 1997. Rehabilitation and development of forest on degraded hills of Hong Kong. For. Ecol. Manage. 99, 197–201.
Composition and diversity of woody regeneration in a 37-year-old teak (Tectona grandis L.) plantation in Northern Thailand Narong Koonkhunthod a,*, Katsutoshi Sakurai b, Sota Tanaka c a
United Graduate School of Agricultural Sciences, Ehime University, Matsuyama 790-8566, Japan b Faculty of Agriculture, Kochi University, Nankoku, Kochi 783-8502, Japan c Graduate School of Kuroshio Science, Kochi University, Nankoku, Kochi 783-8502, Japan Received 23 October 2006; received in revised form 27 April 2007; accepted 30 April 2007
Abstract Patterns of woody regeneration in terms of species composition and diversity were studied in a 37-year-old teak plantation established on degraded mixed deciduous forest (MDF) at Mae Yuak Plantation Station, Ngao District, Lampang Province, Northern Thailand. In order to assess the role of plantations in regeneration of woody tree species within the plantation, the understorey floristic structures and composition were evaluated fifteen 20 m 20 m plots at three sites differing in topographic position, stand structure and distance from natural forest. The average density and species richness of woody regeneration in the plantation was 556.7 stem ha1 and 9.6 species plot1, respectively. The Shannon– Wiener index was 2.47–2.68, and Sorensen’s index of similarity between plantation and the adjacent MDF was 0.38–0.55. A total of 334 woody regeneration individuals were found in 0.6 ha of teak plantation, representing 37 species, with Leguminosae the most common family. Pterocarpus macrocarpus Kurz (Leguminosae) showed the highest density of 73.3 stem ha1. The eight most dominant species were P. macrocarpus, Dalbergia oliveri Gamble, Croton roxburghii N.P. Balakr, Xylia xylocarpa (Roxb.) Tuab., D. cultrate Graham ex Benth., Wrightia arborea (Dennst.) Mabb., Schleichera oleosa (Lour.) Oken and Morinda tomentosa Heyne ex Roth. The proximity to the natural forest, seed dispersal characteristics and site qualities influenced woody regeneration. These results show teak plantations could be effective tools in rehabilitating degraded MDF in Northern Thailand. # 2007 Published by Elsevier B.V. Keywords: Teak; Plantation; Rehabilitation; Woody regeneration
1. Introduction Due to the rapid and extensive deforestation of tropical forests, the restoration and rehabilitation of degraded and secondary forest has become an important issue (Parrotta et al., 1997a). As primary forests have been increasingly kept as protected areas for environment and biodiversity conservation, the importance of the estimated 850 million ha of degraded and secondary forests has grown considerably in relation to their potential for wood production, environmental functions and support for the livelihood of local people (ITTO, 2002). Tree plantations can be effective tools for restoration or rehabilitation of degraded forest (Fang and Peng, 1997; Haggar et al., 1997; Loumeto and Huttel, 1997; Oberhauser, 1997; Zhuang, 1997). Plantations can support biodiversity conserva-
* Corresponding author at: Tel.: +81 88 864 5181; fax: +81 88 864 5181. E-mail address: [email protected] (N. Koonkhunthod). 0378-1127/$ – see front matter # 2007 Published by Elsevier B.V. doi:10.1016/j.foreco.2007.04.053
tion (Hartley, 2002), arrest site degradation (Lugo, 1997) and facilitate forest succession through modification of both physical and biological conditions (Parrotta et al., 1997a). Plantations promote understorey regeneration by shading out grasses and other light-demanding species, changing understorey microclimates, improving soil properties and increasing vegetation structural complexity. These changes lead to increased seed inputs by attracting seed dispersing wildlife (Lugo, 1997; Parrotta et al., 1997a). In addition, forest plantations reduce soil erosion and fire hazards (Cusack and Montagnini, 2004). In Thailand, coincident with population and rapid economic growth, forest resources have been severely depleted (ICEM, 2003). As a result, the forest area has decreased from 60% of the total land area in 1953 (ITTO, 2006) to approximately 33% in 2004 (Royal Forest Department, 2004). After the disastrous flash floods and immense landslide damage in Southern Thailand in 1988, logging in natural forests was banned in 1989 (ICEM, 2003). Thus, the focus of forestry policy moved clearly
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towards conservation and watershed protection, with the remaining natural forests reserved as protected areas (e.g. national parks, wildlife sanctuaries). The forest plantations owned by government were converted to conservation areas and silvicultural operations were no longer allowed in plantations over 10-year old. According to the Thai Forestry Sector Master Plan adopted in 1997, it was a goal to return the forest area to 40% (ITTO, 2006). To meet this goal and to make up for the timber production shortage, reforestation and afforestation were important strategies (Niskanen, 1998). Because of its favorable properties and wide range of uses, teak (Tectona grandis L., family Labiatae) is one of the world’s most versatile and outstanding timbers (Gyi and Tint, 2005). Teak occurs naturally in India, Laos, Myanmar and Thailand (White, 1991). Recently, teak has been planted in at least 36 tropical countries on about 5.7 million ha (Bhat and Ma, 2004). It develops best in a sub-tropical climate with mean monthly minimum and maximum temperatures of 9 and 41 8C, respectively, annual rainfall of 1300–3800 mm and a dry period of 3–5 months (White, 1991). Teak is a light-demanding species and able to resist fire. Under natural conditions, teak occurs throughout the Northern part of Thailand, lat 16–208N and long 97–1018E, and dominates the mixed deciduous forest (MDF) associated with Pterocarpus macrocarpus, Xylia kerii, Afzelia xylocarpa, Largerstroemia calyculata and bamboos (Kaosa-ard, 1992). Forest plantations in Thailand were mainly established by the Royal Forest Department (RFD) for the purpose of conservation. Plantations intended for wood production were undertaken by state enterprises, such as the Forest Industry Organization (FIO) and the Thai Plywood Factory, and the private sector (Thaiutsa et al., 1999). The total extent of planted forest in 2000 was estimated to be 2.81 million ha (excluding rubber and oil palm plantations), of which 30% (836 000 ha) was teak plantations (FAO, 2001). From both conservation and production standpoints, teak plays a major role in forest plantations in Thailand. The first teak plantation was begun in 1906 by the RFD, however, on an area less than 1 ha (Corvanich, 1992). Approximately 69% of teak plantation was owned by RFD, 27% by FIO, and 4% by others (Thaiutsa et al., 1999). Most researchers investigating teak plantations in Thailand have focused on silvicultural management and productivity (Petmark and Sahunalu, 1980; Srisuksai, 1991; Thaiutsa et al., 1999; Lakarnchua, 2004). There have been few studies on the understorey vegetation of teak plantations in Thailand (Neeranathpibul and Sangtongpraow, 2002; Kaewkrom et al., 2005) or other countries (Saha, 2001; Healey and Gara, 2003). The present study investigates the diversity and composition of woody regeneration in a teak plantation established on degraded MDF in Lampang Province, Northern Thailand in comparison with an adjacent natural MDF. The MDF can be regarded as the climax stage in local natural vegetation development. The varying characteristics of the teak plantation sites enabled exploration of physiographic factors that might impact on the amount and type of natural woody regeneration.
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2. Materials and methods 2.1. Study site The present study was conducted at Mae Yuak Plantation Station (MYPS; lat 188550 N, long 998560 E), managed by the RFD in Ngao District, Lampang Province, Northern Thailand (Fig. 1). Between 1951 and 2000 the mean annual precipitation was 1231 mm and the mean monthly rainfall was more than 150 mm May–September and lower than 50 mm November– March (Jutakorn et al., 2002). The mean annual temperature was 26.2 8C, with a mean maximum temperature of 37.1 8C in April and a mean minimum of 14.8 8C in December. The elevation in the study area is 400–600 m above mean sea level and topography is undulating terrain. In general, soils are Lithosols, Brown Forest Soils, Red-Brown Earths and ReddishBrown Lateritic Soils in the Thai soil classification system (Land Development Department, 1982), and parent materials are sandstone, shale and limestone (Boonkird et al., 1960). The first plantation for commercial teak timber production was established in 1968 on degraded MDF. As mentioned previously, due to disastrous floods, the purpose of plantations has been altered to rehabilitate degraded forests and ameliorate watershed areas (Neeranathpibul and Sangtongpraow, 2002). The system is as follows. One-year-old teak stumps are planted with an initial spacing of 2 m 2 m following the clearing and burning of the site. During the first 10 years, weeds are controlled annually using hand tools. The stand is thinned at 10 and 15 years old to 50 and 30% of the initial stem density, respectively. Since 1989, silvicultural operations are not allowed within the plantations. Fertilizer is not applied. The total plantation area established between 1968 and 1994 was 2792 ha. At present, illegal logging and conversion of forest to agriculture are the
Fig. 1. Location of Mae Yuak Plantation Station (MYPS) in Lampang Province, Northern Thailand.
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major causes of degradation of plantations and the MDF, although damage from forest fires can often occur in the dry season. The particular stand used for the present study was chosen as it was the oldest (37 years) and was similar to the adjacent natural MDF in general stand physiognomy, the height of trees in both were similar and there were non-teak trees forming part of the canopy in the plantation. The 160 ha stand was surrounded by MDF and an agricultural area. The study was conducted in November 2004 and July 2005. To assess the heterogeneity of the woody regeneration within the stand, three sites were selected for investigation on the basis of differences in topographic position, stand structure and distance from natural forest. Site 1 was on the upper part of a hill with an elevation 400–470 m, the canopy dominated by teak and regenerated vegetation, and was connected to the MDF. Site 2 was on the top and the ridge of another hill with an elevation 400–440 m, the canopy dominated by small teak and associated with bamboo, and was about 1000 m away from the MDF. Site 3 was by a small stream, on a foothill with an elevation of 400 m, and was dominated by large teak and connected to the MDF. The adjacent MDF was the reference site, with elevation 450–560 m, and dominated by various native tree species.
species number at each site, respectively. The density of a species was the number of trees of that species per hectare. The relative density of a species was calculated as its density divided by the total density of all species and multiplied by 100. The frequency of a species was the number of plots in which that species was found. The relative frequency of a species was calculated as the frequency of a species divided by the total number of sampling plots and multiplied by 100. The number of plots used for calculation of relative density and frequency was 15 for plantation and 5 for MDF. The importance value (IV) was calculated as the sum of the relative density and the relative frequency. The IV was used to evaluate the dominance of a species in the area (Parrotta et al., 1997b). A higher IV value indicates more dominance of that species at the site. Diversity of trees at each site was estimated by the Shannon–Wiener index (Shannon, 1948). Sorensen’s index of similarity (SI) was used to compare floristic composition of the plantation and the MDF (Sorenson, 1948). The differences in density, basal area and species richness among the four sites were statistically analyzed using one-way analysis of variance on the means of the five samples within each site. 3. Results
2.2. Vegetation survey 3.1. Planted teak At each of the four sites, five sample plots 20 m 20 m were established along a line transect at 100 m intervals (Fig. 1). Line transects were laid out in the direction that represented the characteristics of each site, including stand structure and topographic position, and allowed comparison of characteristics of woody regeneration. As much as possible, the transects were from upper to lower parts of the sites. The Site 1 transect began at the plantation-MDF boundary and extended east-to-west. The Site 2 transect began at the hilltop and proceeded along the ridge east-to-west. The Site 3 transect was parallel to the plantationMDF boundary, 50 m away on a flat area. The MDF transect began at the plantation-MDF boundary and extended west-toeast into the MDF, the starting point was 500 m north of the Site 1 transect starting point. In each plot, all trees with a diameter at breast height (DBH) 4.5 cm were measured for DBH and identified to species level. DBH 4.5 cm has been used as the general threshold of tree size in forest ecology in Thailand as at this size they are able to tolerate and survive abiotic and biotic hazards (e.g. soil-water stress, forest fire, herbivores and diseases; Bunyavejchewin, 1984; Dhanmanonda and Sahunalu, 1992). Woody species were also classified by their principal seed dispersal mode (i.e. wind, animals or gravity) based on observation and Gardner et al. (2000). The identification of trees was done in the field and confirmed at the Royal Forest Herbarium, Bangkok. The number of bamboo clumps was also counted. The nomenclature followed The Forest Herbarium (2001) and Gardner et al. (2000). 2.3. Data analysis The species richness and total species richness were calculated as the number of species per plot and the total
Planted and naturally regenerated teak could be identified by spacing differences. In the plantation the average density and basal area of teak was 316.7 stem ha1 and 9.4 m2 ha1 (n = 15), respectively (Table 1). The density of teak was not significantly different among sites (Fig. 2). In contrast, the basal area was highest in Site 3 and lowest in Site 2 (P < 0.05) (Fig. 3). Both average density and average basal area of teak were higher in the plantation than in the MDF (Table 1). 3.2. Composition of woody regeneration The most common family in the teak plantation understorey was Leguminosae which was composed of eight species (Table 2). P. macrocarpus Kurz (Leguminosae) had the highest density of 73.3 stem ha1. The six most common species ranked by density accounted for 53.0% of a total of 334 stems: P. macrocarpus, Croton roxburghii N.P. Balakr. (Euphorbiaceae), Dalbergia oliveri Gamble, Xylia xylocarpa (Roxb.) Tuab., D. cultrata Graham ex Benth. (Leguminosae), and Wrightia arborea (Dennst.) Mabb. (Apocynaceae). On the other hand, eight uncommon species (plotted on the right side of Fig. 4) were represented by only one stem each. According to woody regeneration IV ranking, the most dominant species was P. macrocarpus (IV = 21.5). Eight dominant species comprised 53.8% of the total IV: P. macrocarpus, D. oliveri, C. roxburghii, X. xylocarpa, D. cultrata, W. arborea, Schleichera oleosa (Lour.) Oken (Sapindaceae) and Morinda tomentosa Heyne ex Roth (Rubiaceae) (Table 2). In respect to heterogeneity, there were differences in woody regeneration composition among the three plantation sites (Table 2). Based on the IV (data not shown) the dominant
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Table 1 Characteristics of woody plant species which have DBH 4.5 cm in the teak plantation and the adjacent mixed deciduous forest (MDF) at Mae Yuak Plantation Stationa (mean S.E.; n = 5; plot size = 20 m 20 m) Teak plantationb Site 1 Total species richness Species richness (species plot1)
MDFc Site 2
Site 3
Average
19 9.8 1.1 a
25 10.8 1.1 a
19 8.2 1.0 a
21 9.6 0.6
27 10.8 1.6 a
Density (stem ha1) Woody regeneration Teak
555.0 86.4 a 335.0 67.8 b
615.0 109.7 a 335.0 54.5 b
500.0 70.3 a 280.0 24.2 b
556.7 49.8 316.7 28.7
345.0 64.9 a 40.0 17.0 a
Basal area (m2 ha1) Woody regeneration Teak
9.5 1.4 a 9.1 1.9 bc
7.4 1.6 a 6.2 1.0 b
5.4 0.8 a 12.9 1.2 c
7.4 0.8 9.4 1.0
19.7 2.9 b 1.9 0.9 a
Shannon–Wiener index (H0 )
2.47
2.68
a b c
2.49
2.55
3.00
The different letters within a row denote significant differences between means (P < 0.05). The values of total species richness, species richness and Shannon–Wiener index do not include planted teak. For the MDF, woody regeneration is woody species.
species at each site differed. Ranked by IV; Site 1 was dominated by P. macrocarpus, D. oliveri and S. oleosa; Site 2 by C. roxburghii, W. arborea and Symplocos racemosa Roxb. (Symplocaceae); Site 3 by D. oliveri, D. cultrata and X. xylocarpa. The occurrence of bamboo clumps was also markedly different among sites, the density was highest in Site 1 (mean S.E.; 685.0 109.7 clump ha1), lower in Site 2 (475.0 25.0 clump ha1) and lowest in Site 3 (100.0 41.1 clump ha1). The predominant form of seed dispersal of woody regenerations was by animals (Table 3). However, the proportion of wind-dispersed species (53.3%) was higher than animal-dispersed species (28.1%). Moreover, the dominant woody regenerations (P. macrocarpus, D. oliveri, D. cultrata and W. arborea) were wind-dispersed species (Table 2).
Fig. 3. Basal area of teak and woody plant species which have DBH 4.5 cm in the teak plantation (Sites 1–3) and in the adjacent natural mixed deciduous forest (MDF) at Mae Yuak Plantation Station.
The vegetation under the even-aged teak plantation was characterized by differences in DBH size classes and species composition (Figs. 5 and 6). Within the plantation, the understorey was dominated by woody regenerations with small DBH (Fig. 5). Site 2 had the highest number of stems in the 4.5– 11.5 and 11.5–18.5 cm DBH size classes (76 and 35 stems,
respectively). The highest number of stems in the 18.5–25.5 and >25.5 cm DBH size classes were in Site 1 (16 and 6 stems, respectively). The numbers of stems in the 4.5–11.5 and 11.5– 18.5 cm DBH size classes were higher in all plantation sites compared to the MDF, but lower in the 18.5–25.5 and >25.5 cm size. A total of 334 woody regeneration individuals were recorded in the three plantation sites (total area of 0.6 ha), representing 37 species (Table 2). Fifteen species were recorded both in the plantation and the adjacent MDF. It was noticed that naturally
Fig. 2. Density of teak and woody plant species which have DBH 4.5 cm in the teak plantation (Sites 1–3) and in the adjacent natural mixed deciduous forest (MDF) at Mae Yuak Plantation Station.
Fig. 4. Species rank–density curve of the woody regeneration which have DBH 4.5 cm in the understorey of the teak plantation and the woody plant species which have DBH 4.5 cm in the mixed deciduous forest (MDF), at Mae Yuak Plantation Station.
3.3. Density and species richness in woody regeneration
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Table 2 Woody plant species which have DBH 4.5 cm in the teak plantation and the adjacent mixed deciduous forest (MDF) at Mae Yuak Plantation Station Botanical name
Family
Importance value a
Number of stem Plantation Site 1
Lannea coromandelica (Houtt.) Merr. Spondias pinnata (L.f.) Kurz Cananga latifolia (Hook.f. & Thomson) Finet & Gagnep. Miliusa velutina (Dunal) Hook.f. & Thomson Polyalthia cerasoides (Roxb.) Benth. ex Bedd. Holarrhena pubescens Wall. ex G.Don Wrightia arborea (Dennst.) Mabb. Fernandoa adenophyllla (Wall. Ex G. Don) Steenis Oroxylum indicum (L.) Kurz Stereospermum neuranthum Kurz Garuga pinnata Roxb. Anogeissus acuminata (Roxb. ex DC.) Guill. & Perr. Terminalia alata Heyne ex Roth Dillenia obovata (Blume) Hoogland Shorea siamensis Miq. Diospyros mollis Griff. Croton roxburghii N.P.Balakr. Phyllanthus columnaris Mull.Arg. Phyllanthus emblica L. Irvingia malayana Oliv. Ex. A. W. Benn. Tectona grandis L.f.d Vitex glabrata R.Br. Vitex pinnata L. Careya sphaerica Roxb. Albizia lebbeck (L.) Benth. Dalbergia sp.1 Dalbergia cochinchinensis Pierre Dalbergia glomeriflora Kurz Dalbergia cana Graham ex Kurz Dalbergia oliveri Gamble Dalbergia cultrata Graham ex Benth. Erythrina subumbrans (Hassk.) Merr. Pterocarpus macrocarpus Kurz Xylia xylocarpa (Roxb.) Tuab. Lagerstroemia calyculata Kurz Artocarpus lachucha Roxb. Ficus hispida L.f. Gardenia philasteri Pierre ex Pit. Haldina cordifolia (Roxb.) Ridsdale Morinda tomentosa Heyne ex Roth Schleichera oleosa (Lour.) Oken Turpinia pomifera DC. Eriolaena candollei Wall. Sterculia sp.1 Strychnos nux-vomica L. Symplocos racemosa Roxb. Grewia eriocarpa Juss. Unidentified 3 Unidentified 5
Anacardiaceae Anacardiaceae Annonaceae Annonaceae Annonaceae Apocynaceae Apocynaceae Bignoniaceae Bignoniaceae Bignoniaceae Burseraceae Combretaceae Combretaceae Dilleniaceae Dipterocarpaceae Ebenaceae Euphorbiaceae Euphorbiaceae Euphorbiaceae Irvingiaceae Labiatae Labiatae Labiatae Lecythidaceae Leguminosae Leguminosae Leguminosae Leguminosae Leguminosae Leguminosae Leguminosae Leguminosae Leguminosae Leguminosae Lythraceae Moraceae Moraceae Rubiaceae Rubiaceae Rubiaceae Sapindaceae Staphyleaceae Sterculiaceae Sterculiaceae Strychnaceae Symplocaceae Tiliaceae Unidentified Unidentified
Total a b c d
3 3
MDF
Site 2 1 5 1 2 4 7 14 3
Plantationc
1 1 3 1
3 8
1.0 5.9 1.0 5.3 2.9 5.1 8.7 2.3
6
4
3.2 2.9
1 31
7 8
1 67 1
1 56
2
8 1
1 4
5 4 1 2
1 1 6 23 12 7 13
2 1 1 4 4 2 1
1 2 2 2 10 2
6
7 10 1
13 2
3 2 4
17.8 3.2 3.2 1.0 16.9 3.8 1.0 2.0
1
3 3 3
2 1 4 2 2 4
17.8 1.0 2.0 1.0 3.3
7.1 6.9 20.4 10.3 1.0 21.5 14.1 3.0 1.3 1.0 2.0 6.2 7.8 8.1 3.6 3.3
190
156
3.2
3.2 3.2 15.2 6.3 3.2 3.2 10.8 10.8 6.3 3.2
6.3 3.2 8.9 6.3 6.3 10.8
6.0 7.6
1 1 1
178
14.1
17.1
8 1 1
9 6 12 6 1 32 7 2
7.6
2.3 1
67
MDF
Site 3
3 1
Dispersal agentsb
77
3.2 3.2 200.0
A A A A A W W W W W A W W A W A G A A A W A A A W W W W W W W W W G W A A A W A A A W A A A A ? ?
200.0
Importance value were calculated as the sum of relative density and relative frequency. A = animal dispersal, W = wind dispersal, and G = gravity. Excluding planted teak. In plantation, teak was planted.
regenerated teak under the plantation also had stems with a DBH < 4.5 cm. The total species richness in the plantation was highest in Site 2; which was however lower than in the MDF (Table 1). The average density and species richness of woody
regeneration were 556.7 stem ha1 and 9.6 species plot1 (n = 15), respectively (Table 1). Among sites, both density and species richness tended to be higher in Site 2 than the other sites (Figs. 2 and 6). Average density of woody regeneration in
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the plantation was higher than in the MDF, but average species richness was lower (Table 1). Species diversity of woody regeneration, as evaluated by the Shannon–Wiener index, was 2.68 in Site 2, 2.49 in Site 3 and 2.47 in Site 1, which were lower compared to 3.00 in the MDF (Table 1). In comparing the similarity between plantation and MDF, the highest SI (0.55) was between Site 1 and the MDF, while the lowest SI (0.38) was between Site 2 and the MDF (Table 4). 4. Discussion Fig. 5. Stem number of woody regenerations which have DBH 4.5 cm in the teak plantation (Sites 1–3) and woody plant species which have DBH 4.5 cm in the adjacent natural mixed deciduous forest (MDF) at Mae Yuak Plantation Station according to the different DBH size class.
Fig. 6. Species richness of woody regeneration which have DBH 4.5 cm in the teak plantation (Sites 1–3) and woody plant species which have DBH 4.5 cm in the adjacent natural mixed deciduous forest (MDF) at Mae Yuak Plantation Station.
Table 3 Number of woody plant species which have DBH 4.5 cm according to seed dispersal modes in the teak plantation and the adjacent mixed deciduous forest (MDF) at Mae Yuak Plantation Station Dispersal mode
Plantation
MDF
Wind Animals Gravity Unidentified
15 20 2 0
15 9 1 2
Total
37
27
Table 4 Sorensen’s index of similarity of woody plant species which have DBH 4.5 cm in the teak plantation (Sites 1–3) and the adjacent mixed deciduous forest (MDF) at Mae Yuak Plantation Station
Site 2 Site 3 MDF
Site 1
Site 2
Site 3
0.52 0.50 0.55
0.57 0.38
0.43
In the present study, 37 species of naturally regenerated trees were recorded. This was somewhat smaller than those of previous reports, although the comparison may be affected by differences in sampling methodology, plantation age and other factors. In Phrae Province, Northern Thailand, 39–46 native tree species (DBH 4.5 cm) colonized 13–43-year-old teak plantations established on degraded MDF, with the dominant species belonging to family Leguminosae (Neeranathpibul and Sangtongpraow, 2002). In Lampang Province, Northern Thailand, 59 species of tree seedlings from native forest regenerated in a 12-year-old teak plantation, and the most common family was also Leguminosae (Kaewkrom et al., 2005). In India, Saha (2001) reported 46 regenerated tree species in a teak plantation. On the other hand, 27 species were recorded in the adjacent natural MDF. There have been other reports of larger numbers of species from other areas with natural MDF in Northern Thailand, from 41 species in Maehongson Province (Tangtham, 1971) to 68 species in Phrae Province (Bunyavejchewin, 1984). Although the general circumstances appear favorable for the MDF rehabilitation in this area, there were variations in planted teak and regenerating flora among sites. Understanding the factors influencing these variations will be useful in improving plantation design and management, to accelerate natural succession and the growth of planted trees. 4.1. Planted teak The density of teak was higher in the plantation than in the natural forest. This indicates the advantage of rehabilitation to restore teak numbers in the area. The average density of teak aged 30–42 years in Huay Tak Plantation Station, 30 km south of the MYPS, was found to be 375 stem ha1 (Chalermpongse, 1992). In the present study, the average density of teak was 317 stem ha1. However, based on the thinning practices mentioned earlier, the expected density should be 750 stem ha1 (assuming 100% survival). The estimated loss of planted teak, amounting to 57% (433 stem ha1) of the expected density, could be ascribed to illegal logging and natural thinning. In addition, Chuntanapapb (1969) reported the density of natural teak in the MDF in Northern Thailand was 410 stem ha1 in the absence of logging. This value was much higher than the density of natural teak in the MDF of the present study area (40 stem ha1), and indicates that logging has caused a severe reduction in teak in Northern Thailand.
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The DBH of planted teak varied markedly within the plantation. At Site 3 on the foothill, teak showed the greatest DBH; while at Site 2 on the hilltop, DBH was the lowest. This difference may be related to site quality. In Costa Rica, the variation of DBH and height of teak in plantations depended on rotation length and site quality (Pe´rez and Kanninen, 2005). However, further study on site quality is necessary. Although seedlings with DBH 4.5 cm were observed, the natural regeneration of teak with DBH 4.5 cm was not found in the plantation. This indicates that the planted teak suppressed the growth of teak saplings, probably due to low light intensity. In the natural stands, improvements in felling practices, removal of interior growing stock of all ages, and tending of the better elements of the stand, has increased the natural regeneration rate of teak (Chuntanapapb, 1969). Shade intolerant species usually fail to regenerate in species-rich understoreys (Lugo, 1997), and if a planted species is shortlived and light-demanding, they may eventually disappear from plantations (Parrotta et al., 1997a). In addition, forest fires probably damage teak seedlings, although it is reported that they can resist forest fires when taller than 2 m (Dhanmanonda and Sahunalu, 1992). 4.2. Woody regeneration Although the total number of woody species was higher in the plantation (37 species across three sites) than in the MDF (27 species), the average species richness of the plantation was lower (Table 1). This difference may be partially due to the difference in the number of sampling plots; 15 plots for the plantation and 5 plots for the MDF. However, since there were more stems of small size classes (Fig. 5), the difference could be due to younger age of the plantation compared to the MDF. When the forest community has developed over time, natural thinning from competition can occur. Thus, the tree density at maturity may be lower than at the initial stage, and therefore similar to the natural forest. The variation in species composition between the sites may be explained by the proximity to the natural forest, seed dispersal characteristics and site qualities. Seed dispersal into the plot is probably an important influence on abundance and diversity of the understorey vegetation, as found in other countries (Parrotta et al., 1997b). In the plantation, the dominant woody regeneration species, P. macrocarpus and D. oliveri (Table 2), are wind-dispersed; their fruits, known as samara, have a rigid wing around the entire seed and are 40– 70 and 70–90 mm in size, respectively (Gardner et al., 2000). When released from trees, the samara seeds flutter or spin through the air and, depending on the wind velocity and height, can be carried considerable distances. At Site 2, the dominant tree species W. arborea was also wind-dispersed (Table 2). The seeds of W. arborea have a crown of silky hairs arising directly from the top of the seed, with a total length of 15 mm (Gardner et al., 2000). After release from seedpods, the slightest gust of wind catches the crown and propels the seed into the air like a parachute, thus they can be dispersed long distances.
In contrast to small-seeded species, those with large seeds are more likely to be dispersed over shorter distances and are expected to have lower rates or likelihoods of colonizing far from the seed source (Parrotta et al., 1997a; Wunderle, 1997). The most dominant species in the MDF, Terminalia alata Heyne ex Roth (Combretaceae), was not found in the plantation (Table 2). The fruit of T. alata contains a heavy seed with five rigid wings, 30–60 mm in size (Gardner et al., 2000), although it is wind-dispersed, it only travels short distances. It is likely that trees with large seeds need more time to colonize within plantations. Seed dispersal by animals is also important in increasing the diversity of woody regeneration. In general, even-aged monocultures are less attractive to wildlife than plantations of mixed ages and species. Increased vegetation complexity increases attractiveness to more animal species, thereby improving the likelihood of seed dispersal by generalist or opportunistic frugivores (Wunderle, 1997). Although teak plantations are lacking in food resources to attract seeddispersing animals, there were some animal-dispersed species among the woody regeneration (Table 3). Successful establishment of planted trees shades out grasses and light-demanding species, and modification of site conditions contributes to the development of a woody understorey (Lugo, 1997; Ruiz-Jae´n and Aide, 2005). As a result, increasing structural complexity could attract seed-dispersing wildlife and thus increase seed inputs from neighboring native forest (Parrotta et al., 1997a). One of the important factors influencing colonization by forest plant species is soil fertility (de Keersmaeker et al., 2004). In the tropical rainforest of west Sumatra, the heterogeneity of soil fertility was the important influence on tree species diversity (Kubota et al., 2000); more tree species and higher population occurred on more infertile soil and where there was higher variation in soil properties. In contrast, a relatively low number of species suited to homogeneous environments were dominant on fertile soil. In the present study, soil fertility might be related to species diversity. However, specific study on the relation of site quality and species diversity within teak plantations is necessary to test this hypothesis. 4.3. Teak plantation as a tool for rehabilitating the MDF Although the original objective was timber production, the diversity and abundance of woody regeneration found in the plantation understorey indicated that teak plantations could be effective tools in restoring tree diversity. The recovery of native forest plant species is a measure of restoration success (Ruiz-Jae´n and Aide, 2005). In the reforestation of degraded pastures in the Atlantic lowlands of Costa Rica, 69 woody regeneration species were found in plantation understoreys, one-third of which commonly occurred in the primary forest (Haggar et al., 1997). In the present study, a total of 37 woody regeneration species were found in the plantation understorey, 15 of these species were also found in the adjacent forest. Thus teak plantations can enhance the recovery of the native forest tree species in degraded MDF. Regeneration under plantations has been suggested to restore forests on degraded and deforested lands in the tropics (Powers
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et al., 1997). The beneficial effects of tree plantations are probably due to suppression of grasses or other light-demanding species, improving microclimate conditions (i.e. shade, temperature and soil moisture) and attracting seed-dispersing wildlife (Parrotta et al., 1997a). Thus the teak plantation has been enriched by regeneration of the native tree species. Based on these results, there appear to be three possible management alternatives: (1) abandon the plantation and allow further successions to develop the understorey; (2) carefully thin the plantation to facilitate natural regeneration; (3) stratify sites into suitable or unsuitable classes, and apply intensive silviculture to improve productivity at suitable sites and less at unsuitable sites. The first alternative is the present situation of MYPS, where the manager can only protect the plantation from illegal logging and invasion by agriculture. However more protection and social intervention by the local people is needed to decrease the rate of illegal logging. The second alternative offers revenue from the thinning operation, which can be used to facilitate or introduce primary forest species through direct seeding or seedlings. The third alternative will depend on site quality and requires detailed analyses of the relationships between site quality and productivity. The success of rehabilitation programs and sustainable forest utilization depends on policy makers’ selection of plantation management alternatives. However, currently choice depends on the socio-economic situation rather than on the ecological and environmental circumstances. 5. Conclusion The results show that teak plantations can facilitate the development of native forest trees under their canopy in terms of species composition and diversity, and can be used to rehabilitate degraded MDF in Northern Thailand. In addition, mixed-species plantations could further accelerate the restoration process (Parrotta et al., 1997b; Tucker and Murphy, 1997; Hartley, 2002). Therefore, at the beginning of plantation establishment, teak should be mixed with other tree species, for example fruit-bearing native forest species (e.g. S. racemosa and Polyalthia cerasoides (Roxb.) Benth. ex Bedd.) to attract seed-dispersing animals. Large-seeded species (e.g. T. alata) should also be included since they are slow to disperse into the plantation sites. This will aid the recovery of species diversity to that seen in the primary forest. Acknowledgements We would like to thank the chief, Mr. Kasem Khumma, and the staff of Mae Yuak Plantation Station for supporting our fieldwork; Mr. Jedsada Wongprom, Mr. Rungarun Sumkaew and Mr. Sombat Kokgratiem for their assistance in the field and in preparing soil samples. References Bhat, K.M., Ma, H.O., 2004. Teak growers unite. ITTO Tropical Forest Update. http://itto.or.jp (accessed January 15, 2004).
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