Litter production and leaf-litter decomposition of selected tree species in tropical forests at Kodayar in the Western Ghats, India

Forest Ecology and Management 123 (1999) 231±244

Litter production and leaf-litter decomposition of selected tree species in tropical forests at Kodayar in the Western Ghats, India S.M. Sundarapandian, P.S. Swamy* Department of Plant Sciences, School of Biological Sciences, Madurai Kamaraj University, Madurai ± 625021, India Received 29 June 1998; accepted 12 January 1999

Abstract Litter production, standing crop of litter on forest ¯oor and leaf-litter decomposition of selected dominant tree species were studied in the tropical forests at Kodayar in the Western Ghats, India. Mean annual litterfall in the study sites ranged from 5.63 to 8.65 Mg haÿ1 yearÿ1. A greater amount of annual litter production was observed in sites II and III, when compared to sites I and IV. This variation in litterfall pattern among the sites could be attributed to species composition. Monthly variation in litterfall pattern showed two peaks, one in the dry season (January±April) and another in November. Contribution of leaf litter to the total litter was signi®cantly (p < 0.01) greater compared to other components (woody litter and reproductive parts). In deciduous forests, Terminalia contributed signi®cantly (p < 0.05) greater amount of leaf litter to annual litter production, followed by Careya arborea, Macaranga peltata, Aporosa lindleyana and Dillenia pentagyna, whereas in evergreen forests, Hopea parvi¯ora contributed the most. The results suggest that species composition and their contribution toward litter becomes important in overall community or site litter production as observed in sites II and III. The litter mass decreased linearly with time. Thin and smooth leaf without prominent skeletal tissues decomposed more rapidly, while thick and tough leaves with prominent midribs and veins took longer time for complete decomposition. The species with high nitrogen content exhibited relatively faster decomposition except in H. parvi¯ora and V. indica. The differences in decay rates and half-life periods are related to structure and nutrient concentration of leaf litter and the environmental factors. # 1999 Elsevier Science B.V. All rights reserved. Keywords: Litterfall; Litter decomposition; Tropical deciduous forest; Tropical evergreen forest; Western Ghats; India; Decay rate

1. Introduction The maintenance of soil organic pool in tropical ecosystems is achieved by the high and rapid circulation of nutrients through the fall and decomposition of litter (Ola-Adams and Egunjobi, 1992). The litter on *Corresponding author. Tel.: +91-452-858928; fax: +91-452859139.

the forest ¯oor acts as an input±output system of nutrients (Das and Ramakrishnan, 1985) and the rates at which forest litter falls and, subsequently, decays regulate energy ¯ow, primary productivity and nutrient cycling in forest ecosystems (Waring and Schlesinger, 1985). It is particularly important in the nutrient budget of tropical forest ecosystems on nutrient-poor soils, where vegetation depends on recycling of nutrients contained in the plant detritus (Singh,

0378-1127/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved. PII: S 0 3 7 8 - 1 1 2 7 ( 9 9 ) 0 0 0 6 2 - 6

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S.M. Sundarapandian, P.S. Swamy / Forest Ecology and Management 123 (1999) 231±244

1968). Bray and Gorham (1964) reviewed the rates of litterfall in vegetation types throughout the world. Many reports suggested that density, basal area, age structure (Stohlgren, 1988), altitude (Reiners and Lang, 1987), latitude (Bray and Gorham, 1964) and season are factors that strongly in¯uence litterfall dynamics in natural forests. However, Bray and Gorham (1964) in temperate forest ecosystems, and Kumar and Deepu (1992) in tropical forest ecosystems, reported that the litterfall rates did not directly relate to stand basal area and density. Soil fertility, soil-water retention and species composition are important within the same climate range (Facelli and Pickett, 1991). Although there have been several studies on litter dynamics in tropical forest ecosystems in India (Rai and Proctor, 1986; Kumar and Deepu, 1992; Visalakshi, 1993; Khiewtam and Ramakrishnan, 1993; Tripathi and Singh, 1995), information on litter production and decomposition in natural forest ecosystems in the Western Ghats is limited. Therefore, in the present study an attempt was made to characterise the litter dynamics and standing crop of litter of both deciduous and evergreen forest ecosystems at the Western Ghats of Tamil Nadu to test whether litterfall is a function of ¯oristic composition, density, basal area and disturbance regime. 2. Study area The study area at Kodayar (village), located 400 km south of Madurai (778150 E, 88290 N) is at an 250±

Fig. 1. Map of the study area showing location of the study.

650 m elevation in the Kanyakumari district of Tamil Nadu, South India (Fig. 1). The mean annual rainfall recorded in the study sites was 2338 mm, of which 81% occurred from June to November (Fig. 2). December to March represents a brief dry period. Average monthly maximum and minimum temperatures were 308 and 268C in summer and 288 and 248C in winter, respectively. Besides all other biotic entities, Kanis (local tribals) are a part of the ecosystem here. This forest area has 30 Kani settlements, which occupies an area of 6.85 km2. Four different study sites (two each in deciduous forest ± sites I and II ± and evergreen forests ± sites III and IV) were selected at Kodayar forest ecosystem for the present study. Each study site was divided into three sub-sites. The species that dominate in site I are

Fig. 2. Temperature and rainfall pattern for the study area at Kodayar in the Western Ghats of Tamil Nadu.

S.M. Sundarapandian, P.S. Swamy / Forest Ecology and Management 123 (1999) 231±244

Terminalia paniculata Roth, Careya arborea Roxb., Buchanania lanzan Spr., Emblica of®cinalis Gartner, Dillenia pentagyna Roxb., Pterocarpus marsupium Roxb. and T. arjuna W. and A. The herbaceous community is mostly comprised of monocotyledons such as Themeda cymbaria Hack., Themeda sp., Globba orixensis Roxb., Imperata cylindrica Dur. and Sch. and Thespesia lampas Dalz. Site I has been subjected to annual wild ®re during summer (December±February). Site II is dominated by T. paniculata, followed by Aporosa lindleyana Baill. and Xanthophyllum ¯avescens Roxb. Understorey vegetation is composed of dicotyledonous species, such as Helicteres isora L. and Eupatorium odoratum L. Site II has also been subjected to anthropogenic perturbations, such as grazing and collection of minor forest produce. Sites III and IV are undisturbed evergreen forests. The species that dominate these sites are Hopea parvi¯ora Bedd., Syzygium laetum Gandhi, followed by Artocarpus heterophyllus Lam., Ixora brachiata Roxb., Syzygium sp., Vateria indica L. and X. ¯avescens Roxb. Understorey vegetation consists of Psychotria nigra L., Psychotria sp. Calamus sp., Memecylon sp. and Isonandra lanceolata W. The contribution of grasses is comparatively much lower in sites III and IV than in other sites except under open canopies. The species composition also varied, and consists of Oplismenus compositus Beauv. and Panicum sp. under open canopies of evergreen forests. 3. Methods 3.1. Litter collection Twenty-one 1 m  1 m litter traps, 20 cm high above the ground, were laid out at each site (seven in each sub-site). Litter was collected at monthly intervals from the traps for two years (1993±1995) commencing in June 1993. The litter was taken to the laboratory and categorised into leaf, woody (small branches and bark), reproductive parts and miscellaneous. The leaf litter was then sorted out according to species. Dry weight of each component was determined by drying to a constant weight at 808C and the mean monthly value for each sub-site was worked out on a unit area basis (g/m2 or t/ha). Occasionally a few traps were destroyed by animals and/or ®re in Site I. In

233

such cases, the mean values corresponding to the available traps per sub-site were used to determine the litterfall. However, the damaged traps were subsequently replaced. Standing crop of forest ¯oor litter (litter on the soil surface) was estimated in May 1993 and May 1994 in all the sub-sites. Twenty-one litter samples were collected from each site (seven from each sub-site), using a 0.25 m2 quadrat frame placed randomly, and transported to the laboratory in polythene bags and processed, following the procedures given above for the litterfall. 3.2. Litter decomposition Freshly fallen leaves of eleven dominant species in these sites such as Terminalia paniculata, Macaranga peltata, Dillenia pentagyna, Pterocarpus marsupium, Aporosa lindleyana, Careya arborea, Artocarpus hirsutus, Vateria indica, Xanthophyllum ¯avescens, Ixora brachiata, and Hopea parvi¯ora were collected from the study sites during February and March 1994 for decomposition study. All the leaves were dried at 45± 508C for ca. 48 h after species-wise pooling of the samples from different sites in a ventilation oven. Six sub-samples from each species were analysed for initial nitrogen and phosphorus contents, following the methods given by Allen et al. (1974). The standard litter-bag technique was used for the decomposition studies (Singh and Gupta, 1977), wherein 10 g of dried leaf samples of the eleven selected species were placed in nylon-mesh bags (1 mm) and placed on the forest ¯oor. This litterbag mesh size (1 mm) may underestimate the rate of litter decomposition, because it restricts the entry of large invertebrates, scavengers and decomposers that could be important detritivores. The 1-mm mesh size is common in many studies of decomposition: it is suf®ciently small to prevent major losses of litter through fragmentation and, probably, does not exclude any important decomposers. Hence, the data from 1mm mesh size bags conform with the other decomposition studies and are probably minimal estimates of true litter-decomposition rates. A total of 75 samples each [eleven species by 12 monthly sampling intervals (a total of 11 species, i.e. seven species in sites I and II, and ®ve species in sites III and IV; among these, only

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S.M. Sundarapandian, P.S. Swamy / Forest Ecology and Management 123 (1999) 231±244

one is common in all the four sites)] were placed at each of the sub-sites in all the study sites between June 7 and June 11, 1994. Six bags per species in each subsite were collected at monthly intervals up to one year. The litter bags were transported to the laboratory and cleaned of ingrown roots, if any, brushed free of foreign materials and oven-dried in paper bag to a constant weight. After drying the litter mass, each bag was weighed individually. ANOVA was used to compare litterfall rates among the sampling dates after log transformation of data. ANOVA was also used to test for differences among sites, different litter components and among species. The model for constant potential weight loss (Olson, 1963) is represented by the following equation: X=Xo  eÿkt where X is the weight remaining at time t, Xo the original mass, `e' the base of natural logarithm, k the decay rate coef®cient, and t the time. This equation was ®tted in the data on mass disappearance. Half-life periods (t0.5) of decomposing litter samples were estimated from k values using the following equation (Bockheim et al., 1991): t…0:5† ˆ ln …0:05†=…ÿk† ˆ 0:693=…ÿk†

4. Results 4.1. Litterfall Average annual litterfall (1993±1995) of the study sites ranged from 5.63 to 8.65 Mg haÿ1 yearÿ1 (Table 1). Greater litterfall was recorded in sites II and III compared to sites I and IV. Site I and IV had greater litterfall in 1994±1995 than the previous year (1993±1994). However, it was reversed in case of sites II and III. Contribution of leaf litter to the total litter was signi®cantly (p < 0.01) greater when compared to other categories. Woody litterfall (small branches and bark) was signi®cantly (p < 0.05) greater in sites II and III, when compared to sites I and IV. Contribution of reproductive litter to the total litterfall was signi®cantly (p < 0.01) greater in sites III and IV compared to other study sites. Transformed values of monthly litterfall (log e) of the study sites are presented in Table 2. The total litterfall was signi®cantly (p < 0.05±p < 0.01) variable at different collection intervals. In all the study sites, occurrence of litterfall was signi®cantly (p < 0.05) greater during the dry season (January±April) and it was also greater in the month of November (rainy season). However, minimum litterfall was recorded

Table 1 Vegetation characteristics and litter production in four study sites at Kodayar in the Western Ghats of Tamil Nadu Categories

Site I

Site II

Site III

Site IV

Tree density >10 cm, GBH No./ha Basal area (m2 haÿ1) Average annual litter fall (Mg haÿ1 yearÿ1) Average annual litter fall (Mg haÿ1 yearÿ1) 1993±1994 1994±1995

450 28.05 5.8aa

352 33.77 8.7ba

748 81.38 7.8ba

862 90.44 5.6aa

**b

5.61d 6.02d **b 3.8aa (0.39)e

9.22d 8.11d **b 4.4aa (0.46)e

8.12d 7.51d **b 5.5ba (0.52)e

5.31d 5.92d **b 5.2ba (0.53)e

***c

4.7a1 0.7aa2d 0.3aa3d 0.1 ***c

6.8b1 1.6ba2d 0.3aa3d 0.1 ***c

5.7a1 1.6ba2d 0.5ba3d 0.03 ***c

4.1c1 1.1aa2d 0.5ba3d 0.02 ***d

Standing crop of litter (Mg haÿ1) Mean litter components (Mg haÿ1 yearÿ1) leaf litter woody litter reproductive litter others a

Different letter(s) on the same rows indicates significant differences. p < 0.05. c p < 0.01. d Different subscript(s) on the same column indicates significant differences. b

***c **b ***c

S.M. Sundarapandian, P.S. Swamy / Forest Ecology and Management 123 (1999) 231±244 Table 2 Monthly litter fall (loge) transformed values (Kg haÿ1) of the study sites at Kodayar in the Western Ghats of Tamil Nadu Months

Site Ia

Site IIa

Site IIIa

Site IVa

1993 June July August September October November December

5.2b 5.3bc 5.9c 4.5a 4.7a 6.9g 6.4f

5.4b 5.3b 5.2ab 5.1ab 5.2ab 7.4h 6.6ef

6.0b 6.0b 6.0b 5.3a 5.5a 6.7cd 6.1b

5.7de 6.2fg 6.5ghi 4.2a 5.2c 6.5hi 5.6de

1994 January February March April May June July August September October November December

7.0gh 7.2gh 5.7de 4.6a 5.4bcd 5.2b 5.3b 5.5bcd 5.3bc 4.7a 6.9g 6.5f

7.3h 7.4h 7.1gh 6.9fg 6.2cd 5.4b 5.3b 5.2ab 5.1ab 4.9a 6.8ef 6.5de

6.9de 7.2f 7.0de 6.9de 6.8cde 6.0b 6.0b 5.9b 5.4a 5.5a 6.6c 6.2b

6.4fgh 6.8ij 6.5ghi 5.4cd 5.5de 5.7de 6.2f 6.5ghi 4.9b 5.7de 6.6hi 5.6de

1995 January February March April May Significance level

7.2gh 7.3h 5.6cde 4.6a 5.3bc p < 0.01

7.3h 7.3h 7.1gh 6.9fg 6.1c p < 0.01

6.8cde 7.1ef 6.9cde 6.8cde 6.7cd p < 0.05

6.6hi 6.9i 6.6hi 5.8e 5.5de p < 0.01

a Different letter(s) on the same column indicates significant differences.

during July±October, while it was recorded in April in Site I. Percentage contribution of various litter components, such as leaf litter, woody litter and reproductive parts to the total monthly litterfall of all the study sites are given in Fig. 3. The contribution of leaf litter to the total litterfall was greater during the dry season, whereas the contribution of woody litter to the total litterfall was signi®cantly higher during June±August and November±January compared to other months, except in Site I. Leaf-litter contribution was greater compared to other categories (woody litter and reproductive parts) in all the study sites, except in two (July and August) months.

235

Percentage contribution of some of the dominant tree species litter to the total annual litter production are presented in Table 3. In deciduous forests, Terminalia contributed signi®cantly (p < 0.01) greater amounts of leaf litter to the total annual litterfall, followed by Careya arborea, Macaranga peltata, Aporosa lindleyana and Dillenia pentagyna; whereas in evergreen forests, Hopea parvi¯ora contributed the most to annual litterfall, followed by Dipterocarpus indicus and Artocarpus heterophyllus. Initial nutrient concentration of leaf litter of all the dominant tree species (selected for decomposition study) are presented in Table 4. Higher concentrations of nitrogen were recorded in H. parvi¯ora, followed by P. marsupium and X. ¯avescens; whereas phosphorus was higher in H. parvi¯ora, followed by V. indica and M. peltata. The nitrogen and phosphorus concentrations were low in T. paniculata. 4.2. Litter decomposition Percentage of litter mass remaining in the bags at each sampling date are shown in Fig. 4(a and b). The mass remaining in litter bags decreased linearly with time for all the species and sites. The regressions describing decay rates over time were highly signi®cant (p < 0.01) for all the species and sites (R2 values range from 0.75 to 0.99; most of the values exceeding 0.85). In deciduous forests (sites I and II), all the leaves lost their mass completely within the period ranging from 10±12 months, except for A. lindleyana and A. hirsutus. In site I, M. peltata leaves decomposed in ca. 10 months. In Site II, both M. peltata and P. marsupium leaves decomposed within 10 months. Similarly, rapid mass loss was observed in X. ¯avescens and I. brachiata in evergreen forests (sites III and IV). Decomposition was characterised by an initial faster rate of disappearance, followed by a subsequent slower rate. The percentage of litter mass remaining at the end of 90 days ranged between 38.96% and 72.66%. A. hirsutus, A. lindleyana and V. indica exhibited slower decomposition rates compared to other species. Decay-rate coef®cient (k) and half-life period (t0.5) of decomposing leaf-litter samples are presented in Table 5. Decay-rate coef®cients (k) for all the species ranged between 0.136 (A. hirsutus) to 0.403 (M. peltata) while half-life period ranged for 1.72 to

236

S.M. Sundarapandian, P.S. Swamy / Forest Ecology and Management 123 (1999) 231±244

Fig. 3. Percentage contribution of various litter components to the total monthly litterfall of the tropical forests at Kodayar in the Western Ghats of Tamil Nadu.

S.M. Sundarapandian, P.S. Swamy / Forest Ecology and Management 123 (1999) 231±244

237

Table 3 Contribution of some dominant species litter (Mg haÿ1 yearÿ1) to the total annual litterfall in the study sites at Kodayar in the Western Ghats of Tamil Nadu Species

Site Ia,d,e

Site IIa,d,e

Site IIIa,d,e

Site IVa,d,e

Agrostistachys indica Ancistrocladus heyneanus Aporosa lindleyanea Artocarpus heterophyllus Artocarpus hirsutus Bridelia crenulata Buchanania lanzan Careya arborea Dillenia pentagyna Dipterocarpus indicus Holarrhena pubescens Hopea parviflora Hydnocarpus alpina Ixora brachiata Macaranga peltata Pterocarpus marsupium Psychotria sp. Syzygium mundagam Terminalia bellirica Terminalia sp. Vateria indica Xanthophyllum flavescens Monocots

Ð Ð Ð Ð Ð 0.041a (0.70) 0.28ab (4.83) 1.29c2 (22.43) 0.46bl (7.96) Ð Ð Ð Ð Ð Ð 0.26ab2 (4.51) Ð Ð Ð 1.91dl (33.13) Ð Ð 0.02a2 (0.27) **b

Ð Ð 0.70c (8.14) Ð 0.20a (2.34) Ð Ð 0.04al (0.42) 0.43bl (4.91) Ð 0.04a (0.40) Ð Ð 0.16a2 (1.79) 0.93d (10.71) 0.03al (0.35) Ð Ð 0.54bc (6.24) 1.40el (16.22) Ð 0.03al (0.30) 0.003al (0.03) ***c

Ð 0.04al (0.57) Ð 0.19abl Ð Ð Ð Ð Ð 0.74c (9.49) Ð 1.79dl (22.82) 0.03a2 (0.33) 0.06al (0.73) Ð Ð 0.03al (0.33) 0.01al (0.12) Ð Ð 0.29b (3.75) 0.11ab2 (1.39) Ð ***c

0.005a 0.06a2 (1.08) Ð 0.33b2 Ð Ð Ð Ð Ð Ð Ð 1.68cl (29.84) 0.01al (0.20) 0.08al (1.40) Ð Ð 0.03al (0.56) 0.02a2 (0.32) Ð Ð Ð 0.03al (0.48) Ð ***c

**b ***c

***c NS NS ***c ***c ***c NS ***c NS ***c ***c

a

Different subscript(s) on the same rows indicates significant differences. p < 0.05. c p < 0.01. d Different letter(s) on the same column indicates significant differences. e Values within parentheses represent percentage contribution to total litterfall. b

Table 4 Initial concentration of N and P in the leaves of selected tree species at Kodayar in the Western Ghats of Tamil Nadu (n ˆ 6) Name of the species

Nitrogena (%)

Phosphorusa (%)

Aporosa lindleyana Artocarpus hirsutus Careya arborea Dillenia pentagyna Hopea parviflora Ixora brachiata Macaranga peltata Pterocarpus marsupium Terminalia paniculata Vateria indica Xanthophyllum flavescens

1.03 1.01 1.07 1.04 1.60 1.25 1.24 1.55 0.98 1.27 1.43

0.05 0.06 0.05 0.05 0.11 0.06 0.07 0.05 0.05 0.08 0.06

a

(0.04) (0.16) (0.11) (0.17) (0.27) (0.19) (0.31) (0.26) (0.06) (0.37) (0.25)

Values within parentheses represent standard error.

(0.01) (0.01) (0.004) (0.004) (0.04) (0.02) (0.01) (0.01) (0.003) (0.03) (0.01)

5.10 months. Comparatively greater k values were observed in Site I compared to Site II. 5. Discussion 5.1. Litterfall Litterfall pattern in a rain-forest ecosystem (Hudds, 1971), as in any other forest ecosystem type (Facelli and Pickett, 1991), is determined by a variety of factors, such as species composition, successional stage in its development and related microclimatic differences. Therefore, it is reasonable to expect variations in the litterfall pattern (production) among the sites shown in the present study. The mean annual

238

S.M. Sundarapandian, P.S. Swamy / Forest Ecology and Management 123 (1999) 231±244

Fig. 4. (a) Percentage of litter mass remaining in litter bags at various time intervals in Site I and Site II in tropical forests at Kodayar in Western Ghats of Tamil Nadu. TP, Terminalia paniculata; MP, Macaranga peltata; DP, Dillenia pentagyna; PM, Pterocarpus marsupium; AL, Aporosa lindleyana; CA, Careya arborea; and AH, Artocarpus hirsutus. (b) Percentage of litter mass remaining in litter bags at various time intervals in Site III and Site IV in tropical forests at Kodayar in Western Ghats of Tamil Nadu. AH, Artocarpus hirsutus; VI, Vateria indica; XF, Xanthophyllum flavescens; IB, Ixora brachiata; and HP, Hopea parviflora.

litterfall was signi®cantly (p < 0.05) greater in sites II and III than that in sites I and IV. This variation in litterfall pattern among the sites could be attributed to species composition. Facelli and Pickett (1991) reported that the species composition are important for litter production within the same climate range. In site II, A. lindleyana, M. peltata and Terminalia bellirica contributed greater quantity of litter in addition to the common species (sites I and II; Terminalia sps.) to the total litter production. Similarly, in Site III, D. indicus and V. indica contributed more in addition to common species (sites III and IV; Hopea parvi¯ora). Therefore, the results suggest that species composition and their contribution towards litter becomes important in overall community or site-litter production, as observed in sites II and III. Vogt et al. (1985) also stated that the differences could be explained by either tree behaviour, mean annual tem-

perature, minimum monthly mean temperature, precipitation and latitude. The mean annual litterfall at four study sites of the present study did not appear to be directly related to basal area and density (Table 1). Differences in tree basal area ranged between 28.05 and 90.44 m2/ha. However, these differences failed to manifest itself in terms of litterfall rates. Past studies also failed to establish cause±effect relationships between such parameters and litterfall in temperate forests (Bray and Gorham, 1964) and tropical forests (Kumar and Deepu, 1992). In contrast, Stohlgren (1988) suggested that annual litterfall can be better predicted by a function derived from the individual tree basal area and live crown ratio. In the present study, year-to-year variation in litter production was recorded. Other studies (Songwe et al., 1988; Lisanework and Michelsen, 1994) also showed considerable variation in litter

Species

Site I

Site II 2

Site III 2

Site IV 2

k

t(0.5)

R

k

t(0.5)

R

k

t(0.5)

R

k

t(0.5)

Aporosa lindleyana Artocarpus hirsutus

0.209 0.164

3.321 4.226

0.93 (0.08) 0.88(0.11)

0.157 0.136

4.414 5.096

0.96 (0.06) 0.93 (0.09)

Ð 0.191

Ð 3.638

0.97 (0.06)

Ð 0.205

Ð 3.384

Careya arborea Dillenia pentagyna Hopea parviflora Ixora brachiata Macaranga peltata Pterocarpus marsupium Terminalia paniculata Vateria indica Xanthophyllum flavescens

0.338 0.353 Ð Ð 0.403 0.367 0.330 Ð Ð

2.053 1.963 Ð Ð 1.720 1.889 2.099 Ð Ð

0.77 (0.15) 0.94(0.08)

2.616 2.354 Ð Ð 2.180 1.900 2.416 Ð Ð

0.88 (0.12) 0.92 (0.10)

Ð Ð 0.287 0.363 Ð Ð Ð 0.181 0.250

Ð Ð 2.416 1.908 Ð Ð Ð 3.829 2.774

Ð Ð 0.271 0.279 Ð Ð Ð 0.219 0.296

Ð

0.265 0.294 Ð Ð 0.90 (0.12) 0.318 0.77(0.17) 0.365 0.90(0.10) 0.287 Ð Ð p a 2 Values in the parentheses represents standard error (S.E. ˆ 1 ÿ R =n ÿ 2).

0.88 (0.12) 0.87 (0.13) 0.75 (0.17)

Ð Ð 0.84 (0.14) 0.85(0.13)

0.99 (0.03) 0.82 (0.14)

2.562 2.487 Ð Ð Ð 3.159 2.342

R2 0 . 9 1 (0.009) Ð 0.88 (0.12) 0.83(0.14)

0.93 (0.08) 0.78 (0.16)

S.M. Sundarapandian, P.S. Swamy / Forest Ecology and Management 123 (1999) 231±244

Table 5 Decay rate coefficient (k) and half life (t0.5) of different species in the study sites at Kodayar in the Western Ghats of Tamil Nadu

239

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production between the years. The outcome of the present study suggests that further scienti®c research is to be oriented towards understanding the intricacies of variations in litterfall production between years. The mean annual litterfall in the present study (5.63±8.65 Mg haÿ1 yearÿ1) is comparable with the values reported by others (Table 6). The values obtained in the present study lie among the lower limits of the values (5.05±15.03 Mg haÿ1 yearÿ1) reported by William and Gray (1974) in equatorial forests and is also lower than those reported from elsewhere (Bray and Gorham, 1964; Songwe et al., 1988; Scott et al., 1992; Lisanework and Michelsen, 1994) and India (Gupta and Rout, 1992; Kumar and Deepu, 1992; Khiewtam and Ramakrishnan, 1993; Visalakshi, 1993). Periodicity of litterfall is largely followed by annual cycles of environmental parameters. Our study showed that one major peak of litterfall occurred during the dry season (January±April) and a smaller peak in November. The signi®cant seasonal variation in litter production with highest values in the dry months is in agreement with the results of other authors (Hopkins, 1966; Kumar and Deepu, 1992; Muoghalu et al., 1993). Available studies concerning deciduous plantations clearly showed that the deciduous species yielded maximum litter during the summer period (Kikuzawa et al., 1984). Pascal (1988) reported that the rhythm of leaf shed was characterised by a heavy litterfall during the dry season in wet evergreen forests of Attappadi, Western Ghats, India. Jackson (1978) assumed that, in environments where the temperature variation throughout the year is small and moisture availability is seasonal, dry season leaf fall and wet ¯ushing will occur to avoid seasonal moisture stress. Moore (1980) reported that water stress triggers de novo synthesis of abscissic acid in the foliage of plants which, in turn, can stimulate senescence of leaves and other parts. Besides, the rise in ambient temperatures owing to ®res, as in the present study (Site I), can also spur an accelerated fall during the summer as is reported by Kumar and Deepu (1992) in tropical moist deciduous forests. The second peak of litterfall during November (rainy season) could be attributed to strong winds as well as heavy rain, as is reported in the forests of Sarawak (Proctor et al., 1983) and Nigerian rain forests (Muoghalu et al., 1993). Leaf

litter constituted a substantial portion of the total litter production in the present study, which is also in agreement with the results of others (Morellato, 1992; Scott et al., 1992; Khiewtam and Ramakrishnan, 1993; Muoghalu et al., 1993; Visalakshi, 1993; Stocker et al., 1995). According to Spain (1984), the standing crop of litter in tropical and sub-tropical forests ranges from 2.1 to 12.5 Mg haÿ1. The standing crop of litter estimated in the present study (3.8±5.5 Mg haÿ1) falls well within the ranges reported for other tropical forest ecosystems (Table 6). 5.2. Leaf-litter decomposition An initial faster rate of disappearance, followed by a subsequent slower rate, is in agreement with the results reported by others (Anderson et al., 1983; Swift and Anderson, 1989; Kumar and Deepu, 1992; Jamaa and Nair, 1996). This could be due to higher initial content of water-soluble materials, simple substrates and the breakdown of litter by decomposers, especially the micro¯ora (Songwe et al., 1995). The relatively slower decay rates at the later stages may be due to the accumulation of more recalcitrant constituents in the residual litter mass. The higher relative loss of mass during the rainy season, compared to the dry season in the present study, might be due to physical determinants, particularly soil moisture content, temperature and evapotranspiration for the activity of decomposers (Facelli and Pickett, 1991). The time taken for complete mass loss in litter bags ranged from 10 to 12 months, except in Artocarpus hirsutus, Vateria indica and Aporosa lindleyana. Differences in loss of mass in site and species may be caused either by environmental factors or variation in substrate concentrations (William and Gray, 1974). Nutrient composition and lignin content of litter should become more important in determining the rate of decomposition (Singh and Gupta, 1977; Melillo et al., 1982; Couteaux et al., 1995). Tanner (1981) also stated that 27±96% of decomposition depends on the type of humus and N and P contents of the leaves. Higher nitrogen content of original material of fast decomposing leaf litter such as P. marsupium, X. ¯avescens, I. brachiata and M. peltata promoted decomposition as suggested

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241

Table 6 Total litter fall and standing crop litter of some tropical forests of the world Forest type

Location

Litter production (Mg haÿ1 yearÿ1)

Standing crop litter (t/ha)

Source

India Deciduous forest Evergreen forest Deciduous forest Evergreen forest Decidous forest Tropical forest Rainforest Moist forest Mixed deciduous Moist deciduous Rain forest Dry evergreen Humid forest Dry tropical bamboo savannahs

Kodayar, Tamilnadu Kodayar, Tamilnadu Varanasi Northeast India Kurushetra Karnataka Attapadi, Kerala Karnataka Mornihills, Haryana Thrissur, Kerala Cherrapunji, NE India Coromandel Coast Nelliampathy, Kerala Vindhyan Plateau

5.76±8.65 5.63±7.84 1.0±6.2 9.0 4.8 3.4±4.2 8.5 5.1±10.2 10.4 12.2±14.4 11.7 5.1±11.1 17.5 2.8±5.9

3.8±4.4 5.2±5.5 Ð Ð 5.4 Ð Ð Ð 6.1 Ð Ð 2.1±3.0 ± ±

Present study Present study Singh, 1968 Boojh and Ramakrishnan, 1982 Rajvanshi and Gupta, 1985 Rai and Proctor, 1986 Pascal, 1988 Bhat, 1990 Gupta and Rout, 1992 Kumar and Deepu, 1992 Khiewtam and Ramakrishnan, 1993 Visalakshi, 1993 Chandrashekara, 1991 Tripathi and Singh, 1995

5.0 16.51 Ð 3.0 1.0±2.4 3.9±4.2 6.6 6.1±7.7 Ð Ð Ð 8.1±11.7 5.5 5.9 6.1 7.1 Ð Ð Ð Ð Ð Ð Ð Ð 5.5 Ð Ð Ð

Jenny et al., 1949 Jenny et al., 1949 Bray and Gorham, 1964 Hopkins, 1966 Hopkins, 1966 Cornforth, 1970 Klinge, 1977 Edwards, 1977 Lugo et al., 1978 Kunkel-Westphal and Kunkel, 1979 Brasell et al., 1980 Tanner, 1981 Anderson et al., 1983 Anderson et al., 1983 Anderson et al., 1983 Anderson et al., 1983 Proctor et al., 1983 Spain, 1984 Vitousek, 1984 Cuevas and Medina, 1986 Cuevas and Medina, 1986 Cuevas and Medina, 1986 Songwe et al., 1988 Heaney and Proctor, 1989 Morellato, 1992 Muoghalu et al., 1993 Lisanework and Michelsen, 1994 Stocker et al., 1995

10.8

Songwe et al., 1995

Other countries Lowland Rainforest Lowland Montane Malaysian forest Mixed evergreen Mixed semideciduous Rainforest Lowland forest Lowland forest Deciduous forest Tropical forest Tropical forest Lowland forest Alluvial forest Dipterocarp forest Heath forest Forest over limestone Lowland rainforest Rainforest Montane Rainforest Terra firme forest Tall Amazon forest Caetinga forest Rain forest Tropical forest Semi-deciduous Rainforest Evergreen montane forest Rain forest Semi-deciduous

Columbia 8.5 Columbia 10.1 Malaysia 5.4±14.8 Nigeria 7.2 Nigeria 4.6±6.4 Trinidad 6.8±7.0 Brazil, Manaus 7.6 Papua New Guinea 6.8±7.6 Guanica, Puerto Rico 2.5 Guatemala 9.7 North-Eastern Australia 8.2±9.7 Jamaica 4.9±5.5 Sarawak, Mulu 9.4 Sarawak, Mulu 7.8 Sarawak, Mulu 8.1 Sarawak, Mulu 10.4 Sarawak 8.8-12 Northern Queensland 8.13 Hawaii 5.2±6.3 Amazonia 10.3 Amazonia 5.6 Amazonia 2.4 Cameroon 12.9±14.1 Costa Rica 5.3±9.0 Brazil 7.0±8.6 Nigeria 4.6±6.4 Ethiopia 10.9 North Queensland, Aus-7.04±13.64 tralia Bakundu, Cameroon 13.5

by other authors (Witkamp, 1966; Kumar and Deepu, 1992; Tripathi and Singh, 1995; Martin and Scott, 1997). Nitrogen contents of slow-decom-

posing leaf litter have low values except for H. parvi¯ora and V. indica. However, Daubenmire and Prussco (1963) found poor intraspeci®c correlation

242

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between nitrogen content and decomposition rates. The varying rates of decomposition seemed to be not only due to the nutrient content of the leaves but also to their morphological characters (Songwe et al., 1995). Edwards (1977) noted that thick and tough leaves with prominent midribs and veins decomposed slower than species with thin and less rigid leaves without prominent skeletal tissues. In the present study, A. hirsutus, V. indica, A. lindleyana and H. parvi¯ora, leaves are thick and rigid with prominent midribs and veins which could be the reason for slower decomposition. On the other hand, M. peltata, X. ¯avescens and I. brachiata which have thin leaves without prominent skeletal tissues decomposed at a faster rate. Mass-disappearance rates in the present study were high in comparison with the values reported for other temperate ecosystems. Das and Ramakrishnan (1985) compiled the available literature on different pinespecies litter decomposition and stated that annual decay-rate coef®cient ranged from 0.307 to 0.46. Melillo et al. (1982) also reported that the annual decay rate coef®cients of temperate hardwood species ranged from 0.08 to 0.47. Stohlgren (1988) reported that the annual decay rates of six species in Sierran forest varied from 0.18 to 0.62, and the time required for 95% decay ranged from 11 to 27 years. In the present study, the time required for 50% decay ranged 1.72±5.1 months, which is lower than those of reported ranges. The large differences in decay rates could be attributed to decomposer population dynamics as suggested by Kumar and Deepu (1992). They also reported that tropical moist deciduous forest species exhibited markedly higher decay rates compared to temperate forest species. In the present study, 1-mm mesh litter bags were used. This might have restricted the entry of microfauna into litter bags and resulted in slower rate of litter decomposition. Acknowledgements We thank the Department of Environment and Forest, Government of India, for ®nancial assistance through research grant. S.M. Sundarapandian thanks to CSIR for the award of a Senior Research Fellow-

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