ORIGINAL ARTICLE

Leaf litter decomposition of dominant tree species of NamdaphaNational Park, Arunachal Pradesh, northeast India

Atiqur Rahman Barbhuiya Æ Ayyanadar Arunachalam ÆPrabhat Chandra Nath Æ Mohammed Latif Khan ÆKusum Arunachalam

Received: 20 October 2006 / Accepted: 5 June 2007 / Published online: 12 December 2007

� The Japanese Forest Society and Springer 2007

Abstract Rates of weight loss and nutrient (N and P)

release patterns were studied in the leaf litter of the dom-

inant tree species (Ailanthus grandis, Altingia excelsa,

Castanopsis indica, Duabanga sonneriatioides, Dysoxylum

binectariferum, Mesua ferrea, Shorea assamica, Taluma

hodgsonii, Terminalia myriocarpa and Vatica lancefolia)

of a tropical wet evergreen forest of northeast India.

Nitrogen and phosphorus mineralization rate and decay

pattern varied significantly from species to species. In

general, the decay pattern, characterized by using a com-

posite polynomial regression equation, exhibited three

distinct phases of decay during litter decomposition—an

initial slow decay phase (0.063% weight loss day-1), fol-

lowed by a rapid decay phase (0.494% weight loss day-1)

and a final slow decay phase (0.136% weight loss day-1).

The initial chemical composition of the litter affected

decomposition rates and patterns. Species like D. sonner-

iatoides, D. binectariferum, and T. hodgsonii with higher N

and P content, lower carbon and lignin content, and lower

C:N ratio and lignin:N ratio exhibited relatively faster

decomposition rates than the other species, for example M.

ferrea, C. indica and A. grandis. A slow decay rate was

recorded for species such as M. ferrea, C. indica, and A.

grandis. The initial N and P content of litter showed sig-

nificant positive correlations with decay rates. Carbon and

lignin content, lignin:N, and C:N showed significant neg-

ative correlations with decay rates. Soil total N and P, and

rainfall, soil temperature, and soil moisture had positive

correlations with decay rates. The rapid decomposition

rates observed in comparison with other different forest

litter decay rates confirm that tropical wet evergreen forest

species are characterized by faster decomposition rates,

indicating a faster rate of organic matter turnover and rapid

nutrient cycling.

Keywords Decay rate � Lignin � Litter decomposition �Nitrogen � Phosphorus � Tropical wet evergreen forest

Introduction

The term ‘‘decomposition’’ is defined as the process of

biological disintegration of dead organic materials whereby

mineralization of complex organic compounds into simple

inorganic forms takes place. This loss of nutrients from

decomposing litter is a key process governing the avail-

ability of nutrients in ecosystems (Moore et al. 2006). The

release of nutrients from forest litter through natural

decomposition processes is recognised as an important part

of the plant biomass that is made available for further plant

growth (Maclean and Wein 1978). The importance of litter

decomposition to nutrient cycling and ecosystem function

has long been known, and a huge number of studies has

been undertaken (Gillon et al. 1999; Moore et al. 2006),

many in response to regional or species-specific concerns.

Attempts to predict the effects of climate change have

recently prompted studies of litter from wider ranges of

plant types (Perez-Harguindeguy et al. 2000).

The effect of litter quality is obvious from the different

decay rates of various tissue types, but identifying the

A. R. Barbhuiya � A. Arunachalam � P. Chandra Nath �M. Latif Khan � K. Arunachalam

Department of Forestry, North Eastern Regional

Institute of Science and Technology,

Nirjuli 791109, Arunachal Pradesh, India

A. R. Barbhuiya (&)

Department of Forestry, Mizoram University,

Aizawl 796009, Mizoram, India

e-mail: arbarbhuiya@gmail.com

123

J For Res (2008) 13:25–34

DOI 10.1007/s10310-007-0044-6

particular litter characteristics that are consistently and

closely related to decomposability has proven surprisingly

difficult. Across a broad range of litter type C:N ratio

seems to be the best predictor of decay rate (Perez-Har-

guindeguy et al. 2000), while the lignin content or lignin:N

ratio is better correlated with decay rates (Loranger et al.

2002). Long-term studies have indicated that the factors

that best correlate with rates of early decay are often not

the same as those that relate to long-term decay (Joffre

et al. 2001; Yang and Janssen 2002). Berg and Staaf (1980)

and Sangha et al. (2006) suggested that early decomposi-

tion is regulated by nutrient concentrations (especially N

and P) whereas the late-stage decay is regulated by lignin

concentration. Different species have different nutrient

release patterns, which are related to quality, season, and

environmental factors (Abiven et al. 2005; Arunachalam

et al. 2003).

Namdapha National Park has a variety of tree species, but

there is too little information on the relative rates of decay of

foliar litter of these species and litter chemical parameters

useful for predicting their decay rates. Thus, in this study we

have quantified the decomposition rates and nutrient min-

eralization patterns of the dominant tropical tree species

Ailanthus grandis, Altingia excelsa, Castonopsis indica,

Dysoxylum binectariferum, Duabanga sonneriatioides,

Mesua ferrea, Taluma hodgsonii, Terminalia myriocarpa,

Shorea assamica, and Vatica lancefolia of Namdapha

National Park, Arunachal Pradesh, India, to understand their

role in the organic matter and nutrient turnover that has a

bearing on the overall productivity of the ecosystem.

Study site

The study was conducted in a tropical wet evergreen forest

([200 years old approximately) in the Namdapha National

Park (27�2303000 N to 27�3904000 N latitude to 96�150200 E

to 96�5803300 E longitude) in the Changlang district of

Arunachal Pradesh, northeast India. The total park area is

1,985 km2 over an elevation range of 250–4,571 m asl,

of which 177 km2 is buffer zone. The region experiences

four seasons—winter (mid-November to February), spring

(March to April), monsoon (May to September), and a brief

autumn (October to mid-November). The major perennial

rivers flowing through Namdapha National Park include

the Noa-Dihing, Deban, Namdapha, and Burma Nala. In

addition to these, innumerable seasonal rainfed streams and

streamlets also drain the park. The annual rainfall ranged

from 2,000 to 4,300 mm between 1994 and 2004.

An experimental plot of 100 m 9 100 m was estab-

lished inside the Namdapha National Park (27�26015.800–27�26019.700 N latitude to 96�28012.300–96�28010.400 E lon-

gitude). The vegetation in the plot was dominated by mixed

tropical evergreen species. The experimental plot was on a

plain located at an altitude of 350 m asl with a mean annual

temperature of 21�C. Average monthly soil temperature

and moisture content were 31�C and 38.7%, respectively,

during summer and 16�C and 22.9%, respectively, dur-

ing winter (Fig. 1). Vegetation, microclimate, and soil

0

100

200

300

400

500

600

700

800

900

1000

Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar

Months

Rai

nfal

l (m

m)

0

5

10

15

20

25

30

35

40

45

Soi

l moi

stur

e co

nten

t (%

) &

tem

pera

ture

(°C

)

Fig. 1 Monthly variation of rainfall, temperature (filled triangles),

and moisture content (open squares) of the study area

Table 1 Vegetation, microclimate and soil (0–15 cm) physico-

chemical characteristics of the Namdapha National Park

Parameters Values

Vegetation

Density (plants ha-1)

Trees 610

Shrubs 13,280

Herbs 17,400

Basal area (m2 ha-1)

Trees 98.6

Shrubs 3.8

Herbs 0.424

Leaf litter fall (kg ha-1 year-1) 4896 ± 101

Soil properties

Texture

Sand (%) 58.4 ± 3.1

Silt (%) 19.8 ± 1.1

Clay (%) 21.8 ± 0.1

Texture class Sandy clay loam

Water-holding capacity (g g-1) 0.665 ± 0.003

Bulk density (g cm-3) 0.691 ± 0.032

Moisture content (g g-1) 0.314 ± 0.001

pH (1:2.5 w/v H2O) 5.2 ± 0.08

Organic C (g kg-1) 18.00 ± 1.00

Total N (g kg-1) 3.00 ± 0.20

C:N 6.0 ± 0.001

P concentration (g kg-1) 0.30 ± 0.01

± standard error from five replicate measurements

26 J For Res (2008) 13:25–34

123

characteristics have been summarized in Table 1. Tree

density and basal area were 610 trees ha-1 and 98.6 m2 ha-1,

respectively, in the selected plot. The ten dominant tree

species in the experimental plot are listed in in Table 2. Soil

was sandy clay loam, acidic (pH = 5.2), and the C:N ratio

was 6 (Table 1).

Methodology

Leaf litter chemistry

Freshly fallen leaves of the ten dominant tree species, viz.,

Ai. grandis, A. excelsa, C. indica, D. binectariferum,

D. sonneriatoides, M. ferrea, T. hodgsonii, T. myriocarpa,

S. assamica, and V. lancefolia, were collected during the

peak litter fall period (March). The litter samples were air

dried in the laboratory and sub-samples were kept at 80�C

for 48 h to determine the dry mass. The oven-dried mate-

rials were powdered in a Wiley mill to pass through 1 mm

pore size stainless-steel mesh and analysed for their

chemical composition. The ash content was determined by

igniting 1 g ground litter sample at 550�C for 6 h in a

muffle furnace and a total of 50% of the ash-free mass was

calculated as the carbon (C) content (Allen et al. 1974). Soil

organic carbon (SOC) was determined by the complete

oxidation method (Nelson and Sommers 1975). Nitrogen

(N) was estimated by use of a semi-micro Kjeldahl proce-

dure entailing acid digestion, distillation, and titration, in

accordance with Anderson and Ingram (1993). Total

phosphorus (P) was determined by triacid digestion, fol-

lowed by colorimetric reaction with ammonium and

stannous chloride (molybdenum blue method; Jackson

1958). Lignin, cellulose, and hemicellulose content were

determined gravimetrically according to Allen et al. (1974).

Litter decomposition

Decomposition of leaf litter of dominant tree species

was studied in the forest stand using a nylon bag

(15 cm 9 15 cm) technique (Gilbert and Bocock 1960).

The mesh size was 2 mm, small enough to prevent major

losses of litter samples yet large enough to permit aerobic

microbial activity and free entry of small soil organisms.

Air-dried material (5 g) was placed in each bag, which was

then stitched with nylon thread. For each species 80 bags

were prepared and randomly dispersed on the experimental

forest floor in the month of March 2003. After 30, 60, 90,

Table 2 List of tree species for decomposition study of Namdapha

National Park

Name of the species Family Growth

characteristics

Ailanthus grandis Prain. Simarubaceae Medium

Altingia excelsa Noron. Hamamelidaceae Slow

Castanopsis indica(Roxb.) Miq.

Fabaceae Slow

Duabanga sonneratioidesBuch.

Sonneratiaceae Fast

Dysoxylum binectariferumHk.f ex Bed

Meliaceae Medium

Mesua ferrea L. Clusaceae Slow

Shorea assamica Dyer. Dipterocarpaceae Slow

Talauma hodgsoniiHk. F. & Thom.

Magnoliaceae Slow

Terminalia myriocarpaMuell.

Combretaceae Fast

Vatica lancefolia(Roxb.) Blume.

Dipterocarpaceae Slow

Table 3 Initial chemical composition of leaf litter of the dominant tree species of the Namdapha National Park

Species C (mg g-1) N (mg g-1) P (mg g-1) Lignin (mg g-1) C:N L:N Cellulose

(mg g-1)

Hemicellulose

(mg g-1)

A. grandis 363.3 ± 26.8 10.6 ± 0.2 0.502 ± 0.011 170.3 ± 23.7 34.3 ± 1.3 16.1 ± 1.0 234.8 ± 36.8 61.6 ± 0.8

A. excelsa 341.5 ± 2.5 14.9 ± 0.6 0.513 ± 0.031 248.0 ± 8.8 23.1 ± 2.6 16.8 ± 2.0 320.2 ± 30.1 55.7 ± 4.6

C. indica 285.0 ± 9.7 6.9 ± 0.3 0.713 ± 0.017 180.0 ± 10.0 41.9 ± 3.2 26.5 ± 2.5 28.6 ± 2.1 70.3 ± 5.0

D. binectariferum 302.7 ± 19.3 18.7 ± 3.1 0.645 ± 0.001 157.9 ± 11.6 21.0 ± 1.1 8.4 ± 0.7 395.8 ± 36.1 49.5 ± 8.5

D. sonneriatoides 303.3 ± 51.0 20.5 ± 2.0 0.914 ± 0.024 137.6 ± 13.8 18.8 ± 1.6 6.7 ± 1.0 384.0 ± 29.7 60.2 ± 5.7

M. ferrea 281.7 ± 12.2 5.7 ± 0.8 0.456 ± 0.006 248.5 ± 26.4 49.4 ± 4.5 43.6 ± 2.6 219.0 ± 14.7 78.6 ± 6.3

T. hodgsonii 315.1 ± 21.3 13.2 ± 1.0 0.856 ± 0.001 210.6 ± 31.4 23.9 ± 2.9 16.0 ± 1.2 265.6 ± 45.3 40.8 ± 3.0

T. myriocarpa 301.6 ± 20.0 15.3 ± 3.3 0.474 ± 0.021 187.5 ± 17.6 19.7 ± 2.1 12.3 ± 1.0 241.4 ± 37.0 63.8 ± 7.0

S. assamica 315.0 ± 11.7 10.7 ± 4.5 0.617 ± 0.003 234.0 ± 18.8 29.4 ± 2.5 21.9 ± 1.3 275.1 ± 26.3 60.0 ± 1.9

V. lancefolia 340.1 ± 26.6 13.6 ± 2.3 0.543 ± 0.020 223.4 ± 21.4 25.0 ± 1.1 16.4 ± 2.9 225.6 ± 33.0 95.6 ± 9.3

± standard error from five replicate measurements

L:N, lignin:nitrogen ratio

J For Res (2008) 13:25–34 27

123

120, 150, 180, 210, 240, 270, 300, 330, 360, and 390 days

five-litter bags for each species were brought to the labo-

ratory, carefully avoiding loss of materials from the bags.

The litter bags were washed in a bucket full of tap water,

by swirling briefly, and carefully decanted through a 2-mm

mesh size sieve to remove extraneous matter. The litter was

then dried at 80�C for 48 h and weighed. The samples were

powdered and used for analysis of N and P concentrations.

The annual decay constant (k) was calculated by fol-

lowing the negative exponential decay model (Olson

1963): k = -ln (X/X0)/t, where, X0 is the initial dry weight,

X is the dry weight remaining at the end of the investiga-

tion, and t is the time period. The time required for 50%

(t50) and 99% (t99) weight loss was calculated as t50 =

0.693/k and t99 = 5/k (Olson 1963).

The effects on the rate of decomposition of the litter of

climatic variables, initial litter chemistry, and a few soil

characteristics were assessed by using a simple linear

regression function, Y = a + bx (Zar 1974). ANOVA was

used to test for differences among different species,

A. grandis

0

20

40

60

80

100

120 M. ferrea

A. excelsa

0

20

40

60

80

100

120T. hodgsoni

C. indica

0

20

40

60

80

100

120T. myriocarpa

D. binacterifeum

0

20

40

60

80

100

120S. assamica

D. sonneratoides

0

20

40

60

80

100

120

30 60 90 120 150 180 210 240 270 300 330 360 390 30 60 90 120 150 180 210 240 270 300 330 360 390

V. lancefolia

Dry

mat

ter

rem

aini

ng (

% o

f th

e in

itial

)

Y=98.56+0.33X-2.43X2-0.15X3

r=0.997, P<0.001 Y=99.16+3.15X-2.31X2+0.12X3

r=0.989, P<0.001

Y=95.90+4.61X-4.05X2+0.27X3

r=0.998, P<0.001Y=106.32-10.44X-2.24X2+0.24X3

r=0.991, P<0.001

Y=107.98-6.05X-1.05X2+0.07X3

r=0.991, P<0.001 Y=103.84-9.28X-0.98X2+0.09X3

r=0.993, P<0.001

Y=96.95-1.33X-2.99X2+0.22X3

r=0.999, P<0.001 Y=95.11+0.66X-3.12X2+0.21X3

r=0.994, P<0.001

Y=82.67+3.60X-5.33X2+0.45X3

r=0.996, P<0.001Y=103.21-4.65X-1.65X2+0.11X3

r=0.991, P<0.001

AutumnSummerSpring Winter AutumnSummerSpring Winter

Fig. 2 Decomposition of leaf litter

of different tree species. Verticallines represent standard error from

five replicate measurements

28 J For Res (2008) 13:25–34

123

different litter components, and, during sampling, dates of

decomposition. A composite polynomial regression model

Y = a + bX1 + cX2 + dX3…, was constructed using dummy

factors as the indicator variables to distinguish different

phases of decomposition (Arunachalam et al. 1998). By

using this equation an expected decay curve was fitted to

the litter mass data obtained at different times in the

decomposition study. In this equation, Y is the mass

remaining, a is the Y intercept (constant), b is the rate of

change in Y with respect to time, and c and d are shifts

parameters for adjustment of the Y intercept in Phase-II and

Phase-III, respectively. The shift parameters were the

dummy factors, equivalent to zero if decay was slow or 1 if

decay was fast.

Results

Nitrogen concentration in the leaf litter of the 10 dominant

tree species varied from a minimum of 5.8 mg g-1 for M.

ferrea to a maximum of 20.5 mg g-1 for D. sonneriatoides

(Table 3). Phosphorus concentration varied between

0.456 mg g-1 for M. ferrea to 0.914 mg g-1 for D.

sonneriatoides. Lignin, cellulose, and hemicellulose

concentrations varied significantly (P \ 0.05) among the

species. Lignin and C:N ratio were the greatest for M.

ferrea and minimum for D. sonneriatoides (Table 3).

Besides M. ferrea (49.4), A. grandis, C. indica, and S.

assamica had relatively high C:N ratios whereas for the

other species the C:N ratio was \25. Cellulose concen-

tration was highest for D. binectariferum (396 mg g-1) and

lowest for M. ferrea (219 mg g-1). Hemicellulose ranged

between 40.7 mg g-1 for T. hodgsonii to 95.6 mg g-1 for

V. lancefolia. The corresponding lignin:N ratio ranged

from 6.7 (D. sonneriatoides) to 43.6 (M. ferrea) (Table 3).

Species differences in litter decay rates were evident

from decomposition values expressed as mean percentage

remaining dry weight for the different sampling times

(Fig. 2). The time required for complete disappearance of

the original biomass of different tree leaf litter ranged from

240 to 390 days. In this study, the decomposition occurred

in three phases. The polynomial regression equations

describing decay rates over time were highly significant

(P \ 0.001) for all the species. In all, the first phase lasted

for 30 to 90 days and was characterised by a slow rate of

decay (0.063% weight loss day-1). This was followed by a

period of rapid weight loss (0.494% weight loss day-1) for

up to 210 days. In the third phase (i.e., 210–390 days),

decay continued more-or-less at a constant rate (0.136%

weight loss day-1).

The annual decay constants (k) for the different species

varied significantly (P \ 0.05) and ranged from 1.04 (M.

ferrea) to 5.4 year-1 (D. sonneriatoides) (Table 4). Half-

lives and full-lives (t50 and t99) ranged from 0.126–0.671

to 0.933–4.8 years (Table 4). Differences between decay

rate coefficients were statistically significant between the

species (F test ratio = 22.54; P \ 0.05).

Except for D. sonneriatoides and T. hodgsonii, N and P

content of the decomposing litter followed a continuous

increase with an initial drop after 120–240 days from the

initial concentration, then a final relatively rapid release

phase occurred (Figs. 3, 4). The initial drop in nutrient

concentrations (N and P) coincided with the rainy season

when N and P mineralization rates were greater (Fig. 5).

Species differences in nitrogen and phosphorus concen-

trations on different sampling dates were significant

(P \ 0.05).

Rainfall, soil temperature, and moisture content were

positively correlated with weight loss for the different tree

species. The initial lignin and carbon concentrations, L:N

ratio, and C:N ratio were negatively correlated with decay,

whereas, initial N and P concentrations were positively

correlated with decay (Table 5). For nutrient-related initial

litter chemistry, many significant positive correlations were

found between initial chemical concentrations. Carbon was

negatively correlated with N and P concentrations and

Table 4 Annual decay

constants (k) for different leaf

litter species of the Namdapha

National Park

± standard error from five

replicate measurements

t50 is the time required to

achieve 50% decay; t99 is the

time required to achieve 99%

decay

Species Dry mass

k t50 t99

A. grandis 1.892 ± 0.011 0.367 ± 0.005 2.643 ± 0.031

A. excelsa 2.467 ± 0.084 0.286 ± 0.007 2.033 ± 0.103

C. indica 1.756 ± 0.114 0.391 ± 0.014 2.857 ± 0.073

D. binectariferum 3.893 ± 0.178 0.186 ± 0.004 1.280 ± 0.064

D. sonneriatoides 5.374 ± 0.335 0.126 ± 0.001 0.933 ± 0.043

M. ferrea 1.042 ± 0.031 0.671 ± 0.001 4.806 ± 0.095

T. hodgsonii 3.117 ± 0.104 0.226 ± 0.004 1.604 ± 0.082

T. myriocarpa 2.298 ± 0.031 0.303 ± 0.005 2.184 ± 0.033

S. assamica 2.776 ± 0.012 0.251 ± 0.003 1.812 ± 0.105

V. lancefolia 2.054 ± 0.054 0.343 ± 0.013 2.431 ± 0.041

J For Res (2008) 13:25–34 29

123

showed positive correlations with lignin, C:N, and lignin:N

ratio. However, N and P showed significant positive cor-

relations with lignin, C:N and lignin:N ratio.

Discussion

The ten dominant tree species studied in this work can be

broadly classified in two categories based on the decay

rates recorded, i.e. fast and slow decomposition. D. son-

neriatoides, D. binectariferum, T. hodgsonii, S. assamica,

T. myriocarpa and A. excelsa exhibited relatively fast

decomposition rates (k = 2.46 – 5.37) while M. ferrea, A.

grandis, C. indica and V. lancefolia had slow decay rates

(k = 1.04 – 2.05). The time required for complete dis-

appearance of the original biomass ranged from 8 to

13 months. Mass disappearance rates in this study were

high for all the species in comparison with values reported

from other tropical and subtropical forests (Arunachalam

et al. 1998; Hirobe et al. 2004a, b). This may be due to

favourable temperature, moisture, and greater microbial

activity in the soil. Furthermore, in humid tropical forests

A. grandis

02468

101214161820 M. ferrea

A. excelsa

02468

101214161820

T. hodgsoni

C. indica

02468

101214161820 T. myriocarpa

D.binectariferum

02468

101214161820

S. assamica

D. sonneratoides

02468

101214161820

30 60 90 120 150 180 210 240 270 300 330 360 390 30 60 90 120 150 180 210 240 270 300 330 360 390

V. lancefolia

N c

once

ntra

tion

(mg

g-1)

AutumnSummer Spring Winter AutumnSummerSpring Winter

Fig. 3 Changes in N concentration (mg g-1) in decaying leaf litter of different species. Vertical lines represent standard error from five replicate

measurements

30 J For Res (2008) 13:25–34

123

there is usually very little or no accumulation of litter,

implying faster turnover of organic matter in the soil. In

this context, William and Gray (1974) suggested that dif-

ferences in temperature and moisture, their interactions,

and microbial activity, explain the large variations in litter

decomposition rates between tropical and temperate

regions. Nonetheless, D. sonneriatoides with the highest

initial N content decomposed completely in the shortest

time (k = 5.37). Constantinides and Fownes (1994) also

suggested that initial N content is the best predictor of N

dynamics of at least a few litter samples from tropical tree

species. Greater initial N and/or lower lignin in the foliage

lead to faster decomposition and vice-versa. Thus, several

workers have established a negative correlation between

initial lignin content and decay rate (Arunachalam et al.

1998; Couteaux et al. 1995). For instance, M. ferrea had

greater lignin (248.5 mg g-1) and lower initial N

(5.7 mg g-1) and had a very slow decay rate compared

with the other species. This indicates that decomposition of

the tropical tree species may be governed by both the initial

N and lignin content. Furthermore, when the litter is

exposed to decomposition microorganisms, the easily

decomposable components are attacked first. The soluble

and polymer carbohydrates (cellulose and hemicellulose)

therefore begin disappearing sooner than the lignin (Hirobe

et al. 2004a, b). As decomposition proceeds, the

A. grandis

0

0.5

1

1.5

2

2.5M. ferrae

A. excelsa

0

0.5

1

1.5

2

2.5T. hodgsoni

C.indica

0

0.5

1

1.5

2

2.5T. myriocarpa

D.binectariferum

0

0.5

1

2

2.5

S. assamica

D. sonneratoides

0

0.5

1

1.5

2

2.5

30 60 90 120 150 180 210 240 270 300 330 360 390 30 60 90 120 150 180 210 240 270 300 330 360 390

V. lancefolia

P c

once

ntra

tion

(m

g g-1

)

AutumnSummerSpring WinterAutumnSummer Spring Winter

1.5

Fig. 4 Changes in P

concentration (mg g-1) in

decaying leaf litter of different

species. Vertical lines represent

standard error from five

replicate measurements

J For Res (2008) 13:25–34 31

123

composition of litter continually changes, creating new

conditions for the decomposing organisms (Prescott et al.

2004). Carbon:nitrogen ratio was \25 for all the tree spe-

cies except in M. ferrea (49.4), A. grandis (34.2), C. indica

(41.9), and S. assamica (29.4). This validates the high

quality of their litter according to Myers et al. (1994), who

reported that substrate with C:N \ 25 is of high quality and

releases mineral N at a faster rate than low-quality residues

(C:N [ 25). The initial lignin concentration and lignin:N

ratio had a negative influence on decay rate coefficient (k).

This negative relationship has also been reported by Aber

and Melillo (1980). Nonetheless, in this respect, several

Winter Winter

A. grandis

0

20

40

60

80

100

120 M.ferrae

A. excelsa

0

20

40

60

80

100

120 T. hodgsoni

C. indica

0

20

40

60

80

100

120 T. myriocarpa

D. binectariferum

0

20

40

60

80

100

120 S. assamica

D. sonneratoides

0

20

40

60

80

100

120

30 60 90 120 150 180 210 240 270 300 330 360 390 30 60 90 120 150 180 210 240 270 300 330 360 390

V. lancefolia

% N

and

P r

elea

se

AutumnSummerSpring AutumnSummerSpring

Fig. 5 N (filled squares) and P (open triangles) release (percentage of initial amount) during decomposition of leaf litter of different species.

Vertical lines represent standard error from five replicate measurements

32 J For Res (2008) 13:25–34

123

workers failed to find strong dependence of either lignin or

lignin:N ratio on decay rate coefficients (McClaugherty

et al. 1985; Taylor et al. 1989). However, because this

result was obtained from only ten species and represents

only a part of wet evergreen leaf litter types, we need to

study more species with these initial chemical composi-

tions for wider applications.

In this study, the slow rate of initial decay was followed

by a rapid phase of decomposition, possibly because of the

faster breakdown of litter by the decomposer community

that initially took time to colonize the litter (Songwe et al.

1995). Relatively slower decay at the later stage could,

however, be due to the accumulation of more recalcitrant

materials in the litter. In this context, Berg (1986) and

Taylor et al. (1989) have suggested that the effect of

nitrogen on decomposition rates decreases as the decay

proceeds whereas that of lignin increases. The varying rate

of decomposition seemed to be due not only to the nutrient

content of the leaves but also to their morphological

characteristics (Songwe et al. 1995). For instance, Edwards

(1977) reported that thick and tough leaves with prominent

midribs and veins decomposed more slowly than species

with thin and less rigid leaves without prominent skeletal

tissues. In our current study M. ferrea, A. grandis, C.

indica, and V. lancefolia had thick leaves with prominent

midribs and veins that could have resulted in a slower

decomposition. On the other hand, D. sonneriatoides, D.

binectariferum, T. hodgsonii, S. assamica, T. myriocarpa,

and A. excelsa, which have thin leaves without prominent

skeletal tissues decomposed at a faster rate. Seasonally, a

relatively higher decay rate (30–67% of initial weight)

during the monsoon season (June to August) could be the

effect of physical determinants such as warm and humid

conditions during this season, while a relatively slow rate

(10–25% of initial weight) during the post-rainy season

(September to November) may be attributed to low mois-

ture level and reduced microbial activity (Sangha et al.

2006; Arunachalam et al. 1998). A relatively slow decay

rate during the dry season (December to March) may be

attributed to low moisture content and reduced microbial

activity in the soil (Maithani et al. 1996). We observed

direct relationships between soil microclimate and

decomposition, which demonstrates the complexity of the

interactions between soil and biotic factors. Such climatic

and chemical factors might regulate decomposition mainly

by affecting the abundance and community composition of

soil microorganisms (Berg 1986). Perhaps, lower moisture

and temperature during winter season (December to

March) reduced the decomposition rates in our study.

It was also reported that, in a wet tropical climate,

temperature and moisture are less contrasting and the

decomposition rate depends primarily on soil and humus

properties and on litter quality (Couteaux et al. 1995).

N and P concentrations in the decomposing leaf litter of

different tree species were highly variable and followed a

similar temporal pattern during the decay process. An

increase in the concentration of N in decomposing leaf

litter has been observed by several researchers including

Gilbert and Bocock (1960), Gosz et al. (1973), and Howard

and Howard (1974). During decomposition, mineralization

of the organic N into an inorganic form mainly depends on

the C:N ratio of the material. Therefore, N in litter with a

higher N concentration and a lower C:N ratio was min-

eralised more rapidly than in litter with a lower N

concentration and a greater C:N ratio. As P mineralization

during decomposition was quite similar to that of N

release, the rate of release was slightly slower than that of

N. Berg and Staff (1980) also described a tri-phasic model

for nutrient release from decomposing litter. A marked

decline in N and P concentrations after 120 days of

decomposition may be due to leaching losses caused by

heavy rainfall during that period. A subsequent increase in

N and P concentrations could be the result of microbial

immobilization (Maithani et al. 1996), nutrient inputs from

throughfall, and atmospheric precipitation (Bocock 1963)

and/or atmospheric nitrogen fixation (Wood 1974).

Overall, it can be concluded that the nutrients in

decomposing litter are recycled rapidly within the forest

soil. Rates of decomposition were relatively high and the

rates of disappearance of litter mass differed significantly

among the species. Both initial lignin content and lignin:N

ratio had a negative influence on decay rate coefficients.

Table 5 Litter decomposition rate (t50) as influenced by climatic

variables, soil characteristics, and initial leaf chemistry

Variable df r P

Decomposition rate vs.

Climatic variable

Rainfall (mm) 24 0.544 0.005

Decomposition rate vs.

Soil characteristics

Soil temperature (�C) 24 0.467 0.02

Soil moisture (g g-1) 24 0.389 0.05

Total N (g g-1) 24 0.565 0.005

Total P (g g-1) 24 0.388 0.05

Decomposition rate vs.

Initial chemistry

Lignin (mg g-1) 30 -0.541 0.002

C (mg g-1) 30 -0.642 0.001

N (mg g-1) 30 0.816 0.001

P (mg g-1) 30 0.586 0.001

L:N 30 -0.482 0.01

C:N 30 -0.853 0.001

df, degrees of freedom; r, correlation coefficient; P, significance level;

L:N, lignin:nitrogen ratio

J For Res (2008) 13:25–34 33

123

Thus it is clear that initial lignin and nutrient concentrations

(N and P) play an important role in determining the rate of

litter decomposition in the tropical wet evergreen ecosys-

tem, and hence nutrient cycling in the forest ecosystem.

Acknowledgments The authors thank the Ministry of Environment

and Forests, Government of India, for financial assistance. Special

thanks are due to K. Haridasan for his ungrudging help in identifi-

cation of plant species and to the Principal Chief Conservator of

Forests, Arunachal Pradesh, for permitting us to work in the Namd-

apha National Park. Field and laboratory assistance by Shri J. Saikia

and Shri M. Ingti is thankfully acknowledged. We thank the three

anonymous reviewers for their valuable comments.

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