Carbon storage capacity of high altitude Quercus semecarpifolia,forests of Central Himalayan region

Abstract

Quercus semecarpifolia, Smith. (brown oak) forests dominate the high altitudes of central Himalaya between 2400 and 2750 m and the timber line areas. The species is viviparous with short seed viability and coincides its germination with monsoon rains in July–August. These forests have large reserves of carbon in their biomass (above and below ground parts) and soil. We monitored the carbon stock and carbon sequestration rates of this oak on two sites subjected to varying level of disturbance between 2004 and 2009. These forests had carbon ranging between 210.26 and 258.02 t ha^?1 in their biomass in 2009 and mean carbon sequestration rates between 3.7 and 4.8 t ha^?1 yr^?1. The litter production in both the sites ranged from 5.63 to 7.25 t ha^?1 yr^?1. The leaf litter decomposition of species took more than 720 days for approximately 90% decomposition. Even at 1 m soil depth soil organic carbon was close to 1.0%.     

Colonization and decomposition of leaf litter by ligninolytic fungi in Acacia mangium plantations and adjacent secondary forests

Colonization of leaf litter by ligninolytic fungi and relationships between mass loss and chemical qualities of surface leaf litter were examined in Acacia mangium plantations and adjacent secondary forests in southern Sumatra Island, Indonesia. Leaves were collected from eight A. mangium plantations of different ages and three secondary forests. Partly decomposed leaves beneath the surface leaf litter were used to measure the bleached area which indicated colonization by ligninolytic fungi. Surface leaf litter was used to measure initial chemical content and subjected to the pure culture decomposition test. The bleached area was greater in secondary forests than in A. mangium plantations. Nitrogen content was higher in all the A. mangium plantations than in the secondary forests, and acid unhydrolyzable residue (AUR) content was generally higher in the A. mangium plantations than in the secondary forests. The bleached area of leaf litter was negatively correlated with nitrogen content of surface leaf litter at all sites, indicating an inhibition of the colonization by ligninolytic fungi of leaves with higher nitrogen content. In a pure culture decomposition test inoculating a ligninolytic fungus to surface leaf litter, mass loss of leaves was negatively correlated with AUR content of surface leaf litter. Mass loss of leaves and AUR was not significantly related to nitrogen content. These results suggested that higher nitrogen content in A. mangium leaf litter had a negative effect by colonization of ligninolytic fungi, but the effect of high N in A. mangium leaf litter on the decomposition of leaf litter and AUR remained unsolved.     

Forest composition,leaf litter,and songbird communities in oak- vs. maple-dominated forests in the eastern United States

Within the eastern deciduous forest region, forest composition varies, with some areas dominated by a mix of oaks (Quercus spp.) and other areas dominated by a mix of sugar maple (Acer saccharum) and other tree species. Prescribed fire is being used on an experimental basis to assess its effectiveness in restoring and maintaining oak-dominated forests. Maple-dominated forests are susceptible to invasion by non-native earthworms, such as Lumbricus terrestris, given the palatability of leaf litter and suitable soil conditions, especially in northern parts of the region. What are the implications of this variation on leaf litter availability and habitat for ground-nesting songbirds? We investigated this question by comparing forest composition, leaf litter, and songbird communities in maple-dominated forests in west-central Indiana and oak-dominated forests, recently burned and unburned, in southeastern Ohio. We also assessed abundance of earthworms and decomposition rates of different types of leaves in the maple-dominated forests in Indiana. Leaf litter and ground-nesting bird species were abundant in unburned oak-dominated forests, but were absent or nearly absent in recently burned oak-dominated forests and in maple-dominated forests. The lack of leaf litter and absence of ground-nesting bird species in maple-dominated forests may be due to the combination of abundant non-native earthworms, alkaline and calcium-rich soils, palatable leaves, and rapid leaf litter decomposition rates. Effects of burning on leaf litter and ground-nesting bird species in oak-dominated forests are probably temporary, as long as prescribed fires are not applied on a frequent or widespread basis. Our study is the first one to show a correlation between forest composition, leaf litter availability, earthworm abundance, and songbird populations. Many researchers are investigating effects of non-native earthworm invasions on ecosystem properties in eastern deciduous forests. We recommend that researchers should also monitor songbird populations to assess whether declines in ground-nesting bird populations are occurring in response to these changes.     

Exotic tree leaf litter accumulation and mass loss dynamics compared with two sympatric native species in south Florida,USA

The exotic tree Melaleuca quinquenervia (melaleuca) forms dense forests usually characterized by low plant diversities and dense litter biomass accumulations on forest floors of ecologically sensitive ecosystems, including portions of the Florida Everglades. We quantified litter accumulation in mature melaleuca stands and compared decomposition rates of melaleuca leaves with a sympatric native plant, either Cladium jamaicense (sawgrass) in sawgrass marshes or Pinus elliottii (slash pine) in pine flatwoods habitats that varied in soil types. Total litter accumulation in mature melaleuca forests prior to June 1997 ranged from 12.27 to 25.63 Mg ha⁻¹. Overall, melaleuca leaves decomposed faster in organically rich versus arenaceous soils. Decomposition rates were lower for melaleuca leaves than for sawgrass in both melaleuca-invaded and uninvaded sawgrass marshes. In arenaceous soils of pine flatwoods, melaleuca leaf and pine needle decomposition rates were similar. Complete mineralization of sawgrass leaves occurred after 258 weeks, whereas melaleuca leaves had up to 14% and pine foliage had up to 19% of the original biomass remaining after 322 weeks. Total carbon (C) in intact decomposing leaves varied slightly, but total nitrogen (N) steadily increased for all three species; the greatest being a fourfold in sawgrass. Increases in N concentrations caused decreases in the C/N ratios of all species but remained within an optimal range (20–30) in sawgrass resulting in higher decomposition rates compared to melaleuca leaves and pine needles (C/N ratio >30). Slower decomposition of melaleuca leaves results in denser litter layers that may negatively affect recruitment of other plant species and impede their establishment in invaded communities.     

Comparison of litterfall production in three forest types in Jeju Island,South Korea

Litterfall, which is influenced by physical and biological factors, is a major pathway for carbon and nutrient cycling in forest ecosystems. The purpose of this study was to investigate monthly litterfall production in three forests in Jeju Island differentiated by forest composition and precipitation: Cheongsu(Quercus glauca as the dominant species;low precipitation), Seonheulb(Q. glauca as the dominant species;high precipitation), and Seonheulm(Q. glauca and Pinus thunbergii as the dominant species;high precipitation). Litterfall was collected monthly from April to December 2015 and divided into leaf litter, twig, bark, seeds, and unidentified materials.Seasonal patterns of litterfall production varied across stands according to their species composition. However,the amount of leaf litterfall and total litterfall were comparable among stands, ranging from 362 to 375 g m-2 for leaf litter and 524 g m-2 to 580 g m-2 for total litterfall.Oak leaf litter in May was the highest in all stands, while needle litter was the highest in December in Seonheulm.High twig litterfall in July may be attributable to high rainfall with strong winds and storms during the rainy season. Although forest type and climate factor had no influence on litterfall amounts in this study, the pattern of litterfall production was species dependent, suggesting diverse effects on carbon and nutrient cycling in these forests.     

西南桦和尾巨桉凋落叶分解及其与土壤性质的相关性

[目的]探讨南亚热带西南桦和尾巨桉人工纯林的凋落叶分解动态及其与土壤化学性质之间的相关关系.[方法]采用原位分解袋法研究凋落叶的分解过程.[结果]表明:西南桦、尾巨桉人工林凋落叶分解系数分别为0.96 a^-1和0.88 a^-1.在为期12个月的分解试验中,2种凋落叶有机C含量在整个分解过程中呈逐渐下降趋势;全K含量和C/N比在分解前期迅速下降,之后趋于平缓;全N含量和全P含量在整个分解过程中呈逐渐上升趋势;2种凋落叶N/P比则呈先升高后下降的趋势.无论是分解前期还是分解后期,凋落叶质量损失与N含量均呈显著正相关(前期R=0.877;后期R=0.855),与C/N均呈显著负相关(前期R=-0.735;后期R=-0.697).与尾巨桉林地土壤性质相比,西南桦凋落叶分解提高了林地0~10、10~20 cm土壤的有机C、全N、全P、全K、N/P,对2030 cm土壤有机C、全K、pH值、C/N、N/P则未产生显著影响.相关分析表明:凋落叶初始有机C含量与土壤有机C、全N、全P、全K、N/P显著相关;凋落叶初始全N含量与土壤全N、pH值、C/N显著相关.[结论]凋落叶的养分含量与土壤养分的关系紧密;与尾巨桉相比,西南桦凋落叶的养分含量明显较高,分解速率更快,释放到土壤中的养分也更多.     

文峪河上游河岸林凋落物及其分解过程研究

通过凋落物定点收集调查和分解袋定点埋置实验,对文峪河上游山地溪流河岸带寒温性针阔叶混交林的年凋落量动态和凋落叶在不同环境中的分解进程进行了周年研究.结果表明,研究地区山地溪流河岸林在河岸带和溪流中的年凋落量分别为3.46和4.09 t·hm-2·a-1;河岸带和溪流凋落物中阔叶凋落量占优势,分别占40.55％和40.1...     

Carbon storage of artificial forests in rehabilitated lands in the upper reaches of the Yellow River

We studied 10-to 27-year-old artificial forests on rehabilitated lands in the upper reaches of the Yellow River with the objective of comparing the carbon densities of various artificial and natural forests. Under artificial plantations, the vegetation layer (including roots) had a mean carbon density of 111.3 t/hm², the litter layer a density of 5.1 t/hm², and the soil layer a density of 64.9 t/hm². These values accounted for 28.6%, 13.8%, and 61.0% of their respective counterparts in the natural secondary forests under the same site conditions in the region. The ratios of carbon density among vegetation, litter, and soil pools were 39.6:1.8:58.6 for artificial forests and 57.4:2.7:39.9 for natural forests. The carbon densities of the vegetation and litter layers increased exponentially with forest age. The total carbon density ratios were also increasing gradually. Although the mean total carbon density of the artificial forests in the rehabilitated lands was 281.2 t/hm² in the experimental area, it accounted for only 41.5% of the carbon density of the natural secondary forests (677.4 t/hm²). The annual increase in total carbon density of artificial forests was as high as 15.2 t/hm², which was 11.7% more than that of natural forests and 6.8 times higher than that (1.95 t/hm) of artificial forests in the entire country as measured during 1994–1998. This indicates that growth and carbon storage capacity of artificial forests in the rehabilitated lands were higher than those of forests on the barren hills and the secondary forests. We concluded that the conversion project from croplands to forests and grasslands based on scientific principles is very important in the formation of carbon sinks for reducing greenhouse effects. __________ Translated from Journal of Beijing Forestry University, 2005, 27(6): 1–8 [译自: 北京林业大学学报, 2005, 27(6): 1–8]     

Exotic earthworms of great lakes forests: A search for indicator plant species in maple forests

The invasion of exotic earthworms in previously earthworm-free northern deciduous forests has been linked to the disappearance of forest floor litter, declines in plant species richness, and the development of monotypic stands of Carex pensylvanica. However, the impact of exotic earthworms on the regeneration of trees and understory plants is largely unknown. We examined the relationships between earthworm density, plant species richness, leaf litter accumulation, number of tree (Acer) seedlings, and cover of C. pensylvanica at 14 sites in mesic hardwood forests of the Chequamegon-Nicolet National Forest in northern Wisconsin. Earthworm biomass, especially of the genera Lumbricus, Aporrectodea, and Octolasion was negatively associated with leaf litter mass and number of Acer seedlings. Nine plant species, including two spring ephemerals (Dicentra cucullaria and Osmorhiza claytonii), a sedge (Carex deweyana), and an invasive mint (Galeopsis tetrahit) were negatively correlated with exotic earthworm densities. Dryopteris intermedia and Allium tricoccum, on the other hand, were associated with high earthworm densities. The activities of exotic earthworms appear to have significant impacts on Acer regeneration and the persistence of many herbaceous plants. Our findings suggest that the effects of exotic earthworms on litter mass are strongly related to the observed effects on species composition. Sensitive species can be used as indicators of high and low earthworm densities and might be useful for identifying forests of high conservation value where future invasions of exotic earthworms should be prevented.     

Carbon Stock in Community Managed Hill Sal (Shorea robusta) Forests of Central Nepal

Community forests of developing countries are eligible to participate in the Reducing Emissions from Deforestation and Forest Degradation (REDD+) scheme. For this, estimation of carbon stock and the sequestration is essential. The carbon stock in the living biomass of nine community managed Shorea robusta forests of the mid hill regions of central Nepal (managed for 4–29 yr) were estimated. The carbon stock of trees and shrubs was estimated using an allometric equation while the biomass of herbaceous vegetation was estimated by the harvest method. The carbon stock in the living biomass of the studied forests ranged from 70–183 Mg ha^?1(mean: 120 Mg ha^?1) and it increased with increasing soil organic carbon. However, the carbon stock did not vary significantly with species richness and litter cover. The biomass and carbon stock in the forests managed for >20 yr were significantly higher than in the forests managed for < 20 yr. The carbon stock increased with the management duration (p < .05) with sequestration rate of 2.6 Mg C ha^?1 yr^?1. The local management has had positive effects on the carbon stock of the forests and thus the community forests have been acting as a sink of the atmospheric CO₂. Therefore, the community managed forests of Nepal are eligible to participate in the REDD+ scheme.     

Effects of <Emphasis Type="Italic">Ips typographus</Emphasis> (L.) damage on litter quality and decomposition rates of Oriental Spruce [<Emphasis Type="Italic">Picea Orientalis</Emphasis> (L.) Link.] in Hatila Valley National Park,Turkey

This study investigated the effects of Ips typographus (L.) damage on initial litter quality parameters and subsequent decomposition rates of oriental spruce tree species [Picea orientalis (L.) Link]. The needle litter was collected from highly damaged, moderately damaged and control stands on two aspects (north and south) and two slope position (top and bottom) on each aspect. The litter was analyzed for initial total carbon, lignin and nutrient (nitrogen, phosphorus, potassium, calcium, magnesium and manganese) concentrations. The variability in nitrogen and calcium concentrations and ratios of C:N, lignin:N and lignin:Ca was significantly affected by the insect damaged levels. While nitrogen concentrations in needle litter increased with increasing insect damage (and consequently the ratios of C:N and lignin:N decreased), calcium concentrations decreased (and consequently the ratio of lignin:Ca increased). Aspect and slope positions explained most of the variability in carbon, lignin, phosphorus, potassium, magnesium and manganese concentrations and lignin:P ratio between all studied stands. Litter decomposition was studied in the field using the litterbag technique. The litter from highly damaged stands showed highest decomposition rates followed by moderately damaged and control stands. The mass loss rates were significantly positively correlated with initial nitrogen concentration and negatively with C:N and lignin:N ratios. The effects of microclimate resulting from canopy damage on litter decomposition was also examined at the same time using standard litter with the same litter quality parameters, but they showed no significant differences among the insect damage levels indicating that alteration of the litter quality parameters produced by I. typographus damage played a more important role than altered microclimate in controlling needle litter decomposition rates. However, changes in microclimate factors due to topography influenced decomposition rates.     

Carbon return and dynamics of litterfall in natural forest and monoculture plantation of Castanopsis kawakamii in subtropical China

The amount of carbon returned through litterfall and its seasonal pattern were studied in a natural forest of Castanopsis kawakamii (NF) and adjacent monoculture plantations of C. kawakamii (CK) and Chinese fir (Cunninghamia lanceolata) (CF) in Sanming, Fujian Province, China. Mean annual carbon return through total litterfall over 3 years (from 1999 to 2001) was 5.097 t·hm⁻² in the NF, 4.337 t·hm⁻² in the CK and 2.502 t·hm⁻² in the CF respectively. Of the total carbon return in the three forests, leaf contribution accounted for 58.96%, 68.53% and 56.12% and twig 24.41%, 22.34% and 26.18%, respectively. The seasonal patterns of carbon return from total litterfall and leaf-litter were quite similar among the three forests. A peak of carbon input from litterfall in the NF and the CK occurred in spring except for the highest annual C return through branch litter of the NF in summer, while the CF showed the maximum C return in summer. The results of this study demonstrate that the natural forest has a greater C return through litterfall than monoculture plantations, which is beneficial to the increase of soil organic matter storage and the maintenance of soil fertility. [Supported by the Teaching and Research Award Program of MOE P.R.C. (TRAPOYT) and the Key Basic Research Project of Fujian Province (2000F004)]     

Nutrition and growth of wheat–sorghum rotation in soils amended with leaf litter of trees before planting of wheat

Nutrient release from plant residues can be manipulated as per crop demand through several approaches. A pot study was conducted to study the influence of incorporation of leaf litter of poplar (Populus deltoides), eucalypt (Eucalyptus hybrid) and dek (Melia azedarach) inoculated with cellulolytic fungus culture (Aspergillus awamori) on the nutrition and biomass of wheat (Triticum aestivum, cv. PBW 343) in loamy sand and sandy loam soils. The residual effect of leaf litter after wheat harvest was studied on sorghum (Sorghum bicolor, cv. Punjab Sudax Chari 1). The treatments consisted of a control (no leaf litter) and three uninoculated as well as inoculated leaf litter levels of tree species–0.15%, 0.30% and 0.45% (w/w, dry weight basis). A uniform dose of N, P and K @ 50, 11 and 10 mg kg⁻¹ soil, respectively from inorganic fertilizers was applied to all the treated pots. Straw and grain yield, and nutrient content of wheat increased with increasing level of uninoculated or inoculated leaf litter in both the soils. The inoculated leaf litter augmented the yield and nutrient content of crop significantly (P < 0.05) as compared to the corresponding uninoculated treatments. Poplar and dek leaf litter produced higher wheat yield, plant nutrient content and available nutrients in soil after wheat harvest than eucalypt leaf litter. Dry matter yield of sorghum raised on residual fertility increased significantly with increasing levels of leaf litter application. The comparative responses in yield and nutrient content of crops were higher in loamy sand than in the sandy loam soil. The study shows the beneficial influence of use of cellulolytic microorganisms on enhancement in decomposition and nutrient release from litterfall of tree species.     

Carbon stock measurements of a degraded tropical logged-over secondary forest in Manokwari Regency, West Papua, Indonesia

Several studies have been conducted in the past on carbon stock measurements in the tropical forests of Indonesia.This study is the first related research conducted in the New Guinea Island.In a degraded logged-over secondary forest in Manokwari Regency (West Papua,Indonesia),carbon stocks were measured for seven parts,i.e.,above-ground biomass (AGB),below-ground biomass (BGB),under-storey biomass (B u),necromass of dead leaves (N l),necromass of dead trees (N t),litter (L) and soil (S) using appropriate equations and laboratory analysis.Total carbon stocks were measured at 642.8 tC·ha-1 in the low disturbance area,536.9 tC·ha-1 in the moderate disturbance area and 490.4 tC·ha-1 in the high disturbance area.B u,N l and N t were not significant in the carbon stock and were collectively categorized as a total biomass complex.The carbon stock of litter was nearly equal to that of the total biomass complex,while the total carbon stock in the soil was eight times larger than the total biomass complex or the carbon stock of the litter.We confirmed that the average ratio of AGB and BGB to the total biomass (TB) was about 84.7% and 15.3%,respectively.Improvements were made to the equations in the low disturbance logged-over secondary forest area,applying corrections to the amounts of biomass of sample trees,based on representative commercial trees of category one.TB stocks before and after correction were estimated to be 84.4 and 106.7 tC·ha-1,indicating that these corrections added significant amounts of tree biomass (26.4%) during the sampling procedure.In conclusion,the equations for tree biomass developed in this study,will be useful for evaluating total carbon stocks,especially TB stocks in logged-over secondary forests throughout the Papua region.     

Litter production and decomposition dynamics in moist deciduous forests of the Western Ghats in Peninsular India

A field study was conducted in the moist deciduous forests of the Western Ghats (India) to test the following three hypotheses: (1) Litter production in tropical forests is a function of the floristic composition, density, basal area and disturbance intensity; (2) Decay rate constants of tropical species is an inverse function of the initial lignin/nitrogen ratio; (3) Decomposition rates in tropical forests are faster than temperate forests.

Litter fall was estimated by installing 63 litter traps in the moist deciduous forests of Thrissur Forest Division in the Western Ghats at three sites. Litter fall followed a monomodal distribution pattern with a distinct peak during the dry period from November–December to March–April.Dillenia pentagyna, Grewia tiliaefolia, Macrosolen spp.,Xylia xylocarpa, Terminalia spp.,Lagerstroemia lanceolata, Cleistanthus collinus, Bridelia retusa, andHelicteres isora were the principal litter producing species at these sites. The annual litter fall ranged from 12.18 to 14.43 t ha⁻¹. Structural attributes of vegetation such as floristic composition, basal area, density and disturbance intensity did not directly influence litter fall rates.

Leaf litter decay rates for six dominant tree species were assessed following the standard litter bag technique. One hundred and eight litter bags per species containing 20 g samples were installed in the forest floor litter layer at the same three sites selected for the litter fall quantification exercise. The residual litter mass decreased linearly with time for all species. In general, less disturbed sites and species adapted to higher nitrogen availabilities exhibited relatively higher decay rate coefficients (k). The rapid organic matter turnover observed in comparison with published temperate forest litter decay rates confirms that tropical moist deciduous forest species are characterised by faster decomposition rates.

Mean concentrations of N, P and K in the litter were profoundly variable amongst the dominant species. Initial nitrogen content of the leaf litter varied from 0.65 to 1.6%, phosphorus from 0.034 to 0.077% and potassium from 0.25 to 0.62%.C. collinus, an understorey shrub consistently recorded the lowest litter concentrations for all nutrients. The overriding pattern is one of higher nutrient levels in the overstorey leaf litter and lower concentrations in the understorey litter. Furthermore, as decomposition proceeded, the nitrogen concentration of the residual biomass increased.     

Forest gap size can efficiently promote litter decomposition and nutrient release in south-western China

Forest gaps are important in forest dynamics and management; however, the gap size that is most conducive to the decomposition of litter and promotion of nutrient cycling in forests remains poorly understood. The mass loss and nutrient release from Pinus massoniana and Toona ciliata litter in response to gap size classes were determined in south-western China during a 1.5-year litter decomposition experiment. One site with a closed canopy (CK) and seven sites with forest gaps of 100, 225, 400, 625, 900, 1 225 and 1 600 m² were established in a P. massoniana plantation in the Sichuan Basin of China; the CK site (fully shaded) was treated as the control. After 540 d, the mass and carbon (C), nitrogen (N) and phosphorus (P) contents in the litter of the control treatments decreased by 58.23%, 60.81%, 65.62% and 57.82% for P. massoniana litter and by 91.17%, 80.76%, 73.66% and 64.55% for T. ciliata litter, respectively, compared with the initial amounts. Most of the C, N and P were released from both tree species during the first 90 d of decomposition, although the temperature and moisture conditions were very low. The mass loss and C and N release rates for the two tree species and the P release rate from T. ciliata litter were higher in the 400–900 m² gap sites than in the other gap sites and the CK site, whereas the P release rate from P. massoniana litter was greater under large and medium-sized gaps (400–1 600 m²). The mass loss and C, N and P release rates were positively correlated with the soil moisture content in the seven different gap size treatments, with the soil moisture content representing the best predictor of litter decomposition. Therefore, our results indicate that medium-sized gaps (400–900 m²) can promote decomposition by changing the environmental conditions and may accelerate nutrient cycling in forest ecosystems.     

Leaf Litter Decomposition,Litterfall, and Effects of Leaf Mulches from Mixed and Monospecific Plantations in Costa Rica

Abstract

Rates of litter decomposition and nutrient release from litter provide valuable information on the capacity of different tree species to replenish soil nutrients in degraded tropical areas. Leaf litter decomposition, leaf litterfall, plantation floor leaf litter, and mulch performance were studied for four indigenous timber species, Virola koschnyiWarb, Dipteryxpanamensis(Pittier) Record and Mell, Terminalia amazonia(J.F. Gmel.) Exell., and Albizia gua-chapele(H.B.K.) Little, grown in mixed and monospecific plantations in the Atlantic humid lowlands of Costa Rica. Terminalia amazonialitter decomposed the fastest: no litter remained after 6 months. After 12 months, D. panamensis, A. guachapele, and the mixed litter decomposed completely, while 15% of the original weight of V. koschnyilitter remained. Differences in decomposition rates were closely related to leaf nutrient content. Total annual leaf litterfall was highest in T. amazonia(872.9 g/m²), followed by D. panamensis, V. koschnyi, and the mixed plots. A. guachapelehad the lowest leaf litterfall (236.0 g/m²). The highest plantation-floor leaf litter was found in V. koschnyiand D. panamensis.Both litterfall and plantation-floor litter accumulation fluctuated least in the mixed plots. A. guachapeleand D. panamensismulch most positively affected maize seedling growth, followed by the mixed mulch. Recommendations are drawn from the results to suggest species choice for sustainable land management in the region.     

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

Rates of weight loss and nutrient (N and P) release patterns were studied in the leaf litter of the dominant 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 composite polynomial regression equation, exhibited three distinct phases of decay during litter decomposition—an initial slow decay phase (0.063% weight loss day⁻¹), followed 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. sonneriatoides, 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 significant positive correlations with decay rates. Carbon and lignin content, lignin:N, and C:N showed significant negative 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.     

不同种植年限尾巨桉人工林叶片-凋落物-土壤碳氮磷化学计量特征

[目的]为了解雷州半岛尾巨桉速生人工林生态系统的C、N、P分配格局及化学计量特征。[方法]采用空间换时间的方法,选取雷州半岛4种不同林龄(1、3、5、7 a)的尾巨桉人工林为研究对象,对尾巨桉叶片、凋落物及土壤的C、N、P含量及化学计量特征进行测定分析。[结果]表明:C、N含量表现为叶片凋落物土壤,P含量表现为叶片土壤凋落物,且3个库间差异显著;土壤的C含量随林龄增加而增加,N、P含量差异不显著,土壤C∶N随林龄的增加而增加,说明土壤有机质分解速率逐渐下降;凋落物的C∶N为54. 07 92. 18 ( 25),表明尾巨桉林下凋落物分解速率较慢,N元素成为主要限制凋落物分解的元素,凋落物的C∶N随林龄的增加先增加后下降,凋落物分解速度先降低后升高;叶片的N∶P为10. 80 12. 98,说明中幼林龄尾巨桉受N限制较明显。相关性分析表明:凋落物养分元素含量受叶片限制,土壤养分含量受凋落物限制,表明生态系统内部C、N、P元素在植物、凋落物与土壤之间实现了运输和转换。[结论]雷州半岛尾巨桉中、幼林龄时期土壤有机质及凋落物分解速率较慢;随林龄的增加,土壤有机质、凋落物分解速率下降,N元素成为其主要分解限制性元素,林分生长受N限制明显。     

Comparison of field and laboratory microcosm methods on the mass loss ofQuercus serrata andPinus densiflora leaf litter

The decay rates of Japanese Konara Oak (Quercus serrata Murray) and Japanese Red Pine (Pinus densiflora Sieb. et Zucc.) leaf litter were monitored for one year. It aimed to compare the decomposition of leaf litter using microcosms set up in the field (FM) and in the greenhouse (GM), with the litterbag (LB) method as control. Results showed that incubation setting affected the decay rate (k), respiration rates and the changes in the concentrations of nitrogen (N). Thek value ofQuercus in FM was higher than LB, while thek value ofPinus was higher in the LB than in FM. The decay ratesk for both species, however, were significantly lower in GM than FM and LB, clearly suggesting that decay rate was inhibited in the greenhouse. Significant differences in microclimatic variables and soil biological activities (soil respiration) existed between greenhouse and field microcosms, hence, the decay rates were affected. The N concentrations for both litter types increased as decomposition proceeded. Decomposition studies using laboratory microcosm approach alone may lead to erroneous conclusions especially if no appropriate field studies are conducted along with it. Part of this paper was presented at the XXth International Union of Forestry Research Organization (IUFRO) World Congress, August 6–12, 1995, Tampere, Finland.