Rates Of Litterfall Research Articles

Carbon dynamics in tree plantings: How changes in woody biomass impact litter and soil carbon

Understanding carbon sequestration from tree planting and management activities is important for contributing to the mitigation of climate change. Although rates of growth and resulting sequestration of carbon in live above-ground biomass are relatively well understood in various woody plantings and commercial plantations in Australia, less is known about associated changes in live below-ground biomass, and the turnover and decomposition of biomass, and hence, resulting changes in carbon stocks of litter and soil. Our objective was to develop a modelling approach for predicting these processes and the resulting changes in litter and soil carbon following the establishment and/or management of tree plantings (EMTP) to facilitate their inclusion in carbon abatement projects. We reviewed and collated data on allocation of biomass, litterfall, litter decomposition, litter/harvest residue mass and soil organic carbon (N = 5,655 estimates). Data were sourced from existing field studies of woody plantings (mixed-species environmental and mallee eucalypt), commercial plantations (hardwood and softwood) and in some cases, eucalypt-dominant native forests. After constraining a carbon accounting model to observed measures of growth, allocation of biomass, and rates of litterfall and litter decomposition, the model was calibrated to maximise the efficiency of prediction of litter and soil pools. Although large uncertainties in ‘observed’ results meant that precision of prediction in any given data source was relatively poor, model predictions had negligible overall bias. The size and diversity of datasets applied in the process of calibration improved overall confidence in model predictions of litter and soil carbon pools. The calibrated model will therefore be a useful tool for informing land managers and policy makers seeking to understand on-site dynamics of all carbon pools, and hence, the total contribution to carbon abatement of different EMTP projects in Australia.

Fine Litter Dynamics in Tropical Dry Forests Located in Two Contrasting Landscapes of the Colombian Caribbean

Tropical dry forests (TDFs) represent 42% of all tropical forests; they are extensive, but little is known of their structure and function. The fine litterfall represents the main route of circulation of organic materials and nutrients in these ecosystems. The objective of this study was to compare several remnants of TDFs located in contrasting landscape units—Mountain and Lomerio—and with different precipitation, in terms of the fluxes of organic materials to the soil, derived from the production of fine litterfall from the canopy. The fine litterfall (including woody material up to 2 cm in diameter) was collected monthly from April 2020 to March 2021, in 29 circular plots of 500 m2 randomly established. High rates of litterfall were recorded in the Lomerio landscape (4.9 Mg ha−1) than in the Mountain landscape (4.5 Mg ha−1). The monthly leaf litter production showed clear seasonal patterns, which were largely driven by the importance of the species in the landscape and the effect of precipitation during the study. Annual fine litter production observed in this study in comparison with other TDFs indicates relevant productivity levels, which contribute to the activation of biogeochemical cycles and improved ecosystem functionality.

Functional Role of Mangrove Forests Along the Subtropical and Tropical Coasts of China

Mangroves forests inhabiting the south coast of China are crucial habitats for the functioning of the coastal zone. This role has not been carefully considered in China and compared to their functional role worldwide. China’s mangroves currently occupy 20,303 ha. Average forest biomass is equivalent to the global average, but the mean ratio of below-ground to above-ground biomass is high (46%), reflecting the young age of most forests. Rates of annual litterfall, net primary productivity, and root production are above the global average, indicating that China’s mangrove forests are highly productive within their latitudinal band. High productivity may reflect high rates of organic inputs, young forest ages, and high rates of precipitation. As China’s mangrove forests have short canopies, these data imply that the rates of forest turnover are more rapid than in most other mangroves. Mangrove organic carbon (C<sub>org</sub>) stock averaged 190.96 Mg C<sub>org</sub> ha<sup>-1</sup>, mostly (58%) in soils, less than the global average, reflecting young forest age and frequent soil disturbance. Total C<sub>org</sub> stored in China’s mangroves is 3.9 Tg, only 0.03% of the global total, but the total C<sub>org</sub> sequestration rate is 139.4 Gg C<sub>org</sub> a<sup>-1</sup> while the average C<sub>org</sub> sequestration rate is 6.87 Mg C<sub>org</sub> ha<sup>-1</sup> a<sup>-1</sup>, which is greater than the global average. C<sub>org</sub> losses via microbial mineralization are large as total C<sub>org</sub> export from mangroves accounts for 44% of the total C<sub>org</sub> exported to the South China Sea. Nutrients are efficiently retained suggesting their use and proper management as aquaculture filters. Mangroves have close links to other coastal food webs.

Using measured stocks of biomass and litter carbon to constrain modelled estimates of sequestration of soil organic carbon under contrasting mixed-species environmental plantings

Reforestation of agricultural land with mixed-species environmental plantings of native trees and shrubs contributes to abatement of greenhouse gas emissions through sequestration of carbon, and to landscape remediation and biodiversity enhancement. Although accumulation of carbon in biomass is relatively well understood, less is known about associated changes in soil organic carbon (SOC) following different types of reforestation. Direct measurement of SOC may not be cost effective where rates of SOC sequestration are relatively small and/or highly spatially-variable, thereby requiring intensive sampling. Hence, our objective was to develop a verified modelling approach for determining changes in SOC to facilitate the inclusion of SOC in the carbon accounts of reforestation projects. We measured carbon stocks of biomass, litter and SOC (0–30cm) in 125 environmental plantings (often paired to adjacent agricultural sites), representing sites of varying productivity across the Australian continent. After constraining a carbon accounting model to observed measures of growth, allocation of biomass, and rates of litterfall and litter decomposition, the model was calibrated to maximise the efficiency of prediction of SOC and its fractions. Uncertainties in both measured and modelled results meant that efficiencies of prediction of SOC across the 125 contrasting plantings were only moderate, at 39–68%. Data-informed modelling nonetheless improved confidence in outputs from scenario analyses, confirming that: (i) reforestation on agricultural land highly depleted in SOC (i.e. previously under cropping) had the highest capacity to sequester SOC, particularly where rainfall was relatively high (>600mmyear−1), and; (ii) decreased planting width and increased stand density and the proportion of eucalypts enhanced rates of SOC sequestration. These results improve confidence in predictions of SOC following environmental reforestation under varying conditions. The calibrated model will be a useful tool for informing land managers and policy makers seeking to understand the dynamics of SOC following such reforestation.

Groundwater availability mediates the ecosystem effects of an invasion of Prosopis pallida.

Groundwater levels in arid environments are dropping worldwide due to human extraction, and precipitation events are predicted to become rarer and more intense in many arid areas with global climate change. These changes will likely alter both primary productivity and plant–soil nutrient cycles. To better understand the nature of such alterations, we examined effects of groundwater availability on plant–soil nitrogen (N) cycling in areas invaded by the N-fixing phreatophyte, Prosopis pallida, on the dry leeward coast of Hawai‘i Island. Our aims were to quantify effects of groundwater availability to P. pallida on rates of litterfall N inputs and accretion in soils and to quantify effects of groundwater availability on N mineralization and leaching rates of inorganic N under natural rainfall conditions and simulated rain events. Stem water δ18O values indicate that P. pallida trees in lowland plots accessed shallow groundwater, while in upland plots they relied solely on rainfall. During drought periods, P. pallida at upland plots experienced water stress, evidenced by lower stem water potentials, higher water-use efficiency, and lower predawn photosynthetic performance than at lowland plots. Prosopis pallida basal area was 5.3 times greater at lowland plots, and these plots exhibited 17 times higher carbon (C), 24 times higher N, and 35 times higher phosphorus (P) additions via litterfall, indicating that productivity of this phreatophyte was decoupled from rainfall where groundwater was present. Total N mass in soils was 4.7 times greater where groundwater was accessible, supporting the case that groundwater access increased N2 fixation at a stand level. In contrast, N mineralization and leaching losses from soils, though substantially greater in lowland relative to upland areas, were strongly controlled by rainfall. Results provide clear examples of how invasive species with particular functional attributes (i.e., N-fixing phreatophytes) exploit otherwise inaccessible resources to dramatically alter the functioning of the systems they invade and how anthropogenic changes to hydrological processes can also alter ecosystem-level impacts of biological invasions. Results also illustrate a mechanism by which regional groundwater drawdown may reduce soil nutrient accretion and availability in arid regions.

Contribution of surface leaf-litter breakdown and forest composition to benthic oxygen demand and ecosystem respiration in a South Georgia blackwater river

Many North American blackwater rivers exhibit low dissolved O2 (DO) that may be the result of benthic respiration. We examined how tree species affected O2 demand via the quantity and quality of litter produced. In addition, we compared areal estimates of surface leaf-litter microbial respiration to sediment O2 demand (SOD) and ecosystem respiration (ER) in stream and swamp reaches of a blackwater river to quantify contributions of surface litter decomposition to O2 demand. Litter inputs averaged 917 and 678 g m−2 y−1 in the swamp and stream, respectively. Tree species differentially affected O2 demand via the quantity and quality of litter produced. Bald cypress (Taxodium distichum) contributed most litter inputs because of its dominance and because it produced more litter per tree, thereby making greater relative contributions to O2 demand in the swamp. In the stream, water oak (Quercus nigra) produced litter supporting lower fungal biomass and O2 uptake rates, but produced more litter than red maple (Acer rubrum). Breakdown rates in the swamp were faster, whereas standing stock decreases were lower than in the stream, indicating greater organic matter retention. Surface litter microbial respiration accounted for 89% of SOD (6.37 g O2 m−2 d−1), and 57 to 89% of ER in the swamp. Our findings suggest that surface litter drives the majority of O2 demand in some blackwater swamps, and tree species with higher rates of litterfall may make larger contributions to ER. Forested swamps may be hotspots of O2 demand in blackwater rivers because low water velocities enhance retention.

Differential plant damage due to litterfall in palm-dominated forest stands in a Central Pacific atoll

Abstract:High densities of palms are common in many tropical forests. In some cases, the dominance of palms has been associated with a depauperate understorey and high rates of native seedling mortality. A variety of different potential mechanisms has been suggested to explain the sustained palm dominance in the understorey and canopy of these forests. Working in a Cocos nucifera-dominated wet tropical forest at Palmyra Atoll in the central Pacific, we examine how litterfall from this pantropical, and economically important palm, impacts seedling survival. We compare rates of litterfall, and rates of litterfall-associated damage, between forest stands dominated by C. nucifera (coconut palm) and forest stands with low abundance of C. nucifera. To assess litterfall damage we survey damage to both artificial seedlings (n = 711), outplanted real seedlings of two species (with and without protection via caging; n = 204), and standing rates of litterfall damage. We find that rates of large-litterfall damage were an average of five times higher in sites with high densities of C. nucifera. Associated with these increases we observe that levels of physical damage to artificial model seedlings caused by litterfall over a 4-mo period increased from 4.9% in sites with low abundance of C. nucifera to 16.1% in sites with high abundance of C. nucifera. Extrapolated to annual rates, litterfall damage of this magnitude exceeds the average levels observed in other published studies. Living native seedlings also showed more than 300% higher levels of mortality in forest stands with high densities of C. nucifera, a difference that was greatly reduced when protected by caging from litterfall. In contrast, uncaged C. nucifera seedlings actually had slightly higher survivorship in habitats dominated by conspecifics. We suggest that litterfall damage may be an important mechanism by which this tropical palm reaches and maintains near monodominance in many coastal and insular habitats.

Litter-fall and decomposition in harvested and un-harvested boreal forests

Litter fall and litter decomposition were examined in harvested and unharvested western Newfoundland balsam fir (Abies balsamea) and black spruce (Picea mariana) forests. Rates of litterfall in mature 70-year-old forests were 2.4 to 3.5 Mg ha−1 year−1, which was reduced to 0.2 to 0.3 Mg ha−1 year−1 following harvesting. In contrast, rates of black spruce needle, balsam fir needle, fine (<2 mm diameter) root, and moss (dominated by feather moss) litter decomposition were not affected by forest harvesting at either site during 24 to 54 months of field incubation in litterbags. Mass loss of balsam fir needle, black spruce needle, and moss (dominated by feather moss) were not significantly different indicating that moss forms a labile litter type in a forested setting.

Mangrove litter fall: Extrapolation from traps to a large tropical macrotidal harbour

Mangrove litter is a major source of organic matter for detrital food chains in many tropical coastal ecosystems, but scant attention has been paid to the substantial challenges in sampling and extrapolation of rates of litter fall. The challenges arise due to within-stand heterogeneity including incomplete canopy cover, and canopy that is below the high tide mark. We sampled litter monthly for three years at 35 sites across eight mapped communities in the macrotidal Darwin Harbour, northern Australia. Totals were adjusted for mean community canopy cover and the occurrence of canopy below the high tide mark. The mangroves of Darwin Harbour generate an estimated average of 5.0 t ha −1 yr −1 of litter. This amount would have been overestimated by 32% had we not corrected for limited canopy cover and underestimated by 11% had we not corrected for foliage that is below the high tide mark. Had we made neither correction, we would have overestimated litter fall by 17%. Among communities, rates varied 2.6-fold per unit area of canopy, and 3.9-fold among unit area of community. Seaward fringe mangroves were the most productive per unit of canopy area but the canopy was relatively open; Tidal creek forest was the most productive per unit area of community. Litter fall varied 1.1-fold among years and 2.0-fold among months though communities exhibited a range of seasonalities. Our study may be the most extensively stratified and sampled evaluation of mangrove litter fall in a tropical estuary. We believe our study is also the first such assessment to explicitly deal with canopy discontinuities and demonstrates that failure to do so can result in considerable overestimation of mangrove productivity.

Flows and hypoxic blackwater events in managed ephemeral river channels

As pressure increases on the availability of water resources worldwide, especially in the face of climatic change, it is probable that the likelihood of streams undergoing at least some periods of drying will increase in arid and semi-arid regions. This has implications for the ongoing management of waterways in these areas. One area of concern is the potential occurrence of hypoxic blackwater events upon re-instatement of flows in creek and river channels following periods of drying. Hypoxic blackwater events are characterised by high levels of dissolved organic carbon (DOC), the metabolism of which results in low dissolved oxygen (DO) in the water column, which can cause fish and crustacean mortality. Therefore, understanding hypoxic blackwater events is important in order to reduce the potential for fish mortalities and other water quality impacts from both managed and natural flows. In this study, we set out to determine the factors that influenced the occurrence of a hypoxic blackwater event in the Edward-Wakool river system, in southern NSW, Australia during the previous austral summer (2008–2009). Standing stocks of plant litter, emergent macrophytes and river red gum saplings (Eucalyptus camaldulensis Dehn.), as well as rates of litterfall, were determined in dry and inundated channels. A series of mesocosm experiments were undertaken to determine which carbon source was the greatest contributor to DOC and to DO depletion, and what loadings could result in hypoxia. These experiments were then used to create a simple algorithm relating carbon loading in a dry channel to DOC in the overlying water column following inundation. Results revealed that plant litter was the main contributor to water column DOC and to DO depletion. Litter loadings equal to or greater than 370 g m−2 were found to cause DO in a shallow (20 cm) water column at 20 °C to fall to zero within two days. This loading was approximately half of that found in dry channels in the Edward-Wakool system – thus, initial inundation of these channels at a low flow rate during summer (or when water temperature is equal to or greater than 20 °C) is highly likely to trigger a hypoxic blackwater event. In addition, one month of litterfall in summer was calculated to be sufficient to deliver enough carbon to dry channels to create a hypoxic blackwater event. These findings suggest that to reduce the likelihood of a hypoxic blackwater event occurring as a result of managed flows in ephemeral systems; (1) the principal source(s) of DOC as well as the pathway and timing of accumulation in dry channels should be identified, and (2) the timing of the re-instatement of flows in a dry channel should be considered in light of the timing of maximum rates of accumulation of the principal source(s) of DOC.

The contribution of mistletoes to nutrient returns: Evidence for a critical role in nutrient cycling

AbstractBoth nutrient cycling and nutrient relationships between mistletoe and host have been widely studied; yet it is unclear whether high nutrient concentrations commonly found in mistletoes affect rates of nutrient cycling. To address this question, we assessed 13 elements in the leaf litter of a temperate eucalypt forest in southern New South Wales, comparing concentrations from trees (Eucalyptus blakelyi, E. dwyeri, and E. dealbata) with and without the hemiparasitic mistletoe Amyema miquelii. Results were in accord with previous research on fresh leaves showing that concentrations of many elements were higher in the mistletoe than the host. This was not the case for all elements; most notably for N, where concentrations were significantly lower in the mistletoe. However, the return of all elements increased with mistletoe infection because of the combined effect of enrichment in mistletoe tissues and high rates of mistletoe litterfall. Annual returns of N and P in leaf litter increased by a factor of 1.65 and 3 respectively, with the greatest increase being for K by a factor of 43 in spring. These increased element returns were not significantly influenced by any changes in host leaf litter quality, as mistletoe infection was not found to affect host element concentrations. Mistletoe infection also altered the spatial and temporal distribution of element returns because of the patchy occurrence of mistletoes and extended period of mistletoe litterfall compared with the host. These findings provide a mechanistic explanation for the role of mistletoes as a keystone resource and, together with comparable results from root‐parasitic plants in boreal tundra and cool‐temperate grasslands, suggest that enhancing nutrient return rates may be a generalized property of parasitic plants.

Climate and recent fire history affect fuel loads in Eucalyptus forests: Implications for fire management in a changing climate

Predicted changes to global climates are expected to affect natural fire regimes. Many studies suggest that the impact of these effects could be minimised by reducing fuel loads through prescribed burning. Fuel loads are dynamic and are affected by a range of factors including fire and climate. In this study, we use a 22-year dataset to examine the relative influence of climate and fire history on rates of litterfall and decomposition, and hence fuel loads, in a coastal Eucalypt forest in south-eastern Australia. Litterfall and decomposition were both affected by temperature, recent rainfall and fire history variables. Over the study period prescribed burning immediately reduced fuel loads, with fuel loads reaching pre-burn levels within 3 years of a fire. Modelling fuel loads under predicted climate change scenarios for 2070 suggests that while fuel loads are reduced, the levels are not significantly lower than those recorded in the study. Based on these predictions it is unlikely that the role or value of prescribed burning in these forests will change under the scenarios tested in this study.

Soil Respiration and Ecosystem Carbon Stocks in New England Forests with Varying Soil Drainage

Abstract Northern temperate forests play an important role in the global carbon (C) cycle. Individual stands can differ in C content and storage, based on characteristics such as vegetation type, site history, and soil properties. These site differences may cause stands to vary in their response to extreme weather events such as droughts. We examined ecosystem C pools, soil respiration, and litterfall in four hardwood stands with widely varying soil drainage in Rhode Island. Total ecosystem C increased as soils became more poorly drained, ranging from 181 Mg C ha-1 in the excessively drained Entisol to 547 Mg C ha-1 in the very poorly drained Histosol. The proportion of ecosystem C contained in the soil was much higher in the poorly drained soils, and ranged from 57% in the excessively drained Entisol to 91% in the poorly drained Histosol. While total ecosystem C stocks varied by a factor of three, rates of litterfall and soil respiration were similar among sites. Soil carbon content was highest in the ve...

Asymmetric impacts of two herbivore ecotypes on similar host plants

1. Ecotypes may arise following allopatric separation from source populations. The simultaneous transfer of an exotic plant to a novel environment, along with its stenophagous herbivore, may complicate more traditional patterns of divergence from the plant and insect source populations.2. The present study evaluated herbivory effects by two Cyrtobagous salviniae ecotypes on two species of Salvinia: the larger S. molesta and the smaller S. minima. Evaluations were based on relative growth rates, biomass production, coverage, and nutrient cycling in a series of complementary and comparative laboratory and outdoor tank experiments.3. In general, the experiment results indicated that the smaller Florida ecotype of C. salviniae impacted both Salvinia species more than the larger Brazil ecotype. Herbivory, especially by the Florida ecotype, also improved water quality and accelerated nutrient cycling by increasing the rates of litterfall from the standing crops of salvinia.4. The smaller size of the Florida ecotype may be adaptive by allowing maximal exploitation of host plants via internal larval feeding, which presumably reduces predation risk while increasing damage to the plant. These findings provide support for relying on the suppressive effects of the Florida ecotype in Florida, rather than introducing the Brazil ecotype to counter new infestations of S. molesta.

Patterns of Mangrove Wood and Litter Production Within a Beach Ridge-Fringing Reef Embayment, Northern Great Barrier Reef Coast

Mortality, litter fall, and patterns of stem growth were examined in Rhizophora- and Ceriops-dominated forests located upstream and downstream in four tidally dominated creeks within a beach reef embayment on the northern Great Barrier Reef coast. Although patterns of stem densities, basal area, and diameter-at-breast height (DBH) between upstream–downstream sites and creeks were inconsistent, aboveground biomass, wood production, litter fall, and aboveground net primary productivity (ANPP) were greater in the Rhizophora-dominated forests. Incremental growth of stems (SI, cm year−1) was slow compared to other mangroves, declining among species as follows: Rhizophora stylosa (mean = 0.080) > Bruguiera exaristata (0.066) = Xylocarpus australasicus (0.064) = Ceriops australis (0.056); SI was greater upstream than downstream, possibly due to nutrient inputs from upland sugarcane cultivation. The DBH of dead trees were less than the DBH of live trees, suggesting natural mortality, which was greatest for X. australasicus (annual rate = 3.27%), followed by B. exaristata (0.84%), C. australis (0.48%), and R. stylosa (0.33%). Rates of litter fall were seasonal and equivalent to those measured in other mangroves, but rates of ANPP were, on average, low in most plots. Salinity was likely the main factor limiting growth as correlations of salinity with tree growth and production were negative. Nutrients may have also played a key regulatory role, with positive correlations between mangrove production and N and P content of soils and leaves and the comparatively low nutrient content of these sandy soils. The low ratio of wood to litter production suggests that these forests are in a mature stage of development.

Contrasting patterns of diameter and biomass increment across tree functional groups in Amazonian forests

Species' functional traits may help determine rates of carbon gain, with physiological and morphological trade-offs relating to shade tolerance affecting photosynthetic capacity and carbon allocation strategies. However, few studies have examined these trade-offs from the perspective of whole-plant biomass gain of adult trees. We compared tree-level annual diameter increments and annual above-ground biomass (AGB) increments in eight long-term plots in hyper-diverse northwest Amazonia to wood density (rho; a proxy for shade tolerance), whilst also controlling for resource supply (light and soil fertility). rho and annual diameter increment were negatively related, confirming expected differences in allocation associated with shade tolerance, such that light-demanding species allocate a greater proportion of carbon to diameter gain at the expense of woody tissue density. However, contrary to expectations, we found a positive relationship between rho and annual AGB increment in more fertile sites, although AGB gain did not differ significantly with rho class on low-fertility sites. Whole-plant carbon gain may be greater in shade-tolerant species due to higher total leaf area, despite lower leaf-level carbon assimilation rates. Alternatively, rates of carbon loss may be higher in more light-demanding species: higher rates of litterfall, respiration or allocation to roots, are all plausible mechanisms. However, the relationships between rho and AGB and diameter increments were weak; resource availability always exerted a stronger influence on tree growth rates.

Multiple nutrients limit litterfall and decomposition in a tropical forest

To explore the importance of 12 elements in litter production and decomposition, we fertilized 36 1600 m(2)-plots with combinations of N, P, K, or micronutrients (i.e. B, Ca, Cu, Fe, Mg, Mn, Mo, S, Zn) for 6 years in a lowland Panamanian forest. The 90% of litter falling as leaves and twigs failed to increase with fertilization, but reproductive litter (fruits and flowers) increased by 43% with N. K enhanced cellulose decomposition; one or more micronutrients enhanced leaf-litter decomposition; P enhanced both. Our results suggest tropical forests are a non-Liebig world of multiple nutrient limitations, with at least four elements shaping rates of litterfall and decomposition. Multiple metallomic enzymes and cofactors likely create gradients in the break down of leaf litter. Selection favours individuals that make more propagules, and even in an N-rich forest, N is a non-substitutable resource for reproduction.

Calibration of the forest growth model 3-PG to eucalypt plantations growing in low rainfall regions of Australia

In Australia, tools are required to assess likely commercial and environmental benefits of growing saw logs in regions of low-medium rainfall. The widely used 3-PG model was considered appropriate given that it has a relatively low demand for data and can be applied spatially. Two species of high potential for saw log production in such regions are Eucalyptus cladocalyx (sugar gum) and Corymbia maculata (spotted gum). For both of these species, we harvested 12 trees over a range of sizes (from 4 to 52 cm diameter at breast height) to derive 3-PG parameters, including stem density, specific leaf area, relationships between stem diameter and mass, and the branches and bark fraction. We also collated stem diameter data together with data on stocking and survival from 55 stands of E. cladocalyx, and 37 stands of C. maculata. By simulating growth at each of these sites using 3-PG, we calibrated parameters determining sensitivity to frost, optimum temperature for growth, and rates of litterfall to attain an efficiency of prediction of stem diameter of 80% for both species. It was also ensured that prediction of biomass of tree components were in the order of that calculated based on allometric relationships, although efficiencies of these predictions were particularly poor for foliage. We found 3-PG gave a 9–34% greater efficiency of prediction of stem diameter than when using stand age alone as an explanatory variable, indicating that even when only the most basic of site information is available (i.e. rainfall, temperature, solar radiation, number of frost days as well as some information regarding stocking and management), 3-PG can potentially account for some variations in growth across a wide range of sites. Accuracy of 3-PG predictions could be further improved by better quantifying site data (i.e. fertility rating, soil texture and available water) and improving model structure to better predict soil water availability, survival, and partitioning of biomass between tree components.

Spatial associations of humus, nutrients and soils in mixed dipterocarp forest at Lambir, Sarawak, Malaysian Borneo

Discrete humus layers are common on podzols under temperate coniferous and tropical heath forests, and patchy layers also occur under some temperate broadleaved forests on non-podzolic soils. We used multiple data sets to test the reported association of humus with oligotrophic but non-podzolic soils under non-heath dipterocarp forest at Lambir, Sarawak. We examined the distribution, morphology and nutrient dynamics of necromass on soils derived from sandstone and shale. Concentrations of the main mineral nutrients were lower in fresh litter on the very oligotrophic sandstone soils than on shale. The rates of litterfall were similar, so that annual litterfall fluxes of all nutrients were lower on sandstone. The lower nutrient concentrations and fluxes in the litter on sandstone resulted in slower decomposition, longer residence times and larger standing crops of forest-floor necromass, with lower concentrations of nutrients. The necromass on sandstone sequestered significantly more N, K and Mg but less Ca and Mn than on shale, with no significant difference for P. The variations in necromass nutrient dynamics were associated with morphological differences. There were mats of densely rooted humus under the litter on sandstone, whereas litter lay directly over the mineral topsoil on shale. Spatial associations with soil nutrients were weak for necromass thickness, but clear for humus. The proportions of nutrients in the litterfall and necromass reflected the stoichiometric profiles of the soils. We attribute the differences in necromass nutrient dynamics and their association with soil reserve nutrients to lower rates of nutrient replenishment from the weathering of sandstone than from shale. Necromass characteristics are robust field indicators of multivariate edaphic differences in these and other tropical forests on Acrisols/Ultisols derived from Tertiary clastic sediments.

LITTER PRODUCTION AND LITTER NUTRIENT CONCENTRATIONS IN A FRAGMENTED AMAZONIAN LANDSCAPE

We analyzed the effects of distance to forest edge and soil texture on fine‐litter production and on nutrient concentrations in the leaf fall in an experimentally fragmented landscape in Brazilian Amazonia. Production of fine litter (leaves, twigs <2 cm in diameter, flowers, and fruits) was measured over a 3‐yr period. Litter traps were installed in plots located near (<100 m) and far (>250 m) from forest edges, and in clayey or sandy soils. In total, 28 plots were established, with 10 litter traps per plot. Results reveal a significant effect of distance to forest edge on litter production, but no significant effect of soil type or interaction between soil type and edge distance. On average, annual litter production on edge plots exceeded that on the interior plots by 0.68 Mg/ha (9.50 ± 0.23 vs. 8.82 ± 0.14 Mg·ha−1·yr−1, mean ± 1 se, based on a 3‐yr period). With regard to nutrient concentrations in the leaf fall, we detected a significant effect of soil type on three of eight nutrients analyzed. Concentrations of N, Mg, and Mn were greater in leaves on clayey than on sandy soils. Distance to forest edge only significantly affected the concentration of Ca, which was greater near than far from edges, perhaps due to strong Ca mobilization by the roots of pioneer trees.Several factors may account for the observed increase in litterfall near forest edges, including the greater prevalence of winds, increased plant desiccation stress, and higher rates of tree recruitment, especially of pioneer trees, near edges. Elevated rates of litterfall are likely to have cascading effects on the ecology of fragmented forests, affecting the invertebrate fauna, increasing seed and seedling mortality, and causing forest fragments to be more vulnerable to destructive surface fires.