Microbial Decomposition Rates Research Articles

Continental‐scale measurement of the soil organic carbon pool with climatic, edaphic, and biotic controls

We present data on soil organic carbon (SOC) inventory for 7050 soil cores collected from a wide range of environmental conditions throughout Australia. The data set is stratified over the spatial distribution of trees and grass to account for variability of SOC inventory with vegetation distribution. We model controls on SOC inventory using an index of water availability and mean annual temperature to represent the climatic control on the rate of C input into the SOC pool and decomposition of SOC, in addition to the fraction of soil particles <63 μm in diameter as a measure of textural control on SOC stabilization. SOC inventories in the top 30 cm of soil increase from 35 mg/cm2 in the driest regions to a modeled plateau with respect to a threshold of water availability at 335 mg/cm2, excluding variables controlling SOC decomposition. Above this threshold, decomposition factors begin to control SOC inventory, which we attribute to energetic control on microbial decomposition rates, and relatively weak stabilization of SOC in association with fine particles. When combined, these relationships provide an overall prediction of SOC inventory that accounts for 89–90% of the variance observed in the measured data set. Deviations from this relationship are most likely due to additional factors that also control decomposition rate such as hydrochemical and soil drainage conditions not accounted for by soil texture. Outliers within this data set are explained with respect to these conditions.

Fertility of tropical soils under different land use systems—a case study of soils in Tabasco, Mexico

Increasing deforestation in Mexico in the past 40 years has led to significant land use changes. It is important to establish land use systems that allow for the necessities of an increasing population and the conservation of soil fertility in the long term. In this study, we investigated the influence of different land use forms on soil fertility in Tabasco, SE Mexico. We chose two different commonly used pastures ( Cynodon plectostachyus and Brachiaria decumbens) and a succession forest. We characterised soil fertility by physico-chemical parameters (texture, density, pH, P, Corg., Ntot., cation exchange capacity (CEC)) as well as by biological parameters, such as litter decomposition, microbial biomass and earthworm community. To estimate litter decomposition we used leaves of Gliricidia sepium, a common fodder tree in the region. The three land use systems had very similar soil chemical characteristics. All three can be characterised as acidic (pH between 4.1 and 5.3) with a high content of organic matter and total nitrogen. However, the three land use systems differed significantly with respect to their soil biological characteristics. Earthworm density as well as litter decomposition were significantly lower under B. decumbens than in the other soils. In all land use systems, the participation of macrofauna and mesofauna accelerated litter decomposition rate significantly as compared with decomposition with microfauna and microflora alone. We extracted two components of the pool of data by main component analysis. The acidity component explained mainly the microbial litter decomposition rate. The rate of litter decomposition – with participation of soil meso- and macrofauna – could be explained by the humus component. We assume that biological parameters were more suitable to characterise differences between the different land use systems. The use of C. plectostachyus and succession forest showed a positive effect on soil fertility.

The Effect of Recycling on Plant Competitive Hierarchies

Evidence from field studies suggests that some plant species enhance their persistence by reinforcing patterns of N availability through differences in litter quality. Using mathematical models of nutrient flow, we explore whether and how recycling affects plant growth, competition, and coexistence and whether it leads to positive feedbacks. Two mechanisms are considered: the ability of plants to access two forms of soil N, complex (e.g., organic) and simple (e.g., nitrate), and the effect of density-dependent limitation of growth. Except in the trivial case of limitation by N in one form without density dependence, differences in litter quality can prevent the establishment of competitors. Feedback can, conversely, facilitate the invasion of competitors. At equilibrium, the rate of decomposition does not affect the outcome of competition. Species affect their long-term persistence if they alter the fraction of nitrogen that is returned to the soil and becomes available for plant uptake. Increasing the fraction of N that is recycled favors specialists in complex nitrogen and species that suppress the growth of others at high nitrogen availability. Increasing the rate of microbial decomposition of complex nitrogen favors specialists in simple nitrogen.

Effects of tree species and topography on soil chemistry, litter quality, and decomposition in Northeast Turkey

Leaf litters from beech ( Fagus orientalis Lipsky.) and oak ( Quercus robur L.), and needle litters from fir ( Abies nordmanniana Spach.) and pine ( Pinus sylvestris L.) trees were collected from north-facing site and south-facing site and at three slope positions (top, middle and bottom) on each aspect that varied in soil chemical characteristics (soil pH, cation exchange capacity and base saturation). The litters were analysed for initial total carbon, nitrogen, acid detergent fibre, lignin and cellulose concentrations. Nitrogen, acid detergent fibre and lignin concentrations and carbon:nitrogen and lignin:nitrogen ratios varied significantly within and between species according to soil chemical characteristics on aspects and slope positions. Litter decomposition was studied in the field using the litterbag technique. The litters were placed on two aspects and at three slopes on each aspect in October 2001, and were sampled every 6-month for 2 years. The main effects of aspect, species and slope position on decomposition rates were all statistically significant. Oak leaf litter showed highest decomposition rates, followed by pine, fir and beech litter, and the litters placed on north-facing site decomposed faster than those on the south-facing site. The litters placed at the top slope position decomposed slower than at those at either the bottom or middle positions. Initial lignin concentrations explained most of the variation in decomposition rates between species, and within species for the aspects and the slope positions, but the explained variance showed differences between aspects and slope positions. This result illustrates the important point that litter quality may define the potential rates of microbial decomposition but these are significantly influenced by the biotic and abiotic environment in which decomposition takes place.

Species‐specific patterns of litter processing by terrestrial isopods (Isopoda: Oniscidea) in high intertidal salt marshes and coastal forests

Summary The species‐specificity of litter processing by three species of isopods at the interface between salt marsh and coastal forest habitats in the south‐eastern United States was examined. To quantify isopod performance, measurements were taken of feeding, digestion and growth of isopods fed on three litter types (Juncus roemerianus, Quercus virginiana and Pinus palustris) and on artificial diets containing one of three classes of model phenolic compounds (simple phenolics and hydrolysable and condensed tannins). To quantify the ecosystem impact of isopods, promotion of microbial respiration, changes in detritus chemistry, and the quantity of litter processed by isopod populations were measured. The results support three hypotheses concerning isopod–litter interactions. (i) Isopod performance on different litter types can be predicted based on chemical litter traits, e.g. phenolic concentrations and C : N ratios. (ii) Fully terrestrial isopods are better adapted to the range of phenolics found in angiosperm litter than are semiterrestrial species inhabiting the supralittoral. (iii) Isopod species differ with respect to their impact on decomposition processes due to species‐specific digestive capabilities, different effects on microbial decomposition and different rates of net litter processing. Because isopods are transitional between semiterrestrial and terrestrial habitats, unlike most other salt marsh detritivores, they are likely to play a unique role in decomposition processes and in the flux of materials between salt marsh and terrestrial habitats.

Biodegradation of low molecular weight organic acids in coniferous forest podzolic soils

Organic acids have been hypothesised to play a central role in long-term soil pedogenic processes such as podzolisation and also in short-term rhizosphere processes such as nutrient mobilisation. Their spatial and temporal patterns in soil, however, are poorly understood. This study was designed to quantify the rate of microbial decomposition of three low molecular weight organic acids (citrate, oxalate and acetate) as a function of soil depth (O, A, E, B and C horizons) in three podzolic coniferous forest soils and to assess their contribution to total soil CO 2 fluxes. Soil solution extraction indicated that generally, most organic acids were present in the highest concentration in surface O horizons (10–100 μM) declining with soil depth. Correspondingly, the rate of organic acid mineralisation was also greatest in the surface organic horizons. In contrast, the mineral horizons possessed low rates of biodegradation which appeared not to be due to a lack of microbial activity but moreover due to strong sorption to the solid phase preventing microbial uptake. Concentration-dependent mineralisation experiments indicated that decomposition could be adequately described by a single Michaelis–Menten kinetics equation. The results showed that generally most horizon samples had the greatest mineralisation capacity for citrate or oxalate ( V max=<1–340 nmol g −1 h −1) in comparison to acetate. The V max values typically declined with soil depth. K M values ranged from 10 to 7000 μM, however, if adsorption was accounted for the K M values decreased (<1–5000 μM) especially in B horizons. Calculations of the contribution of organic acids to total soil respiration indicated that between <0.1 and 47% of total CO 2 production from an individual horizon could be accounted for by organic acid mineralisation alone. The findings are discussed in the context of soil forming and rhizosphere processes.

Effect of dissolved organic carbon quality on microbial decomposition and nitrification rates in stream sediments

1. Microbial decomposition of dissolved organic carbon (DOC) contributes to overall stream metabolism and can influence many processes in the nitrogen cycle, including nitrification. Little is known, however, about the relative decomposition rates of different DOC sources and their subsequent effect on nitrification.2. In this study, labile fraction and overall microbial decomposition of DOC were measured for leaf leachates from 18 temperate forest tree species. Between 61 and 82% (mean, 75%) of the DOC was metabolized in 24 days. Significant differences among leachates were found for labile fraction rates (P &lt; 0.0001) but not for overall rates (P=0.088).3. Nitrification rates in stream sediments were determined after addition of 10 mg C L–1 of each leachate. Nitrification rates ranged from below detection to 0.49 μg N mL sediment–1 day–1 and were significantly correlated with two independent measures of leachate DOC quality, overall microbial decomposition rate (r=–0.594, P=0.0093) and specific ultraviolet absorbance (r=0.469, P=0.0497). Both correlations suggest that nitrification rates were lower in the presence of higher quality carbon.4. Nitrification rates in sediments also were measured after additions of four leachates and glucose at three carbon concentrations (10, 30, and 50 mg C L–1). For all carbon sources, nitrification rates decreased as carbon concentration increased. Glucose and white pine leachate most strongly depressed nitrification. Glucose likely increased the metabolism of heterotrophic bacteria, which then out‐competed nitrifying bacteria for NH4+. White pine leachate probably increased heterotrophic metabolism and directly inhibited nitrification by allelopathy.

The influence of advective transport on redox fronts in column experiments and their numeric modelling (part 1): the influence of variable flow velocities on turnover rates of primary redox processes

The redox processes as well as the establishment of lateral redox sequences along a flowpath were investigated in column experiments containing natural sediments from a sand aquifer. While the concentration of the reducing agent acetate was held constant, the flow velocity was varied from 0.21 to 0.46 and 0.82 m/day. The redox processes were quantified by applying a numerical model that combines transport and reaction. Oxygen, manganese and ironminerals, and sulfate were reduced, before bacterial fermentation led to the production of methane. We observed that these redox processes all took place within the first 6 to 7 cm of the column length. The microbial decomposition rates increased proportionally with increasing flow velocities, resulting in a local establishment of a redox sequence.

Short Communication: Elevated δ15N values in aquatic plants from cleared catchments: why?

δ15N values of plants and animals are being increasingly used to identify the flow of nitrogen through aquatic ecosystems. The δ15N values of crops, riparian trees, emergent and submerged aquatic vegetation in streams from both cleared (agricultural) and forested (rainforest) catchments were sampled. Riparian and aquatic plants had similar δ15N values in forested streams,suggesting a similar source of inorganic nitrogen.In cleared catchments, however, aquatic plants had δ15N values 4–8‰ higher than adjacent riparian vegetation and aquatic plants from streams in forested catchments. The elevated δ15N values of aquatic vegetation in streams with cleared catchments suggest that these plants either have access to a different source of N than those in undisturbed catchments or that high rates of microbial decomposition and nutrient cycling in the cleared catchments influence the δ15N value of available N. This also suggests that the aquatic plants in disturbed catchments are incorporating a different source of nitrogen than the adjacent riparian vegetation. This supports the proposal that in-stream processing of N affects the δ15N value of available N in streams with cleared catchments. These results begin to identify potential pathways for nitrogen transport to streams and the effect that internal cycling may have on a stream’s nitrogen load.

Decomposition of woody legume nodules in two tree/grass associations under contrasting environmental conditions

Turnover of nitrogen-rich root nodules follows the pruning of legume trees, forming a potentially important yet little studied way of N release to the soil. The effects of soil moisture, herbivory by soil mesofauna and microbial decomposition on the disappearance rate of woody legume nodules was studied in two tree/grass forage production associations. Litter bags containing nodules of Erythrina variegata L. (Papilionoideae: Phaseoleae) were incubated for four weeks in grass-covered alleys between Gliricidia sepium (Jacq.) Walp. (Papilionoideae: Robinieae) hedgerows, established on a deep alluvial Oxisol under a humid tropical climate and on a shallow Vertisol under a subhumid tropical climate in Guadeloupe, French Antilles. Soil moisture was regulated by irrigating or covering small plots from natural rainfall. Fine nylon mesh bags were used to study the rate of microbial decomposition, and open-ended perforated cylinders were used to estimate nodule herbivory. The chemical traits, especially the lignin: nitrogen ratio, of E. variegata and G. sepium nodules were similar (lignin: N 1.70 and 1.55, respectively), and suggest that the results are probably also applicable to the G. sepium nodules in the associations. Both soil moisture and decomposing agent (microbes or mesofauna) had a significant effect on the nodule disappearance rate, but soil type did not have any apparent effect. The nodule half-life varied from three to seven days under different treatments. The N release rate from the nodules was high, with N half-life varying from three to five days. Herbivory accounted for ca. 10% of total mass and N loss from nodules during the four-week field incubation period, but its importance increased towards the end of the incubation, especially in Vertisol, after the most easily decomposable part of the nodules had decayed. After pruning, the nodule N is released to soil more rapidly than from mulch.

Use of biochemical indices in the mediterranean environment: comparison among soils under different forest vegetation

In the present study, soil biomass activity, organic carbon storage, and turnover times were compared in adjacent mediterranean biotopes with different forest vegetation, to analyze the effects of litter diversity and soil management protocols on microbial decomposition rates. Samples of forest soil from four vegetation types were collected at depths of 0–20 and 20–40 cm in the ‘Tenuta Presidenziale di Castelporziano’ Reserve on the Tyrrhenian coast, near Rome (Italy). The samples were incubated under standard laboratory conditions (−33 kPa water tension, and 30°C), in order to compare the microbial activity independently of temperature and humidity. The CO 2-C accumulation curves over a 28-d incubation period showed substantially different kinetics between the samples; in particular, soils with above-ground diversity were characterised by high mineralization activity when compared with those sampled under monospecific vegetation. For all the sites, statistically significant linear correlation was observed between nitrogen concentration and potentially mineralizable carbon ( r=0.97), and microbial biomass carbon (C mic) to total organic carbon (C org) ratio and the microbial metabolic quotient q(CO 2) ( r=−0.96). The q(CO 2), indicator of the stability of ecosystems, was enhanced by plant diversity, while the C mic:C org ratio was reduced.

Persistence of metal stress in a forested ecosystem near Sudbury, 66 years after closure of the O'Donnell roast bed

The world's largest open ore roasting bed operated at O'Donnell, near Sudbury from 1915 to 1929. It processed the sulphur-rich, copper—nickel ores of the Canadian Copper Company prior to smelting. By the time it was closed, the ground level fumigations of sulphur dioxide had devastated vegetation for miles around. Sixty-six years later, the roast bed itself is still almost devoid of vegetation. However, recolonization and recovery elsewhere has allowed a forest, albeit unusual in species composition, to grow almost to the edge of the roast bed. The primary colonizers are metal-tolerant grasses, sedges and mosses. The surface soils of the recovered forest are still strongly acidic, as is the roast bed itself (pH 3.89–4.2). Concentrations of nickel and copper in the roast bed still exceed several thousand μg/g, while several hundred μg/g Ni and Cu occur in surface forest soils to 300 m from the roast bed edge. Plant biodiversity increases substantially away from the roast bed and a clear zonation occurs from mosses and grasses through dwarf shrubs, to white birch trees. This recovery forest is different to that of forests in the area not affected by these ground level fumigations. In the soil, copper has been better retained relative to nickel and cobalt. Despite a recovery period of 66 years, the rates of microbial decomposition of litter in the forest around the roast bed are still inhibited.

Variability in the quality of Pinus sylvestris needles and litter from sites with different soil characteristics: Lignin and phenylpropanoid signature

Intact Pinus sylvestris needles and litter from the soil surface were sampled from several stands in SW England growing on soils with different chemical characteristics. The intrinsic chemical and biochemical characteristics of needle and litter samples were measured. The total concentration of lignin, measured by proximate analysis, and the chemical characteristics of the lignin-polymer in P. sylvestris needles and litter, varied between soil types. Lignin concentrations increased from 180 to 316 mg litter g −1 with increasing soil base saturation, although no similar trends in the concentration of lignin in needles were observed. The total concentration of phenylpropanoid moieties, released on CuO-oxidation, increased from 65.6 to 96.1 mg lignin g −1 in needles and 35.3–83.6 mg lignin g −1 in litters, which followed a trend of increasing soil base saturation under P. sylvestris stands. The concentration of NaOH-extractable moieties in needles increased from 1.79 to 2.35 μg sample g −1 with soil base saturation, as did the acid to aldehyde ratios of phenylpropanoid moieties in NaOH-extracts from litters. We conclude that the quality of lignin in needles and litter, as measured by its phenylpropanoid characteristics, varied significantly in P. sylvestris stands. In the light of the evidence from other studies that phenylpropanoid moieties have significantly different rates of microbial decomposition, this aspect of lignin quality should be considered when modelling the rate of litter mass loss and organic matter accumulation in forest soils. Furthermore, we have shown that by combining the CuO-oxidation technique with a NaOH-extraction procedure, phenylpropanoid signatures of a ‘bound’ and a relatively ‘labile’ lignin derived fraction in needles and litters can be more accurately monitored. A more extensive study is required to clarify the apparent relationships between the soil chemical characteristics beneath stands and the quality of lignin in plant materials.

Gas fluxes achieved by in situ convective flow in Phragmites australis

The Common Reed ( Phragmites australis Cav. Trin. ex Steud.) possesses an outstanding capacity to vent its underground tissues by pressurized through-flow. Phragmites-dominated wetlands therefore potentially provide a significant source of trace gas emissions to the atmosphere. In this paper we present results of in situ studies on gas exchange through Phragmites, and evaluate various methodologies used for measuring gas transport and the fluxes they record. Gas exchange rates were related to atmospheric humidity, temperature and light. Green shoots were influx culms and dead culms and broken or damaged green shoots were efflux culms. Gas exchange through the plants fluctuated diurnally, with highest rates in the early afternoon (up to 11 l m −2 h −1) and lowest rates during the night. The net flux of O 2 to the below-ground tissues and sediment was up to 5.7 1 m −2 day −1, and the net emissions of CO 2 and CH 4 up to 5.1 and 0.27 l m −2 day −1 respectively. Net gas exchange rates varied with season and sediment characteristics, being highest during hot and dry summer days, and on organic sediments with a high oxygen demand and high rates of microbial decomposition. Hence, the convective throughflow mechanism in Phragmites not only accelerates gas exchange between the sediment and the atmosphere, but the oxygen delivered through the plant may also affect the microbial processes in the sediment. Therefore, the role of the plants for rhizosphere oxidation and conveyers of gases should be further assessed in future studies. A comparison of current methods for measuring flow suggested that they need refining if they are to quantify gas exchange through Phragmites wetlands on a large scale or over longer time periods.

Decomposition in situ of the sublittoral Antarctic macroalgaDesmarestia anceps Montagne

Large amounts of detached Antarctic macroalgae accumulate in hollows of the seabed, where decomposition rates of the detached macroalgae are expected to be low, caused by lack of contact of the major part of the macroalgae with the sediment. To determine decomposition rates in Antarctic waters, untreated and pre-killedDesmarestia anceps fronds contained in nylon net bags were studied for 10 months under natural conditions in Factory Cove, Signy Island. Physical decomposition was shown to be more important than microbial decomposition. A weight loss of 40% occurred in untreated material within 313 days, while prekilled material almost all disappeared within 90 days. Despite the weight loss, changes in chlorophylla content were negligible during the experiment. Changes in the C:N ratio and tissue N indicated low rates of microbial decomposition. Therefore, it was concluded that weight loss was mainly caused by fragmentation, and particles disappearing from the nets accounted for most of the loss of original tissue. It remains unknown as to how long nutrients stay in Antarctic macroalgal litter before they become available to the system.

Effects of Gap Size on Litter Decomposition and Microbial Activity in a Subtropical Forest

We examined the effects of gap size on rates of mass loss of leaf, branch and bark litter, and microbial activity in a Castanopsis kawakamii forest over a 360—d period. Fiver forest gap size classes that compromise a gap size gradient were chosen: (1) closed canopy of pure Castanopsis kawakamii vegetation; (2) small gaps with a diameter of &lt; 5 m; (3) small—to—intermediate gaps with a diameter of 5—15 m; (4) intermediate—to—large gaps with a diameter of 15—30 m; (5) large gaps with a diameter of &gt; 30 m. After 360 d, plant litter decomposing under closed canopy or within the small gaps lost mass more rapidly than those in large gaps. Among the litter quality parameters measured, initial N concentrations were most strongly positively correlated with the annual decay rates, and among the microclimatic factors, soil moisture content was the best predictor. Total substrate—induced respiration (SIR) was highest under closed canopy, intermediate in small gaps, and lowest in large gap size classes. Within gap size classes, total microbial respiration was highest for leaves, intermediate for bark, and lowest for branches. Across all sample dates, soil moisture content was the best predictor of microbial activity among the measured microclimatic factors. Plant litter C/N ratios were best predictors of microbial activity among the measured litter quality indices. Decomposition rate constants were linearly correlated with overall mean values of microbial activities for all three types of decomposing litter within five different gap size classes (R2 = 0.984). The SIR rates of decomposing plant litter as a measure of potential active microbial biomass reflected the microclimate and litter quality. Our results suggest that large gaps significantly reduce microbial activity and decomposition rates by changing environmental conditions that consequently should reduce nutrient cycling rates in this system.

C and N fluxes between pools of soil organic matter: Model calibration with long-term field experimental data

NCSOIL, an updated simulation model of C and N behaviour in soil, was calibrated with data from published field experiments in which various authors studied the decomposition of C- or N-labelled plant materials under a wide range of climatic and soil conditions. Four organic pools were included in the new version of NCSOIL viz. plant residues (decay rate constant = 0.3 d −1); microbial biomass with a labile (0.33d −1) and a resistant (0.04 d −1) component; humads (0.006 d −1); and stable OM (5.5 10 −5d −1). Experimental data were fitted with a reduction factor (RED1), which applied to all decomposition rates and for the whole of the simulated period. This parameter took into account the effect of climatic and soil conditions on microbial decomposition rates. Optimization of this reduction factor gave values which ranged from 0.06 to 1.0 and which were related well to the climatic and edaphic conditions given by the authors. Optimization of the size of the humads pool showed that the active soil organic fraction represented 13–35% of the total soil organic matter.

Suitability of a winery-sludge as soil amendment

A laboratory study was carried out to assess the suitability as soil amendment of a sludge obtained through aerobic depuration of wastewaters from a winery (‘winery-sludge’). During a 180-day incubation period, changes in chemical and biological properties of a soil amended with 0·5 and 2·5% of sludge were evaluated. At the end of the experiment, winery-sludge increased the amount of available N, P, K and S, organic and potentially mineralizable carbon, and total microbial activity, while pH, biomass C, dehydrogenase activity, decomposition rate, water-soluble sugars, phenolic compounds and chemical oxygen demand (COD) were not affected by the sludge application. A germination test indicated that the winery-sludge did not show toxicity even immediately after its addition to soil. The great build-up of salinity in soil amended with the highest dose could give rise to risks to crops and environment, so there is a need for field tests.

Abiotic and microbial decomposition of pre- and post-bloom leaves of water hyacinth (Eichhornia crassipes (mart.) Solms)

Rates of abiotic and microbial decomposition in pre- and post-bloom leaves of water hyacinth are determined under laboratory conditions. Decomposition in all types of hyacinth leaves is dominated by physical leaching in an initial phase of 4 days duration, and later by microbial processes. The largest part of physical leaching takes place within the first 4 h. Thereafter, the weight loss due to physical leaching declines exponentially. The weight loss by microbial decomposition is minimal in the initial phase but increases exponentially in the later phase. Pre-bloom leaves decompose significantly faster than post-bloom leaves, and post-bloom green leaves decompose faster than post-bloom brown leaves. The rate constants of abiotic decomposition are significantly higher in post-bloom leaves as compared with pre-bloom leaves, while microbial decomposition is significantly higher in pre-bloom leaves. After 30 days, the dry mass loss by abiotic and microbial decomposition is 15% and 55%, respectively, in pre-bloom leaves, 33% and 19% in post-bloom green leaves, and 24% and 6% in post-bloom brown leaves.

Use of Scattered Resources in Rain Forest of Humid Tropical Lowlands

Well developed, complex rain forests of humid tropical lowlands (RFHTL) do not seem to support large populations of animals compared with other types of forest. Recent studies of terrestrial and understory species of tropical and subtropical forests indicate that the resources available to animals of RFHTL are generally scattered and uncommon. On the forest floor only ants and termites, among insects, are consistently common; they are utilized as food by a variety of specialized ground insectivores. Terrestrial herbivores that eat large fallen fruit are also generally scarce as are the often specialized insectivores that seek typically uncommon understory foliage insects. The low densities and high degrees of specialization that accommodate animal species to resources of RFHTL may be ultimately due to a combination of relatively low net primary production of undisturbed mature rain forest and the rapid rate of microbial decomposition of forest litter. -from Authors