Litter Macroinvertebrate Research Articles

Rainforest litter invertebrates decimated by high severity burns during Australia's gigafires

AbstractClimate change is increasing the frequency of extreme fires. In 2019–2020, extreme fires burned 97 000 km2 of native vegetation in south‐eastern Australia, affecting many areas of rainforest, which has historically burned less frequently. One year post‐fires, we surveyed litter macroinvertebrates in 52 temperate rainforest sites. Sites had experienced increasing levels of fire severity (unburnt, medium severity and high severity). We asked how fire severity affected: (1) litter macroinvertebrate habitats; (2) the abundance of litter macroinvertebrate taxa per unit area; and (3) abundance relative to litter habitat (volumetric density). We also estimated the loss of litter macroinvertebrates across rainforests in the study region. High severity burns supported only a fifth of the litter volume and canopy cover as unburnt sites, lower soil moisture and higher herb cover. Medium burns were intermediate. Macroinvertebrate abundance declined with burn severity: high severity burns supported only 26% of the abundance in unburnt sites; medium severity burns supported 80% of that in unburnt sites. Patterns were similar for all taxa, with millipedes declining most. High severity fires resulted in up to 1.90 million fewer macroinvertebrates per hectare; 0.53 million fewer per hectare of medium burn rainforest. Across the study region, we estimate that 60 billion fewer litter macroinvertebrates persisted in temperate rainforests alone. Volumetric densities of many litter macroinvertebrate taxa in high severity burns were marginally higher than in unburnt sites, suggesting nutrients may be more available post‐fire, or that persisting individuals become concentrated in the leaf litter. For less desiccation‐tolerant groups (e.g., amphipods), density declines with increasing severity may reflect the combined impact of low soil moisture and reduced litter cover. Many taxa persisted following high severity fires, but declines were substantial, and taxa differed in their vulnerability. Longer‐term monitoring is required to understand the recovery trajectory and impacts on ecological function.

Resource stoichiometry and availability modulate species richness and biomass of tropical litter macro-invertebrates.

High biodiversity and biomass of soil communities are crucial for litter decomposition in terrestrial ecosystems such as tropical forests. However, the leaf litter that these communities consume is of particularly poor quality as indicated by elemental stoichiometry. The impact of resource quantity, quality and other habitat parameters on species richness and biomass of consumer communities is often studied in isolation, although much can be learned from simultaneously studying both community characteristics. Using a dataset of 780macro-invertebrate consumer species across 32 sites in tropical lowland rain forest and agricultural systems on Sumatra, Indonesia, we investigated the effects of basal resource stoichiometry (C:X ratios of N, P, K, Ca, Mg, Na, S in local leaf litter), litter mass (basal resource quantity and habitat space), plant species richness (surrogate for litter habitat heterogeneity), and soil pH (acidity) on consumer species richness and biomass across different consumer groups (i.e. 3 feeding guilds and 10 selected taxonomic groups). In order to distinguish the most important predictors of consumer species richness and biomass, we applied a standardised model averaging approach investigating the effects of basal resource stoichiometry, litter mass, plant species richness and soil pH on both consumer community characteristics. This standardised approach enabled us to identify differences and similarities in the magnitude and importance of such effects on consumer species richness and biomass. Across consumer groups, we found litter mass to be the most important predictor of both species richness and biomass. Resource stoichiometry had a more pronounced impact on consumer species richness than on their biomass. As expected, taxonomic groups differed in which resource and habitat parameters (basal resource stoichiometry, litter mass, plant species richness and pH) were most important for modulating their community characteristics. The importance of litter mass for both species richness and biomass indicates that these tropical consumers strongly depend on habitat space and resource availability. Our study supports previous theoretical work indicating that consumer species richness is jointly influenced by resource availability and the balanced supply of multiple chemical elements in their resources.

Biodiversity is affected by changes in management intensity of cocoa-based agroforests

In the humid tropics, the rapid rate of deforestation has resulted in a race to protect remaining forest patches that are increasingly isolated within a rapidly expanding agricultural matrix. In these landscapes, a significant area consists of complex agro-forestry systems with high structural and functional plant diversity, providing critical resources for biodiversity conservation, such as food and habitat. Although not a substitute for natural forests, these anthropogenic habitats are gaining increasing conservation value as deforestation progresses. Shaded tree crops, such as cocoa, provide habitats for numerous forest dependent species of high conservation value and play a largely undocumented role in providing other ecological services. Following previous work on the botanical composition and structural complexity of cocoa agroforests in Talamanca (Costa Rica), we assessed if differences in the vegetation composition and structure of 36 cocoa agroforests could affect the wild diversity of small mammals, amphibians, reptiles, soil and litter macro-invertebrates and epiphytes found on cocoa trees and associated plants. Results show that Alpha-diversity is not affected by changes in vegetation structure and composition, except for amphibians and epiphytes found on cocoa trees. However, five taxa among eight showed distinct species composition patterns when compared among cocoa-based agroforestry clusters and with forest control. We showed that beta-diversity assessment enhances our understanding of the effect of management intensification on species composition and on habitat quality. The proper design of the shade component in these AFS will certainly play a key role in segregating wild species hosted in these systems and will open a new field of research for the intensification of both cocoa and associated productions in these highly diverse systems.

Distribución espacial de la macrofauna edáfica en bosque mesófilo y agroecosistemas derivados en la reserva La Cortadura, Coatepec. Veracruz

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Effect of Sub-Canopy on Habitat Selection in the Blue-spotted Salamander (Ambystoma laterale-jeffersonianum unisexual complex)

Elucidating the mechanisms that influence spatial distribution patterns is vital to understanding how populations persist. We examined distribution in one of the most common salamanders in southeastern Michigan, the Blue-spotted Salamander (Ambystoma laterale-jeffersonianum unisexual complex). Three major tree species dominate the sub-canopy in the study site and form monospecific patches, which may have an effect on the distribution of terrestrial phases of local amphibian species. To examine this, we tested whether adult salamanders are significantly associated negatively or positively with patches of particular tree species. We then examined two potential causal factors: habitat quality, using leaf litter macroinvertebrate biomass as a proxy, and behavioral site choice in the Blue-spotted Salamander. We found that this species is positively associated with patches of red maple and negatively associated with patches of black cherry. We also found that, when presented with a choice, salamanders choose red maple leaf litter over black cherry leaf litter. In the absence of differences in physical leaf litter characteristics between patches of red maple and black cherry, we suggest that the Blue-spotted Salamander may be utilizing chemical cues to select habitat. Our findings imply that salamander populations may be affected not only by habitat loss, but also by changes in forest composition. These results provide evidence for a more complex model than the traditional amphibian metapopulation concept, where even fully forested habitat may form a matrix of optimal and sub-optimal, or even intolerable, patches.

Rate of litter decay and litter macroinvertebrates in limed and unlimed forests of the Adirondack Mountains, USA

Acid deposition can reduce the rate of litter decay in forests by changing environmental and substrate quality for macroinvertebrates and microbes. Terrestrial application of lime can ameliorate many of the negative effects of acid deposition, but the effects of liming on forest litter decay and fauna are poorly understood. We used reciprocal transplants of litter bags to better understand the effects of substrate calcium content and incubation context (limed plots versus unlimed plots) on rate of litter decay and abundance of litter-dwelling macroinvertebrates. Our study took place in the Adirondack Mountains (Adirondacks) of New York State, USA, a region affected by chronic acid deposition. Lime was added to randomly-selected plots at a rate of 10Mgha−1; control plots were not limed. Leaves for high-calcium litter bags were collected under trees grown in limed plots, and leaves for low-calcium litter bags were collected in unlimed plots. High-calcium and low-calcium leaves differed in %Ca but not in %N or C:N at the beginning of our study. Leaf litter decay was faster for bags containing high-calcium leaves than for those litter bags containing low-calcium leaves, and decay was slower in limed than unlimed plots. Assemblages of litter-dwelling macroinvertebrates were markedly different between litter bags collected from limed and those collected from unlimed plots. Snails increased in abundance; whereas, millipedes and spiders decreased in abundance at limed plots following liming. Millipedes likely were important litter-eating macroinvertebrates at these sites, and the decline in millipedes may have contributed to the reduction in rate of litter decay. The liming of areas negatively affected by acid deposition may decrease rate of litter decay immediately following lime application. This was a short-term study. Understanding the long-term, as well as immediate, effects of liming is necessary to determine the advisability of lime application in regions affected by acid deposition.

Grupos funcionales alimentarios de macroinvertebrados acuáticos en el río Gaira, Colombia

Tropical rivers are frequently described on their biodiversity but few studies have considered the ecological value of this richness in their food webs. We determined the trophic structure of aquatic macroinvertebrate communities (expressed in the richness and abundance of taxa and biomass proportions of different functional feeding groups) at the level of the river, stretch and microhabitats (functional units - UFs). We evaluated the spatial and temporal variation of these descriptors during wet and dry events, and selected three sites associated with different altitudinal belts. We reported 109 taxa, with 11167 individuals who contributed 107.11g of biomass. Density of macroinvertebrates was favored with increasing height, and biomass showed the opposite pattern (K-W = 10.1, d.f. = 1, p < 0.05), due to the addition of large crustaceans (Macrobrachium), and the taxa diversity was higher in the middle stretch of the river (H'=3.16). The Gaira stream runs through a mid-sized river basin, for this reason we found mainly bedrock (epilithon = 50.5%), gravel and sand (43.7%). The functional unit with more habitat and food resources that contains a higher abundance of leaf litter macroinvertebrates was foliage followed by epilithon, fine sediment and gravel-sand (K-W = 25.3, d.f. = 3, p < 0.05). The biomass values of these organisms were higher in leaves followed by gravel-sands, epilithon and sediment (K-W = 15.3, d.f. = 3, p < 0.05). Autochthonous biomass input by different functional feeding groups can be considered very low, but they define the functionality of the stream, being represented almost exclusively by shredders (Macrobrachium, 73%), present only in the lower reaches, followed by shredder Leptonema with 15%, located mostly in the upper reaches and predatory stoneflies of the genus Anacroneuria to 6.56%, which dominated in the middle stretch of stream. Excluding Macrobrachium from the analysis, there was dominance of Anacroneuria in the lower reaches. Between rainfall and drought events, biomass of functional feeding groups was higher in rain (W = 10.1, d.f. = 1, p < 0.05), favoring the growth of decapods, but the abundance was much higher during drought events.

Patterns and mechanisms responsible for the relationship between the diversity of litter macro-invertebrates and leaf degradation

Laboratory microcosms were used to determine how leaf degradation processes (C–CO2 release and leaf mass loss) are affected by the diversity of soil macro-invertebrate assemblages (comprising earthworms, woodlice and millipedes). The relationships were tested using different measures of diversity (number of species and trait dissimilarities). Net diversity effects and transgressive overyielding were calculated to disentangle the relative impacts of negative, neutral and positive species interactions on the relationships observed. Minimum trait dissimilarities were found to be correlated with leaf mass loss and, to a lesser extent, with C–CO2 release. This suggests that process rates increase as trait similarity in species assemblage decreases. Conversely, increasing the number of species resulted in the saturation of process rates after 1–2 species had been added to a microcosm. The process rates observed could mainly be explained by positive species interactions (40–50% of microcosms being process-dependent), followed by neutral interactions (20–40%) and selection effects or negative interactions (less than 20%). These results thus suggest that the effects of a soil macro-invertebrate assemblage on soil processes are more likely to be driven by complementarity or facilitation than by competition.

Species-specific characteristics of trees can determine the litter macroinvertebrate community and decomposition process below their canopies

This paper tests whether individual trees in a mature forest stand influence the process of litter decomposition and the macroinvertebrate communities in the soil underneath their canopies, as a result of species-specific characteristics. A field decomposition experiment was performed in a mature forest stand of tropical montane cloud forest in Mexico. The areas under the canopies of Quercus laurina Humbl. & Bompl., Oreopanax xalapensis (Kunth) Decne. & Planchon and Beilschmedia ovalis (Blake) C. K. Allen trees were used as experimental units. The natural soil and litter macroinvertebrate communities were monitored and compared to the community that invaded decomposition boxes with reciprocally transplanted leaf litter. The abundances of four macroinvertebrate taxa in natural litter differed among tree species independently of season. No differences were found in the soil community. The response to experimental litter by macroinvertebrate taxa suggests that the production of a specific quality of litter is an important mechanism by which a tree influences the litter macroinvertebrate community that develops under its canopy. However, not all differences in community composition naturally found between tree species can be explained by differences in litter quality during the first year of decomposition. Differences in nutrient release that occur after the first year, and physical properties of litter also probably play an important role. Independently of the canopy tree, the initial chemical quality (N, P, Ca, Mg and lignin) of experimental litter largely determined the decomposition rate and nutrient dynamics of decomposing leaves. However, it was found that under O. xalapensis trees the breakdown of lignin from the litter produced by the same species of tree was particularly effective. This suggests that a feedback has developed between this tree species and the decomposer community prevailing under its canopy.

Successional changes in soil, litter and macroinvertebrate parameters following selective logging in a Mexican Cloud Forest

The environmental and vegetation shifts associated with logging disturbance and secondary succession in Tropical Montane Cloud Forests have been studied in detail, however little is known about the consequences that these changes have for the soil system. The present study was undertaken to determine the impact of selective logging and subsequent secondary succession on soil microenvironmental conditions, leaf litter quality and quantity, soil nutrient concentration and soil and litter macroinvertebrate community composition. The study was carried out in three successional chronosequences, two recently logged sites and two pristine tropical mountain cloud forest sites in Oaxaca, Mexico. Results showed that selective harvesting of Quercus spp. trees caused an increase in soil temperature of ca. 4 °C that is not completely reversed after 100 years of succession. During 100 years of secondary succession litter diversity increased and soil organic matter accumulated (16.4% increase in total C). The availability of cations (Ca, Mg, Na, and K) in the topsoil decreased by more than 50% as a result of logging, and only Mg increased again between 75 and 100 years after disturbance. Pristine cloud forests sustain a diverse litter and soil macroinvertebrate community, but its composition and diversity was negatively affected by logging. The effect of Quercus harvesting activities on the litter community was apparent within 2 months of disturbance (total abundance declined by ca. 65%, higher taxa richness by ca. 10% and diversity by ca. 35%). For the soil community there was a time-lag in the effect of logging. Two months after disturbance there was no significant effect on the soil community but 15 years after abandonment, total macroinvertebrate abundance in the soil was ca. 80% lower and higher taxa richness ca. 30% lower compared to undisturbed sites. Full recovery of the macroinvertebrate community composition appeared to take more than 100 years both in the litter and soil. Reduced abundances of Coleoptera and Enchytraeidae were apparent even after 100 years of succession. The endemic earthworm Ramiellona wilsoni was found almost exclusively in the pristine forests and therefore its abundance could be used as a sensitive indicator of disturbance in these forests.

The role of leaf litter macroinvertebrates in stream-floodplain dynamics

The floodplain has been viewed as a transitional system or ecotone between aquatic and terrestrial habitats. This research has evaluated the role of floodplain macroinvertebrates in the degradation of leaf litter in a Michigan woodland floodplain, and examined the interrelationships among floodplain-stream macroinvertebrates, microbial colonization and selected environmental factors. Although taxonomically different decomposer groups operate in both systems, their functional roles as leaf litter detritivores are basically the same. Leaf litter processing rates were compared and contrasted between the stream and adjacent floodplain using leaf packs and litter bags, respectively. In the stream, the major time period for detritus processing by invertebrates is in the fall and winter, while in the floodplain it is during the spring. Therefore, the sequence of events involved in processing are similar, yet the timing and rate of these events are strikingly different. An understanding of the significant ecological processes linking the stream and floodplain as complementary systems is discussed within the context of watershed management.

Environmental fate and distribution of technetium-99 in a deciduous forest ecosystem

The aims of the present research are to describe the uptake of 99Tc by trees intercepting contaminated groundwater from a radioactive waste storage site, to identify the major 99Tc pools within the woodland ecosystem and to assess the relative mobility of 99Tc in the existing element cycle. Technetium in the groundwater freely passed through a dialysis membrane with a molecular weight exclusion limit of approximately 3500 amu and 99Tc in the groundwater chromatographed on Biogel P-2 in a manner similar to pertechnetate anion (TcO 4 −). Reducing conditions and organic associations at the study site were probably responsible for the relatively large amount (83–92%) of the 99Tc that was nonextractable from soil by 0·01 m CaCl 2. More than one-third of the 99Tc was released from the soil by oxidizing reagents, indicating the presence of chemically reduced forms. The highest average 99Tc concentrations in vegetation were found in herbaceous plants (18 530 pCi g −1 dry wt). Although 99Tc was progressively accumulated over the growing season in tree leaves, average concentrations in tree wood and twigs were equal to or greater than concentrations in leaves. Tree wood was the major above-ground pool for 99Tc because of the high concentrations in wood as well as the large amount of wood relative to other biomass at the site. Technetium was not easily leached from the trees by rainfall and was not readily extractable from forest floor leaf litter by water. The relative importance of return pathways for 99Tc to the forest floor was leaf fall>stemflow >throughfall, indicating that 99Tc was conserved by the trees. Snails and millipedes from the leaf litter layer concentrated technetium 20- and 16-fold, respectively, above levels found in the soil. Pertechnetate was rendered less bioavailable after ingestion by a leaf litter macroinvertebrate ( Porcellio sp.) common to the study site.