Depth Of Litter Layer Research Articles

Stand stage affects wild bee communities in working pine forests

Wild bees provide critical pollination services to both crops and native forest plants. Evidence suggests that wild bees are declining due to factors such as habitat loss, disease, pesticide use, and climate change. Privately owned, working loblolly pine (Pinus taeda L.) forest landscapes cover a large area in the southeastern U.S. and may be important for wild bee conservation. However, there is little research on wild bees in private, working forests. Hence, our research objectives were to compare wild bee populations and communities among different stages within working, loblolly pine forest landscapes and assess stand structure and composition effects on wild bees. We sampled bees and forest attributes in four stages [0–3 years (recently established), 4–7 years (pre-thinned, closing canopy), 8–13 years (pre-thinned, closed canopy), and 14–20 years (post-thinned)] of privately owned, working pine forests in the Southeastern Plains Ecoregion of Georgia. We collected 5,933 bees from 88 species in two years. Wild bees were 2–5 times more abundant in recently established stages, and more diverse in recently established and post-thinned stages. Functional dispersion, a measure of beta diversity, was also greater in recently established and post-thinned stages. Canopy openness, percent of plants flowering, and percent cover of minimally decayed woody debris were important variables driving the bee community composition in recently established stages. Number of snags and litter layer depth were important variables driving the bee community composition in older stages with a closing or closed canopy. Working pine forests support a diverse community of wild bees and have high conservation value for these pollinators. Overall, wild bees appear to benefit from various stand stages, especially open canopy stands with a diverse structure. Promoting and maintaining open canopy conditions in managed pine landscapes may assist with conserving wild bee communities in this region. This can be achieved by planting trees at wider spacing, thinning as early as possible, and supporting fewer trees per hectare or a lower basal area.

Collembola biocenoses (Arthropoda: Hexapoda) in the archipelago of Fernando de Noronha, Brazil

The biota on oceanic islands commonly contains high percentage of endemic species, although their vulnerability is usually greater in relation to continental species. Here, we determined the composition, distribution and environmental factors influencing Collembola communities in three coastal environmental habitats of the Fernando de Noronha Archipelago, Brazil. In total, we sampled 20,308 collembolans belonging to 30 species. We report that the sandy beach environments studied harbor a single endemic specialist species (Isotogastrura mucrospatulata Palacios-Vargas, de Lima, & Zeppelini, 2013); environments of slope forest sites and top forests display a generalist fauna with wide distribution on the mainland. In most cases, abundance, richness and diversity did not significantly vary between site, coastal environmental habitat or moisture content levels. However, among the environmental factors, moisture content and litter layer depth were the most important ones structuring the collembolan communities of the archipelago in the Db-RDA analysis. Our results indicate that the beaches of the archipelago harbor completely different collembolan communities from the forests and because they harbor endemic species, and endemic collembolan species have been shown to be more sensitive to disturbance than non-endemics, we also suggest that Sandy Beaches and Slope Forests environments deserve attention in dedicated nature conservation policies as these often are either not soil-specific, or focused on soil physical properties rather than soil biodiversity.

A method for soil quality assessment in the metropolitan greenery: A comprehensive view of ecosystem services and soil functions

The soils in urban greenery considerably contribute to providing ecosystem services. However, appropriate tools to assess and manage urban soil quality under consideration of ecosystem services and soil functions are unavailable. In this study, we aimed to 1) provide detailed instructions for assessing a novel urban soil quality index (uSQI) and 2) propose the application of uSQI in urban soil quality management. The uSQI is the average of the scores for six soil functions. Each soil function was estimated by several measurable indicators that have high correlation with soil functions. The measurable soil indicators are bulk density, saturated hydraulic conductivity, litter-layer depth, mineral-associated organic matter, clay + silt content, inorganic nitrogen concentration, fluorescein diacetate hydrolytic activity, cation exchange capacity, concentrations of potentially toxic elements, and pH. The uSQI effectively identified the soils with low quality due to disturbances. The radar chart of six soil functions comprising uSQI could suggest the direction of management for urban stakeholders.•The uSQI represents soil functions necessary for urban greenery to provide ecosystem services.•The uSQI successfully identified the soils with low quality due to disturbances.

Ecosystem services-based soil quality index tailored to the metropolitan environment for soil assessment and management

The soils in urban greenery provide essential ecosystem services. However, only a few studies have assessed urban soil quality based on a comprehensive view of ecosystem services and soil multi-functionality. In this study, we suggest an urban soil quality index (uSQI) to evaluate soil status in various spatial types of urban greenery. Our objectives are 1) to develop an uSQI incorporating a range of urban soil ecosystem services in metropolitan environments and 2) to test the efficacy of the developed uSQI by applying it to nine different sites. To fully consider ecosystem services provided by the urban soil, a DPSC (drivers and pressures, state, and changes) framework was constructed. Drivers and pressures are influencing factors that continuously alter the state of the urban greenery, eventually leading to changes in ecosystem services and soil functions. The six soil functions considered were physical stability and support, water storage and infiltration, habitat provision, organic matter stabilization, nutrient supply and retention, and pollutant immobilization and decomposition. These functions were measured using ten soil indicators which can be quantified: bulk density, saturated hydraulic conductivity, litter-layer depth, mineral-associated organic matter, clay+silt content, fluorescein diacetate hydrolytic activity, cation exchange capacity, inorganic nitrogen concentration, pH, and concentrations of potentially toxic elements. The uSQI was calculated as the arithmetic mean of the scores of the six soil functions, obtained through the fuzzy logic functions. The uSQI successfully identified the low soil quality sites among nine urban greeneries with different spatial types (point, line, and polygon). In addition, we could examine the degraded soil function of each site and suggest a management guideline using our uSQI. Our novel index can help urban stakeholders evaluate and monitor the soil quality of urban greenery.

Plant species diversity of Carex peat mire in Changbai Mountains, China

We investigated the plant species richness both in cespitose Carex mires (C. schmidtii, C. meyeriana) and non-cespitose Carex mire (C. lasiocarpa) in Changbai Mountain. A total of 83 species (36 families, 59 genuses) was recorded in three sites. Among which, 71 species occurred in the C. meyeriana site, 61 species in the C. schmidtii site, and 26 species in the C. lasiocarpa site. The total species number and species richness in the two cespitose Carex mires were much higher than that in the non-cespitose Carex mire, while those on tussocks were much higher than between tussocks in the two cespitose Carex mires. Plant species richness on tussocks was positively related to the height, basal circumference and surface area of the tussocks, suggesting that tussocks were important for plant species diversity in Carex mires. Results of the canonical correspondence analysis indicated that the differences in soil water content, nutrient (soil organic carbon, total N, total P and C/N), and litter layer depth were the main factors influencing the differences of plant community composition on tussocks and between-tussocks. In the cespitose Carex mires, the hummock-hollow microtopography could foster high diversity by increasing surface area and creating multiple micro-habitats. Given its function in maintaining high species diversity, cespitose Carex could be a preferred species for vegetation restoration in degraded peat mires.

Soil-dwelling communities of weevils (Coleoptera, Curculionoidea: Brentidae, Curculionidae) in Central European floodplain forests: a comparative interaction with environmental parameters

Floodplain forests represent the habitats sensitive to environmental and ecological changes. Assessing their impact on dynamics of weevil communities requires a detailed understanding of the environmental demands of each species. Therefore, we studied the epigean communities of weevils in eight similar habitats of floodplain forests during 2015–2016. The study material of Curculionoidea was obtained by pitfall trapping. We focused on a comparison of the occurrence of weevils in floodplain forests and their ecotones alongside three rivers, the Danube in Slovakia and the Tisa and Begej in Serbia. We investigated the dependence of weevil’s occurrence on plant diversity of vegetation layers, cover of vegetation layers, area and circumference of forest stands, age of forest stands, distance to the forest edge, thickness of litter layer, physical-chemical properties of soil and litter (conductivity, pH, N, P, C, H) and anthropogenic impact. Total epigeic activity of weevils showed a significant continual proportion with number of plant species in shrub vegetation layer and inverse proportion with relative content of H in soil and circuit of fragment in which we located the traps. Species richness was significantly positively related to the number of plant species in herb and negatively to stand canopy of tree vegetation layers, the area, circuit and age of forest fragment, depth of litter layer, and also to relative content of N and H in soil. Shannon diversity showed a significant continual proportion with the circuit of the fragment. Evenness was positively linked to the fragment area and circumference.

Recruitment into the seedling bank of an undisturbed Mediterranean pinewood: Increasing forest resistance to changing climates

Although typically considered shade-intolerant, Mediterranean pine species may form seedling banks due to the existence of facilitative interactions between seedlings and canopy trees. Consequently, seedling banks could be considered as part of the seedling pool that should restock managed Mediterranean pinewoods, thus increasing the resistance of these forests to climate change. The study investigated the characteristics of the seedling bank in a silviculturally undisturbed forest of Pinus nigra subsp. salzmanii exposed to increasingly arid conditions. The study site was located in the southernmost range limit of the species. The dynamics of the seedling bank was studied by comparing current seedling (height < 1.30 m, age < 2 yr) and pole tree (height ≥ 1.30 m and diameter at breast height < 12.5 cm) altitudinal distributions, using altitude as a proxy of aridity. Aridity was proved to have increased in the study area along the last four decades. These climatic trends were identified by means of Mann-Kendall tests for trend. Additionally, the effects of summer drought, light availability, soil compaction, litter layer and micro-slope as explanatory variables of the recruitment outcome were analysed by means of Generalized Linear Mixed Models and survival analysis. Altitude affected positively seedling establishment, but had no effect on the current abundance of pole trees, indicating a recent upwards displacement of the regeneration niche due to increasingly arid conditions. Water and light availability, the latter at intermediate levels of irradiance, affected tree recruitment positively, whereas the effects of soil compaction, litter layer depth and micro-slope were negative. Implementing extended rotation periods and maintaining intermediate values of tree cover are proposed as important management recommendations to achieve successful natural regeneration in Mediterranean pinewoods.

Long-term effects of wild ungulates on the structure, composition and succession of temperate forests

Ungulates in temperate regions are increasing in range and abundance, leading to concerns that browsing and trampling reach levels that hamper tree recruitment and forest regeneration. However, studies that actually quantify the long-term effects of ungulates on forest succession are scarce. Here, we use a chronosequence of ungulate exclosures (fenced) and control (unfenced) plots to assess the long-term effects of ungulates on forest structure, diversity and litter depth in forests on poor sandy soils at the Veluwe, the Netherlands, which have moderate ungulate densities (x¯ = 13.6 ungulates km−2). We surveyed the vegetation in 27 paired fenced and unfenced plots that ranged from 1 to 33 years old, and measured seven variables to characterize forest structure (stem density, canopy cover and understory vegetation cover), composition (Shannon diversity, species richness and conifer proportion) and leaf litter depth. We found on average that fencing compared to unfencing reduced understory vegetation cover (fenced = 64.3 ± 20.2%, unfenced = 80.3 ± 19.4%), increased canopy cover (fenced = 47.4 ± 30.1%, unfenced = 29.3 ± 21.1%), tree species richness (fenced = 4.5 ± 1.3 spp., unfenced = 2.7 ± 1.2 spp.), tree Shannon diversity (fenced = 1.1 ± 0.3 index, unfenced = 0.7 ± 0.3 index) and litter layer depth (fenced = 4.4 ± 1.4 cm, unfenced = 2.4 ± 1.1 cm). While fenced plots developed woody vegetation with palatable broadleaved species such as Betula pendula, Betula pubescens, Prunus serotina, and Quercus robur, unfenced plots were not associated with any particular tree species. Our results show that current ungulate densities in this system have pronounced long-term effects on forest structure, composition and litter depth, implying that ungulates can slow down natural succession of temperate forest, from light demanding to shade tolerant species, by keeping the system in an arrested state consisting of light demanding species.

EARTHWORM POPULATION AT THE POST COAL MINING FIELD IN EAST KALIMANTAN, INDONESIA

Coal mining activities in Indonesia result in heavy soil degradation and significant decrease in earthworm population. This study aims to explore the population of earthworms at different ages of the plant in the post coal mining rehabilitation areas. PT. Kideco Jaya Agung, East Kalimantan. In this study, 5 samples (30 cm x 30 cm, 20 cm depth) of soil were collected from 5 rehabilitation sites. Sites were selected based on age after rehabilitation: 2, 4, 6, 8 and 10 years after replanting, and sampled with 20 m distances between samples to determine earthworm population. The depth of litter layer and species of plants were also recorded at each site. Chi square analysis was conducted to determine the significance of earthworm density in rehabilitation sites at different ages, while correlation analysis was conducted to determine correlation between litter thickness and the number of earthworms found in the research sites. Only 2 species of earthworms were found in this study; their abundance increased increased in line with the age of rehabilitation areas. The number of earthworms (density) at 10 years after rehabilitation was almost similar to that in the natural forests. In conclusion, planting tree species producing significant amount of litter might stimulate the earthworm community and initiate succession. It might also take more than 10 years to return to the previous state for the earthworms in terms of density after land rehabilitation of the coal mining areas is conducted.

The influence of abiotic and biotic factors on the invasion of Ixodes scapularis in Ontario, Canada

In northeastern North America, the blacklegged tick, Ixodes scapularis, is the vector of numerous tick-borne pathogens, including the agent of Lyme disease, Borrelia burgdorferi sensu stricto. Since 1990, there has been a rapid spread of I. scapularis northward into the province of Ontario, Canada. Climate change has been implicated as one of the driving factors for the spread of this vector. Other ecological factors also influence survival of I. scapularis populations and may facilitate invasion. The objective of this study was to identify local abiotic and biotic factors of significance for the invasion of I. scapularis in Ontario. The presence of ticks was determined by drag sampling at 154 sites in southern, eastern and central Ontario from May to October in 2014 and 2015. At each site, data on site aspect, forest cover, understory density and composition, soil moisture and composition, and the depth of litter layer were collected. Cumulative degree days above zero °C, total precipitation and elevation were attributed to each site using a geographic information system. A mixed multi-variable logistic regression model was created to assess the impact of the ecological factors on the presence of I. scapularis. In total, I. scapularis was found at 29 sites (18.8%) across the study area. The density of the understory, the presence of shrubs and the interaction of these two ecological factors were statistically significant, as well as longitude and cumulative degree days above zero. Our findings illustrate that local ecological factors are of importance for the invasion of I. scapularis into Ontario, and may be used to enhance local public health interventions and current predictive models and risk maps for I. scapularis.

Modeling cover management factor of RUSLE using very high-resolution satellite imagery in a semiarid watershed

Vegetation cover is regarded as one of the most important protection measures for controlling soil erosion caused by water. Numerous articles have been published about the fact that more delicate, practical, and reliable estimations can be made through normalized difference vegetation index (NDVI) for calculating “cover management (C) factor” in the Revised Universal Soil Loss Equation (RUSLE), the most commonly recognized erosion prediction model worldwide. In this study, the C-factor map of the Tortum-North sub-watershed in the mountainous northeastern part of Turkey was estimated using NDVI values derived from the 50-cm resolution WorldView-2 satellite imagery. The C-factor values, collected from 55 sampling plots by measuring crown closure, canopy height, litter layer depth, and surface cover of the study area, were plotted against the NDVI values and then curved using the simple linear regression method. The resulting regression models (linear, cubic, exponential, growth) and five other best-known NDVI-related models from the literature (Knijff, Smith, Karaburun, De Jong, and Durigon) were compared using model diagnostic statistics (\(R_{{\text{adj}}}^{2}\), RMSE, MAE, Mallows’ Cp) and information criterion statistics (Akaike’s information criterion, the Sawa’s Bayesian information criterion, Schwarz’s Bayesian criterion). The curve estimation results showed that the cubic model (R2 = 0.83, RMSE = 0.063), the Knijff et al. (1999)’s model (R2 = 0.85, RMSE = 0.059), and the linear model (R2 = 0.81, RMSE = 0.067) were the top three estimators of the C-factor. The least estimator of the C-factor was the growth model (R2 = 0.46, RMSE = 0.113). The residual analysis results showed that the cubic model performed well (total score of 57) by the best fitting of the overall regression model selection process. It was concluded that the C-factor estimation can be improved by the NDVI-based per-pixel approach using very high-resolution satellite imagery in the semiarid mountainous areas.

Spillover of Secondary Foundation Species Transforms Community Structure and Accelerates Decomposition in Oak Savannas

Secondary foundation species facilitate biodiversity by providing complex habitat within the protective structures of many primary foundation species; whether they retain this role when they are dispersed in novel environments is unclear. Here, we explore how secondary foundation species’ density within hosts controls the rate at which individuals accrue and test if dislodged secondary foundation species then bolster the abundance and diversity of associated species and decomposition in a widespread system: southern live oaks, Quercus virginiana, hosting festoons of the bromeliad, Tillandsia usneoides, in southeastern US savannas. One year of monitoring showed that as Tillandsia density within oaks increases, Tillandsia deposition beneath oaks increases linearly in kind. Once on the ground, two manipulative experiments revealed that: on small scales, individual festoons retain moisture, reduce temperature, and facilitate invertebrates and fungi which combine to accelerate litter decomposition and, on larger scales, continual deposition of festoons dramatically reduces grass cover and increases litter layer depth, invertebrate and fungi richness and density, and decomposition. Surveys further suggest that Tillandsia populations within oaks, in moderating festoon accumulation, are shaping understory communities throughout this geographic region. Thus, disturbance-induced spillover enables secondary foundation species to define biodiversity and ecosystem functioning beyond the boundaries of their hosts.

천연기념물 제432호 제주 상효동 한란 자생지의 환경 및 식생

천연기념물 제 432호 제주 상효동의 한란 자생지(39 ha)를 대상으로 2013년 10월부터 2014년 2월까지 생물(식물상, 식생다양성 및 임분 구조) 및 비생물 환경(미기상, 수관열림도, 임내 광량 및 토양 온 습도)의 특성을 분석하였다. 한란 자생지의 일평균온도(<TEX>$5.7^{\circ}C$</TEX>)는 서귀포시 보다 <TEX>$3.3^{\circ}C$</TEX> 낮았고, 일평균습도(75.8%)는 서귀포시 보다 15% 높았다. 토양 온도는 평균 <TEX>$16.5^{\circ}C$</TEX>, 토양습도는 평균 37.3%, 그리고 낙엽층 두께는 평균 4.3 cm이었다. 수관열림도 및 임내 광량의 평균은 각각 15.5%, 및 <TEX>$8.5mol{\cdot}m^{-2}{\cdot}day^{-1}$</TEX> 이었다. 한란 자생지 보호구역 내 관속식물은 총 221 분류군이며, 희귀 및 멸종위기식물로는 한란, 죽백란 및 꼬리족제비고사리 등이 확인되었다. 식생다양성 평가 결과, 구실잣밤나무군락 등 총 6개의 식생단위가 분석되었다. 조사구역의 임분구조는 구실잣밤나무가 가장 높은 밀도(1,777 개체/ha) 및 흉고단면적 (<TEX>$90.3m^2/ha$</TEX>)을 나타내었다. In the Natural Monument (No. 432) Jeju Sanghyo-dong Cymbidium kanran Habitat (39 ha), flora, vegetation diversity, stand structure, mirco-climate, canopy openness, light environment and soil temperature and moisture were quantified from Oct. 2013 to Feb. 2014. Compare to Seogwipo-si, daily mean temperature (<TEX>$5.7^{\circ}C$</TEX>) and moisture (75.8%) in study area were lower at <TEX>$3.3^{\circ}C$</TEX> and 15%, respectively. Mean soil temperature and moisture were <TEX>$16.5^{\circ}C$</TEX> and 37.3%, respectively, and mean litter layer depth (n = 81) was 4.3 cm. Mean canopy openness and light availability at forest floor were 15.5% and <TEX>$8.5mol{\cdot}m^{-2}{\cdot}day^{-1}$</TEX>, respectively. Total of 22 species including vascular and bryophyte plants and 6 vegetation group were observed. Castanopsis siebildii was dominant species in study area, and density and basal area were 1,777 stem/ha and <TEX>$90.3m^2/ha$</TEX>.

Variations in prey consumption of centipede predators in forest soils as indicated by molecular gut content analysis

Predation is an important ecological factor driving animal population structures, community assemblages and consequently ecosystem stability and biodiversity. Many environmental factors influence direction and intensity of predation, suggesting that trophic linkages between animals vary between different habitats. This in consequence has particular relevance in anthropogenically altered habitats such as managed forests, where disturbance regime, tree composition and stand age may change the natural food web structure. We investigated how prey consumption of three common centipede predators (Lithobiusspp., Chilopoda), representing two body sizes varies between four differently managed forest types in two regions across Germany. We hypothesized that prey preference of these generalist predators is independent of forest type but rather driven by habitat structure, prey abundance and predator body size. Applying specific PCR assays to test for DNA of three abundant prey groups, i.e. Collembola, Diptera and Lumbricidae, in the predators’ guts, we tracked trophic interactions. The results showed that management type indeed has no influence on centipede prey consumption but depth of litter layer and soil pH. Trophic interactions varied between the two sampled forests regions mainly due to changes in the detection of Lumbricidae and Diptera. Also, effect of litter layer and prey abundance significantly differed between the smallerL. crassipesand the largerL. mutabilis, indicating a body size effect. The results complement food web analyses using fatty acids and stable isotopes by elucidating trophic interactions in soil in unprecedented detail.

Does high biodiversity reduce the risk of Lyme disease invasion?

BackgroundIt has been suggested that increasing biodiversity, specifically host diversity, reduces pathogen and parasite transmission amongst wildlife (causing a “dilution effect”), whereby transmission amongst efficient reservoir hosts, (e.g. Peromyscus spp. mice for the agent of Lyme disease Borrelia burgdorferi) is reduced by the presence of other less efficient host species. If so, then increasing biodiversity should inhibit pathogen and parasite invasion.MethodsWe investigated this hypothesis by studying invasion of B. burgdorferi and its tick vector Ixodes scapularis in 71 field sites in southeastern Canada. Indices of trapped rodent host diversity, and of biodiversity of the wider community, were investigated as variables explaining the numbers of I. scapularis collected and B. burgdorferi infection in these ticks. A wide range of alternative environmental explanatory variables were also considered.ResultsThe observation of low I. scapularis abundance and low B. burgdorferi infection prevalence in sites where I. scapularis were detected was consistent with early-stage invasion of the vector. There were significant associations between the abundance of ticks and season, year of study and ambient temperature. Abundance of host-seeking larvae was significantly associated with deer density, and abundance of host-seeking larvae and nymphs were positively associated with litter layer depth. Larval host infestations were lower where the relative proportion of non-Peromyscus spp. was high. Infestations of hosts with nymphs were lower when host species richness was higher, but overall nymphal abundance increased with species richness because Peromyscus spp. mouse abundance and host species richness were positively correlated. Nymphal infestations of hosts were lower where tree species richness was higher. B. burgdorferi infection prevalence in ticks varied significantly with an index of rates of migratory bird-borne vector and pathogen invasion.ConclusionsI. scapularis abundance and B. burgdorferi prevalence varied with explanatory variables in patterns consistent with the known biology of these species in general, and in the study region in particular. The evidence for a negative effect of host biodiversity on I. scapularis invasion was mixed. However, some evidence suggests that community biodiversity beyond just host diversity may have direct or indirect inhibitory effects on parasite invasion that warrant further study.

Change of arthropod abundance in burned forests: Different patterns according to functional guilds

Forest fires are one of the most frequent and important causes of forest disturbances, the occurrence of which is globally increasing due to the effects of climate change. This study aimed to determine the impacts of fire and human activity on arthropod communities in affected forests. Twelve study sites in three burned areas were selected for this study. Intensities of disturbance in the study sites were characterized as follows: Disturbance Degree (DD) 0 (no fire), DD 1 (surface fire), DD 2 (crown fire), and DD 3 (crown fire followed by reforestation). Arthropods were collected using pitfall traps. Fourteen arthropod taxa (families, orders or classes), which are relatively homogeneous in their feeding habits and abundant, were analyzed. Depth of litter layer was selected as an environmental indicator for disturbance intensity, as it decreases linearly as the degree of disturbance increased. Changes of arthropod abundance in response to disturbance differed among functional guilds. As disturbance intensity increased, the abundance of detritivores decreased, but the abundance of herbivores increased. However, the abundance of predators varied between taxa. Formicidae and Araneae increased in disturbed sites, whereas Carabidae and Staphylinidae did not change. The abundance of Thysanura and Diptera was highly correlated with disturbance intensity, and may be suitable as a bioindicator for forest disturbance. Arthropod communities were more heterogeneous in forests of intermediate disturbance.

Indirect and direct effects of exotic earthworms on soil nutrient and carbon pools in North American temperate forests

Earthworm invasions in North American temperate forests cause considerable changes to soil and litter horizons, which can lead to changes in soil biogeochemistry and plant communities. These ecosystem changes have complex causal relationships, and the cascades of indirect effects from earthworm burrowing and feeding may have larger net effects on soil biogeochemistry than direct effects. In this study we partitioned the effects of earthworms on particular soil nutrient and carbon pools into direct and indirect effects. We defined direct effects as consisting of the association between the soil nutrient or carbon pool and earthworm biomass, whilst indirect effects included the impacts earthworms have on these soil pools through changing litter layer depth and soil chemical and biotic factors. We quantified these direct and indirect effects using a path analysis approach applied to data collected from 24 plots across an earthworm gradient in a northern hardwood forest stand in Ontario, Canada. As potential predictors, we measured earthworm functional group biomass, litter depth, microbial biomass, soil pH, texture, and organic matter. We related these predictors to extractable nutrient and carbon concentrations, including nitrate/nitrite, ammonium, orthophosphate, and dissolved organic nitrogen, phosphorus, and carbon. We found few direct effects and primarily indirect effects of earthworms on the soil nutrient and carbon pools we measured. Endogeic earthworms had the strongest indirect effects via changes to pH, microbial biomass carbon, and proportion of soil organic matter. Anecic earthworms only indirectly affected soil and nutrient pools through changes in pH, and epigeic earthworms did not have either direct or indirect effects. Because endogeic earthworms had indirect effects through changing multiple soil factors, for some soil and nutrient pools these indirect effects augmented each other (primarily yielding negative effects), although in some cases indirect positive effects mitigated negative effects. Overall, the net effects of exotic earthworms on soil and nutrient pools were mostly negative. Of particular concern was the potential exacerbation by endogeic earthworms of phosphorus limitation in N-saturated forest systems, as well as carbon loss from mineral soils in addition to losses from the forest floor.

Structure and distribution of enchytraeid communities from Mountain Changbaishan in China, with emphasis on the influence of environmental variables

Enchytraeids are an important group of soil animals, which plays a key role in many ecosystems. However, the ecological studies related to this group have not still been conducted in China. The effect of different forest types on community, and the influence of environmental variables on faunal distributional patterns were investigated in Changbaishan Mountain Natural Reserve (CMNR) in northeastern China. Altogether 30 enchytraeid species belonging to 8 genera were identified, among which, Fridericia was the species-richest group, followed by Henlea and Mesenchytraeus. Mesenchytraeus, Henlea, Fridericia and Bryodrilus were the numerically dominant genera. The most abundant species were Mesenchytraeus monodiverticulus, Mesenchytraeus megachaetus, Fridericia vixdiverticulata and Fridericia bretshceri. There were no significant differences in total enchytraeid richness and abundance across five forest types. However, significant differences were detected in major genera. Bryodrilus had higher species number and abundance in spruce-fir forests compared to other forest types. Fridericia spp. mainly occurred in hardwood forest, Henlea spp. in mixed forest, and Mesenchytraeus spp. in higher altitude regions. The depth of litter layer was strongly correlated with the faunal gradient revealed by canonical correspondence analysis. Other predictor variables were altitude, soil moisture and the content of potassium.

Regeneration ecology of sugar maple (Acer saccharum): seedling survival in relation to nutrition, site factors, and damage by insects and pathogens

The possible regeneration failure of sugar maple ( Acer saccharum Marsh.) as part of their decline has been not well explored using field studies. We sought to clarify the roles of maternal effects and dynamics of early-season survival in contributing to the previously documented pattern of larger seedlings and higher seedling densities on a Ca-treated watershed (CAL) at Hubbard Brook Experimental Forest. We used a reciprocal seed planting experiment at four sites, two sites per watershed blocked by elevation. Regardless of maternity, sugar maple seedlings planted in CAL had higher survival than seedlings in the reference watershed. However, this advantage was not as clearly linked to the Ca amendment as in our previous work, probably, in part, because Ca availability has decreased over time. Maternal effects on seed chemistry and some seedling traits were detected, but these were not strong determinants of survival. Site was a good predictor of early seedling survival with litter layer depth, pathogen prevalence, and soil chemistry all contributing to the explanatory power of site. The strength of Ca,addition effects on sugar maple regeneration from seed depends on initial soil characteristics, application amounts, and interactions of the amendment with other factors such as leaf litter cycling, weather, and pathogens.

Distribuição espacial em pequena escala de um anfípode exótico em fragmento florestal e plantio de espécies nativas

Anthropogenic interferences in natural environments cause the breakage of spatial and competitive barriers, which may influence the spatial distribution of species. In this study, we describe the spatial distribution of an exotic amphipod, Talitroides topitotum, in two distinct sites, a forest fragment and a plantation of native arboreal species. We analyzed possible variations in this spatial distribution in different periods of the year and verified whether the vegetation cover and the litter 36 layer depth may explain the distribution pattern of this species. We performed analyses of frequency distribution to determine the pattern of this species spatial distribution, as well as correlation tests to determine the effect of these two variables of habitat structure. The spatial distribution analysis revealed that T. topitotum presents aggregated distribution in both areas, indicating that this species has low environmental demands or that both areas are below a minimum environmental quality threshold. However, even with this similarity, the population in the fragmented site presented a higher index of aggregation when compared with the population of the plantation site. Corroborating previous studies, there was a negative correlation between abundance of T. topitotum and litter layer depth in the plantation site. Studies on invaded habitats can help understand how invasive species occupy new environments and the factors that can influence their spatial distribution.