Response of macroarthropod assemblages to the loss of hemlock (Tsuga canadensis), a foundation species

In eastern North American forests, eastern hemlock (Tsuga canadensis) is a foundation species. As hemlock is lost from forests due to the invasive hemlock woolly adelgid (Adelges tsugae) and preemptive salvage logging, the structure of assemblages of species associated with hemlock is expected to change. We manipulated hemlock canopy structure at hectare scales to investigate the effects of hemlock death on assemblages of ants, beetles, and spiders in a New England forest. Relative to reference hemlock stands, both in situ death of hemlock and logging and removal of hemlock altered composition and diversity of beetles and spiders, and logging increased the species richness and evenness of ant assemblages. Species composition of ant assemblages in disturbed habitats was non-random relative to the regional species pool, but we found no evidence that interspecific competition shaped the structure of ant, beetle, or spider assemblages, in either manipulated or intact forest stands. Environmental filtering by hemlock appears to maintain low levels of species richness and evenness in forest stands, suggesting that the loss of hemlock due to the hemlock woolly adelgid or human activities will not likely lead to extirpations of ant, beetle, or spider species at local scales

Response of macroarthropod assemblages to the loss of hemlock (Tsuga canadensis), a foundation species

In eastern North American forests, eastern hemlock (Tsuga canadensis) is a foundation species. As hemlock is lost from forests due to the invasive hemlock woolly adelgid (Adelges tsugae) and preemptive salvage logging, the structure of assemblages of species associated with hemlock is expected to change. We manipulated hemlock canopy structure at hectare scales to investigate the effects of hemlock death on assemblages of ants, beetles, and spiders in a New England forest. Relative to reference hemlock stands, both in situ death of hemlock and logging and removal of hemlock altered composition and diversity of beetles and spiders, and logging increased the species richness and evenness of ant assemblages. Species composition of ant assemblages in disturbed habitats was non-random relative to the regional species pool, but we found no evidence that interspecific competition shaped the structure of ant, beetle, or spider assemblages, in either manipulated or intact forest stands. Environmental filtering by hemlock appears to maintain low levels of species richness and evenness in forest stands, suggesting that the loss of hemlock due to the hemlock woolly adelgid or human activities will not likely lead to extirpations of ant, beetle, or spider species at local scales

Response of Macroarthropod Assemblages to the Loss of Hemlock (Tsuga canadensis), a Foundation Species

In eastern North American forests, eastern hemlock (Tsuga canadensis) is a foundation species. As hemlock is lost from forests due to the invasive hemlock woolly adelgid (Adelges tsugae) and pre-emptive salvage logging, the structure of assemblages of species associated with hemlock is expected to change. We manipulated hemlock canopy structure at hectare scales to investigate the effects of hemlock death on assemblages of ants, beetles, and spiders in a New England forest. Relative to reference hemlock stands, both in situ death of hemlock and logging and removal of hemlock altered composition and diversity of beetles and spiders, and logging increased the species richness and evenness of ant assemblages. Species composition of ant assemblages in disturbed habitats was non-random relative to the regional species pool, but we found no evidence that interspecific competition shaped the structure of ant, beetle, or spider assemblages, in either manipulated or intact forest stands. Environmental filtering by hemlock appears to maintain low levels of species richness and evenness in forest stands, suggesting that the loss of hemlock due to the hemlock woolly adelgid or human activities will not likely lead to extirpations of ant, beetle, or spider species at local scales.Organismic and Evolutionary BiologyOther Research Uni

Thermal treatment and leaching of biochar alleviates plant growth inhibition from mobile organic compounds

Recent meta-analyses of plant responses to biochar boast positive average effects of between 10 and 40%. Plant responses, however, vary greatly across systems, and null or negative biochar effects are increasingly reported. The mechanisms responsible for such responses remain unclear. In a glasshouse experiment we tested the effects of three forestry residue wood biochars, applied at five dosages (0, 5, 10, 20, and 50 t/ha) to a temperate forest drystic cambisol as direct surface applications and as complete soil mixes on the herbaceous pioneers Lolium multiflorum and Trifolium repens. Null and negative effects of biochar on growth were found in most cases. One potential cause for null and negative plant responses to biochar is plant exposure to mobile compounds produced during pyrolysis that leach or evolve following additions of biochars to soil. In a second glasshouse experiment we examined the effects of simple leaching and heating techniques to ameliorate potentially phytotoxic effects of volatile and leachable compounds released from biochar. We used Solid Phase Microextraction (SPME)–gas chromatography–mass spectrometry (GC-MS) to qualitatively describe organic compounds in both biochar (through headspace extraction), and in the water leachates (through direct injection). Convection heating and water leaching of biochar prior to application alleviated growth inhibition. Additionally, growth was inhibited when filtrate from water-leached biochar was applied following germination. SPME-GC-MS detected primarily short-chained carboxylic acids and phenolics in both the leachates and solid chars, with relatively high concentrations of several known phytotoxic compounds including acetic acid, butyric acid, 2,4-di-tert-butylphenol and benzoic acid. We speculate that variable plant responses to phytotoxic organic compounds leached from biochars may largely explain negative plant growth responses and also account for strongly species-specific patterns of plant responses to biochar amendments in short-term experiments

Exotic earthworm (Oligochaeta: Lumbricidae) assemblages on a landscape scale in central Canadian woodlands: Importance of region and vegetation type

A growing understanding about the impacts of earthworms (Oligochaeta: Lumbricidae) on ecosystem processes and forest restoration necessitates an examination of their role in Canadian forests where they have become invasive. Little is known about the landscape-scale responses of earthworm populations to different regional characteristics and vegetation types within Canada’s central woodlands. We examined the regional variation of earthworm species richness, biomass, and assemblage composition across a range of four municipal regions (from south to north: Halton, Wellington, York, and Simcoe) and four habitat types (deciduous forest, mixed forest, tree plantation, and meadow) with varying soil characteristics in woodlands of south-central Ontario, Canada. In general, earthworm communities differed by region but not by habitat type. The most southern regions supported the highest earthworm species richness, biomass (i.e., Lumbricus and Octolasion), and density, and this was associated with a south-north gradient in soil characteristics. Assemblage composition differed by region but not by habitat type. The observed south-north gradient suggests an underlying effect of invasion spread associated with human settlement and density. Our results provide baseline information about earthworm communities in south-central Ontario forests and will enable managers to plan for the increasing role of earthworms in Canada’s future forests.Fil: Choi, Amy. University of Toronto; CanadáFil: Sackett, Tara E.. University of Toronto; CanadáFil: Smith, Sandy M.. University of Toronto; CanadáFil: Bellocq, Maria Isabel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Ecología, Genética y Evolución de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Ecología, Genética y Evolución de Buenos Aires; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ecología, Genética y Evolución; Argentin

Determinants of the detrital arthropod community structure: the effects of temperature and resources along an environmental gradient

Understanding the factors that shape community structure, and whether those factors vary geographically, has a long history in ecology. Because the abiotic environment often varies in predictable ways along elevational gradients, montane systems are ideal to study geographic variation in the determinants of community structure. In this study, we first examined the relative importance of environmental gradients, microclimate, and food resources in driving spatial variation in the structure of detrital communities in forests of the southeastern USA. Then, in order to assess whether the determinants of detrital community structure varied along a climatic gradient, we manipulated resource availability and microclimatic conditions at 15 sites along a well-studied elevational gradient. We found that arthropod abundance and richness generally declined with increasing elevation, though the shape of the relationship varied among taxa. Overall community composition and species evenness also varied systematically along the climatic gradient, suggesting that broad-scale variation in the abiotic environment drives geographic variation in both patterns of diversity and community composition. After controlling for the effect of climatic variation along the elevational gradient, food resource addition and microclimate alteration influenced the richness and abundance of some taxa. However, the effect of food resource addition and microclimate alteration on the richness and abundance of arthropods did not vary with elevation. In addition, the degree of community similarity between control plots and either resource-added or microclimate-altered plots did not vary with elevation suggesting a consistent influence of microclimate and food addition on detrital arthropod community structure. We conclude that using manipulative experiments along environmental gradients can help tease apart the relative importance and detect the interactive effects of local-scale factors and broad-scale climatic variation in shaping communities

Appendix B. An ANOVA table showing herbivore damage to young leaves of Inga goldmanii and I. umbellifera.

An ANOVA table showing herbivore damage to young leaves of Inga goldmanii and I. umbellifera