552 publications from this institution
Soil organisms provide crucial ecosystem services that support human life. However, little is known about their diversity, distribution, and the threats affecting them. Here, we compiled a global dataset of sampled earthworm communities from over 7000 sites in 56 countries to predict patterns in earthworm diversity, abundance, and biomass. We identify the environmental drivers shaping these patterns. Local species richness and abundance typically peaked at higher latitudes, while biomass peaked in the tropics, patterns opposite to those observed in aboveground organisms. Similar to many aboveground taxa, climate variables were more important in shaping earthworm communities than soil properties or habitat cover. These findings highlight that, while the environmental drivers are similar, conservation strategies to conserve aboveground biodiversity might not be appropriate for earthworm diversity, especially in a changing climate. One sentence summary Global patterns of earthworm diversity, abundance and biomass are driven by climate but patterns differ from many aboveground taxa.
No abstract is provided for this article.
Vegetation research in boreal forests has tended to focus on the tree component, while little attention has been paid to understory components such as dwarf shrubs, mosses, and reindeer lichens. However, the productivity of understory vegetation is probably comparable to that of the trees. We review recent research in the boreal forest of northern Sweden to highlight the ecological importance of understory vegetation, both in the short term by influencing tree seedling regeneration, and in the longer term by affecting belowground processes such as decomposition, nutrient flow, and buildup of soil nutrients. Wildfire resulting from lightning strike is a primary determinant of understory vegetation, and as such is a major driver of forest community and ecosystem properties. Forest management practices that alter the fire regime and the composition of understory vegetation may have long-term consequences for both conservation goals and commercial forest productivity.
Fire is a global driver of carbon storage and converts a substantial proportion of plant biomass to black carbon (for example, charcoal), which remains in the soil for thousands of years. Black carbon is therefore often proposed as an important long-term sink of soil carbon. We ran a 10-year experiment in each of three boreal forest stands to show that fire-derived charcoal promotes loss of forest humus and that this is associated with enhancement of microbial activity by charcoal. This result shows that charcoal-induced losses of belowground carbon in forests can partially offset the benefits of charcoal as a long-term carbon sink.
An ongoing study initiated in August 1990 investigated the effects of disturbances (organic mulching, cultivation, herbicides) on the detritus food-web in
Summary form only given. Raman scattering in optical fibres is of renewed interest as a result of its application in a number of novel fibre amplifier systems. While the general features of Raman scattering in silica fibres are well known, the work reported here allows determination of both the parallel and perpendicular Raman gain per unit length over a frequency range of 57 THz from the pump radiation. The results are consistent (within experimental error) with previous measurements in bulk glass.
Partially covering a converging lens can produce either vignetted or dimmed real images, depending on how the image is observed. A field lens captures non-paraxial rays, allowing the dimming effect to be observed directly, without using a screen.
No abstract is provided for this article.
'Keystone Species: Competition for Honeydew Among Exotic and Indigenous Species' published in 'Biological Invasions in New Zealand'
Summary There is increasing awareness that similar suites of plant traits may govern foliage palatability and litter decomposability, but whether there is an association between the response of vegetation to herbivory and litter decomposition rates across plant species remains unexplored. We collected 141 samples of litter from 59 understorey and 18 canopy tree species from a total of 28 sites under natural forest throughout New Zealand. We assessed whether variables related to decomposition and quality of litter of the understorey species showed a statistical relationship with the response of vegetation density (assessed using a pole‐intercept method) of the same species at the same locations to browsing by deer and goats. Decomposition and nutrient‐loss data from litter were obtained using standardized laboratory bioassays. There was a significant positive correlation between litter decomposition rate and the extent to which vegetation density was reduced by browsing mammals ( r = 0·488, P < 0·001). Further, decomposition rate and vegetation response to herbivory were both correlated with several of the same litter quality variables. The proportion of total initial phosphorus and nitrogen released from litter during decomposition was correlated with litter decomposition rate, but not with vegetation density response to browsing. This suggests that effects of browsers on vegetation composition are more likely to influence ecosystem carbon flow than nitrogen or phosphorus flow. Litter‐mixing experiments showed that good quality litters produced by plant species reduced by browsers tended to promote the decomposition of other litters. Meanwhile, poor quality litters from species promoted by browsers tended to decompose more rapidly when mixed with other litter types than when by themselves. However, these effects were weak and likely to be less important than the more direct effects of browsing mammals on vegetation composition. The relationships between litter decomposition and effect of herbivory on vegetation density were driven primarily by differences among the main plant functional groups, which showed the same decreasing rank order for both variables: large‐leaved dicots, small‐leaved dicots, Nothofagus , ferns, and monocots. The implications of these results for understanding how herbivores affect the decomposer subsystem are considered. Because the results of this work are only partially consistent with those of an earlier study on how browsers affect decomposer organisms and processes, conducted at the same 28 field sites, other mechanisms through which browser effects are manifested below‐ground must often override that investigated in this study.
Work on the impacts of herbivores on ecosystems has traditionally focused on aboveground effects, but a growing number of ecologists are beginning to consider how herbivores affect belowground organisms and processes. Human activity has caused considerable changes in densities of mammalian herbivores throughout the world, through the introduction of herbivores to new regions, the creation of conditions that promote high herbivore densities, and the reduction of their population sizes, sometimes to the point of extinction. These human influences on high mammal densities can have major effects on the decomposer subsystem. Whether these effects are positive or negative depends on the mechanisms involved: for example, whether the changes are in the quantity or quality of the decomposers' resources or in the pathway of vegetation succession. In turn, these belowground effects may influence aboveground biota by altering the supply of available nutrients from the soil. Changes in large mammal densities through human activity may represent an important, though frequently underappreciated, element of global change.
No abstract is provided for this article.
The microbial metabolic quotient (respiration-to-biomass ratio) or qCO2, conceptually based on Odum's theory of ecosystem succession, is increasingly being used as an index of ecosystem development (during which it supposedly declines) and disturbance (due to which it supposedly increases). We investigated the suitability of qCO2 as an bioindicator using: (1) data from the Franz Josef Glacier chronosequence, spanning over 22,000 years; and (2) data recalculated from published studies. In the Franz Josef sequence, a detectable decline in qCO2 occurred in the first 250 years in both the L-layer and mineral soil layer. However, in the later phases of the succession there was a sharp increase in qCO2 indicating reduced microbial efficiency, which appeared to be related to stress (independent of disturbance) resulting from steady-state conditions. Calculation of qCO2 from three previous studies on disturbance and ecosystem development indicated that this index responds unpredictably and does not necessarily decline during succession. Plant litter decomposition studies demonstrate that while qCO2 usually declines initially, a significant increase in qCO2 can eventually follow on litter types resistant to decomposition. Correlation analysis of each of 24 previous studies demonstrated that qCO2 often declines with increasing pH, clay content and amounts of microbial biomass; these three soil properties are all indicative of varying stress rather than disturbance levels. Reanalysis of data from 16 previous studies indicated that some disturbances such as fertilization and liming can either increase or decrease qCO2 values depending on whether the disturbance alleviates stress (reducing qCO2)or is more extreme than the stress it alleviates (enhancing qCO2). Although cultivation represents a severe disturbance, qCO2 is not predictably enhanced by this perturbation. While qCO2 undoubtedly provides a useful measure of microbial efficiency, our data suggests it has limitations because it can be insensitive to disturbance and ecosystem development, fails to distinguish between effects of disturbance and stress, and does not decline predictably in response to ecosystem development whenever stress increases along successional gradients.
Community structure and ecosystem processes often vary along elevational gradients. Their responses to elevation are commonly driven by changes in temperature, and many community- and ecosystem-level variables therefore frequently respond similarly to elevation across contrasting gradients. There are also many exceptions, sometimes because other factors such as precipitation can also vary with elevation. Given this complexity, our capacity to predict when and why the same variable responds differently among disparate elevational gradients is often limited. Furthermore, there is utility in using elevational gradients for understanding community and ecosystem responses to global climate change at much larger spatial and temporal scales than is possible through conventional ecological experiments. However, future studies that integrate elevational gradient approaches with experimental manipulations will provide powerful information that can improve predictions of climate change impacts within and across ecosystems.
