Exotic species affect the biogeochemical pools and fluxes of materials and energy, thereby altering the fundamental structure and function of their ecosystems. Rapidly accumulating evidence from many species of both animal and plant invaders suggests that invasive species often increase pool sizes, particularly of biomass, and promote accelerated flux rates, but many exceptions can be found. Ecosystem dynamics are altered through a variety of interacting, mutually reinforcing mechanistic pathways, including species’ resource acquisition traits; population densities; ability to engineer changes to physical environmental conditions; effects on disturbance, especially fire; regimes; the ability to structure habitat for other species; and their impact on food webs. Local factors of landscape setting, history, and other sources of disturbance constrain ecosystem responses to invasions. New research directions are suggested, including the need for whole-system budgets, the quantification of abundance-impact relationships for particular ecosystem processes, and a better exploration of food web impacts on ecosystem processes.

Ecosystem Consequences of Biological Invasions

Despite intensive research during the past decade on the effects of alien species, invasion science still lacks the capacity to accurately predict the impacts of those species and, therefore, to provide timely advice to managers on where limited resources should be allocated. This capacity has been limited partly by the context-dependent nature of ecological impacts, research highly skewed toward certain taxa and habitat types, and the lack of standardized methods for detecting and quantifying impacts. We review different strategies, including specific experimental and observational approaches, for detecting and quantifying the ecological impacts of alien species. These include a four-way experimental plot design for comparing impact studies of different organisms. Furthermore, we identify hypothesis-driven parameters that should be measured at invaded sites to maximize insights into the nature of the impact. We also present strategies for recognizing high-impact species. Our recommendations provide a foundation for developing systematic quantitative measurements to allow comparisons of impacts across alien species, sites, and time.

/pdf/ecological-impacts-of-alien-species-quantification-scope-4xfjh1tyvb.pdf

Ecological Impacts of Alien Species: Quantification, Scope, Caveats, and Recommendations

Canada’s managed boreal forest, 54% of the nation’s total boreal forest area, stores 28 Pg carbon (C) in biomass, dead organic matter, and soil pools. The net C balance is dominated by the differen...

Carbon in Canada’s boreal forest — A synthesis1

This book is the Proceedings of the 6th International Soil Zoology Colloquium held in Uppsala in June 1976. The major theme is the interactions of plant roots, microorganisms, and soil animals. Four subthemes were chosen for the plenary sessions. These were: (i) Community structure and niche separation; (ii) The role of soil organisms in nutrient cycling; (iii) Plant roots in the soil system; and (iv) Models of soil organisms and their environment. In addition tothe 51 papers (14, 16, 13, and 8) presented in the above sessions, there are summarized versions of 41 papers given in poster session. The individual papers range from excellent to poor, with about one-fourth in the poor category. About half the remainder are autecological in subject matter treatment and lack the perspective promised in the colloquium title. Most of the papers in the first plenary session are on niche exploitation and responses by members of the soil fauna rather than on their roles as ecosystem components. The papers on nutrient cycling are, with few exceptions, excellent contributions. Particularly commendable is the comprehensive discussion offered by D. E. Reichle. The bulk of the papers in the third session concern either the activities or the effects on plants of rhizophagic invertebrates. Good discussions are given by Vancura and associates on quantitative aspects of root exudation and by Sihanonth and Todd on transfer of nutrients by ectomycorrhizal fungi. Readers expecting to find any noteworthy array of simulation models on soil organisms will be disappointed. Most of the papers in this session might have been placed just as appropriately in some other session. The closing session address by J. E. Satchell is thought-provoking as well asentertaining. The reader, while being told that earthworms are the trombones of the grave, gains the impression that as a group, the soil zoologists are alive and well. Mechanistically the book is soft cover and generally excellently edited. There are about 200 illustrations, mostly line graphs and histograms, but also some light microscope and scanning electron micrographs. Unfortunately, some of the hand-drawn diagrams are so overcrowded with small-scale details as to be practically unreadable. This volume belongs primarily in the personal libraries of invertebrate zoologists. Its reading by systems ecologists and soil scientists will be, in part, time well spent.--FRANCIS E. CLARK, Federal Research, Western Region, U.S. Department of Agriculture, P.O. Box E, Fort Collins, CO 80522.

Soil Organisms as Components of Ecosystems

Environmental disturbances seem to be increasing in frequency and impact, yet we have little understanding of the belowground impacts of these events. Soil fauna, while widely acknowledged to be important drivers of biogeochemical function, soil structure and sustainability, and trophic interactions, are understudied compared to other belowground organisms such as archaea, bacteria, and fungi. In this review we summarize the current state of knowledge of soil fauna as it relates to and is influenced by various disturbances. We focus our review on three main natural and anthropogenic disturbance types: 1) natural disturbances, including damage from wind and flooding; 2) invasive species, including above and belowground flora and fauna; and 3) climate change impacts on the atmosphere and temperature. We do not address the impacts of wildfires, forestry, agricultural practices, mining, or human-caused pollution, as these topics have all been covered in other works. We highlight knowledge gaps and suggest future avenues of research, with hope that the importance of soil fauna and their influences on ecosystems will be given greater emphasis in future research.

/pdf/soil-fauna-responses-to-natural-disturbances-invasive-6litjgv5m9.pdf

Soil fauna responses to natural disturbances, invasive species, and global climate change: Current state of the science and a call to action

In Canada it is generally accepted that most indigenous earthworms did not survive glaciation, and that the majority of the earthworms now inhabiting Canadian soils are relatively recent introductions of European origin. Although these exotic earthworms are generally considered to be beneficial in agricultural soils, their effects can be less benign in forested ecosystems. Studies have shown that invading earthworms can significantly alter the forest floor, affecting the distribution of carbon, nitrogen and other chemicals, roots, microbes and other elements of the soil fauna, and even understory vegetation. This paper summarizes the current distribution of exotic and native earthworm species in Canadian forests and draws on the results of studies of invasion patterns and environmental impacts in northern forests in North America and Europe to discuss potential outcomes for forests in Canada. The potential for variables such as temperature, pH, litter palatability and dispersal, to limit or promote the invasion of exotic earthworms in Canadian forests is discussed, and areas for future research are proposed. The same earthworm species that are invading forests in northern Europe and the US are also invading Canadian forests. Several species of exotic earthworms are already established in a wide range of deciduous and coniferous forest types, including the boreal. Evidence is presented to suggest that further expansion into Canadian forests is likely.

J. A. Addison

Papers

Distribution and impacts of invasive earthworms in Canadian forest ecosystems