Biological invasions into wholly new regions are a consequence of a far reaching but underappreciated component of global environmental change, the human-caused breakdown of biogeographic barriers to species dispersal . Human activity moves species from place to place both accidentally and deliberately-and it does so at rates that are without precedent in the last tens of millions of years. As a result , taxa that evolved in isolation from each other are being forced into contact in an instant of evolutionary time. This human-caused breakdown of barriers to dispersal sets in motion changes that may seem less important than the changing composition of the atmosphere , climate change , or tropical deforestation-but they are significant for several reasons. First , to date , biological invasions have caused more species extinctions than have resulted from human-caused climatic change or the changing composition of the atmosphere . Only land use change probably has caused more extinction, and (as we later discuss) land use change interacts strongly with biological invasions. Second, the effects of human-caused biological invasions are long-term: changes in climate, the atmosphere, and land use may be reversible in hundreds to thousands of years, but the breakdown of biogeographic barriers has resulted in self-maintaining and evolving

Biological invasions by exotic grasses, the grass/fire cycle, and global change

I. CONTEXT * The Ecosystem Concept * Earth's Climate System * Geology and Soils * II. MECHANISMS * Terrestrial Water and Energy Balance * Carbon Input to Terrestrial Ecosystems * Terrestrial Production Processes * Terrestrial Decomposition * Terrestrial Plant Nutrient Use * Terrestrial Nutrient Cycling * Aquatic Carbon and Nutrient Cycling * Trophic Dynamics * Community Effects on Ecosystem Processes * III. PATTERNS * Temporal Dynamics * Landscape Heterogeneity and Ecosystem Dynamics * IV. INTEGRATION * Global Biogeochemical Cycles * Managing and Sustaining Ecosystem * Abbreviations * Glossary * References

Principles of Terrestrial Ecosystem Ecology

While ecologists involved in management or policy often are advised to learn to deal with uncertainty, there are a number of components of global environmental change of which we are certain–certain that they are going on, and certain that they are human—caused. Some of these are largely ecological changes, and all have important ecological consequences. Three of the well—documented global changes are: increasing concentrations of carbon dioxide in the atmosphere; alterations in the biogeochemistry of the global nitrogen cycle; and ongoing land use/land cover change. Human activity–now primarily fossil fuel combustion– has increased carbon dioxide concentrations from °280 to 355 mL/L since 1800; the increase is unique, at least in the past 160 000 yr, and several lines of evidence demonstrate unequivocally that it is human—caused. This increase is likely to have climatic consequences–and certainly it has direct effects on biota in all Earth's terrestrial ecosystems. The global nitrogen cycle has been altered by human activity to such an extent that more nitrogen is fixed annually by humanity (primarily for nitrogen fertilizer, also by legume crops and as a by product of fossil fuel combustion) than by all natural pathways combined. This added nitrogen alters the chemistry of the atmosphere and of aquatic ecosystems, contributes to eutrophiction of the biosphere, and has substantial regional effects on biological diversity in the most affected areas. Finally, human land use/land cover change has transformed one—their to one—half of Earth's ice—free surface. This in and of itself probably represents the most important component of global change now and will for some decades to come; it has profound effects on biological diversity on land and on ecosystems downwind and downstream of affected areas. Overall, any clear dichotomy between pristine ecosystems and human—altered areas that may have existed in the past has vanished, and ecological research should account for this reality. These three and other equally certain components of global environmental change are the primary causes of anticipated changes in climate, and of ongoing losses of biological diversity. They are caused in turn by the extraordinary growth in size and resource use of the human population. On a broad scale, there is little uncertainty about any of these components of change or their causes. However, much of the public believes the causes–even the existence–of global change to be uncertain and contentious topics. By speaking out effectively, we can help to shift the focus of public discussion towards what can and should be done about global environmental change.

https://www.jstor.org/stable/pdfplus/1941591.pdf

Beyond Global Warming: Ecology and Global Change

Estimates of national-scale forest carbon (C) stocks and fluxes are typically based on allometric regression equations developed using dimensional analysis techniques. However, the literature is inconsistent and incomplete with respect to large-scale forest C estimation. We compiled all available diameter-based allometric regression equations for estimating total aboveground and component biomass, defined in dry weight terms, for trees in the United States. We then implemented a modified meta-analysis based on the published equations to develop a set of consistent, national-scale aboveground biomass regression equations for U.S. species. Equations for predicting biomass of tree components were developed as proportions of total aboveground biomass for hardwood and softwood groups. A comparison with recent equations used to develop large-scale biomass estimates from U.S. forest inventory data for eastern U.S. species suggests general agreement (±30%) between biomass estimates. The comparison also shows that differences in equation forms and species groupings may cause differences at small scales depending on tree size and forest species composition. This analysis represents the first major effort to compile and analyze all available biomass literature in a consistent national-scale framework. The equations developed here are used to compute the biomass estimates used by the model FORCARB to develop the U.S. C budget. FOR. SCI. 49(1):12-35.

https://www.fs.fed.us/ne/newtown_square/publications/other_publishers/OCR/ne_2003jenkins01.pdf

National scale biomass estimators for United States tree species

Succession is a process of continuous colonization of and extinction on a site by species populations. The process has long been central in ecological thinking; much theory and many data about succession have accumulated over the years. Since nearly all species in all communities participate in successional interactions, and because physiological ecology encompasses everything that a plant does during its life cycle, a complete review of physiological ecology of all species in all successions is not possible. Thus in this review I discuss the physiological adaptations of species of one successional gradient-from open field to broad-leaved deciduous forest. I concentrate on the physiological adaptations of early successional plants to environmental variability and collate the literature on tree physiology to make comparisons with early successional plants. My discussion may not be applicable to seres where there is little difference in physiognomy between early and late successional plants or where the designation of species as early or late successional is unjustified (e.g. for certain desert and tundra habitats). I discuss the nature of successional environments, seed germination, seedling and mature plant development, plant growth, photosynthesis, water use, and the physiological ecology of competition and interference.

https://www.jstor.org/stable/info/2096796

The Physiological Ecology of Plant Succession

Action des porcs sauvages sur la faune superficielle, les elements nutritifs, la biomasse de la litiere forestiere et du sol

Effects of wild pig rooting in a deciduous forest

Forest succesion was studied in a species—rich cove forest of the Great Smoky Mountains, Tennessee. Long—term compositional and structural changes in secondary stands, 15—63 yr after agricultural abandonment circa 1920, were compared to an adjacent old—growth stand. Later successional trends were projected by computer simulation. The colonizing stand (15 yr) was dominated by Liriodendron tulipifera and Robinia pseudoacacia. Common old—growth species absent at this early stage included Aesculus octandra, Fagus grandifolia, and Tsuga Canadensis. By year 40, Liriodendron dominated the overstory and all old—growth dominants were represented in the understory. After 60 yr, Acer saccharum was clearly the most abundant understory species; gap model projections indicated that after 200 yr it will dominate the forest. The actual old—growth stand was dominated by Acer saccharum. Species richness peaked at mid—succession (°50 yr), while diversity (H') and evenness (J') of species biomass were highest at the old—growth stage. Richness peaked with the coexistence of shade—intolerant colonizers in the overstory and shade—tolerants in the understory. Canopy—gap processes of the secondary and old—growth stands differed sharply. The old—growth canopy was composed of large, spreading, and overlapping crowns, while the second—growth stand was composed of narrow, nonoverlapping crowns. Gaps in the secondary stand tended to be small (<100 m2) but numerous. The regeneration of intolerants was low and individual gap microsites were not markedly different from the understory as a whole. Old—growth gaps were often larger, higher light microsites which contrasted sharply with the shaded forest floor. The wider range of gap sizes in old forests accommodates a variety of species, including intolerants, contributing to the high canopy species diversity of old—growth cove forests.

Secondary Succession, Gap Dynamics, and Community Structure in a Southern Appalachian Cove Forest

Allelopathy seems to be the mechanism that allows Sassafras albidum to main- tain itself in relatively pure stands through many stages of old-field succession. Field studies revealed that 10 species consistently occurred exclusively outside of clump canopies and 7 other species predominated beneath the sassafras canopy. We suggest that annual herbs are being effectively excluded from the understory flora. 2-pinene, oa-phellandrene, eugenol, safrole, citral, and d-camphor were isolated within and outside of sassafras stands from leaves, litter, soil, and roots. Germinating seeds watered with aqueous leachates of leaves, litter, and canopy washings showed varying degrees of radicle reduction during germination. Germination on soil discs from beneath sassafras stands was significantly lower in four of the test species; in seeds overwintered in sassafras litter it was significantly lower in all species. There was a positive correlation between a-phellandrene concentration and reduction in radicle growth in Acer negundo and Ulmus americana. Sufficient incoming and buried seeds were available to support a richer and more abundant understory flora than was found in the vegetational survey. The different modes of sassafras for releasing phytotoxins into the environment at different times of the year operate to continually influence its surroundings.

/pdf/the-allelopathic-influences-of-sassafras-albidum-in-old-3qj3ggsim5.pdf

The allelopathic influences of sassafras albidum in old-field succession in tennessee'

PAULEY, E. F. AND E. E. C. CLEBSCH (Graduate Program in Ecology, University of Tennessee, Knoxville, TN 37996-1610. Pattems of Abiesfraseri regeneration in a Great Smoky Mountains spruce-fir forest. Bull. Torrey Bot. Club 117: 375-381. 1990.-Abiesfraseri (Pursh) Poir. (Fraser fir) has incurred high mortality from infestation by Adelgespiceae Ratz. (balsam woolly adelgid). Vegetational changes in the spruce-fir forest since Adelges infestation have included a large increase in the density of Rubus canadensis L. (thomless blackberry). Size and age structures, microsite and aspect distributions, and growth of Abies seedlings (stems < 137 cm tall) were quantified on Mt. Collins, Great Smoky Mountains National Park in 1988 to determine pattems of co-occurrence between Abies seedlings and Rubus. The majority (87%) of seedlings were c25 cm tall, and most (62%) were at least five years old. No germinal (< 1 year old) Abies were found. Dead wood substrates and bryophyte-covered surfaces both supported more seedlings than expected by chance. Seedling growth trends showed a recent increase in terminal shoot length and recent decreases in lateral shoot lengths, suggesting a combination of normal growth pattems and recovery from Adelges infestation. Effects of Adelges infestation were noted for 26% of all seedlings and were more frequent among older seedlings. Density of Abies seedlings was low at high Rubus densities, but seedling shoot growth showed no clear relationship with Rubus density. Rubus appeared to interfere with establishment or survival of Abies seedlings but not with annual growth.

Patterns of Abies fraseri regeneration in a Great Smoky Mountains spruce-fir forest

Aboveground biomass and aboveground net primary production (ANPP) were determined for leaf, branch, and bole compartments of cove forests in the Great Smoky Mountains, Tennessee. The sample plots i...

Edward E. C. Clebsch

Papers

Effects of wild pig rooting in a deciduous forest

Secondary Succession, Gap Dynamics, and Community Structure in a Southern Appalachian Cove Forest

The allelopathic influences of sassafras albidum in old-field succession in tennessee'

Patterns of Abies fraseri regeneration in a Great Smoky Mountains spruce-fir forest

Biomass and production of southern Appalachian cove forests reexamined