Changes In Forest Ecosystems Research Articles

Historical and Anticipated Changes in Forest Ecosystems of the Inland West of the United States

Euro-American settlement of the Inland West has altered forest and woodland landscapes, species composition, disturbance regimes, and resource conditions. Public concern over the loss of selected species and unique habitats (e.g., old-growth) has caused us to neglect the more pervasive problem of declining ecosystem health. Population explosions of trees, exotic weed species, insects, diseases, and humans are stressing natural systems. In particular, fire exclusion, grazing, and timber harvest have created anomalous ecosystem structures, landscape patterns, and disturbance regimes that are not consistent with the evolutionary history of the indigenous biota. Continuation of historical trends of climate change, modified atmospheric chemistry, tree density increases, and catastrophic disturbances seems certain. However, ecosystem management strategies including the initiation of management experiments can facilitate the adaptation of both social and ecological systems to these anticipated changes. A fairly ...

A Process for Improving Wildlife Habitat Models for Assessing Forest Ecosystem Health

Vertebrate wildlife will probably continue to be a primary surrogate for assessing biological diversity in forested ecosystems. However, assessment tools such as wildlife-habitat models generally have proved to be poor predictors of wildlife population responses to landscape-scale changes in forest ecosystems. Forest ecosystem assessment therefore will require improved models. To improve modeling capabilities, scientists must clarify the primary determinants of wildlife habitat selection, which is a behavioral process that links wildlife populations with ecosystem processes. Wildlife populations respond to functional redundancies caused by multiple interactions among landforms, soils, and vegetation. Therefore, probing wildlife habitat selection responses to attributes of landforms, soils, and vegetation should result in improved wildlife-habitat models. In this paper, radiotelemetry data from a study on northern spotted owls (Strix occidentalis caurina) are used to illustrate how remote sensing and geographic information systems (GIs) analysis might clarify basic determinants of habitat selection.

Changes and disturbances of forest ecosystems caused by human activities in the western part of the mediterranean basin

The development of socio-economic activity over the past ten years in the Mediterranean region has induced severe changes in the main natural forest ecosystems. In the northern Mediterranean, rural depopulation has accelerated since the end of the second World War, particularly since the establishment of Common Market agricultural policies, and led to an under-utilization of species causing a strong biological resurgence of the forest, even at high altitudes. This means that, at the present time, the extension of expansion model coniferous forests is favored by their capacities for spatial, biological and ecological selection. Along with this, the under-utilization of sclerophyllous (resistance model) and deciduous (stabilization model) oak coppices has led to the establishment of new forest structures and architectures which are notably different from the main climatic groups defined up to now by phytosociological and synchronic methods. Two new forms of disturbances have appeared: In the southern Mediterranean, particularly in North Africa, demographic pressure and grazing have widely disturbed the main forest ecosystems which show a continual regression of their surface. Many forest tree species with a low spatial and biological selection, such as Mediterranean firs and black pines (Pinus nigra subsp. mauritanica), are threatened with extinction, as are the deciduous oak forests which, considering the climatic stress and edaphic constraints, are permanently in a state of imbalance. Human disturbances induce a complete modification of structures and architectures tending towards the installation of simplified forest models (trees-grasses) where tree regeneration is nearly impossible. The sclerophyllous coppices well-adapted to stress are also threatened by shorter and shorter cutting cycles and by the high usage of tree canopies for grazing. In all bioclimatic groups, the increase in grazing pressure throughout the southern Mediterranean ecosystems can even lead to the total disappearance of perennial species from the ecosystem with the exception of the dominant tree. Regardless of the altitude or ecosystem, invasive therophytes are then the only plants to occupy the understory and indicate hyperdegradation (forest therophytization).

Forest-pest interaction dynamics: The simplest mathematical models

This paper is devoted to the investigation of the simplest mathematical models of non-even-aged forests affected by insect pests. Two extremely simple situations are considered: (1) the pest feeds only on young trees; (2) the pest feeds only on old trees. The parameter values of the second model are estimated for the case of balsam fir forests and the eastern spruce budworm. It is shown that an invasion of a small number of pests into a steady-state forest ecosystem could result in intensive oscillations of its age structure. Possible implications of environmental changes in forest ecosystems are also considered.

Soil changes in forest ecosystems: evidence for and probable causes

SynopsisA review of the literature on forest soil change in North America, Central Europe. Sweden, U.K., and Australia reveals that changes are occurring in both polluted and unpolluted sites at a greater rate than previously suspected. Acid deposition has played a major role in recent acidification in some areas of Europe and, to a more limited extent, in Sweden and eastern North America. However, rapid rates of soil acidification are occurring in western North America and Australia due to internal processes such as tree uptake and nitrification associated with excessive nitrogen fixation. The presence of extremely acid soils is not necessarily an indicator of significant acidic deposition, as evidenced by their presence in unpolluted, even pristine forests of the north-western U.S.A. and Alaska. Numerous studies in Sweden, Australia, and North America show the important effects of tree uptake and harvesting upon soil acidification in managed forests. Furthermore, arguments can be presented that harvesting takes a greater toll upon the pools of potentially limiting cations than leaching.The rate at which soils are changing in some instances calls for a re-evaluation of the budget analyses used to predict soil change. Specifically, inter-horizon changes due to uptake and recycling by vegetation, the interactions of such changes with naturally- and anthropogenically-produced acids, and the effects of aluminium uptake and recycling need further evaluation and study.