Northern species not only tolerate but even benefit vegetatively from a slightly warmer climate than they have been adapted to. If the climatic warming remains below 5 celsius in annual mean temperature, the present forest will not be subject to direct disaster. Reproductive processes are likely to be enhanced through increased flowering and better seed maturation. There are few empirical studies on reproductive biology in new environments.

Air pollutants such as ozone may affect tree host-pathogen interactions by altering plant tissue susceptibility, plant resistance, pathogen virulence and inoculum density. Ozone has been shown to weaken trees in natural stands and increase their susceptibility to invasion by plant pathogens, such as Heterobasidion annosum. Ozone has also been shown to enhance disease development by fungi that are normally saprophytic in nature.

Forest Scientists must recognize that numerous diseases and insect occurrences as well as more subtle environmental stresses are prevalent as causes of changes in forest health. Their interactions often lead to "natural" declines of individual tree species or site-species declines of multiple species. The role of air pollution should be carefully investigated in an integrative sense with these other endemic and sometimes epidemic outbreaks of biotic agents and environmental stresses.

The potential effects of long-term exposures to widespread low but raised concentrations above natural levels in Central Europe are still being discussed. This uncertainty results from an inadequate mechanistic understanding of the influence of air pollutants and other environmental factors of trees.

Depending on their concentrations, air pollutants are dangerous to forests. With the exception of some industrial areas in the east, concentrations of air pollutants in Central Europe are below the damaging threshold as shown by the records of the monitoring stations.

The ranges of the ecosystems move when the climatic pattern changes. Simulations have shown that a global warming would cause important changes of the species composition in subalpine forests. Deciduous trees would invade today's subalpine belt. Various conifers would be displaced and migrate into alpine zone. The model simulations are based on the IPCC climate scenarios.

Calcium avaiability to forests has been shown to be reduced by acidic deposition in several ways including: increased leaching from foliage, increased leaching from soils, and decreased availability from poorly buffered soils when aluminium is mobilized. Studies documented that acidic deposition has altered the growth and vigour of red spruce during the past three decades by changing calcium availability.

Destruction of forests leads to the release of carbon dioxide stored in the wood and also usually results in major releases of carbon dioxide stored in soil. Annual releases of carbon dioxide from destruction of tropical forests was estimated at about 1650 million tonnes per year.

Two modeling approaches were applied to evaluate the potential risks of increasing atmospheric carbon dioxide concentrations and possible climate change on the vegetation cover of the Alpine region. The first model is a stochastic forest succession simulator, the second is a static regression type model. The questions of the study were as follows: (1) Which temporal vegetation changes might occur under given carbon dioxide and climate scenarios? (2) Which region of the Alps might be most susceptible to a vegetation change?

Tropospheric ozone is the most important single air pollutant of importance to forests in eastern United States. Both broadleaf and needled trees may suffer premature foliar senescence following even low ozone exposure years. Genetic sensitivity within species is likewise prevalent.