Unconsidered sporadic sources of carbon dioxide emission from soils in taiga forests.

Long-term monitoring in the Russian taiga zone has shown that all known extreme destructive effects resulting in the weakening and death of tree stands (windfalls, pest attacks, drought events, etc.) can be sporadic, but significant sources of CO2 soil emission. Among them are (i) a recently found effect of the multiyear CO2 emission from soil at the bottom of deadwood of spruce trees that died due to climate warming and subsequent pest outbreaks, (ii) increased soil CO2 emissions due to to the fall of tree trunks during massive windfalls, and (iii) pulse CO2 emission as a result of the so-called Birch effect after drought events in the taiga zone. According to the modeling, while depending on the spatial and temporal scales of their manifestation, the impact of these sporadic effects on the regional and global soil respiration fluxes could be significant and should be taken into consideration. This is due to continuing Climate Change, and further increase of local, regional and Global human impacts on the atmospheric greenhouse gases balance, and land use, as well.

[Succession in forest coenoses: a model of second-order phase transition].

The changes of arboreous coenoses composition resulting from natural and anthropogenic impacts are considered. The mathematical model is proposed and verified that describes arboreous cenoses transition from one succession state into another by analogy with phase transition in statistical physics. It is demonstrated that the model is concordant with the data of full-scale observations. The model allows to explain the trend of succession processes and determine the stage of forestation process at which succession transitions should be expected. The analysis of full-scale observations data by means of the proposed approach makes it possible to calculate, for given regions and forest types, the critical values of planting phytomass that, upon being attained, initiate the succession transition. Those values are important to be known for middle- and long-term forecasting of forest cover dynamics.

[Phenomenological models of the forest plantations growth].

Phenomenological models of the forest plantations growth are analyzed. Those derived from the Verhulst's model are shown to fail describing qualitative effects reflecting tree growth, phytomass withdrawals, and plantation restoration. The method of phase portraits is used for exploration of the forest ecosystem dynamics, which allows to describe regulatory mechanisms of the growth processes, regulation delay, and feedback types. A bistable phenomenological model is suggested herewith to characterize dynamic processes in the forest ecosystems. Principal patterns of formation of the forest plantations at different stages of the forest generation processes are considered on the basis of that model, and ecological effects responsible for the plantation dynamics are revealed.

The use of aerospace methods for forest state assessment.

Siberian forests occupy a significant part of the Asian continent. Their role as an essential component of the Earth's surface, biomass and oxygen producer is increasing annually. Expanded reproduction of taiga forests necessitated by the intensive development of Siberian productive forces, results in an evergrowing need of forest productivity constancy and increase. Proper forest exploitation is a crucial part of the solution of such important problems as the rational use of land and water resources, stable crop yields, and the creation of favourable conditions for human life.To solve these important economic problems, the Siberian branch of the USSR Academy of Sciences has devised a long-term programme of ecological monitoring of Siberian forest resources using aerospace techniques. The programme provides for the establishment and improvement of ecogeographical and physicotechnological principles of the remote sensing of forests and the development of fundamental forest-biological research based on new methodologies, the results of which are used to solve urgent forestry and nature protection problems. The research is carried out in the following major directions: studying spectral characteristics of forest vegetation for forest-state indication; thematic mapping of taiga territories; assessing biological productivity of natural complexes; environmental state monitoring; fire protection of forests; pest and disease control; developin instruments and methods for automatized aerospace data processing for real-time use.We consider forest-state monitoring to be one of the crucial tools in providing the optimum use of forest ecosystems for resource and ecological functions.

Natural regulation of herbivorous forest insect populations.

From basic principles of positive/negative feedback control and classical density-dependent/independent population theory we outline a general explanation for the regulation of herbivore populations in forested ecosystems. We identify three fundamental patterns of behavior; (i) populations regulated close to equilibrium ("tight" regulation) by fast-acting negative feedback processes, (ii) populations regulated by delayed negative feedback processes ("loose" regulation) which often exhibit wide-amplitude density cycles, and (iii) populations characterized by positive feedback processes over certain density ranges that may exhibit divergent (metastable) behavior. We then discuss the effects of these different kinds of herbivore population behavior on the dynamics of forest ecosystems and explore some elemental models of herbivore/forest interactions. Finally, using the spruce bark beetle, Ips typographus, as an example, we demonstrate how the theory can be used to explain the dynamics of specific herbivore populations and to develop general strategies for managing destructive herbivore outbreaks.