Ecoinformatics and Soil-Plant Formations - New Ecoinformatics Tools in Environmental Science: Applications and Decision-making - page 645

systems (Polishchuk 1992; Ugolnitsky 1999), modeling the spatial-temporal
dynamics of the ecological systems, and many others.
Many authors solve the problem of modeling a succession of vegetation com-
munities basing on their points of view on succession processes. There are two
fundamental interpretations of these processes based on the concepts of endo-
ecogenesis and exo-ecogenesis. The most stable idea of the character of the
dynamic phenomena in phytocenoses is an idea of a single process of the vegetation
development under the in

uence of both external and internal factors. In this case,
the process of succession covers such factors as soil development, layer-by-layer
division of the vegetation community, change of the height of plants and their
accumulated biomass, microclimate formation, change of the species diversity, and
relative stability of the community. The classi

fl

cation of the forms of the vegetation
community dynamics and its affecting factors is important for further synthesis of
the numerical model. Vasilevich (1983) introduced the following categories of
successions: endogenic (autogenic), exogenic (allogenic), continuous, post-disrup-
tive (post-catastrophic). In the case of endogenic succession, the source of changes
is located in the vegetation itself and it is affected by changes in the medium. There
are no stages in continuous successions. In the course of post-disruptive succession,
changes in the community take place from unstable to stable conditions. Exo-
ecogenesis is characterized by prevailing external factors.
Population dynamics was a novel development in succession modeling. Thus,
Hulst (1979) proposed three types of the models of succession. The

first type is a
model of succession with response but without competition, that is, there is an effect
of reaction of the vegetation community to changes in the environmental condi-
tions. Succession is described by the usual differential equation:

dN i = dt ¼ r i N i k i N i ð Þ= k i

where N i is the number of individuals of the ith species, ri i is the rate of an
exponential growth, ki i is a maximum of population density.
The second type of the succession model is based on suppression of one species
by another in the process of intrusion. In this case, the coef

cient of competition is

used:

a ij ¼ @ ½ dN i = dt =@ N j =@ ½ dN i = dt =@ N i ;

and the model itself is written as:

dt ¼ r i N i ð k i X dN i = a ij N i Þ= k i

rst
two models the population density is a function of the size of previous species of
vegetation, a maximum of population density ki i depends on time.
The production of organic matter by vegetation community depends on physi-
ological processes in the organisms of the plants, resources of solar radiation,

The third type of the model of succession has alternative character. If in the