Abstract :
The aim of this study is to present some examples and models associated with the issue of the diversity of vegetation in agricultural landscapes. Research into this matter was carried out in landscapes located in different places in Poland e.g. near Warsaw (central Poland), in the area near Pinczow (southern Poland) and near Lake Wigry (northeast Poland). In particular, this paper is concerned with: (a) the relationship between the intensity of anthropogenic influences and synthetic indices of the diversity of vegetation landscapes, as well as tests of the usefulness of a model based on the Maxwell distribution in the description of the relationships, and (b) the influence of the degree of synanthropisation of plan communities on such topological features of phytocoenoses as the sizes of patches, the number of borders and a shape index. To determine the relationship between the intensity of anthropogenic influences and synthetic indices of diversity for vegetation landscapes, use was made of a model based on a Maxwell distribution, which may be expressed in a generalised form by the formula: Y = a + b × Xc × exp(d + e × Xf). The actual vegetation in the vicinity of Lake Wigry was analysed in order to determine the relationship between topological characteristics of patches of vegetation and the level of anthropogenic impact.
Use of the Maxwell model allowed for more than half of the variance to be explained in each of the examples analysed (R2 ranged from 0.52 to 0.68). This attests to the usefulness of the model in the description and diagnosis of the influence of anthropogenic impacts on the typological and spatial diversity of vegetation. It follows from the model applied that various measures may be used to describe disturbance and diversity, without losing sight of the general relationships.
Analysis of the correlative model allowed us to state that anthropogenic influences increase the values of topological components of the overall spatial diversity of vegetation landscapes (through an increase in the total number, and number of types of plant patches). However, anthropogenic influences may lead to a decrease in diversity (through the lowering of the number of neighbours for each plant community, and through a decrease in the shape index).
