Species composition of woody vegetation of three types of mid-field woodlots in intensively managed farmland [Wroclaw Plain, South-Western Poland]

The paper presents the results of studies devoted to woody species composition in three types of mid-field woodlots (N = 183), located on the area of 5480 ha in the intensively managed agricultural landscape of Wrocław Plain (Lower Silesia, south-western Poland). The woodlots studied were divided into mid-field clumps (n = 74), water-edge hedgerows (n = 75) and avenues (n = 34). In general, in the three types of woodlots 77 woody plant species were found. To the most common species (50% frequency in all the woodlots) belonged: elder (Sambucus nigra), single-neck hawthorn (Crataegus monogyna), blackberry (Rubus spp.) and blackthorn (Prunus spinosa). For 21 species, statistically significant differences between frequency of occurrence in water-edge hedgerows and clumps were found. Ten species differed in frequency of occurrence between water-edge hedgerows and avenues. Differences between clumps and avenues were documented for 15 species. No significant differences were found in the occurrence of species dispersed by wind, animals and water, and between native species and those of foreign origin, in the respective types of woodlots. For the three types of woodlots studied, high statistically significant correlations were found between the size of woodlots (length for water-edge hedgerows and avenues, and area for mid-field clumps) and the number of recorded woody species. Based on the results obtained and literature data the mechanisms of the floristic diversity of mid-field woodlots were discussed.