The importance of marginal habitats for the conservation of old trees in agricultural landscapes

Abstract

Deterioration of unfarmed habitats resulted in a considerable decrease of biological diversity in agricultural landscapes. The most important elements of cultural landscapes determining a high level of biological diversity are woodlots and the trees themselves. This paper presents the results of a study carried out in 2000–2001 on the distribution and number of champion (heritage) trees on the area of 5480 ha of intensively managed agricultural land (Lower Silesia, south-western Poland). The fieldwork consisted in localizing and measuring all champion tree specimens on the area of 5480 ha of an agricultural fragment of Wrocław Plain (Lower Silesia Province, SW Poland). Champion trees were found in 116 (50.1%) of all 228 surveyed sites. The overall number of champion trees in the study area was 493, belonging to 34 species. The most numerous were native species (276 specimens). The four species of cultivated trees amounted to 40% of all champion trees. The largest percentage of habitats with at least one champion tree specimen was characteristic for manor parks (100%), the lowest—for village areas (27.8%) and mid-field clumps (39.2%). A high, statistically significant correlation was found between the size of a mid-field clump and the number of champion trees it contained. The highest number of champion trees was found in water-edge hedgerows. The current occurrence of champion trees in the agricultural landscape is the result of many centuries of rural areas management. Apart from a number of exotic species of trees, introduced mainly for aesthetic reasons to the inhabited areas (villages, parks, cemeteries), many champion specimens of native trees have survived in mid-field woodlots, planted and managed in the past due to their high economic value ( Quercus robur, Fraxinus excelsior, Ulmus laevis). The pattern of occurrence of native champion trees indicates that some of them may arrived here as a result of natural processes, such as dispersion (e.g. Crataegus monogyna and Rhamnus cathartica that occurred in mid-field clumps).