Samenvatting

Heathland, with its frail character, has always been one of the most essential habitats for almost all indigenous reptile species in the Netherlands. Situated in the Drents-Friese Wold National Park, the Doldersummerveld ranks as one of the best developed heathland areas of Western Europe and counts as one of the most bio diverse areas within the province of Drenthe. Managed by the non-profit foundation, Stichting Het Drentse Landschap, the area has seen a variety of management measures including some fairly recent practices such as sod cutting, mowing and grazing by large herbivores (i.e. Highland cattle and Schoonebeeker sheep). Heathland, being a successional stage on its own, would evolve into woodland when left unmanaged. The management measures applied to the Doldersummerveld are primarily conducted in order to avoid encroachment by purple moor grass (Molinia caerulea). However, combined with common heather (Calluna vulgaris), this vegetation is essential to most reptile species that inhabit these heathlands while the management measures that are applied here could also have detrimental effects on reptile populations when applied too intensively or on an extensive scale. The combination of said management measures might also be contradictory to the envisioned goal as a highly nitrogenous (N) and phosphorized (P) soil due to a high volume of faecal matter by grazers (particularly on sod cut areas) could favour the regrowth of purple moor grass over common heather. In order to test the effects of sod cutting, mowing and grazing on reptile populations, the 12 largest and most recently sod cut and mowed areas were selected as plots throughout the area (6 of each) for monitoring the Grass snake (Natrixnatrix), European adder (Vipera berus) and Viviparous lizard (Zootoca vivipara) using line transects while each managed area was appointed a, vegetation wise, control plot. In order to assess the grazing intensity and vegetation composition of the plots, (random) quadrants were set out where a variation of the Braun-Blanquet method was performed combined with a faecal count. Between the 17th of June and the 21st of August 2014, 177 individuals of the target reptile species were found while sampling the various transects (7 grass snakes, 37 European adders and 133 viviparous lizards). The results from the Generalized Linear Mixed Models analysis (GLMM) indicated a significant difference between the cores of both sod cut and mowed plots compared to their respective control plots (by a factor of 0,115 in the case of sod cutting and 0,165 in the case of mowing), suggesting a decimation of the present reptile population in said areas where sod cutting or mowing was applied. Grazing did not show to have significant effects on reptile populations or heather vegetation (i.e. Calluna vulgaris and Erica tetralix), although this could just be due to the chosen method or the eventual low sample size and lack of variety among the faecal density scale. Sod cutting should only be applied when one wants to establish a new area that contains both Calluna and Erica vegetation, and only on a small enough scale and a large enough timeframe on (homogenous) nutrient rich heathland. When only Calluna is desired, fencing a nutrient rich area to avoid grazing should be sufficient. Nutrient poor heathland needs neither mowing or sod cutting when grazing is applied moderately in order to avoid succession. Placing fences around sod cut and mowed areas for the first few years after said management measure is conducted, to retain grazing animals from entering these areas, is recommended.