Species area-relationships and frequency - Floristical data analysis of 44 isolated woods in northwestern Germany

44 isolated ancient woods (9,3-8579 ha) in southeastern Lower Saxony (northwestern Germany), where the Tertiary hilly country meets the Pleistocene plain, were investigated. Complete lists of 273 vascular plant species showing a more or less strong preference for woodlands were made for each wood including all the species of the groups Querco-Fagetea, Trifolio-Geranietea, Galio-Calystegietalia (selection of species) and Epilobietea. The majority of character species of woods show either a low or a high frequency, whereas fewer ones have medium frequencies. Most of the rarer species have their main occurrence in the larger woods. The number of species of all of the four groups increases with area of the wood and the correlation between the number of species and the log of area is related by a highly significant linear regression. Comparison of a single wood with two smaller woods of the same total area reveals that the two smaller woods on average have the greater number of wood species. Considering this and the fact that the rarer species have their main occurrence in the larger woods, when discussing questions of nature conservation a simple comparison of number of species and area is problematical.