This is somewhat surprising as tree diameter has previously been shown to be positively correlated with the number of species

(Grove 2002; Ranius and Jansson 2000; Sverdrup-Thygeson et al. 2010). However, in the present study, the trap catches and the circumferences are estimates CP673451 relevant on stand scale rather than on the scale of individual trees. Therefore, other variables might have confounded the results. Furthermore, all sites were characterised by trees that had reached a size and age defining them as ancient, and the degree of ancientness may be more important than diameter itself. Pollarding slows down growth and because of that, thin trunks may be ancient trees. In oaks, 50% of trees form hollows by about 250 years of age (Ranius

et al. 2009). For lime trees, this age is probably lower, as lime rots faster than oak and especially so in pollarded trees as the formation of hollows is enhanced where branches are shed. However, hollowness need not imply a rich fauna if the trees are too young, as seen in the case SBE-��-CD cell line of 80-year old hollow limes in the park at Drottningholm, which had fewer species, especially red-listed species, than the old limes in the same park (Jonsell 2008). The amount of habitat, measured as number of hollow lime trees on each site (No. of trees), had significant relationship to species number for all wood and bark living species, and it was negative. This lack of relation, or relation opposite to what should be expected, could be due to that the variables no. of trees and type were confounded with somewhat more trees in parks than in the other type of sites (2.6 compared to 1.9 for the two others). Also problems with quantifying this variable may contribute. First the data collected for each

locality had several uncertainties in itself (see “Materials and methods”). The numbers obtained also give just the present situation, totally disregarding the history of the site. In addition to that, the definition of where the borders for a locality should be drawn is also problematic. Most of these sites are found in regions where old hollow trees may occur here and there. Data on suitable trees for the whole landscape with estimates Vitamin B12 of connectivity related to distance to each of these occurrences should probably be more explanatory (Ranius et al. 2010). Such an analysis would probably suggest that the rich saproxylic beetle fauna on several sites in the Mälaren area is due to a dense patchwork of sites. The number of sites is high, there is a high connectivity between them, several sites are large and the individual trees in them are often a high quality habitat, all factors that contribute to a sustainable metapopulation system (Hanski 1994; Ranius 2007).