Wild bee communities were studied on one- to five-year-old set-aside fields
with naturally developed vegetation (n = 20), and old orchard meadows (n =
4) to analyse effects of secondary succession on species diversity, resour
ce use and associated life history traits. General theory predicts a steady
increase of species richness with age of succession. In contrast, we found
a first maximum in species richness of bees on two-year-old set-aside fiel
ds and a second on old meadows. Successional changes of bee communities wer
e related to changes of vegetation. The transition from pioneer successiona
l stages, dominated by annuals, to early successional stages, dominated by
perennials. resulted in the highest species richness of flowering plants in
the second year within the first five years of succession. Species richnes
s of flowering plants was the best predictor variable for species richness
of bees, whereas the cover of flowering plants correlated with the abundanc
e of bees. Annual plants were visited more often and perennials less often
than expected from their flower cover. Halictidae tended to prefer flowers
of annuals, whereas Megachilidae, Apidae and Anthophoridae significantly pr
eferred perennials. In departure from successional theory, body size, propo
rtion of specialised bees and proportion of parasitic bees did not signific
antly increase with successional age, but number of generations and the pro
portion of soil-nesting bees decreased with successional age. Comparison of
different management types showed that set-aside fields with naturally dev
eloped vegetation supported much more specialised and endangered bee specie
s than set-aside fields sown with Phacelia tanacetifolia.