Herbaceous plant community structure of ancient and recent forests in two contrasting forest types

It has already been extensively documented that major floristic differences between ancient and recent temperate broad-leaved forests exist. Hence, the question raises whether the herb layer community structure and organization of ancient and recent forests also differs and whether these differences are the same in productive vs. unproductive forest types? Therefore, we selected 127 releves situated in productive Alno-Padion forests and 69 releves situated in less productive Quercion forests out of a larger data-set containing 640 releves from northern Belgium. The plots differed with respect to land use history but it was assured that no covariation between land use history on the one hand, and soil texture, soil drainage and canopy composition on the other occurred. In both forest types, about 30% of the studied species exhibited an association with either ancient or recent forests. Persistent differences between ancient and recent forests in life-form spectra in general and in the number and abundance of geophytes in particular were found as well. Few changes in the community structure of productive Alno-Padion forests were observed after 70 years of recovery. Only in the youngest Alno-Padion forests (i.e. < 70 years) species numbers and total cover of the herb layer were lower and co-occurrence patterns did not differ from random. In general, community recovery appeared to be slower in unproductive Quercion forests. Species numbers, species abundance distributions, species co-occurrence patterns and plot dissimilarity still changed after 120 years. The persistent differences in both communities can be explained by the strong dispersal limitation of many of the involved species, but in the Quercion forests recovery is probably also severely hampered by establishment limitation.