Interannual variability in abundance of field layer species in a south Swedish deciduous wood

Abstract

Variability in cover of five field layer species was recorded during ten consecutive years in thirty permanent plots within a south Swedish Carpinus betulus forest. The studied species were Oxalis acetosella, Lamium galeobdolon, Stellaria holostea, Hedera helix and Holcus mollis . We observed great interannual variability in cover percentage of all studied species with 76 % out of all year-to-year differences being statistically significant ( P < 0.05). However, a very high persistence of all species was recorded with very few colonizations or extinctions at the sample plot scale. Regression analyses showed that cover changes of Oxalis, Lamium, Stellaria and Holcus were related to amounts of rainfall. Longer periods of dry weather during early summer of the current year or during late summer of the previous year reduced the abundance of these species. Cover of pairs of species was mostly positively correlated, indicating that interspecific competition was less important in accounting for abundance changes during the study period. Long-term trends were observed in Hedera helix (decrease) and Holcus mollis (increase) and may be explained by current soil acidification in the study area. Our results show that environmental monitoring of permanent plots for the study of long-term vegetation changes must account for interannual variability in species cover.