Resurveying hedgerows in Northern Germany: Plant community shifts over the past 50 years

Abstract

Resurveying is a powerful approach to investigate responses of plant species communities to a changing environment. We present a resurvey of hedgerows from the “Knick” landscape of eastern Schleswig-Holstein, Germany. The original survey was done by H. E. Weber in 1967 and new data from totally 51 semi-permanent plots was sampled in 2015. Hedgerows are a key near-natural habitat that can harbour a great biodiversity in otherwise agriculturally intensified landscapes.Our study reveals a distinct shift in the herbaceous species composition of the hedgerows over the past five decades. To understand the reasons for these changes, we compared the mean Ellenberg indicator values (EIVs) and measured pH values, as well as hedge shape parameters of the hedgerows between the recent and the original study. The main driver behind the change in species composition appeared to be the increase in nutrient supply. The hedge shape changed as well, indicating an altered hedgerow management. Interestingly, we found a contradictory relationship between measured pH values and mean EIVs for reaction: while the former showed a decrease over time, the latter suggested an increase.Species richness decreased in some groups (shrubs and herbaceous forest species) but increased in others (grass species and arable weed species), with an overall decline in species richness. An analysis of the species' changes in frequency in relation to their EIVs showed that species with higher nitrogen and temperature scores were more likely to have increased.