Pervasive early 21st‐century vegetation changes across Danish semi‐natural ecosystems: more losers than winners and a shift towards competitive, tall‐growing species

Abstract

1.Semi-natural open habitats in north-western Europe are highly prioritized for conservation, and optimization of management planning is essential for continued protection of their diversity. We evaluate whether current management practices, which consist mainly of summer grazing by livestock, are sufficient to maintain plant species composition in a stable state across semi-natural areas in Denmark, or if shifts in functional composition are taking place. Further, we investigate important drivers of any ongoing changes through trait differences between winner and loser species. 2. Using a data set of 6513 annually inventoried (2004-2010) vegetation plots from 202 seminatural NATURA 2000 protected areas, we assessed changes in cover of all plant species and, using boosted regression trees, whether winners and losers differ in regard to autecological characteristics and traits. 3. There were consistent changes in cover for 123 out of 603 species across the 6-year study period, with more species losing than winning (78 vs. 45). Winner and loser species were strongly differentiated by competition-related traits, but traits related to soil nutrients and soil moisture also had some importance. Generally, our results indicate a trend towards taller and more competitive species. 4. Synthesis and applications. Despite conservation actions in order to maintain a so-called favourable conservation status, vegetation in NATURA 2000 protected areas is still undergoing compositional changes. Overall, autecological characteristics and trait differences between winners and losers match expectations given the contemporary anthropogenic pressures, especially reduced livestock grazing. Atmospheric nitrogen deposition and increased soil moisture due to reduced drainage might also be involved in observed changes. Current management (i.e. summer grazing by livestock) is insufficient to preserve the diversity of less-competitive, low-statured and stresstolerant herbaceous species, potentially leading to species losses. Such patterns can thus be expected across semi-natural ecosystems in north-western Europe and other places where traditional land use (i.e. previous widespread extensive livestock grazing) have been replaced with various degrees of conservation management. A greater focus on returning large grazing herbivores to conservation areas is recommended for the protection of plant species diversity and to counteract ongoing changes.

More is less: net gain in species richness, but biotic homogenization over 140 years

“…This observation indicates that anthropogenic land‐use change, rather than competitive effects of invasive plant species, is the main driver of the compositional changes. In other words, the exotic species are passengers rather than drivers of the observed biotic change at the regional scale (Didham et al ; Thomas & Palmer ). In present data, we found a high proportion of species being exotic (45%), much higher than the figure reported for Great Britain (20%; Thomas & Palmer ).…”

Topographically determined water availability shapes functional patterns of plant communities within and across habitat types

“…In semi-natural habitat types such as grasslands and heathland, traditional land use has been replaced by various degrees of conservation management. Together with a higher pressure of nutrients ), this change has proven to lead to a change in functional structure toward more competitive, tallgrowing species across the last decade (Timmermann et al 2014). Hence, local factors may strongly affect the functional structure of plant communities, may be even to a degree where it overshadows the effect of hydrology.…”

“…We hypothesize that geography and history related to a given site play a role in community assembly (Eriksson et al 2009). Management, especially grazing, has large impacts on the composition of plant communities as it keeps open habitat types like grasslands and heath from being colonized by trees and shrubs (Prévosto et al 2011;Timmermann et al 2014;Zobel 1992). Furthermore, communities in proximity to each other may be more similar in their response because they are similar in species composition compared to spatially distant communities (Brunbjerg et al 2012;Doxford and Freckleton 2011).…”

Land surface greening suggests vigorous woody regrowth throughout European semi‐natural vegetation

“…Relative increases (i.e., ΔLAI expressed in percentages) were highest in "transitional woodland-shrub" and "sclerophyllous vegetation," consistent with increasing woody cover in these semi-open vegetation types (Timmermann, Damgaard, Strandberg, & Svenning, 2015). Greening rates in conservation areas did not exceed greening in unprotected semi-natural vegetation, suggesting that increased conservation efforts have not contributed to greening.…”