Effects of global change on plants: tracing the footprints of climate warming and land use from herbaria to forest understories.

Abstract

Over the last centuries humans have drastically changed the global environment. Since the industrial revolution, they altered the climate of the Earth by emitting greenhouse gases, deteriorated its ecosystems and decimated biodiversity by intensifying land-use. One of the most apparent fingerprints of this anthropogenic global change is that all over the world the rhythms of life of plants and animals are changing. In order for species to survive and thrive in their natural environments, their life-history events (for example the leaf-out, flowering or leaf-coloring of plants, or the appearance, hatching, migration or reproduction of animals) must be timed well with particular environmental conditions. This is especially true for forest understory plants who flower in spring while the canopy in deciduous forest is still open and allows light to reach the forest floor. I used long-term data derived from herbaria to show that flowering time of forest wildflowers advanced around a week over the last century. However, the responses of plants differed significantly between regions in Europe. Thus, my analyses demonstrate, that it is crucial to account for geographic variation when analyzing phenology trends. I could further show that not only climate warming, but also land-use change affects the flowering time of these species. So far little is known about the impact of other global change drivers besides climate change on phenology. However, especially in forests, management that influence tree species composition and stand structure could affect the phenology of forest understory herbs through changes in radiation, microclimate or other factors. My analysis of field data (collected on 100 forest plots in Germany) showed that in intensively managed forests plants flowered around two weeks later than in unmanaged forests - partly, but not solely, because management altered microclimate. Such phenological shifts can have potential far-reaching ecological consequences – especially when for example plants and their pollinators shift differently and their synchrony gets out of tune. Therefore, it is important to understand why and how the phenologies of plants (and animals) shift to estimate the vulnerability of species, populations, and ecological communities to ongoing global change.