Natural, Anthropogenic Disturbances Can Reduce Resistance of Ecosystems to Changing Climatic Conditions

Undisturbed ecosystems can be resistant to changing climatic conditions, but this resistance is reduced when ecosystems are subject to natural or anthropogenic disturbances. Plants are particularly sensitive to climatic changes in early life stages and even small climatic changes can cause vegetation shifts when ecosystems are disturbed by fires, insect outbreaks or other disturbances.

This is the conclusion from one of the world's longest running climate change experiments conducted by the European network INCREASE, involving scientist from several European countries and headed by professor Inger Kappel Schmidt at the University of Copenhagen's Department of Geoscience and Natural Resources Management. The results have been published in an article in the international scientific journal "Nature Communications".

Two of the network's climate studies were situated in Danish heathland ecosystems. The results of the study showed that climate change impacts on the vegetation were minimal in undisturbed heathland. However disturbances occur commonly in heathlands and other ecosystem and it appears that recovery is dependent on climate: "After a heather beetle outbreak heather plants re-established in control plots, but not in plots subjected to extended summer drought. The combination of disturbance and drought caused a shift from heathland to grassland" says Professor Inger Kappel Schmidt.

Results from the experimental sites in the other countries also confirmed the importance of disturbance for ecosystem responses to climate change. "The long-term impact of climate change on plant communities is more dependent on short periods where plants are relatively vulnerable, like regeneration phases, than on the longer periods between disturbances where established vegetation is relatively robust." says Johannes Ransijn, Postdoc at KU IGN and one of the lead authors of the article. "The higher sensitivity after disturbance should also be considered by land managers. Reducing disturbance intensity and frequency in ecosystems could help making them less vulnerable to climatic change."

The study demonstrates that many ecosystems are resistant to climate fluctuations. But even small climatic changes can have lasting effects on ecosystems when they are subjected to disturbances such as fires or insect outbreaks. The research points out that disturbance and successional stage should be considered when predicting ecosystem responses to climate change.