Atmospheric and climatic change affects fundamental drivers of ecosystem processes and is therefore likely to affect structure and functioning of terrestrial ecosystems. Such changes have been investigated over recent decades by a large number of field scale ecosystem experiments manipulating water, temperature or CO2. Most such experiments have applied single factors and only in a few cases multifactor experiments were applied. The single factor experiments often support our hypothesis for above and belowground responses to the individual factors. However, recent findings suggest that the responses to climate change involving all climate change factors may not be easily upscaled from our single factor understanding because of non-linear interactions among the climate change related factors. Another complicating factor is that impacts of extreme events may not be well known and tested from past experiments. These complications are well illustrated by CLiMA!TE, a long term multifactor climate change experiment in Denmark. CLIMAITE exposed a shrubland ecosystem to moderate changes in temperature, CO2 and water in all combinations.
Results/Conclusions
After 8 years of treatments the results show that the responses to the individual factors cancel out each other in many cases when the factors are combined. Consequently, the effects of the full combination of all climate change factors are often insignificant relative to the untreated control. The effects of the full suite of pressures may therefore not be easily predicted from the individual responses. This is true for both specific plant and soil processes as well as aggregate processes at the system level such as net ecosystem exchange. In a world where the majority of our knowledge related to impacts of climate drivers comes from single factor experiments, this has of course implications for our ability to upscale results to combined drivers over longer time spans. However, it has to be born in mind, that these findings to some extent may reflect the fact CLiMA!TE applied relatively moderate treatments, while more extreme changes as forecasted for the future were not tested. Such extreme changes may have significant importance for long term impacts of climate change but these also involve an additional challenge for field scale experimentation.