Modeling rates of life form cover change in burned and unburned alpine heathland subject to experimental warming (original) (raw)
Climate variability is expected to increase in future but there exist very few experimental studies that apply different warming regimes on plant communities over several years. We studied an alpine meadow community under three warming regimes over three years. Treatments consisted of (a) a constant level of warming with open-top chambers (ca. 1.9 °C above ambient), (b) yearly stepwise increases in warming (increases of ca. 1.0, 1.9 and 3.5 °C), and (c) pulse warming, a single first-year pulse event of warming (increase of ca. 3.5 °C). Pulse warming and stepwise warming was hypothesised to cause distinct first-year and third-year effects, respectively. We found support for both hypotheses; however, the responses varied among measurement levels (whole community, canopy, bottom layer, and plant functional groups), treatments, and time. Our study revealed complex responses of the alpine plant community to the different experimentally imposed climate warming regimes. Plant cover, height and biomass frequently responded distinctly to the constant level of warming, the stepwise increase in warming and the extreme pulse-warming event. Notably, we found that stepwise warming had an accumulating effect on biomass, the responses to the different warming regimes varied among functional groups, and the short-term perturbations had negative effect on species richness and diversity A growing number of studies have shown that a poleward movement of plant and animals is occurring. Although this trend has often been attributed to global warming, a simple northward movement of species cannot always be linked to climate change 1. Climate change may also affect interspecific interactions, including mutualism between animals and plants 2. However, the majority of existing studies are not evenly distributed among taxa or geography, and Europe and North America are commonly the source of these studies 3. In the future, extreme climatic events, such as droughts, floods, heavy rainfall and heat waves, will become more common and more severe 4 , which may impact species as well as whole ecosystems 5. How vegetation responds to extreme climatic events may depend on many factors 5 , such as functional diversity 6,7 , species diversity 8 , timing during succession, and various environmental factors 9. Climate change is already causing an increasing number of ecosystems to encounter novel climatic events. In some cases, plant communities and ecosystems may switch to alternative regimes in response to a single climate event 10,11. Heat waves have been observed to cause peat moss die-offs in the genus Sphagnum 12. The timing of the climatic event is also of consequence; however, the consequences may differ among species in the same plant community, for example, a study found a negative impact on the net photosynthetic rate of the bry-ophyte Hylocomium splendens, whereas the lichen Peltigera aphthosa was unaffected by experimentally imposed winter warming 13. Organisms in polar and alpine ecosystems are thought to be at high risk to be affected by climate change as the temperatures remain above freezing for a very short summer season. Thus, a vast number of experimental studies using open-top chambers (OTCs) have been performed in these ecosystems to simulate climate change. These studies cover a wide range of taxa, from singular species to the community-level responses of vascular