Exclusion of herbivores slows down recovery after experimental warming and nutrient addition in an alpine plant community

Abstract

Summary 1.Global change, such as climate warming and nitrogen deposition, has been predicted to induce non-reversible regime shifts in natural ecosystems. However, we lack knowledge of the potential for recovery from global change perturbations and factors influencing the recovery rate. 2. We examined the recovery of an alpine plant community from a combined warming and nutrient addition experiment, which initially caused profound changes in plant community composition and diversity. We also examined whether the recovery process was affected by herbivory, as the presence of herbivores has been shown to modify the response of plant communities to global change. 3. Many aspects of the alpine plant community had not recovered from experimental warming and nutrient addition 6 years after cessation of the treatments. A persistent shift in vascular plant species composition seemed to inhibit recovery and maintain a community dominated by highly competitive grasses at the expense of the previously dominating dwarf shrub Dryas octopetala, lichens and bryophytes. 4. The exclusion of herbivores decreased the community recovery rate by maintaining unfavourable conditions for lichens and bryophytes. 5. Synthesis. Our findings suggest that a shift in dominance hierarchies in arctic and alpine plant communities due to global change is not readily reversible. Herbivory may, however, facilitate plant community recovery.

Testing reliability of short-term responses to predict longer-term responses of bryophytes and lichens to environmental change

“…Despite this, the number of experimental environmental change studies on bryophytes and lichens is small. While numerous studies have investigated vascular plants in these severe environments, there are few that have resolution at species level or community responses that include bryophyte and lichen diversity (Bjerke et al, 2011;Klanderud, 2008;Lang et al, 2012;Olsen and Klanderud, 2014;Potter et al, 1995). Bryophytes and lichens are frequently used as ecological indicator species (Cristofolini et al, 2014;Mölder et al, 2015), but in experimental environmental change studies bryophytes and lichens are not usually identified at species level Hill and Henry, 2011).…”

Legacy effects of experimental environmental change on soil micro‐arthropod communities

“…Contrastingly, for Collembola and Oribatida species composition, we found differences in community composition between treatments and controls to persist nine years after cessation of the treatments. Although mammalian herbivory did influence community composition of both Collembola and Oribatida, it did not promote trajectories toward the original community composition as was found for the vegetation (Olsen and Klanderud ). Hemi‐edaphic Collembola that live near the soil–surface interface, in particular F. quadrioculata , were most responsive to environmental treatments and remained dominant in Collembola communities nine years after treatments were discontinued.…”

“…We propose several mechanisms that can explain why Collembola abundances returned to pre‐treatment levels, even though treatments are still visible in the vegetation composition (Olsen and Klanderud ; K. Klanderud, S. L. Olsen, and R. E. Roos, personal observation ). First, nutrient addition may have had a direct, stimulatory effect on the microbial and fungal community, which is an important part of the micro‐arthropod diet (Mack et al.…”

“…In addition, herbivory can act as a buffer against the effects of climatic change (Olofsson et al. ) and can decrease legacy effects of environmental manipulations (Olsen and Klanderud , Kaarlejärvi et al. ).…”

Sensitivity to environmental change of the treeline ecotone and its associated biodiversity in European mountains

“…Increased nutrient availability in the soil, either through artificial fertilization or increased decomposition, will change the species composition. In particular, the cover and frequency of lichen and bryophyte species are reduced, while graminoids and some deciduous shrubs are generally favored (Klanderud 2008, Olsen & Klanderud 2014. This change in species composition most often results in reduced biodiversity.…”