Contrasting Effects of Extreme Drought and Snowmelt Patterns on Mountain Plants along an Elevation Gradient

Despite the evidence that increased frequency and magnitude of extreme climate events (ECE) considerably affect plant performance, there is still a lack of knowledge about how these events affect mountain plant biodiversity and mountain ecosystem functioning. Here, we assessed the short-term (one vegetation period) effects of simulated ECEs [ extreme drought (DR), advanced and delayed snowmelt (AD and DE), respectively] on the performance of 42 plant species occurring in the Bavarian Alps (Germany) along an elevational gradient of 600-2000 ma.s.l. in terms of vegetative growth and reproduction performance. We demonstrate that plant vegetative and generative traits respond differently to the simulated ECEs, but the nature and magnitude treatment effects strongly depend on study site location along the elevational gradient, species' altitudinal origin and plant functional type (PFT) of the target species. For example, the negative effect of DR treatment on growth (e.g., lower growth rates and lower leaf nitrogen content) and reproduction (e.g., lower seed mass) was much stronger in upland sites, as compared to lowlands. Species' response to the treatments also differed according to their altitudinal origin. Specifically, upland species responded negatively to extreme DR (e.g., lower growth rates and lower leaf carbon concentrations, smaller seed set), whereas performance of lowland species remained unaffected (e.g., stable seed set and seed size) or even positively responded (e.g., higher growth rates) to that treatment. Furthermore, we were able to detect some consistent differences in responses to the ECEs among three PFTs (forbs, graminoids, and legumes). For instance, vegetative growth and sexual reproduction of highly adaptable opportunistic graminoids positively responded to nearly all ECEs, likely on the costs of other, more conservative, forbs and legumes. Our results suggest that ECEs can significantly modify the performance of specific plant groups and therefore lead to changes in plant community structure and composition under ongoing climate change. Our study therefore underlines the need for more experimental studies on the effects of extreme climate events to understand the potential consequences of climate change for the alpine ecosystem

Combined Effects of Extreme Climatic Events and Elevation on Nutritional Quality and Herbivory of Alpine Plants

Climatic extreme events can cause the shift or disruption of plant-insect interactions due to altered plant quality, e.g. leaf carbon to nitrogen ratios, and phenology. However, the response of plant-herbivore interactions to extreme events and climatic gradients has been rarely studied, although climatic extremes will increase in frequency and intensity in the future and insect herbivores represent a highly diverse and functionally important group. We set up a replicated climate change experiment along elevational gradients in the German Alps to study the responses of three plant guilds and their herbivory by insects to extreme events (extreme drought, advanced and delayed snowmelt) versus control plots under different climatic conditions on 15 grassland sites. Our results indicate that elevational shifts in CN (carbon to nitrogen) ratios and herbivory depend on plant guild and season. CN ratios increased with altitude for grasses, but decreased for legumes and other forbs. In contrast to our hypotheses, extreme climatic events did not significantly affect CN ratios and herbivory. Thus, our study indicates that nutritional quality of plants and antagonistic interactions with insect herbivores are robust against seasonal climatic extremes. Across the three functional plant guilds, herbivory increased with nitrogen concentrations. Further, increased CN ratios indicate a reduction in nutritional plant quality with advancing season. Although our results revealed no direct effects of extreme climatic events, the opposing responses of plant guilds along elevation imply that competitive interactions within plant communities might change under future climates, with unknown consequences for plant-herbivore interactions and plant community composition

Mixed effects model statistics of the response variable herbivory with the explanatory variables altitude, treatment, plant guild, sampling time and their interactions.

<p>The explanatory variable treatment was removed from the model as it was neither significant as single variable nor in the interactions. Herbivory was arcsine square root transformed. The final model is presented.</p

Relation between herbivory [%] and CN ratio of three plant guilds (grasses, legumes, forbs).

<p>The black line shows the significant relation between herbivory and CN ratio. **** <i>P</i>≤0.0001, n.s. <i>P</i>>0.1.</p

Experimental design with four treatments per study site.

<p>(A) advanced snowmelt, (B) delayed snowmelt, (C) drought treatment with rain-out shelter and (D) unmanipulated control. Each treatment plot measured 4×4 m and the distance between the plots was 1 m (Photos: A. Leingärtner and B. Hoiss).</p

Final day of snowmelt for three different treatments (advanced snowmelt, delayed snowmelt, control) on 15 study sites in relation to altitude.

<p>**** <i>P</i>≤0.0001</p

Effects of altitude, treatment and their interaction on CN ratio of three plant guilds (grasses, legumes, forbs) at three sampling times (A–I).

<p>CN data are presented as mean values per study site and treatment. Points symbolise the study sites and different colours represent the four treatments (blue: advanced snowmelt, green: delayed snowmelt, yellow: extreme drought, red: control). Black lines are based on the simplified model and show different slopes for CN ratio with altitude. Statistics see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0093881#pone-0093881-t001" target="_blank">Table 1</a>.</p

Herbivory [%] as a function of (A) treatment (advanced snowmelt, delayed snowmelt, extreme drought, control) and (B) plant guild (grasses, legumes, forbs) at three sampling times (mean ± se).

<p>**** <i>P</i>≤0.0001, n.s. <i>P</i>>0.1. Statistics see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0093881#pone-0093881-t002" target="_blank">Table 2</a>.</p

Smaller, more diverse and on the way to the top: Rapid community shifts of montane wild bees within an extraordinary hot decade

Aim Global warming is assumed to restructure mountain insect communities in space and time. Theory and observations along climate gradients predict that insect abundance and richness, especially of small‐bodied species, will increase with increasing temperature. However, the specific responses of single species to rising temperatures, such as spatial range shifts, also alter communities, calling for intensive monitoring of real‐world communities over time. Location German Alps and pre‐alpine forests in south‐east Germany. Methods We empirically examined the temporal and spatial change in wild bee communities and its drivers along two largely well‐protected elevational gradients (alpine grassland vs. pre‐alpine forest), each sampled twice within the last decade. Results We detected clear abundance‐based upward shifts in bee communities, particularly in cold‐adapted bumble bee species, demonstrating the speed with which mobile organisms can respond to climatic changes. Mean annual temperature was identified as the main driver of species richness in both regions. Accordingly, and in large overlap with expectations under climate warming, we detected an increase in bee richness and abundance, and an increase in small‐bodied species in low‐ and mid‐elevations along the grassland gradient. Community responses in the pre‐alpine forest gradient were only partly consistent with community responses in alpine grasslands. Main Conclusion In well‐protected temperate mountain regions, small‐bodied bees may initially profit from warming temperatures, by getting more abundant and diverse. Less severe warming, and differences in habitat openness along the forested gradient, however, might moderate species responses. Our study further highlights the utility of standardized abundance data for revealing rapid changes in bee communities over only one decade