Summer aridity rather than management shapes fitness‐related functional traits of the threatened mountain plant Arnica montana

Abstract

Semi‐natural mountain grasslands are increasingly exposed to environmental stress under climate change. However, which are the environmental factors that limit plants in these grasslands? Also, is the present management effective against these changes? Fitness‐related functional traits may offer a way to detect changes in performance and provide new insights into their vulnerability to climate change. We investigated changes in performance and variability of functional traits of the mountain grassland target species Arnica montana along a climate gradient in Central German low mountain ranges. This gradient represents at its lower end climate conditions that are expected at its upper end under future climate change. We measured vegetative, generative, and physiological traits to account for multiple ways of plant responses to the environment. Using mixed effects and multivariate models, we evaluated changes in trait values among individuals as well as the variability of their populations in order to assess performance under changing summer aridity and different management regimes. Fitness‐related performance of most traits showed strongly positive associations with reduced summer aridity at higher elevations, while only specific leaf area and leaf dry matter content showed no association. This suggests a higher performance level at less arid montane sites and that the physiological traits are less sensitive to this climate change factor. The coefficient of variation of almost all traits declined steadily with decreasing site aridity. We suggest that this reduced variability indicates a lower environmental stress level for A. montana toward its environmental optimum at montane elevations, especially because the trait performance increased simultaneously. Surprisingly, management factors and habitat characteristics had only low influence on both trait performance and variability. In summary, summer aridity had a stronger effect to shape the trait performance and variability of A. montana under increased environmental stress than management and other habitat characteristics.

Drought stress triggers differential survival and functional trait responses in the establishment of Arnica montana seedlings

“…Weißhuhn et al, 2011;Larson & Funk, 2016;Ludewig et al, 2018). It is noteworthy that these responses to drought also correspond to earlier observations on adult A. montana along an aridity gradient, where plants in drier sites had smaller trait values (Stanik et al, 2020). In that study, reproductive capacity declined at dry sites, while in the current study vegetative reproduction of juveniles was reduced with increased drought.…”

“…In the present study, limitations of the experimental approach to evaluate drought effects on seedlings can arise from the experimental set up, even when the experimental drought treatments reflect current climate conditions for A. montana lowland populations in Central Europe (Stanik et al, 2020). The experiment considered a competition-free environment, characterised by edge effects, e.g.…”

“…Based on the temperature and precipitation regimes, the treatments differed in their whole-month mean aridity (after Martonne, 1926) between May and August: treatment T0 aridity 3.51 AE 0.23, T1 2.43 AE 0.19 and T2 1.39 AE 0.11. The aridity of T0 and T1 thus represent current climates in Central European sites at elevations of approximately 500 and 200 m a.s.l., respectively, (Stanik et al, 2020).…”

“…Hence, functional trait performance, the combined effects of functional traits on plant vigour (cf. Stanik et al, 2020), can provide insights into the actual threats to seedling survival well before a species starts to disappear from a site. Therefore, knowledge about the ecological response of seedlings to drought is of high ecological relevance to obtain a comprehensive assessment of drought impacts on species.…”

Extreme droughts in oligotrophic mountain grasslands cause substantial species abundance changes and amplify community filtering

“…low‐productive species) and species from agricultural grasslands increased, which changed to an increase in character species later in the experiment. This subsequent increase also included species with a clear montane distribution, like Arnica montana , for which negative functional trait responses to climate stress have been identified (Stanik et al, 2020). However, these low competitive species might have benefited from more suitable community structures, owing to the less dense and lower herb and moss layer in the years after the most severe drought in 2018 (Hollmann et al, 2020).…”