Abstract
Global warming leads to drastic changes in the diversity and structure of Arctic plant communities. Studies of functional diversity within the Arctic tundra biome have improved our understanding of plant responses to warming. However, these studies still show substantial unexplained variation in diversity responses. Complementary to functional diversity, phylogenetic diversity has been useful in climate change studies, but has so far been understudied in the Arctic. Here, we use a 25 year warming experiment to disentangle community responses in Arctic plant phylogenetic β diversity across a soil moisture gradient. We found that responses varied over the soil moisture gradient, where meadow communities with intermediate to high soil moisture had a higher magnitude of response. Warming had a negative effect on soil moisture levels in all meadow communities, however meadows with intermediate moisture levels were more sensitive. In these communities, soil moisture loss was associated with earlier snowmelt, resulting in community turnover towards a more heath-like community. This process of ‘heathification’ in the intermediate moisture meadows was driven by the expansion of ericoid and Betula shrubs. In contrast, under a more consistent water supply Salix shrub abundance increased in wet meadows. Due to its lower stature, palatability and decomposability, the increase in heath relative to meadow vegetation can have several large scale effects on the local food web as well as climate. Our study highlights the importance of the hydrological cycle as a driver of vegetation turnover in response to Arctic climate change. The observed patterns in phylogenetic β diversity were often driven by contrasting responses of species of the same functional growth form, and could thus provide important complementary information. Thus, phylogenetic diversity is an important tool in disentangling tundra response to environmental change.
Highlights
High-latitude climate change, characterized by above-average warming and increases in precipitation (Stocker et al 2013, Pithan and Mauritsen 2014, Vihma et al 2016), has drastic consequences for highlatitude ecosystems and their biodiversity (Post et al2009, Elmendorf et al 2012b)
Since climate change has accelerated during the 25 years the study has proceeded, we hypothesize that the ambient plots have experienced changes in the phylogenetic β diversity. We expect these responses to increase in magnitude over the soil moisture gradient and vary among community types as these have been found to be important factors in modulating plant functional type and trait responses to warming (Elmendorf et al 2012a, 2012b, Bjorkman et al 2018). Using this improved measure of phylogenetic β diversity we aim to improve our understanding of how warming influences Arctic plant community structure over soil moisture gradients, and disentangle some of the hitherto masked responses within growth forms seen in biome-wide Arctic syntheses (e.g. Elmendorf et al 2012a, 2012b, Bjorkman et al 2018)
We observed a significant increase in dispersion in phylogenetic β diversity over time in warmed mesic (F2,15 = 4.62, P = 0.02) and wet (F3,16 = 7.2, P = 0.01) meadow communities, as is shown in the non-metric multidimensional scaling (NMDS) plots (figures 3(a) and (b))
Summary
High-latitude climate change, characterized by above-average warming and increases in precipitation (Stocker et al 2013, Pithan and Mauritsen 2014, Vihma et al 2016), has drastic consequences for highlatitude ecosystems and their biodiversity (Post et al2009, Elmendorf et al 2012b). Measures of functional diversity, such as the diversity of growth forms and functional traits, have received significant scientific attention as they provide more readily interpretable mechanistic drivers for plant community feedback (Chapin et al 1995, Myers-Smith et al 2011, Elmendorf et al 2012a, 2012b, Bjorkman et al 2018). Biome-wide syntheses (Elmendorf et al 2012a, 2012b, Bjorkman et al 2018) of plant functional responses to experimental and ambient warming have shown increases in shrub abundance and in vegetation height, effects that lower the surface albedo (Sturm et al 2001). Soil moisture has emerged as an important factor modulating plant functional type and trait response to warming (Elmendorf et al 2012a, 2012b, Bjorkman et al 2018), though plot-scale soil moisture changes are rarely considered as potential drivers of community change
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