Abstract
One significant unanswered question about biotic responses to climate change is how plant communities within topographically complex landscapes will respond to climate change. Alpine plant communities are strongly influenced by topographic microclimates which can either buffer or compound the effects of more regional climatic changes. Here, we analyzed species changes over 20+ years in a complex alpine landscape with pronounced gradients in microtopography and consequently large variation in temperatures, snow depths, and nitrogen availability across small (10 m) scales. Using data from long‐term monitoring plots from six community types, we asked how species composition and functional diversity changed over time in these different areas of the landscape, and whether fine‐scale heterogeneity allowed species to move in response to temporal changes in the environment. We found site‐wide patterns of increasing species and functional diversity. However, the majority of variability in composition over time was non‐directional, both within and between community types. Within community types, Carex‐dominated snow banks and wet meadow communities were the most variable in composition over time, while Sibbaldia‐dominated snow banks, fellfield, dry meadow and moist meadow exhibited moderate change. Over forty percent of the plots also transitioned between community types during the census intervals, but these also were largely transient, with a shift occurring in one time interval and then shifting back in the next interval. Thus, even with evidence of directional change over time in climate, N deposition, and release from grazing, vegetation is tracking finer‐scale variability both in time and space. Environmental heterogeneity may allow vegetation to track this finer‐scale variability and enhance resilience to underlying directional changes in alpine and other topographically‐complex environments.
Highlights
Mountain ecosystems, and alpine ecosystems above treeline, are receiving much attention as systems sensitive to climate change (Diaz et al 2003, Korner 2003)
One reason for the call to refine the uphill migration paradigm is that alpine plant species distributions are limited by a complex suite of environmental factors rather than solely by temperature (Callaghan et al 2011, Gottfried et al 2012)
Many alpine plant species are strongly limited by snowpack and moisture availability (Engler et al 2011), with warming effects translating to stronger or weaker water limitation depending on the timing and amount of snowpack (Pauli et al 2012)
Summary
Alpine ecosystems above treeline, are receiving much attention as systems sensitive to climate change (Diaz et al 2003, Korner 2003). Variability in responses across mountain systems has caused some to challenge the assumption that climate change will cause a general uphill migration of plant species (Randin et al 2009, Engler et al 2011, Malanson et al 2012). One reason for the call to refine the uphill migration paradigm is that alpine plant species distributions are limited by a complex suite of environmental factors rather than solely by temperature (Callaghan et al 2011, Gottfried et al 2012). Many alpine plant species are strongly limited by snowpack and moisture availability (Engler et al 2011), with warming effects translating to stronger or weaker water limitation depending on the timing and amount of snowpack (Pauli et al 2012). Grazing can strongly mediate vegetation response to climate change, often dampening the influence of warming (Klein et al 2004, Speed et al 2012)
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