Some of the biggest effects of climate warming are being observed in the polar regions; but the climate in mountainous regions are also rapidly changing. For example, the rate at which climate change is happening in the European Alps, is more than double that of the average across the Northern Hemisphere.
Plants are moving pole-ward and uphill trying to keep up with the climate they thrive in. Clear examples of this are treelines that are advancing uphill (but that doesn’t happen everywhere). We know that plants adapted to cold climates are being driven out of their natural ranges – and in the mountainous areas they might run out of space! However, beyond observing changes in the distributions of species, we still have a very poor understanding of the processes that accompany the climatic changes occurring in mountainous areas.
Sweden-based Dr. Jordan Mayor and David Wardle (SLU in Uppsala), organised and set up a study with an international research team, including myself, to investigate whether, at a global scale, we see universal shifts in ecosystem properties across elevational gradients. Our paper was published in Nature this week.
Mayor J, et al. Elevation alters ecosystem properties across temperate treelines globally – Nature, 25 Jan 2017 nature.com/articles/doi:10.1038/nature21027
The long-term and broad-scale changes that are instigated by climate change are hard to study using experiments. So instead, we used elevation as a surrogate for climate warming. This is possible because, as a consequence of warming, in 80 years from now, any particular elevation is expected to experience the temperature that is currently found 300 meters lower. Studying the properties of vegetation and soil along elevational transects near the treelines in seven regions (including the European Alps, Hokkaido Japan, Rocky Mountains USA-Canada, Patagonia, New Zealand, and Australia) allowed us to predict the effects of warming across temperate mountain regions world wide.
We found remarkably consistent patterns across these extremely varied mountain regions. Decreasing elevation (increasing temperature) consistently increased the availability of soil nitrogen for plant growth – so we can expect that warming will consistently improve plant nitrogen nutrition. However, plant phosphorus availability was not controlled by elevation (and thus temperature) in the same way. This resulted in a pattern where the balance of nitrogen-to-phosphorus in plant leaves was very similar across the seven regions at higher elevations, but diverged greatly across the regions at lower elevation. This means the nitrogen-to-phosphorus ratio is constrained by low temperatures but at higher temperatures, regional factors and differences between regions become more important.
We also found that with increasing temperature, the patterns in plant nutrition were paralleled by changes in the amount and quality of organic matter in the soil and the microbial community. Our study allowed us to untangle the effects of vegetation type (forest below treeline, and alpine above it) on these patterns, and we found that the changes were at least partly independent of any effect of the vegetation. This means that effects of warming on ecosystem properties will occur irrespective of whether treeline shifts up-slope.
Our results not only suggest that warming could affect the way that plants grow, but also that these changes are linked to effects of warming on soils, especially the cycling of key nutrients that sustain the growth of plants. It provides evidence that expected temperature changes over the next 80 years have the potential to greatly disrupt the functional properties of mountain ecosystems and result in increased disequilibrium in the above- and below-ground ecosystem components, and the links between them.
The changes in mountain ecosystem processes identified in this study may have important implications for which plants grow in mountain ecosystems (affecting biodiversity), and the potential upward shift of treelines. Such shifts are expected have an effect on the local climate itself, and may indeed speed up the warming process, as forests reflect less and retain more heat than lower, less green vegetation.
We used elevational gradients to predict what will happen in mountainous ecosystems as the climate warms – this is a powerful approach to understanding the processes that are occurring at an increasing pace in these areas. However such changes are also likely to occur in lower lying areas. Much remains unknown about how human-driven climate change will affect the Earth in the long-term and over larger spatial scales.
This article in the news:
Manchester university Study reveals that climate change could dramatically alter fragile mountain habitats. Related content also reported by Phys.org , Reddit.com , New Zealand Ministry of Foreign Affairs , EurekAlert
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