Continent-wide response of mountain vegetation to climate change
In a nutshell ▼
Temperatures on mountain summits are colder than at lower elevations, and the plants found there are adapted to cope with these lower temperatures. When the paper was written, the decade 2000–2009 was the warmest so far recorded. Many computer models predict that plant species richness (the number of plant species found in an area) in high altitude mountain areas will increase as the climate warms. Previous studies have shown this to be true in many places.
This may initially sound like a good thing, but it actually indicates that many plants growing lower down mountain slopes (where it is warmer) are expanding their ranges upwards. As they do so, they compete with the cold-adapted species. These tend to be short and slow growing plants that are less able to compete for light and nutrients against larger, faster-growing species. Declines in extreme high-altitude species at their lower range margins have recently been observed in the Alps.
Much of what we know about changes in mountaintop plant communities comes from a small number of studies at a limited number of sites. In contrast, this study was much broader. Plants were recorded at 60 sites covering 17 major European mountain regions. Data from the ECN Cairngorms site enabled the extreme northwestern part of Europe to be represented in the study.
The researchers used a standard method to make data comparison easier. They recorded plants in 2001 and again in 2008. They also measured soil temperature in these recording plots at hourly intervals from 2001 to 2007. Using information about the altitudinal range that each plant species tends to inhabit, the researchers worked out a value called the thermic indicator.
They then looked at how this indicator changed between 2001 and 2008. A positive change indicated a shift towards plant species preferring lower altitudes (that is, plants that are better adapted to warmer temperatures).
Taking all the data together, the scientists found a positive change in the indicator at the European continental scale. For 16 of the 17 regions, and 42 of the 60 summits, the mix of plant species had shifted towards more warm-adapted species between 2001 and 2008.
To investigate whether a change in temperature might have driven the observed changes, the team used the difference in mean temperature for two periods prior to their surveys. These prior periods were 1996-2000 (prior to 2001) and 2003–2007 (prior to 2008). The observed change in plant communities correlated well with the pattern of temperature change across Europe between these two periods, i.e. larger changes tended to be seen at sites experiencing the greatest temperature change.
The observed change took place in less than a decade, which the paper's authors say is a rapid ecosystem response.
About 2,500 vascular plant species – approximately 20% of the Europe’s native vascular flora – inhabit the alpine zone from the treeline up to the highest mountain summits. The results of this study indicate a progressive shrinking of low-temperature, high-elevation habitats.
The European Union has set ambitious targets to halt the loss of biodiversity by 2020. The potential loss of alpine species – many of them beautiful and remarkable plants, uniquely adapted to their environment – should therefore be a cause for concern, especially given that not only plants are at risk. Plant communities support a wide variety of animal species, from insects and other invertebrates to larger animals like birds and mammals. Hence, when plants are threatened by rising temperatures, so too are the species that rely upon them.
This study, along with others, suggests that mountaintop plant communities are vulnerable to rising temperatures. Plant species richness on the summits appears to be increasing. However, this comes at a price: the loss of those species that have evolved to live in cold regions.
▲The tops of mountains are generally colder than lower down their flanks. Plants on mountains tend to have preferred altitude ranges.
▲In Europe, and indeed globally, average temperatures are increasing.
▲This study, along with others, found evidence that the mix of plants on many mountaintops is changing. Plants that prefer lower altitudes, where it is warmer, are expanding their ranges and growing higher up.
▲Plants that prefer colder conditions have to compete with the new arrivals. Because they tend to be slower growing and smaller, they may struggle to compete for light and nutrients.
▲Because they already inhabit the highest altitudes available, these species risk local and even regional extinction as they have no space to migrate into. As a consequence, the biodiversity of these habitats is also threatened.