Reviewed: Steinbauer MJ, Grytnes JA, Jurasinski G, et al. Accelerated increase in plant species richness on mountain summits is linked to warming. Nature. 2018;556(7700):231-234.
Climate warming is affecting many natural habitats, including mountainous regions. Mountain summits, which serve as natural, permanent study sites that are easy to find, are well-suited for long-term studies of biotic responses to environmental changes. Records of vegetation on European mountain summits date back more than a century. Thus, it is possible to resurvey the occurrences of plant species in these locations and determine changes in the number of species over time. The authors of this journal article resurveyed plant communities on European mountain summits and assessed trends in plant diversity dynamics. They sought to determine whether climate warming is accelerating changes in plant species richness (i.e., the number of plant species in any given location).
This study is based on 698 surveys, dating from 1871, of 302 European mountain summits with historical vegetation records. For each survey, the authors assessed all plant species generally occurring on the top 10 meters of elevation. For each summit, the authors calculated the mean monthly temperature and precipitation and analyzed changes in species richness across the summits for the entire time period. They reported that the number of plant species has significantly increased during the past 145 years on 87% of the surveyed European mountain summits (P < 0.001), with an accelerated increase during the past 20 to 30 years. This trend was observed for all nine geographic regions studied.
From 1957 to 1966, the summits gained an average of 1.1 species, and from 2007 to 2016, the summits gained an average of 5.4 species. A positive relationship was observed between the magnitude of increase in plant species richness and the rate of warming across all sampled mountain summits (P < 0.001).
Although precipitation change had a moderate positive effect on changes in species richness across Europe, the effect was not consistent or significant compared with the effect of temperature change in the studied regions.
The authors also observed growth strategies in new plant colonizers that are characteristic of species from lower elevations, such as larger size (P < 0.001), greater specific leaf area (P < 0.001), and association with warmer temperatures (P < 0.001), compared with established species. As more species become established at higher elevations, the slow-growing alpine species may be replaced by more vigorous generalist species that benefit from warming. However, according to the authors, replacement of resident species requires large populations of new colonizers.
From 364 resurveys that included 12,738 observations of 873 species, plant trait values of new established colonizers were compared with those of species found in previous surveys. New colonizers had significantly greater specific leaf area (P < 0.001) and plant height (P < 0.001) compared to resident species, but there were no significant differences in seed mass (P = 0.85). According to the authors, the new species also adapted to warmer climates better than resident species (P < 0.001).
Local studies suggest that grazing and frequent disturbance by tourists may suppress the upward advance of alpine plants in response to warming on mountains. However, “Without a consistent impact on species re-distribution, it is unlikely that changes in grazing and tourism can account for the consistent continent-wide increase in plant species richness evident in our data,” the authors noted.
The findings of this study support the hypothesis that climate warming is the primary driver of the upward shifts of species on mountains and agree with shorter-term studies demonstrating that the number of cold-adapted plant species is declining while those that prefer warmer conditions are increasing.1-3
According to the authors, results of this study “provide a particularly compelling example of the human-driven impact on terrestrial biota” that is consistent with the Great Acceleration, a term that refers to the hastening trends in societal development and human impact on the environment since the mid-20th century. They conclude that the “accelerating increases in species richness on mountain summits across this broad spatial extent demonstrate that acceleration in climate-induced biotic change is occurring even in remote places on Earth, with potentially far-ranging consequences not only for biodiversity, but also for ecosystem functioning and services.”
- Gottfried M, Pauli H, Futschik A, et al. Continent-wide response of mountain vegetation to climate change. Nat Clim Chang. 2012;2:111-115.
- Bertrand R, Lenoir J, Piedallu C, et al. Changes in plant community composition lag behind climate warming in lowland forests. Nature. 2011;479(7374):517-520.
- Alstad AO, Damschen EI, Givnish TJ, et al. The pace of plant community change is accelerating in remnant prairies. Sci Adv. February 19, 2016;2(2):e1500975. doi: 10.1126/sciadv.1500975.