Reference: Steinbauer, M.J. et al. (2018) Accelerated increase in plant species richness on mountain summits is linked to warming. Nature, 558: 231-234. DOI: 10.1038/s41586-018-0005-6. (https://www.nature.com/articles/s41586-018-0005-6)
Plants, mountains and climate change
As a forester by training, and a nature enthusiast since childhood, I have always been attentive and marveled by vegetation and where they grow, and what drives their development. In my occasional mountain hikes (for work or leisure) at various places (deserts, tropical forests, Andes, temperate forests, etc.) I have always been amazed by the strength and little resources mountaintop plant species can live from. For example, in high altitude grasslands of Ecuador, you can find small communities of plants that live and grow on top of rocks and have adapted their leaves and roots to capture as much fog as possible. Such specializations makes it hard to for this type of plant to migrate when fog occurrence decreases, which has been documented in recent years for the Ecuadorian páramos (1). Unfortunately, this is not exclusive to the páramos, and has been documented across various environments and vegetation types around the world as climate change increases at a rapid rate.
Climate change is leading to many negative impacts to our world, including melting icecaps, sea-level rise, intensification of extreme weather events, droughts, wildfires, increase in vector-borne diseases and many more. Climate change is also responsible for many species getting displaced from their natural habitat, making it the major threat to Earth of our generation. The global trend of sea and air temperature warming have been shown to directly impact living organisms, for instance by delaying the reproductive season of larval fishes (2) and shifts on timing of tree flowering, fruiting and leafing (3). Unlike animals, plants cannot readily “escape” and change habitats if climate change causes their environment to deteriorate. As a result, if plants that are not evolutionarily adapted to a wide range of habitat conditions are highly susceptible to large mortality rates.
The most vulnerable plants are those which grow in sites with extreme climate conditions, but little seasonal variation. For instance, mountaintop plant communities are adapted to cold temperatures, occasional frost and strong winds all year round, and can be very sensitive to a change in climate. A recent study conducted in multiple mountaintop sites in Europe has found compelling evidence that there has been an increasingly higher number of alpine and high-altitude plant species as a result of climate change.
FIGURE 1. Example of European mountain summit environment studied for this research. Picture from Switzerland alps (Source: Flickr)
145 years and 87% more species later…
This study by Dr. Manuel Steinbauer (Aarhus University, Denmark) and collaborators was based on surveys conducted since 1871 on 302 European mountain summits (including nine mountain regions). By using this impressive and rich dataset, the authors addressed the ultimate question: “Does the recent acceleration of climate change drive a similar acceleration of change in species richness in European mountaintops?”.
The authors showed that number of alpine plant species increased in all European mountain summits during the past 145 years, and that the rate of increase has been fastest in the past 20-30 years. The authors also found warming air temperature played a major role throughout all regions, while the effects of changes in precipitation varied with region. This proves that warming is the primary driver of upward shifts of plant species in mountain ecosystems.
But wait: isn’t that a good thing?
Although an increase in the number of plant species might sound positive, it is an alarming sign that rare and exclusive slow-growing alpine plant species are not surviving and, thus, being replaced by more resistant lower-elevation “warm-temperature-loving” plants. The authors recognize that there might be a time-lag between fast-growing, invasive plants and how long it would take to fully overcome the native alpine plants. Consequently, the increase in species richness maybe considered as a short-lasting phenomenon that hides a more critical extinction rate. The growth and time of extinction depends on factors such as the longevity of high-elevation species, plant clonal abilities and the local microclimate diversity. Hence, if global warming continues to accelerate at its current pace irreversible tipping-points maybe approached sooner than expected. Alpine and high-altitude plants have major roles in the water cycle. If such species are gone, water supply to local communities can be compromised, along with more severe effects on the local vegetation.
FIGURE 2: Close-up of the diversity within an European alpine plant community (Source: Flickr)
“It’s getting hot up here!”
This publication is a major “eye-opener” for people that care about the environment, especially plants. The astounding fact that increase in species number has grown five times as quickly the last 20-30 years compared to previous decades is already very worrisome. However, the dangers to rare alpine species does not end there. They are also threatened by popular anthropogenic activities, such as tourism and grazing, which are not always well regulated. This study supports a wide body of work indicating that climate change can cause irreversible damage to our biodiversity, and we will have to undertake better conservation efforts to avoid reaching the tipping point. During your next mountain hike, stop and look around, and try to see if the plants you used to see are not looking the same for the season; or they are not there anymore; or a larger number of unknown plants have taken its place. I would not be surprised if you see all the above.
FIGURE 3. Example of cattle grazing on native alpine plants in Europe (Source: Flickr).
(1) Aparecido, L.M.T. et al. (2018) Ecohydrological drivers of Neotropical vegetation in montane ecosystems. Ecohydrology, e1932. DOI: 10.1002/eco.1932.
(2) Asch, R.G. (2015) Climate change and decadal shifts in the phenology of larval fishes in the California Current ecosystem. PNAS, 112 (30) E4065-E4074. DOI: 10.1073/pnas.1421946112.
(3) Cleland, E.E. et al. (2007) Shifting plant phenology in response to global change. Trends in Ecology & Evolution, 22 (7) 357-365. DOI: 10.1016/j.tree.2007.04.003.