Fragile but resistant tundra vegetation in a warming climate

Tundra vegetation, the treeless vegetation in high latitude (arctic tundra) and high altitude (alpine tundra) areas, is expected to undergo dramatic changes due to global climate warming. A magnitude of changes has already been observed but some changes are lagging behind their expected velocity. An important question is that what controls changes in tundra vegetation besides climate, and can these factors decelerate or mitigate the effects of climate warming.
Solitary reindeer in tundra

Climate is warming two to three times faster in high latitude areas than the global average, predisposing arctic tundra vegetation to major changes. In alpine tundra, plants have no other way to escape warmer temperatures and upward spread of lowland plants than migrating upward themselves, making these systems especially strongly affected by climate change.

Climate change has already altered tundra ecosystems in many ways. Species adapted to warmer conditions have already migrated upward and treelines have shifted higher in elevation and latitude, shrinking the home range for tundra plants. Although tundra plants may be able to cope with warmer climate alone, a combination of higher temperature and competition from warm-adapted lowland plants may severely hamper their chances to survive. The timing of flowering and greening, phenology, has also changed, creating mismatches between plants, pollinators and grazing animals who depend on flowers and plant production as forage. For example, populations of caribou and reindeer in arctic tundra can suffer from altered phenology of plants which can also have impacts on people whose livelihood depends on grazing animals.

These changes are, however, not consistent everywhere and there are lags in vegetation responses to changing climate. There is “resistance” in tundra vegetation.

Tundra systems and vegetation are often regarded as “fragile” or “vulnerable”. But equally well one could consider tundra plants and ecosystems as tough and resistant. Plants in tundra compete fiercely for nutrients and can cope with very low resource levels. They also facilitate each other by providing shelter to neighbors and form alliances with other organisms like bacteria and fungi that can benefit them in nutrient-poor conditions. They grow incredibly fast during the short growing season and tolerate huge changes in climatic conditions while still maintaining growth. Especially in alpine areas, topography creates a mosaic of temperature, soil moisture, and nutrient conditions, due to which plants can cope with a variety of conditions. This small-scale heterogeneity in environmental conditions also provides safe sites where to escape when conditions change. Tundra plants can acclimate and adapt to novel conditions via changes in their functional traits, and these traits may also make them more resistant to changing climate.

The responses of tundra plants to climate change can strongly depend on grazing animals, such as reindeer and caribou, or livestock in alpine systems. By eating tree seedlings, shrubs, and more palatable lowland plants grazers can help small tundra plants that would otherwise suffer from competition with taller species. We know from experimental research that grazing can mitigate loss of tundra plant diversity and the expansion of taller shrubs to open tundra that would otherwise result from warming. Interactions with grazing animals can be therefore critically important in mitigating or delaying the effects of climate warming, and can make these systems more resistant to warming.

Some responses to climate warming may also be delayed because it takes time for plants to disperse to newly suitable habitats. Plants are sessile organisms, adult plants bound to stay where they are, and can move only via spreading seeds or sprouting vegetatively. If up- and northward movement is further impaired by reduced establishment success, because grazers eat seedlings and tree saplings, successful range shifts may take more time than expected.

Many tundra areas are naturally relatively nutrient-poor. This is partly because nutrients are bound to organic matter that decomposes slowly in cold conditions, and partly because of low nutrient content in tundra vegetation itself that produces material for decomposition. These patterns should change gradually under warmer climate when decomposition speeds up and tundra plants are replaced by more nutrient-rich lowland plants. However, initial invasion of lowland plants to open tundra may be hampered by nutrient scarcity, delaying the change in nutrient-poor areas.

Research that aims to increase understanding of contingencies that affect tundra plant responses to climate change is essential so that we can predict why, how, and where tundra vegetation changes or does not change. By understanding these contingencies, we can apply appropriate conservation measures, for example, by maintaining grazing in heavily affected areas, that help preserving this unique and beautiful biome and its biodiversity.

Further reading:

Alexander, J.M. (2017). Lags in the response of mountain plant communities to climate change. Global Change Biology 24: 563–579.

Bjorkman, A. et al. (2018). Plant functional trait change across a warming tundra biome. Nature 562: 57–62.

Eskelinen, A., Kaarlejärvi, E. & Olofsson, J. (2017). Herbivory and nutrient limitation protect warming tundra from lowland species’ invasion and diversity loss. Global Change Biology 23: 245–255.

Gottfried, M. et al. (2012). Continent-wide response of mountain vegetation to climate change. Nature Climate Change 2: 111–115.

Kaarlejärvi, E., Eskelinen, A., & Olofsson, J. (2017). Herbivores rescue diversity in warming tundra by modulating trait-dependent species losses and gains. Nature Communications 8, art. 419.

Körner, C., & Hiltbrunner, E. (2021). Why is the alpine flora comparatively robust against climatic warming? Diversity 13: 383.

Post, E. et al. (2019). The polar regions in a 2°C warmer world. Science Advances 5: eaaw9883.

Olofsson, J. et al. (2009). Herbivores inhibit climate-driven shrub expansion on the tundra. Global Change Biology 15: 2681–2693.

Prevéy, J.S. et al. (2019). Warming shortens flowering seasons of tundra plant communities. Nature Ecology & Evolution 3: 45–52.

The blog post is part of a series of blogs relating to multidisciplinary Arctic research at the University of Oulu.

Anu Eskelinen is an Associate Professor in Biodiversity Change and Ecosystem Health (tenure track) at Ecology and Genetics Research Unit. Her research focuses on understanding the consequences of multiple interacting anthropogenic global changes on plant communities and seeks to understand how global change impacts interact with biotic factors, such as herbivory and competition, to drive community resistance and resilience.