Climate Change Impacts on Alpine Plant Communities

Argument Statement

Climate change will cause widespread loss of fragile plant species in alpine ecosystems.

Introduction

Alpine plant communities are particularly sensitive to climate change. Their habitats are restricted by elevation, temperature, and precipitation. Although it is generally well understood that climate change will impact fragile alpine plant communities, there is not a solid understanding of how to mitigate these impacts. The challenges alpine plants across the globe will face due to climate change will result in significant loss of plant species in alpine ecosystems. This literature review seeks to use the current knowledge base surrounding climate change impacts on alpine plants to affirm climate change will cause significant loss, and potentially extinction of plants in alpine ecosystems.

The impacts of climate change on alpine ecosystems are widespread. There are a variety of alpine ecosystems across the world which will react differently to climate change, but almost all of them are likely to suffer under these changes (e.g. Mizel et al., 2016; Watts et al., 2023; Steinbauer et al., 2022; Nigro et al., 2022). Alpine areas will undergo changes in temperature, snowpack, and precipitation (IPCC, 2023). These changes will have an overwhelmingly negative effect on fragile alpine plants that rely on specific timings and conditions in their ecosystems.Alpine plants provide many benefits to their ecosystem.

They prevent soil erosion, stabilize slopes, and provide nutrients for wildlife (Lobmann et al. 2020; Watts et al., 2022). Additionally, these plants contribute to carbon storage which can help slow climate change (Zhang et al. 2021). Thus, a widespread loss of alpine plants would likely result in increases in soil erosion on alpine slopes, and could lead to a decline in animal and insect populations that currently rely on them for food and shelter.

Impacts

The impacts of climate change on alpine plants are plentiful, although more research is necessary to fully understand how alpine ecosystems will change with the climate (Verrall & Pickering, 2020). The most obvious and direct impacts are changes to snow, temperature, and water availability in alpine communities. However, these direct impacts have ripple effects upon plant communities. For example, a change in snow cover can impact flowering times and subsequently availability of pollinators (Inouye, 2008). Additionally, due to shifts in temperature and water availability, trees, shrubs, and forbs are moving upwards in elevation. These plants will ultimately outcompete higher elevation alpine plants which shrinks their range even further (Watts et al., 2023; Steinbauer et al., 2022).

This section outlines the most severe and threatening impacts of climate change on alpine plant communities including temperature, changing snowpack, drought, range shift, and plant maladaptation.

Temperature

Temperature plays a substantial role in the way alpine ecosystems function. Temperature in large part determines the timing of snow melt, how thick winter snowpack will be, and whether precipitation will fall as snow or rain (IPCC, 2023). Alpine plants are cold adapted meaning that they can survive in colder temperatures than most other plants. They rely on a specific snow and temperature synchronized chronology for many of their processes including flowering (Inouye, 2008). Frost can freeze plants that emerge from the snow too quickly, and can also prolong growing seasons (Wipf et al. 2009). Cold temperatures contribute to determining tree lines that mark the boundary between subalpine and alpine zones. Additionally, higher temperatures can increase species richness in alpine plants and insects. Although this may seem like a benefit, these effects can lead to changes in species composition and result in a decline in some plants due to being outcompeted by plants that thrive in higher temperatures (Ohlar et al. 2020).

The effect that warming has differs greatly between alpine plant species. It is believed that this individualistic response to warming can be predicted by phylogeny or by a plant’s microbial communities. In the Rocky Mountains, warm temperatures reduced alpine plant abundance by 2.3% per year in their southern range margins (Lesica and Crone, 2016). This can make it difficult to predict how alpine plant communities will respond to climate change. Regardless, the rising temperatures associated with climate change will cause all mountain ecosystems to undergo changes that will impact the plants that inhabit them. In large part, the warmer temperatures will contribute to alpine plant population decline or replacement by lower elevation plant species that are better adapted to warmer temperatures.

Snow Impacts

Due to rising temperature and changing seasonal precipitation patterns, winter snow cover in alpine environments is changing rapidly (IPCC, 2023). The ratio of snow to rain is decreasing, snowpack is thinning, and snow cover duration is contracting. Already, mountain ecosystems have warmer growing seasons that last longer, and these changes will only get more dramatic over time (IPCC, 2023). These changes are shown to have strong impacts on the alpine plant communities. Although the projected longer and warmer growing seasons would have positive effects on plant ecosystems, it has been found that this benefit will not outweigh the drawbacks of thinner snowpacks and resulting colder winters for plants (Wipf et al. 2009). Snow acts as an insulator for plant species during the winter and protects plants from the extremely cold temperatures that occur in mountain ecosystems. Thinning of the snowpack and early melting can expose alpine plants to frost, and therefore reduces aboveground growth in most species (Wipf et al. 2009).

The timing of the growing season depends on snowmelt and heat sum in the early summer (Inouye, 2008; Kudo, 2020). The difference between temperature and snowmelt is an important distinction because the timing of snowmelt is fairly variated, but rising temperatures are more consistent. Flowering patterns that depend on temperature typically exist where little snow cover exists, while flowering patterns that are determined by snowmelt occur in areas that experience snowier winters (Kudo, 2020). Plants that wait until snowmelt to put forth their flower buds are at significant risk due to climate change. The new mismatch in timing between snowmelt and the beginning of the growing season can be harmful for plant development. This is partly because flower buds are particularly fragile to cold temperatures. The loss of flower buds to frost can lead to a reduction of seed production and subsequently a loss of recruitment of plant populations (Inouye 2008).

Regardless of whether a plant flowers based on temperature or melting snowpack, phenological mismatch between new flowering times and plant- pollinator reactions is predicted to increase plant and pollinator loss in alpine ecosystems (Inouye, 2008). Bumblebees are the most important pollinators for alpine plants. Bumblebees are most active in late July and August. (Mizunaga et al., 2017). In the future, plants are expected to bloom earlier. This means that there will be fewer flowers to sustain bumblebees, and fewer bumblebees to pollinate alpine flowers (Kudo, 2020).

Drought

Climate change is already causing more pronounced drought in many areas. Higher temperatures are leading to increased evapotranspiration, and it is projected that future climate will lead to shifts in seasonal precipitation patterns (IPCC, 2023). Increased rates of evapotranspiration can have negative effects on plant growth due to a decrease in soil moisture (Xue et al., 2022). In mountainous regions affected by drought, there will be an loss of habitability of mountain ecosystems for alpine plants.

Some alpine plants are less resistant to drought than other lowland plant species, as one study found along an elevational gradient in the Bavarian Alps (Rosbakh et al., 2017). Additionally, drought damage to alpine plants strongly amplifies the stress they experience when exposed to rising temperatures (Buchner et al., 2017). These sensitivities to drought could cause some alpine plants to decline rapidly in their ranges.

Many scientists are currently examining the effects of drought on alpine plants in different mountainous ecosystems. In a recent study in the Alps, Apennines, and Mediterranean mountain regions, it was not found that there was significant biodiversity loss due to drought (Steinbauer et al., 2022). However, other studies have reported losses of plant productivity and clear signs of drought stress, especially in conjunction with warming temperatures (De Boeck et al., 2016; Xu et al., 2021). As climate change becomes more extreme, more alpine ecosystems are anticipated to undergo amplified species loss due to drought, especially in areas where the majority of plant species are not adapted to be drought tolerant.

Range Shift, Disappearing Habitat, and Out-competition

Mountain ecosystems experience harsh conditions that act as a barrier for many plant species. Alpine plants are adapted to withstand freezing temperatures, high levels of UV radiation, strong winds, and short growing seasons (Steinbauer et al., 2022). As such, these plants are considered specialists. Their adaptations limit them to areas with these specific harsh conditions. As climate change begins to change the conditions in alpine plant’s native habitats, plants will be pressured to move upslope to maintain the temperatures they rely on to survive. It is unlikely that plants will be able to move upslope quickly enough to outrun the effects of climate change due to their long lifespans and consequently slower migration speeds (Watts et al. 2022). Additionally, even if alpine plants can migrate upslope at the necessary rate, it is unlikely that the mountain they reside on will have a high enough maximum elevation to maintain alpine plant communities long term in the face of extreme climate change.

Compounding on the issues that alpine plants are having with migrating upslope to avoid climate change impacts, they will also be facing new competition from lower elevation plants (Watts et al., 2022). Similarly to alpine species, plants from lower elevations are also fleeing the consequences of higher temperatures and other climactic changes in their historic ranges. Generalist plant species such as shrubs and trees are slowly moving to higher elevations. In the case of these generalist species, the migration may not be because of necessity but simply out of availability. Elevations that were previously uninhabitable to them due to high winds and cold temperatures are becoming more tolerable for generalist species (Watts et al., 2022). Seedlings that previously were unable to survive are now populating in areas higher upslope. As the effects of climate change become more severe, areas that are inhabitable by shrubs and trees will become more widespread. Alpine plants generally grow low to the ground to avoid the high winds in alpine environments. Lower elevation plants like shrubs and trees generally grow taller. Because of this, lowland plants can outcompete alpine plants (Watts et al., 2023). This is contributing to a significant loss in alpine plants in their historic ranges. Loss of habitat and upslope migration is occurring in mountainous regions across the world. Studies have found plant elevational shifts across the world in Australia, the Alps, the Apennines, the Mediterranean, the Arctic, and the Rocky Mountains (e.g. Mizel et al., 2016; Watts et al., 2023; Steinbauer et al., 2022; Nigro et al., 2022).

Over time, tree encroachment and the introduction of outcompeting plant species will overtake alpine ecosystems. This will substantially contribute to the significant loss and potential extinction of alpine plant species.

Maladaptation

As discussed above, climate change will drastically change species’ range. In the case of alpine plant species, this shift will likely result in widespread habitat loss. Although most plant adaptation moves slowly, it is thought that due to gene flow, there may already be warming adaptive haplotypes present in alpine ecosystems (Wessely et al., 2022). These adaptations may buffer against the effects of predicted future warming. Even though this appears to be a benefit, adaptation towards warming climates might lead to maladaptation and be blocked due to founder effects. Founder effects refer to the idea of an adaptation becoming isolated leading to a reduction in genomic variability. The idea is that cold adapted haplotypes will reproduce upslope and will block the warm adapted haplotypes from reproducing or expanding. This blocking effect is made worse by the longer life spans of alpine plants. These difficulties are projected to decrease the number of warm adapted haplotypes in alpine plant communities (Wessely et al., 2022).

A Lack of Viable Solutions

Climate change will cause significant decline in alpine plant populations. The scientific community is beginning to recognize the danger that mountainous ecosystems face, as well as potential widespread ripples of repercussions that alpine and surrounding ecosystems will encounter when these alpine plants begin to disappear. As such, research and ideas for conservation and preservation have begun to come forth in this field. A few of these ideas include new monitoring techniques, seed preservation, and translocation (Tirell et al., 2023; Ohler et al., 2020; Thomas, 2011). Unfortunately, no viable long-term solutions have been discovered that can definitively preserve alpine ecosystems and the fragile plants that inhabit them (Verall and Pickering, 2020).

Microclimate Heterogeneity

Alpine ecosystems display noticeable microclimate heterogeneity. Microclimate heterogeneity is the term used for small areas that have diverse climates associated with them. A proposed benefit of these microclimates is that they have the potential to provide a buffer for climate change impacts on alpine plants. Temperature variation is primarily caused by differences in elevation and slope. Temperature decreases by about 0.6 degrees Celsius per 100 meters in increased elevation (Ohler et al., 2020). It is suggested that as the climate warms, plants will only need to move a few meters up in order to meet the necessary conditions for survival. This could reduce the dangers of desynchronized flowering. It also brings the added benefit of increasing species diversity which could lead to increased ecosystem stability (Ohler et al., 2020). Although microclimates may prove useful in the short term for acting as a buffer for climate change in alpine communities, it can only prevent the most severe impacts for a limited time. Eventually the impacts of warming will overtake the benefits of microclimates. Even if plants continue to escape uphill, there is a limit in elevation to every mountaintop and they will reach the end of their access to a suitable habitat.

Translocation

The concern that native plant species in alpine communities will not be able to adapt to warming, outcompete immigrant species, and migrate to more suitable climates lead the community to believe that there will be widespread extinction of these species. One suggestion has been to translocate species beyond their natural ranges (Thomas, 2011). The extreme nature of this suggestion lends strength to the idea that without action, many of the current alpine plants will go extinct as a result of climate change. There is an argument to be made that there is no solution that can conserve these species due to a lack of suitable areas. High alpine areas will likely be covered in historically lower elevation montane and subalpine tree species that are extending their current ranges. Additionally, many areas that may currently be suitable for translocation might soon be too warm for fragile alpine species to tolerate (Lesica et al. 2017).

Seed Banks

Another potential solution for preserving alpine plants is seed collection and storage. As established, many alpine plants will not be able to survive the impacts changing climate will have on their habitats. Experts have been exploring the idea of collecting seeds and storing them long term until conditions become suitable again for alpine plants. This is a relatively new idea in the field, and more research needs to be conducted (Verrall & Pickering, 2020). The concern with this solution is that researchers are still unsure of how long these seeds will be viable. Until recently, it was thought that alpine plants had shorter seed longevity than other plants. A new study found that climate change may actually be increasing alpine seed longevity, and that the seeds could last for over 20 years (White et al., 2022). The hope is that the seeds will last until the climate becomes more suitable for alpine plants to be reestablished. Unfortunately, even if global emissions halt completely by 2023, the climate will still warm considerably before it returns to the historically cooler temperatures (IPCC, 2023). It is difficult to know right now whether or not seeds can remain viable for as long as they need to in order to be reestablished in alpine ecosystems.

Conclusion

If emissions remain at current levels, climate change will result in the loss of fragile alpine plant communities. The impacts of climate change on these plants are broad and widespread. The solutions currently being proposed may slow the damage to alpine ecosystems, but it will not prevent it.

The research highlighted in this paper focuses on the fragility of alpine plant communities in the face of climate change. However, it should not be ignored that plant communities are only one facet of the workings of an ecosystem. If alpine plants suffer due to climate change, the remainder of the ecosystem will suffer in kind. Alpine species such as ptarmigan, pikas, and marmots rely on plants for nourishment, as do pollinators such as bumblebees (Yandow et al., 2015; Mizunaga et al., 2017). The topography relies heavily on plants to prevent erosion and maintain slope integrity. It is critical to conserve, preserve, and restore these plant communities as much as possible.

Currently, there is very little research on viable solutions for preserving alpine plant communities. Moving forward this field will require a focus on discovering suitable and viable long term preservation techniques, advances on methods of study and research, and continuing to strive for better understanding and predictions the range and severity of the impacts that climate change will have on alpine plant communities. Otherwise, we can expect to see alpine plant loss and localized mountaintop extinction in alpine ecosystems worldwide.

Emma Tunks is a Master of Science student in Environmental Science.