Forecasting Phytoclimates 

Mark Altaweel

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Phytoclimate refers to the distribution of plant species based on climate conditions. As the climate changes, the distribution of specific plant species also shifts. Scientists have long predicted changes in plant distribution due to climate shifts, but recent studies emphasize the importance of accounting for nonlinear and unpredictable effects of climate change.

With new research, scientists are trying to better understand and forecast how plants will be distributed across the globe. With a shift in climate, many or even most of our land surfaces will experience some significant vegetation change in the coming decades although most regions will not be completely change their vegetation composition.

In new research published in Nature, scientists from Germany and Switzerland forecast that roughly 33% to 68% of the global land surface will experience major change to their phytoclimate by 2070.[1] However, this specific range may not tell us the whole story as ecological changes don’t always match up directly with climate changes due to complex plant responses and interactions.

Plants thrive within specific ranges of environmental factors, including rainfall, sunlight, temperature, soil quality, and other variables, which determine their distribution in particular regions. For some species, a substantial climate change is necessary before they can no longer be sustained in their current habitats.


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A photo looking up towards the sky of conifer trees on a blue sunny day.
As climate change affects microclimatic conditions, plant species composition may shift in biomes around the world. Mixed-conifer forest in Northern California. Photo: Caitlin Dempsey.

Analyzing how climate change will affect plants

Using a large plant species database, called BIEN,[2] researchers studied 135,153 vascular plant species to forecast their potential range based on future climate scenarios. A model, called TTR-SDM, derives species distribution and can be suited to identify climatically suitable grid cells for each plant species and provide given forecasts. The model can be used to estimate vegetation biomass and growth for given species using 25 x 25 KM grided cells that cover the Earth’s surface with monthly climate-based input.

The results showed that under different scenarios varying biomass change can be forecast. If Representative Concentration Pathway (RCP), used in climate projections to determine greenhouse gas concentrations, is at roughly 2.6, which is a scenario of relatively low greenhouse gas concentration, then 33% of the Earth’s terrestrial surface would show significant plant biomass change by 2070. Changing RCP to 8.5, which is the top-end estimate for greenhouse gas concentrations and closer to current trends, then 68% of the land surface’s plant biomass changes by 2070.

Series of world maps showing suitability of various plant forms in 2070.
Series of maps by plant species for each growth form based on climate suitability in 2070 under RCP 8.5. Suitability is measured as a proportion of how many plant species of a particular type can thrive in an area’s climate, based on a plant growth model that looks at environmental factors.Figure: Conradi et al., 2024, CC BY 4.0.

Such projections are based on global circulation models (GCMs) used for climate scenarios. These changes are most pronounced in regions sensitive to climate variability and that have less resilient vegetation, including: south China, the Himalayas, northwestern Russia, the Baltic countries, Scandinavia, the southeastern and northeastern United States, Alaska, central Mexico, the tropical Andes, southeastern South America, southeastern Australia and northern New Zealand.

Northern and colder climate regions are most affected

In general, it is northern and colder climate regions that are most affected, such as boreal forests and tundra region, where these regions have susceptible vegetation that could change from cold to more temperate species. Some tropical regions will likely shift to more savanna-like vegetation as rainfall conditions change. The Amazon, in general, shows some of the greatest uncertainty, with results not showing clearly how significant the region will change as different possibilities may occur. 

Despite these projected changes and effects, the actual phytoclimates that emerge are going to be based on current scenarios in most cases. Projection are that currently 0.3% of the land surface on Earth will change completely in their vegetation composition, when RCP is 2.6, while this increases to 2.2% for RCP 8.5 scenarios.

A small percentage of current phytoclimates could disappear completely with climate change

Southeastern South America and Australia show the most novelty in phytoclimates, where current tropical and subtropical areas change the most. Vegetation could change to evergreen trees, dry-deciduous trees, and climbing vegetation in these regions.

In some scenarios, higher temperatures may adversely impact needleleaf and cold-deciduous woody species, leading to a significant shift towards more temperate types of vegetation becoming prevalent and dominant. Overall, looking at current phytoclimates, about 0.1% (RPC 2.6) to 1.3% (RPC 8.5) current phytoclimates may entirely disappear. 

Mitigating inevitable changes to phytoclimates

We are currently living in a scenario where RCP is closer to 8.5, meaning we are more likely to see changes to vegetation affecting most of our land surfaces. The results also suggest we should move away from a purely preventative model in landscape change management to one that accommodates and adapts to inevitable changes. We can see forecasts indicate vegetation change will be impossible to prevent even in more climate favorable scenarios for many of Earth’s regions.

Other factors, particularly how societies affect land use, could clearly change some of the projections given. Nevertheless, the changes we see may not be very dramatic in most of the Earth’s region. In fact, many vegetation changes may be more subtle and be based on existing species and vegetation types found, such as some species becoming more dominant which are already present. It is clear, however, some more sensitive areas will experience completely different plant ecology in the near future.  

References

[1]    For more on recent research that projects phytocliamte change, see:  Conradi, Timo, Urs Eggli, Holger Kreft, Andreas H. Schweiger, Patrick Weigelt, and Steven I. Higgins. 2024. “Reassessment of the Risks of Climate Change for Terrestrial Ecosystems.” Nature Ecology & Evolution, February. https://doi.org/10.1038/s41559-024-02333-8.

[2]    The Botanical Information and Ecology Network (BIEN) database can be found here:  https://bien.nceas.ucsb.edu/bien/.

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About the author
Mark Altaweel
Mark Altaweel is a Reader in Near Eastern Archaeology at the Institute of Archaeology, University College London, having held previous appointments and joint appointments at the University of Chicago, University of Alaska, and Argonne National Laboratory. Mark has an undergraduate degree in Anthropology and Masters and PhD degrees from the University of Chicago’s Department of Near Eastern Languages and Civilizations.