Identifying the Climate Factors Driving Vegetation Change

Plant ecologists at the University of Bayreuth have revealed how global climate change is affecting the Earth’s terrestrial ecosystems in a study published in Nature Geoscience. Temperature and soil moisture changes could describe most changes in vegetation activity, while variations in solar radiation and atmospheric CO2 levels played a key role.

Vegetation changes in wilderness areas are reliable “fingerprints” of climate change. The study from Bayreuth shows how ecosystems in wilderness areas—such as here in Kruger National Park in South Africa—have changed over recent decades. Image Credit: Cyrus Samimi.

Years of expanded vegetation activity have been followed by years of decreased activity in some of the ecosystems studied. Such trend changes pose the question of whether terrestrial ecosystems will keep on making significant contributions to atmospheric carbon sequestration.

Dr. Steven Higgins, Chair of Plant Ecology at the University of Bayreuth, directed the study group that associated global remote sensing data from the past 40 years with a new dynamic model of plant growth.

This new model identifies the climate factors involved in global climate change that drive vegetation change. These variables include air temperature, soil temperature, soil moisture, solar radiation, and CO2 levels in the atmosphere. For the first time, the method enables the attribution of evaluated changes in vegetation activity to specific climate factors.

Being able to establish causal relationships between elements of climate change and vegetation changes, and thereby identifying the influence of individual climate parameters such as temperature and precipitation, is an important advance for ecosystem research. It provides evidence that human-induced climate change is already altering the Earth’s ecosystems. Based on the knowledge gained in this way, we can better understand why the Earth’s ecosystems are changing.

Dr Steven Higgins, Professor and Chair, Plant Ecology, University of Bayreuth

This knowledge is obviously valuable for guiding environmental and climate policy,” adds Higgins.

Previously, we could detect changes in vegetation activity, but it has often been difficult to tell whether it was really climate change that caused these changes. Even the most recent report of the Intergovernmental Panel on Climate Change (IPCC) contains surprisingly few case studies where observed changes in ecosystems could convincingly be attributed to climatic changes.

Dr. Timo Conradi, Study Co-Author and Research Associate, Department of Plant Ecology, University of Bayreuth

The new research is based on decades of satellite observations collected at 100 research sites across continents. Each of the Earth’s major ecosystems is depicted by at least five examples in this sample of study sites: tropical evergreen forests, temperate forests, boreal forests, scrublands, grasslands, tundra, savannas, and Mediterranean ecosystems.

Satellite observations of vegetation changes at these sites were used to ascertain the degree to which the vegetation changes could be described by changes in air temperature, soil temperature, soil moisture, solar radiation, and atmospheric CO2 levels.

These analyses, when combined, point to some global trends: Ecosystems in dry and warm areas, particularly savannas and some grasslands, were primarily affected by changes in soil moisture.

In contrast, cooler-climate ecosystems, like temperate forests, boreal forests, and tundras, were especially sensitive to temperature changes. Remarkably, changes in atmospheric CO2 and solar radiation had little impact on vegetation changes.

Study Co-Author Edward Muhoko M.Sc. from Namibia states, “Our findings show how the long term remote sensing record can support and significantly advance ecosystem research. Especially in this field, close international cooperation will continue to be necessary to identify the influence of climate factors on a global scale and to effectively understand how and why ecosystems are changing in different regions of the world.”

He is currently pursuing a Ph.D. at the Department of Plant Ecology and specializes in remote sensing techniques, geoinformation systems, and geostatistics.

The Bayreuth scientists discovered substantial evidence of trend reversals in various climatic zones around the world. Increasing air and soil temperatures appear to have initially increased vegetation activity for decades at many sites, resulting in a “greening” visible from space.

However, continued temperature rises may eventually cause soils to dry out, resulting in decreased vegetation activity. As a result, the more recent parts of the satellite record suggest ecosystem “browning” at some sites. Similar trend reversals have been observed in field research in tropical forests measuring changes in tree size.

If this trend reversal is confirmed by further studies, it would indeed be worrying, because in the past, terrestrial ecosystems have, by ‘greening’ for decades, absorbed significant portions of anthropogenic carbon emissions. Up till now, this carbon capture service provided by vegetation has saved us from more dramatic climate change.

Dr. Steven Higgins, Professor and Chair, Plant Ecology, University of Bayreuth

Journal Reference:

Higgins, S. I., et al. (2023) Shifts in vegetation activity of terrestrial ecosystems attributable to climate trends. Nature Geoscience.


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