Dr Rocio Hernandez-Clemente, a senior lecturer from the University's Department of Geography, joined an international team of researchers from the Dryland Ecology and Global Change Lab at the University of Alicante to examine the Earth's dryland ecosystem, which covers 41% of the world's surface and is home to around a third of its population.

The study found for the first time that as aridity increases, dryland ecosystems undergo a series of abrupt changes. This results first in drastic reductions in the capacity of plants to fix carbon from the atmosphere, followed by substantial declines of soil fertility and ending with the disappearance of vegetation under the most arid and extreme conditions.

Climate change and ecosystems

The team found that increases in aridity in line with current climate change forecast, led to abrupt shifts in dryland ecosystems worldwide which limit their capacity to sustain life. This is because climate largely determines the amount and types of plants that can be found in a given place, how fertile the soil is, and how the landscapes look like. Understanding how changes in climatic conditions affect organisms and the ecosystem processes and services that depend on them, such as food and biomass production, is key to understanding, forecasting and mitigating climate change impacts on both ecosystems and societies.

The study

The team led by Dr. Miguel Berdugo, at the University of Alicante, pulled together the largest compilation of empirical data to date to evaluate how key ecosystems change along the wide aridity gradients that can be found in drylands worldwide. Dr Hernandez-Clemente performed the data extraction, processing and Normalized Difference Vegetation Index data analysis of 60000 points distributed worldwide and used as an indicator of plant productivity in drylands. She also contributed to the quality assessment analysis and validation of the data and derived trends to detect abrupt shifts through remote sensing data.

Dr. Berdugo said: "The purpose of our work was to look at how these ecosystem change as we move towards more arid zones in order to better understand what we may expect in the future as the climate becomes drier, and more arid, in drylands worldwide."

The study identified three phases of accelerated ecosystem change in response to increases in aridity, measured as the inverse ratio between rainfall and the rate by which water evaporates from the land to the atmosphere.

Key findings

The key findings of the study were:

• If aridity increases just a small amount of 0.5, there are rapid and often abrupt ecosystem changes
• The landscape changes and is dominated by species adapted to more arid conditions and drought.
• If aridity increases by 0.7, soil loses its structure and becomes more vulnerable to erosion.
• Soil organisms that play essential roles in maintaining ecosystem functioning are also negatively affected.
• There are large increases in the presence of pathogens at the expense of more beneficial organisms.
• If aridity levels are raised beyond a threshold of 0.8, the system collapses, plants cannot thrive and the land becomes desert.

According to climatic forecasts, more than 20% of land may cross one or several of the thresholds identified in this study by 2100 due to climate change.

Dr Berdugo said: "Life will not disappear from drylands with forecasted aridity increases, but our findings suggest that their ecosystems may experience abrupt changes that will reduce their capacity to provide ecosystem services more than 2 billion people, such as soil fertility and biomass production."

Dr Rocio Hernandez-Clemente said: "The reduced global ability of the land to sustain life is predicted to become an increasing problem with climate change. This study demonstrates the possibility of detecting abrupt changes and monitoring how land turns into desertification processes with remote sensing data.

"The use of satellite image data helps scientists to monitor, predict and quantify the consequences of the increasing aridity in drylands ecosystems worldwide. International cooperation is essential for assessing land degradation and abrupt shifts. The next steps of our research will be focused in the use of earth observation data for look for changes of desertification processes."

Story Source:

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Journal Reference:

1. Miguel Berdugo, Manuel Delgado-Baquerizo, Santiago Soliveres, Rocío Hernández-Clemente, Yanchuang Zhao, Juan J. Gaitán, Nicolas Gross, Hugo Saiz, Vincent Maire, Anika Lehman, Matthias C. Rillig, Ricard V. Solé, Fernando T. Maestre. Global ecosystem thresholds driven by aridity. Science, 2020; 367 (6479): 787 DOI: 10.1126/science.aay5958