Published in the prestigious journal Science, the study shows how increases in aridity can alter the capacity of these ecosystems to sustain life, also limiting the provision of essential ecosystem services to more than 2 billion people living in those areas.
Drylands cover about 41% of the Earth’s land surface and host one in three humans inhabiting our planet. In these areas, life is highly influenced by aridity, i.e. the balance between the amount of rainwater and the water lost by evaporation. In this sense, aridity is increasing worldwide as a result of climate change. A study conducted by the Dryland Ecology and Global Change Lab at the University of Alicante (UA) led by Fernando T. Maestre and published in Science revealed for the first time that as aridity increases, dryland ecosystems on the planet undergo a series of abrupt changes.
“In the study we found that numerous ecosystem characteristics had a non-linear response to small aridity increases. This means that there are levels at which faster, sometimes even abrupt shifts occur as a result of relatively small aridity increases. Therefore, it can be said that, when certain aridity thresholds are crossed, the ecosystem undergoes disproportionate changes and becomes even more arid”, Santiago Soliveres, Ramón y Cajal researcher at the UA and co-author of the study, explains.
Three phases of change were identified by the researchers. First, when aridity levels cross values of around 0.54, “the ecosystem becomes limited by the lack of water. The vegetation changes and it becomes dominated by species adapted to drought, such as grasses and shrubs, as is already the case in many areas in the Iberian Peninsula”, UA researcher Fernando T. Maestre points out.
After these initial vegetation changes, when aridity values exceed 0.7, the soil becomes much less fertile. It loses its structure and becomes more vulnerable to erosion. Moreover, soil organisms that play essential roles in maintaining soil nutrients are radically affected, with a dominant presence of pathogens at the expense of more beneficial organisms.
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