A recent study published in Oikos reveals that in arid areas species-rich plant communities thrive under plant protection facilitators, which promote the growth and survival of other plants. These results highlight the importance of plants facilitators for the conservation of biodiversity, especially in the current context of climate change.
Arid zones cover more than 40% of the land surface and are home to a third of the planet’s inhabitants. These ecosystems are subject to increasing pressures, such as overgrazing as well as increasingly severe and frequent droughts. However, at the same time, a growing number of studies show that positive interactions between species are omnipresent throughout life, particularly between bacteria, plants and animals, and that they play a major role in the functioning of ecosystems.
This is the case in arid areas, where there are plant facilitatrice (say nurses in English) which can improve local environmental conditions in drylands. A greater number of species and better functioning of the ecosystem are generally found near these plants. However, we know little about the mechanisms at play.
This new study, published in Oikos, revealed that plants facilitators are most beneficial to drylands when they are part of communities of diverse species. It shows that plant communities have a higher survival rate and produce more biomass during droughts when located under a plant facilitator and when they are richer in species. Conversely, the benefits of plants facilitators are absent when the beneficiary plant communities are in monoculture (therefore poor in species) or when they are watered (a treatment supposed to imitate the improvement effect of the plants facilitators).
The study shows that plants facilitators promote the maintenance of biodiversity and the functioning of ecosystems through three mechanisms. They first reinforce complementarity between species in species-diverse communities, thereby increasing biomass production. They also modify the competitive hierarchy between species, by favoring more the less competitive species. Finally, the study suggests that plants located under plant canopies facilitators develop life strategies associated with reducing water stress.
However, although plants facilitators can reduce these pressures in their neighborhood, and thus maintain the biodiversity and functioning of these ecosystems, these positive interactions increase their dependence on plants facilitators. The risk associated with this dependence is a sudden and irreversible desertification of ecosystems when plants facilitators are no longer enough to maintain ecosystems subject to extreme pressures.
