The article highlights the vulnerability of cacti to climate change and foresees scenarios involving significant losses of areas suitable for their survival, with high risks of extinction.
Chile is among five bioregions that could experience significant losses of cactus species by the end of the century, due to habitat changes associated with the occurrence of extreme climatic events, according to an international study published in the renowned scientific journal Nature.
Cacti—a family of plants comprising more than 1,900 species, most of them endemic to the Americas—are considered a symbol of resilience to extreme environmental conditions, but have proven to be highly sensitive to climate change.
The article—in which the University of Concepción participated—presents concerning data on the loss of areas with climates suitable for cacti, with an increased risk of extinction for up to 30% of species due to global warming and severe droughts.
"Because these plants are adapted to arid conditions, they were thought to be invulnerable to climate change. However, there is growing evidence showing that they are being severely affected," commented University of Concepción researcher Pablo Guerrero Martin.
Extreme heat events could be an essential component of these impacts, stated the researcher, who is also a member of the Institute of Ecology and Biodiversity and the BASE Institute, and has extensive experience in studies on extinction risks, evolution, and the poaching of cacti.
The academic from the Faculty of Natural and Oceanographic Sciences is part of the team of authors of the study led by Michiel Pilliet, from the University of Arizona, which also includes Beatriz Mariño, a doctoral student in Systematics and Biodiversity.
Beyond the averages
The research highlights the vulnerability of this plant family to climate change, which is often underestimated by conventional species distribution models (SDMs), a tool used to assess or predict the status, distribution, or conservation problems of biological organisms.
Most of these models are based on climatic averages—temperature and precipitation—which leave out the impacts of extreme events, increasingly frequent and intense in the context of global warming.
Thus, the objective of the international study was to determine whether the explicit inclusion of severe climatic events in SDMs substantially changes predictions regarding cactus extinction risks under climate change.
The researchers used new spatial data on severe droughts—including the combined effects of higher temperatures—drawn from a database of cactus records comprising more than 688,000 observations.
Using these data, scenarios were modeled for 993 species through the end of the century, yielding more drastic projections than those provided by conventional models.
"Projections for the future of climatically suitable areas for cacti, that is, areas ideal for their growth, reproduction, and survival, change considerably when the models incorporate severe droughts," explained Dr. Guerrero.
This suggests that, when defining the climatic conditions in which cacti can live, the intensity and duration of extreme episodes may be more relevant than average rainfall, added Beatriz Mariño.
The study projected that 66% of the 993 species modeled using severe drought variables would experience a reduction in areas suitable for their survival, compared with 55% in models that did not include these variables.
The magnitude of these reductions would also depend on the dispersal capacity of the species—that is, their ability to migrate to more favorable locations—in combination with climate change scenarios.
Projections indicate that when dispersal is not possible, between 84% and 85% of species would lose areas with suitable climates, compared with the 69–72% predicted by conventional models.
With a dispersal capacity of 100 kilometers, models incorporating severe drought data increased the proportion of affected species from 58–61% to 69–72%.
Likewise, the observations indicate that between 55% and 58% of cacti could lose at least one-quarter of the areas optimal for their survival, while between 25% and 35% would lose 80%.
A discouraging future
In the assessment of species richness, projections showed significant declines in several areas of high species concentration, highlighting five bioregions: Chile and the border area with Argentina, with 29%; Central America, with 32%; and Peru, Ecuador, and part of central Colombia, with 34%.
In some areas of Central America, the Venezuelan coast, and northwestern Brazil, the reduction in species would exceed 50%.
"Although these projections refer to the end of the century, it is important to note that we are already observing impacts that are currently limiting plant distribution," stated the article's lead author, Michiel Pilliet.
Pilliet indicated that this work will help update the conservation assessments of the International Union for Conservation of Nature (IUCN) Red List, which currently classifies 31% of cactus species as threatened.
The researcher foresees a discouraging future for these plants if the persistent threats of habitat destruction and illegal collection are added to these projections.
"In Chile, this concern also has a present-day counterpart. The article shows specimens of Copiapoa solaris affected by drought in Antofagasta. Their ability to store water does not make them immune to prolonged droughts intensified by warming," said Pablo Guerrero.
In the academic's view, these results reinforce the urgency of protecting their populations and strengthening the monitoring of their survival and regeneration.
This work represents a contribution toward advancing understanding in an area of climate change that remains poorly understood: its effects on species distribution and extinction risks.
And although the study focuses on cacti, its authors believe the results could be relevant to the assessment of other plant families.
