Ecosystems do not fail because of any single threat. They fail because threats accumulate. An international study published in Nature Geoscience in August 2024, led by the Institute of Natural Resources and Agrobiology of Seville (IRNAS-CSIC) of the Spanish National Research Council, found that the resistance of terrestrial ecosystems to global change decreases significantly as the number of environmental stressors increases — especially when that stress is sustained over time. In other words, the combined impact of multiple stressors is greater than the sum of their individual effects, and the natural functions ecosystems provide, from carbon sequestration to soil fertility, weaken disproportionately as pressures multiply.
The Compounding Threat to Ecosystem Resistance
The study's central finding reframes how we should think about environmental decline. For years, much research has examined one stressor at a time — a drought here, a warming trend there. But real ecosystems rarely face threats in isolation. When researchers analyzed how ecosystems respond to multiple global change factors simultaneously, they found that ecosystems become more and more sensitive as the number of factors rises, reducing their natural capacity to resist the impacts of environmental perturbations.
This sensitivity is not additive. According to the study's results, reported by the Spanish National Research Council, the weakening of resistance is disproportionate: two stressors together do more damage than the sum of their separate effects would suggest. The finding is especially pronounced when stress persists over long periods, meaning that ecosystems under chronic, layered pressure are the most vulnerable to being pushed past the point where they can continue functioning.
Understanding Environmental Stressors
The study examined what researchers call global change factors — the human-driven forces that degrade land and destabilize ecosystems. The evidence names drought and overgrazing as factors that can lead to degraded land, and fires as a degradation factor that, when applied over longer periods, affects an ecosystem's ability to provide its services. These stressors rarely arrive alone. A grassland may simultaneously face prolonged drought, recurring fire, and heavy grazing pressure; each one compounds the others' effects.
What makes this combination so damaging is that ecosystems have a finite capacity to absorb disturbance. A healthy ecosystem can buffer a single shock — a dry year, a localized fire — and recover. But when several stressors act at once and persist, that buffering capacity erodes. The study's conclusion, in the words of its researcher Guiyao Zhou, is that "the sustainability of our ecosystems depends on reducing the number of global drivers of change associated with human activity."
