Nature is not an equilibrium. It is a process.
For a long time, ecology described ecosystems as systems tending toward a state of equilibrium. In this view, biological communities evolve toward relatively stable configurations and, after a disturbance, tend to return to their original condition.
In recent decades, this perspective has been progressively revised. Ecosystems are not static structures but dynamic systems, shaped by continuous changes in species composition. This process—known as species turnover, meaning the replacement of species over time—is one of the mechanisms through which biodiversity renews itself and adapts to environmental change.
In recent years, however, several studies have identified an unexpected dynamic. In many biological communities, species turnover appears to be slowing down, despite the acceleration of climate change and anthropogenic pressures.
This paradox suggests a profound transformation of contemporary ecosystems. In many cases, biodiversity is not only declining—it is becoming less dynamic.
Species turnover describes the process by which some species disappear from a community while others colonize it. It does not necessarily represent a loss of biodiversity; on the contrary, it is a structural component of how ecosystems function.
Even under relatively stable environmental conditions, ecological communities change over time. Populations fluctuate, new species arrive from nearby areas, others decline or disappear locally. These dynamics result from the interaction between ecological factors—competition, dispersal, natural disturbances—and evolutionary processes.
For this reason, biodiversity cannot be described solely in terms of the number of species present at a given moment. It is also necessary to consider how community composition changes over time. This aspect, known as temporal beta diversity, is now a central dimension in ecosystem studies.
A resilient ecosystem is not simply rich in species—it is a system capable of continuous renewal.
In light of these dynamics, many ecologists expected that the profound environmental transformations of recent decades would accelerate species turnover. Climate change, land-use alteration, and the spread of invasive species were expected to drive rapid reorganization of biological communities.
However, some global analyses suggest a different picture.
A study based on the international BioTIME database—which compiles time series of biological communities from numerous terrestrial and marine ecosystems—found that short-term species turnover has decreased in more communities than it has increased over the past century.
This observation appears counterintuitive. The Earth system is changing rapidly, yet many biological communities seem to be responding more slowly than expected.
One possible explanation concerns the reduction of the so-called regional species pool—the set of species potentially able to colonize a given ecosystem.
When habitats are degraded or fragmented, the number of species available to colonize new areas declines. Even if some species disappear locally, others may not be able to replace them.
Ecological models show that this phenomenon can emerge when environmental degradation reduces population growth or limits species dispersal. Under these conditions, ecosystems become progressively less dynamic: communities change more slowly because the number of potential colonizers decreases.
The system does not only lose species—it also loses its capacity to reorganize.
Other studies suggest that anthropogenic pressures produce more subtle but equally significant transformations. Analyzing North American bird communities, some researchers have observed a phenomenon described as slower but deeper community change.
In these communities, short-term turnover tends to slow down, but over the long term significant changes occur in population structure. Rather than introducing new species, environmental pressures alter the frequency and relative abundance of species already present.
Some species become dominant, others progressively rarer. The overall composition of the community changes slowly, but substantially.
The result is an ecosystem that may appear stable in the short term but undergoes deep reorganization over time.
This temporal dynamic is accompanied by a spatial dimension. In many regions of the world, climate change is driving geographic shifts in species distributions.
Studies on tropical forests in the Andean-Amazon region show that some areas are gaining species while others are losing them. Mountain forests can become climate refuges for species migrating to higher elevations, while warmer and drier regions tend to experience declines in biodiversity.
This process leads to a redistribution of biodiversity at regional and continental scales. Overall species richness may remain relatively stable, but community composition changes.
The ability of ecosystems to adapt to these changes depends largely on landscape connectivity.
Habitat fragmentation—caused by urbanization, infrastructure, and intensive agriculture—reduces the ability of species to move between areas. When habitats become isolated, species dispersal becomes more difficult.
This limits one of the fundamental mechanisms of turnover. In fragmented landscapes, the loss of a species may not be compensated by the arrival of another.
Over time, this process can lead to biological communities that are both poorer and less dynamic.
These dynamics help clarify the meaning of a term that is becoming increasingly central in environmental debate: regeneration.
Regenerating an ecosystem does not simply mean increasing the number of species present. It means restoring the ecological processes that allow ecosystems to function over time.
These processes include:
In this sense, regeneration means restoring ecosystems’ capacity to transform.
Trees can play a fundamental role in this process.
Forests and agroforestry systems create complex habitats, modify microclimates, and promote the formation of soils rich in organic matter. This ecological structure increases the number of niches available for many species.
At the same time, trees can help rebuild ecological connectivity across landscapes. Tree lines, forest corridors, and agroforestry mosaics can connect fragmented habitats, facilitating species movement.
In this way, the regeneration of forest and agricultural landscapes can help reactivate the processes of dispersal and colonization that sustain species turnover.
The biodiversity crisis is often described as a loss of species. But ecological research in recent years suggests that the issue runs deeper.
In many ecosystems, biodiversity is not only declining—it is becoming less dynamic.
The slowing of species turnover indicates that some natural systems are losing their ability to reorganize in response to environmental change.
In this context, regeneration means rebuilding the conditions that allow ecosystems to evolve.
Because a healthy ecosystem is not a static system. It is one that continues to change.
Fred Pearce (2026). Species Slowdown: Is Nature’s Ability to Self-Repair Stalling? Yale Environment 360 https://e360.yale.edu/features/ecosystem-turnover-slowdown
Terry, J. C. D., & Rossberg, A. G. (2024). Slower but deeper community change: intrinsic dynamics regulate anthropogenic impacts on species temporal turnover. Ecology.
https://esajournals.onlinelibrary.wiley.com/doi/10.1002/ecy.4430
Nwankwo, E. C., & Rossberg, A. G. (2026). Widespread slowdown in short-term species turnover despite accelerating climate change. Nature Communications.
https://www.nature.com/articles/s41467-025-68187-1
Dornelas, M. et al. (2025). Large-scale patterns of biodiversity change across ecological communities. Nature Ecology & Evolution.
https://www.nature.com/articles/s41559-025-02956-5
Antão, L. H. et al. (2025). Global patterns of biodiversity change in the Anthropocene. Nature Communications.
https://www.nature.com/articles/s41467-025-63246-z