In dryland ecosystems, increased environmental stress often triggers a change from a uniform vegetation cover to patchy vegetation patterns. Some theoretical studies suggest that this spatial self-organization of vegetation helps ecosystems delay desertification or even avoid it altogether. Using a new theoretical framework that takes account of previously neglected but for capturing reality highly relevant parameters, Dr. David Pinto-Ramos and Dr. Ricardo Martinez-Garcia from the Center for Advanced Systems Understanding (CASUS) at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) demonstrate that this is not the case in general. They argue that such vegetation patterns can, by contrast, be a sign of reduced resilience and favor ecosystem collapse. Their work, published in PNAS (DOI: 10.1073/pnas.2511994123 ), focuses on the transition from dryland to desert but the general framework provides a better understanding of tipping processes in other ecosystems as well.
Ecosystems, from coral reefs to tropical forests to drylands, can undergo abrupt and sometimes irreversible changes once critical environmental thresholds are crossed. Such regime shifts usually have profound ecological, social, and economic consequences. Global warming and other human pressures are increasing the likelihood of regime shifts, making it increasingly urgent to understand how and when these transitions occur.
Spatial dynamics are key to this understanding. Many ecosystems organize themselves into characteristic spatial patterns, and advances in satellite and airborne observations now allow researchers to monitor these structures better than ever before. Nevertheless, interpreting what such patterns reveal about ecosystem stability remains difficult when relying on observations alone, says Dr. Martinez-Garcia: “Changes in spatial patterns occur over several decades and often across hundreds of kilometers. So despite accumulating observational data, theoretical models are crucial for understanding how spatial dynamics influence ecological stability.” Martinez-Garcia leads the “ Dynamics of Complex Living Systems ” group at CASUS, which combines mathematical, computational, and data-analyses tools to understand the emergence of ecological patterns and dynamics across scales.
On the way to becoming a desert – or perhaps not?
Desertification is one of the most extensively studied examples of ecological tipping. In arid environments, characterized by little or no precipitation and, in general, almost no availability of water, vegetation often reorganizes into stripe- or spot-like patterns as environmental stress increases. This relationship between environmental stress and pattern structure suggests that patterns emerge as plants optimize water use. For a long time, these patterns have been seen as a response to increased aridity that either reverse in less arid conditions or, after having passed the ecological tipping point, disappear completely with a desert as a result. However, recent studies have indicated that, in certain scenarios, these patterns could also provide a path for drylands to remain functional even at aridity levels that are even beyond the tipping point. The result of these theoretical studies: ecosystems exhibiting regular vegetation patterns could withstand harsher conditions and delay or even avoid collapse.
“The studies bringing up the concept of collapse avoidance rely on very simplified models that do not take into account the spatial constraints and environmental heterogeneities characteristic of real ecosystems,” says Dr. Pinto-Ramos, main author of the study and a postdoc in Martinez-Garcia’s group. “So we set out to address this gap.”
Not assuming perfect spatial symmetry
The new theoretical framework presented by the CASUS team in PNAS incorporates key spatial features of real ecosystems. Previous models typically assumed ecosystems to be infinitely large and environmentally uniform. In contrast, the new model accounts for the finite spatial extent of vegetated areas, including their interfaces with the surrounding desert, as well as for environmental heterogeneities that can create directional interactions between vegetation patches. “Interfaces between vegetated regions and deserts are key because they can trigger ecosystem collapse through the spatial propagation of desertification waves,” explains Pinto-Ramos. “At the same time, landscape features such as hills and depressions influence how water is distributed after rainfall. By breaking the assumption of perfect spatial symmetry, our model captures essential processes of real dryland dynamics.”
The improved model reveals that vegetation patterns do not have a universal ecological meaning. Instead, their implications for ecosystem stability depend on how spatial processes operate under specific environmental conditions. “We find that spatial context fundamentally changes how patterns should be interpreted,” says Martinez-Garcia. “For example, when environmental gradients such as slopes are gentle, patterned vegetation can enhance ecosystem resistance to drought. But when these gradients are strong, the same pattern can instead signal an increased risk of collapse.” For all those interested in desertification processes, this is highly relevant: If, according to the theoretical work, strong environmental gradients like steep slopes or a steady wind always coming from one direction can be observed in a patch-patterned dryland, even a small increase in aridity will quickly lead to a collapse into a desert.
Capturing full reality is the long-term goal
An open task for the future is to quantify the relevance of this desertification mechanism in nature. “We hope our results motivate experts to look into their data. We are confident that so far hard-to-explain quick desertification events can be connected with one or more strong environmental gradients,” says Martinez-Garcia. Nevertheless, he and Pinto-Ramos are aware that their new model still does not capture full reality. Hence, they are currently working on integrating more relevant topographic, water, and wind data into their models. Martinez-Garcia: “Drylands are extremely complex systems. So even when studying them over small regional scales, there are a multitude of variables that must be taken into account. Given the global changes we face, there is no excuse: we more sophisticated models that can interact with different types of data to effectively combat desertification.”
Proceedings of the National Academy of Sciences
Computational simulation/modeling
Not applicable
How spatial patterns can lead to less resilient ecosystems
30-Mar-2026