Not long ago, our planet was largely covered by expansive natural landscapes. However, in the blink of an eye, human activity has altered almost 75% of the Earth's surface. The rapid expansion of agriculture and urbanization, coupled with deforestation and other anthropogenic pressures, has significantly diminished both the extension and quality of global ecosystems, leading to profound impacts on biodiversity and human well-being. In this context, protected areas emerge as a paramount strategy aiming to preserve, at least in part, the remaining natural ecosystems on our planet.

In December 2022, the Kunming-Montreal Global Biodiversity Framework (GBF) marked a historic moment as representatives from 188 governments committed to ensuring and facilitating the effective conservation and management of at least 30% of terrestrial areas by 2030. While the GBF undoubtedly marks a significant milestone in global biodiversity conservation, we envision that international strategies for the enduring preservation of healthy and resilient ecosystems could be enriched through a more profound comprehension of the geometric aspects of protected lands. Why? Essentially, the achievement of the 30% protection target can be accomplished through contrasting design strategies of protected areas.

The geometry of protected lands, considering both their shape and size, plays an increasingly crucial role in biodiversity conservation and human well-being. As human pressures on the biosphere accelerate, the geographical protected space more exposed to the unprotected surroundings becomes more vulnerable to anthropogenic stressors. Agricultural encroachment, poaching, biological invasion or chemical and physical pollution are just a few examples of these pressures. Small, isolated, intricately shaped protected areas also enable us to identify a mismatch for sustaining the diverse ecological flows in nature, from movement of species (especially critical under a changing climate) to the connectivity of nutrients and energy across habitats (with effects on the structure and functioning of ecosystems).

In our research, we scrutinized the geometry of protected areas globally and regionally, considering cultural (e.g., "Latin America and the Caribbean", "western Europe") and biogeographic units (e.g., rainforests, deserts, and wetlands). Our analysis revealed that the justified and widely celebrated expansion of protected areas state over the past three decades predominantly involved integrating small, perforated, and fragmented units. Currently, one-third of global protected land is within 2 km of the unprotected surroundings, with only 0.6% representing "deep" protected cores located more than 100 km away from edges. The widespread trend of shrinking size and decreasing compactness in protected areas designation, along with the exposure of nature to unprotected surroundings, poses a potential threat to the strategic goal of protected areas: "to improve the status of biodiversity by safeguarding ecosystems, species, and genes". Therefore, strategies for expanding protected networks should reconsider the geometry of protected lands to effectively manage the proximity of stressors from a potentially hostile matrix. Additionally, consideration must be given to how the multi-use landscape matrix surrounding protected areas should be carefully managed.

Contrasts

Our results take on even greater significance, considering that smaller, more exposed protected areas are concentrated in the world's most critically threatened biomes. Conversely, a remarkable pattern emerged in conservation efforts: larger, more compact protected areas, which distance human pressures from their interiors, are predominantly driven by peripheral or developing countries. A notable fact is that 15 out of the 20 countries with the largest and most compact protected areas are located in the sub-Saharan Africa. In contrast, most developed countries have relatively small protected areas with particularly complex, perforated, and fragmented shapes. These conspicuous disparities demand attention in discussions about global biodiversity conservation strategies. A comprehensive understanding and acknowledgment of the varied geometric imprints of protected areas, particularly in light of the contrasting circumstances between developing and developed nations, are imperative for formulating effective and fair conservation policies on a global scale.

The research team included researchers Germán Baldi and Esteban Jobbágy from IMASL-UNSL/CONICET, San Luis, Argentina; and Josep Peñuelas from CREAF-CSIC, Catalonia, Spain.