Repensando a restauração ecológica sob a lente das mudanças climáticas e dos sinais de alerta precoce para a desertificação

Abstract

Caatinga contemplates a great amount of biological diversity and ecosystem services functioning as an important carbon sink. However, this biome is located within one of the most sensitive regions of the globe to climate variations and its present environmental conditions and anthropic influence can diminish its resilience causing severe degradation. To optimize the success of restoration programs this work intends to: 1) Identify early warning signals to detect how degraded areas could develop to vegetated or desertified states, indicating priority areas and emergency actions to combat desertification and encourage natural regeneration; 2) Create guidelines of sustainable forest restoration based on changes in species composition due to loss, gain or replacement of plant species in the face of expected climate changes; and 3) Provide lists of species for 1,112 municipalities that can be planted today and resist to future climate changes using an interactive website available for decision makers and the general public. For chapter one we used a 20-year time series of Enhanced Vegetation Index (EVI, 2000-2019) data, calculated the residual autocorrelation (critical slowing down) and the linear trend of the time series to identify whether the system tends to recover or collapse in terms of vegetation cover. We found that 8.77% of the Caatinga has been approaching a critical transition point, from this amount, 66,121 km showed a tendency for recovery and 7,938 km2 for vegetation cover collapse. Both recovery prone and collapse-prone sites are concentrated in areas of natural vegetation, indicating that few degraded areas are tending to recover, and that many areas of natural vegetation are tending to lose important ecosystem services. We believe that all of these areas need either passive or active forest restoration with different levels of urgency. For chapter two and three we built climate suitability models for 606 Caatinga woody species, using the present climate and the future climate predicted by 2050. In chapter two, we suggested guidelines for restoration in the face of future climate change by identifying areas that will gain species in the future, areas that will lose species in the future and areas where species will be replaced. For the whole Caatinga territory, we foresee that 28.5% of the species will present geographical area expansion, 71.5% reduction and 0.5% will suffer extinction. Local extinctions, on the other hand, occur in 88.9% of the region, with only 11.1% of the Caatinga areas gaining species. Scenarios of species loss and high species turnover were registered, which makes restoration planning much more challenging. Besides these scenarios, we identified six combinations of changes in plant species composition that require different guidelines for sustainable restoration practices. This ecological restoration guideline for each scenario was based on the following questions: 1) which restoration method should be prioritized, spontaneous restoration or tree planting?; 2) when one should prioritize the use of adjacent conservation units that will function as source areas for future species colonization in restored areas?; 3) which species to plant and where to plant threatened species restricted to the biome in the face of expected climate changes? In chapter three, we detected changes in species richness in 1,112 municipalities, created 1,112 lists with the species that would best respond to predicted climate changes in each municipality, published the lists on an interactive map-based website and, finally, prepared a schematic description of the workflow so it could be applied in other regions of the world. We predicted that for the 1,112 Caatinga municipalities, 809 will show a reduction in species richness, 286 will gain new species and 17 will maintain its species richness. Even in the municipalities where the balance was positive, future species loss may occur while a larger number of species might colonize. Therefore, all regions to be restored need lists of species suitable for planting and these lists should be accessible to decision-makers and the general public. Our interactive webpage is an example of how to bring scientific production closer to the practical needs of enterprises and people who need to implement restoration projects. With only a mobile phone connected to the internet, one can obtain on our webpage the list of the best species that can be successfully planted in a given municipality, because these species are adapted to the current local climate and because they will also survive future climate changes. This dissemination of information can foster a large-scale sustainable restoration project in mid and long term.