Strong floristic distinctiveness across Neotropical successional forests

Forests that regrow naturally on abandoned fields are important for restoring biodiversity and ecosystem services, but can they also preserve the distinct regional tree floras? Using the floristic composition of 1215 early successional forests (≤20 years) in 75 human-modified landscapes across the Neotropic realm, we identified 14 distinct floristic groups, with a between-group dissimilarity of 0.97. Floristic groups were associated with location, bioregions, soil pH, temperature seasonality, and water availability. Hence, there is large continental-scale variation in the species composition of early successional forests, which is mainly associated with biogeographic and environmental factors but not with human disturbance indicators. This floristic distinctiveness is partially driven by regionally restricted species belonging to widespread genera. Early secondary forests contribute therefore to restoring and conserving the distinctiveness of bioregions across the Neotropical realm, and forest restoration initiatives should use local species to assure that these distinct floras are maintained

Pervasive gaps in Amazonian ecological research

Biodiversity loss is one of the main challenges of our time, and attempts to address it require a clear understanding of how ecological communities respond to environmental change across time and space. While the increasing availability of global databases on ecological communities has advanced our knowledge of biodiversity sensitivity to environmental changes, vast areas of the tropics remain understudied. In the American tropics, Amazonia stands out as the world's most diverse rainforest and the primary source of Neotropical biodiversity, but it remains among the least known forests in America and is often underrepresented in biodiversity databases. To worsen this situation, human-induced modifications may eliminate pieces of the Amazon's biodiversity puzzle before we can use them to understand how ecological communities are responding. To increase generalization and applicability of biodiversity knowledge, it is thus crucial to reduce biases in ecological research, particularly in regions projected to face the most pronounced environmental changes. We integrate ecological community metadata of 7,694 sampling sites for multiple organism groups in a machine learning model framework to map the research probability across the Brazilian Amazonia, while identifying the region's vulnerability to environmental change. 15%–18% of the most neglected areas in ecological research are expected to experience severe climate or land use changes by 2050. This means that unless we take immediate action, we will not be able to establish their current status, much less monitor how it is changing and what is being lost

Resilience of Amazonian landscapes to agricultural intensification

ISBN: 978-94-6257-443-4 Author: Catarina C. Jakovac Title: Resilience of Amazonian landscapes to agricultural intensification Swidden cultivation is the traditional agricultural system in riverine Amazonia, which supports local livelihoods and transforms landscapes. In the last decades, riverine Amazonia has been undergoing important transformations related to population migration and market integration. In this study I investigated whether these socio-economic transformations could be inducing agricultural intensification and what are the consequences of such intensification for the resilience of the swidden cultivation systems in the region of the middle-Amazonas river, Brazil. This region is one of the largest producers of cassava flour (farinha in Portuguese) in the Brazilian Amazon, which is the local staple food. By combining information from field surveys, farmers interviews and remote sensing time-series, I investigated how agricultural intensification is taking place at the landscape level, and what are the consequences for secondary forests (fallows) regrowth and swiddens productivity. The results of this study show that swidden cultivation has been intensified in the last three decades, evidenced by an increase in the frequency of swidden-fallow cycles and a decrease in the length of the fallow period, from 9 to 5 years on average. I also found that agricultural intensification was associated to land accessibility and market orientation. Across the region, swiddens are dominated by a single cassava variety that is preferred by the market, reducing the possibilities for adaptation to pests outbreaks and environmental variations. At the field level, repeated swidden-fallow cycles under a short-fallow-period regime (of 5 yrs) leads to a decrease in the recovery capacity of secondary forests (reduced regrowth rate, lower species alpha- and beta-diversity, and changed species composition). Intensification also leads to a reduction in the labour productivity of swiddens (reduced cassava yield and higher weeding labour demand), and consequently in household income. I found that management-environment feedbacks play a key role in the decrease of swiddens and fallows productivity. The sprouting and persistent species favoured by cutting, burning and weeding practices are slow growing and form secondary forests with limited potential to fertilize the next cropping field and to suppress weeds. This results in a higher demand for weeding, which in itself will further favour strong-sprouting species. Such feedbacks reinforce the adverse effects of intensification on the environment and for livelihoods. Although farmers recognize thresholds for managing resilience, such as the formation of tired lands (terras cansadas in Portuguese), the combination of a low-nutrient-requiring crop, increasing farinha prices and shortage of accessible land, is encouraging farmers to keep on cultivating in already exhausted lands, and is pushing the system over such threshold. To enhance the resilience of swidden cultivation systems in the context of riverine Amazonia, management-environment feedbacks should be broken and market opportunities should be broadened beyond cassava, to include forest products that can be harvested within the swidden-fallow landscape, such as nuts, fruits and timber from fast-growing species. Thus, the proper management of secondary succession is key for assuring resilience to swidden-fallow landscapes and for promoting the integration of production and nature conservation in human modified landscapes

Editorial: Enhancing Natural Regeneration to Restore Landscapes

With this Research Topic we aimed to advance our understanding of how natural regeneration can effectively contribute to achieve restoration goals by compiling evidence on (1) processes that drive natural regeneration at the regional scale, and their consequences for spatially prioritizing natural regeneration as a restoration strategy, (2) successional processes driving recovery, (3) how management can enhance natural regeneration to achieve restoration targets, and (4) how external factors shape the restoration potential of natural regeneration

Biomass resilience of Neotropical secondary forests

Land-use change occurs nowhere more rapidly than in the tropics, where the imbalance between deforestation and forest regrowth has large consequences for the global carbon cycle. However, considerable uncertainty remains about the rate of biomass recovery in secondary forests, and how these rates are influenced by climate, landscape, and prior land use. Here we analyse aboveground biomass recovery during secondary succession in 45 forest sites and about 1,500 forest plots covering the major environmental gradients in the Neotropics. The studied secondary forests are highly productive and resilient. Aboveground biomass recovery after 20 years was on average 122 megagrams per hectare (Mg ha-1), corresponding to a net carbon uptake of 3.05 Mg C ha 1 yr-1, 11 times the uptake rate of old-growth forests. Aboveground biomass stocks took a median time of 66 years to recover to 90% of old-growth values. Aboveground biomass recovery after 20 years varied 11.3-fold (from 20 to 225 Mg ha-1) across sites, and this recovery increased with water availability (higher local rainfall and lower climatic water deficit). We present a biomass recovery map of Latin America, which illustrates geographical and climatic variation in carbon sequestration potential during forest regrowth. The map will support policies to minimize forest loss in areas where biomass resilience is naturally low (such as seasonally dry forest regions) and promote forest regeneration and restoration in humid tropical lowland areas with high biomass resilience

Biodiversity recovery of Neotropical secondary forests

Unidad de excelencia María de Maeztu MdM-2015-0552Old-growth tropical forests harbor an immense diversity of tree species but are rapidly being cleared, while secondary forests that regrow on abandoned agricultural lands increase in extent. We assess how tree species richness and composition recover during secondary succession across gradients in environmental conditions and anthropogenic disturbance in an unprecedented multisite analysis for the Neotropics. Secondary forests recover remarkably fast in species richness but slowly in species composition. Secondary forests take a median time of five decades to recover the species richness of old-growth forest (80% recovery after 20 years) based on rarefaction analysis. Full recovery of species composition takes centuries (only 34% recovery after 20 years). A dual strategy that maintains both old-growth forests and species-rich secondary forests is therefore crucial for biodiversity conservation in human-modified tropical landscapes

Multidimensional tropical forest recovery

Tropical forests disappear rapidly because of deforestation, yet they have the potential to regrow naturally on abandoned lands. We analyze how 12 forest attributes recover during secondary succession and how their recovery is interrelated using 77 sites across the tropics. Tropical forests are highly resilient to low-intensity land use; after 20 years, forest attributes attain 78% (33 to 100%) of their old-growth values. Recovery to 90% of old-growth values is fastest for soil (12 decades). Network analysis shows three independent clusters of attribute recovery, related to structure, species diversity, and species composition. Secondary forests should be embraced as a low-cost, natural solution for ecosystem restoration, climate change mitigation, and biodiversity conservation