Secondary forest regrowth in a Brazilian cassava field. Photo credit: Catarina Jakovac
By T. Trevor Caughlin, Publications Editor
Resilience, the capacity to retain function and structure after disturbance, is critical for long-term sustainability of social and ecological systems. Many tropical agricultural systems involve cycles of cultivation and fallow. In these systems, secondary forest resilience plays a critical role in biodiversity maintenance and human livelihood, since forest regrowth can restore soil productivity. Predicting secondary forest resilience in a changing world is complicated by the spatially-variable interplay of human activity and ecological context. A new study by Catarina Jakovac and co-authored by PARTNERS member Frans Bongers provides novel insight into how to untangle these complex drivers to understand secondary forest resilience in the Brazilian Amazon.
The study was conducted in five communities in the municipalities of Tefé and Alvarães in the Central Amazon, a region where manioc is cultivated by smallholders in small fields managed with swidden agriculture. Within this region, recovery time of cultivated land in a fallow period ranges from 2 to >15 years. As the region’s population has increased, agricultural production is intensifying with decreases in fallow period and an increase in number of agricultural cycles. The authors relate secondary forest structure and biodiversity in 38 sites to management intensity and ecological variables that represent landscape context (amount of nearby old growth forest) and site context (soil properties). This study design addresses not only how land-use intensification affects secondary forest resilience but also how ecological context could mediate the effects of management activity.
The important conclusion of the study is that agricultural intensification is likely to impair secondary forest resilience. Increased management intensity, including current fallow age, number of cycles and weeding, led to degradation in 5-year old secondary forest structure. This degradation includes shifts in reproductive strategy from seeds to sprouts, increases in weedy liana abundance and decreases in tree canopy height and basal area. The results also reveal that remnant forest patches help maintain secondary forest resilience, with significant increases in tree biodiversity for sites with old growth forest in the surrounding landscape. By linking human activity with ecological process, this study contributes to our understanding of resilience and provides actionable science that could inform land use policy in the Amazon.
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