Abstract
Societal Impact StatementThe Brazil nut is a highly valuable non‐timber forest product from a wild, hyperdominant, emergent tree species that is increasingly vulnerable and exposed to habitat degradation. We provide evidence for how Brazil nut genetic resources are negatively affected by forest degradation and discuss the consequences of this for reproductive success. To avoid negative effects of genetic erosion and inbreeding, we discuss the need to cease large‐scale forest conversion and to promote landscape connectivity. This could support gene flow, maintain genetic diversity across individuals reproducing in clustered patterns and contribute to securing the long‐termed reproductive viability and resilience of this high socio‐economically and ecologically valuable species.Summary Ecosystem degradation in the Amazon drives this biodiverse rainforest toward an ecological tipping point. Sustainable management and restoration of degraded rainforest therein are central to counteract this crisis. One hyperdominant, keystone species of high ecological and socio‐economic value, the Brazil nut tree, offers additional benefits as a major carbon sink and a nutritional source of the most prominent globally traded non‐timber forest product. Despite Brazil nut trees being protected by conservation regulation, forest degradation threatens sufficient gene‐flow among Brazil nut tree populations. This has impacts on the reproductive success, genetic diversity, and consequently on the resilience of this species to environmental change. We used 13 microsatellite loci to explore the consequences of forest degradation on the reduction in genetic diversity of Brazil nut populations. We examined the clustering of genetically related individuals as fine‐scale genetic structure (FSGS) and the variation in genetic diversity and inbreeding across adult trees and seedlings along a categorized forest‐degradation gradient ranging from conserved to degraded areas. In addition, we applied direct and indirect approaches to estimate contemporary pollen‐mediated gene flow. We found significant levels of FSGS, comparable to other similar tropical tree species. Brazil nut seedlings had consistently lower genetic diversity and higher inbreeding than adults, significantly associated with the degree of forest degradation of their origin. We observed limited pollen dispersal, differential patterns in pollen heterogeneity, and disproportionate paternal‐assignment rates from few individuals shaping the effective population size in our dataset. We discuss how this evidence for reproduction vulnerability may affect the genetic resources and undermine the resilience of this ecological and socio‐economic system in Peru.
Highlights
The Amazon basin accounts for the world's largest rainforest, is home to globally important biodiversity regions and provisions multiple planetary services, from climate change mitigation to supporting millions of rural livelihoods
We asked the following: What is the historical scale of fine-scale genetic structure (FSGS) prior to forest degradation of Brazil nut adult populations in comparison to other longlived tropical tree species? Are there signs of loss of genetic diversity and of inbreeding in Brazil nut populations undergoing processes of forest degradation? What is the distance and heterogeneity of pollen-mediated gene flow of Brazil nut populations and are these disrupted by forest degradation? For this, we used genotypic data from 13 microsatellite loci from adults as mother trees and potential pollen donors, and from nursery-germinated seedlings in common garden experiments
A bar graph showing population assignments of each study site, together with overall allele frequency linked to the Brazil nut populations in this study demonstrated significant and strong patterns of fine-scale genetic structure (FSGS), for shorter distances than 700–1000 meters
Summary
The Amazon basin accounts for the world's largest rainforest, is home to globally important biodiversity regions and provisions multiple planetary services, from climate change mitigation to supporting millions of rural livelihoods. Tree genetic erosion can negatively affect population recruitment (Ismail et al, 2014a), reduce resistance of individuals and populations against environmental stressors and risk long-term viability and future adaptive potential of tree populations (Rellstab et al, 2016) All together, these processes can have further negative consequences on the Brazil nut market and on the local communities that depend on it. To better understand how landscape context may influence state of Brazil nut genetic resources, we evaluated pollen-mediated gene flow within different sites across this gradient and examined the evidence that fragmentation genetics could undermine the reproductive patterns and genetic diversity of Brazil nut populations To this end, we asked the following: What is the historical scale of FSGS prior to forest degradation of Brazil nut adult populations in comparison to other longlived tropical tree species? We discuss the evidence from the results of these questions and the implications of these findings for sustainable management of Brazil nut ecological and socio-economic systems in Madre de Dios and the Amazon more broadly
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