A large‐scale assessment of plant dispersal mode and seed traits across human‐modified Amazonian forests

Abstract

Quantifying the impact of habitat disturbance on ecosystem function is critical for understanding and predicting the future of tropical forests. Many studies have examined post-disturbance changes in animal traits related to mutualistic interactions with plants, but the effect of disturbance on plant traits in diverse forests has received much less attention. 2. Focusing on two study regions in the eastern Brazilian Amazon, we used a trait-based approach to examine how seed dispersal functionality within tropical plant communities changes across a landscape-scale gradient of human modification, including both regenerating secondary forests and primary forests disturbed by burning and selective logging. 3. Surveys of 230 forest plots recorded 26,533 live stems from 846 tree species. Using herbarium material and literature, we compiled trait information for each tree species, focusing on dispersal mode and seed size. 4. Disturbance reduced tree diversity and increased the proportion of lower wood-density and smaller-seeded tree species in study plots. Disturbance also increased the proportion of stems with seeds that are ingested by animals and reduced those dispersed by other mechanisms (e.g. wind). Older secondary forests had functionally similar plant communities to the most heavily disturbed primary forests. Mean seed size and wood density per plot were positively correlated for plant species with seeds ingested by animals. 5. Synthesis. Anthropogenic disturbance has major effects on the seed traits of tree communities, with implications for mutualistic interactions with animals. The important role of animalmediated seed dispersal in disturbed and recovering forests highlights the need to avoid defaunation or promote faunal recovery. The changes in mean seed width suggest larger vertebrates hold especially important functional roles in these human-modified forests. Monitoring fruit and seed traits can provide a valuable indicator of ecosystem condition, emphasising the importance of developing a comprehensive plant traits database for the Amazon and other biomes.

Wood Density and Dispersal Modes of Trees Regenerating in Disturbed Forests and Agroforests in Indonesia

“…The main constraint to dipterocarp trees in rubber agroforests still is in the policy domain: as farmers fear to be caught for illegal logging if they harvest native tree species, they rather remove them in an early stage (Tata et al , 2009. Our results align with a recent analysis for the Amazonian forests (Hawes et al 2020) that used compiled trait information (focusing on dispersal mode and seed size) for 846 tree species encountered in two study regions with regenerating secondary forests and primary forests disturbed by burning and selective logging. Their data con rmed that disturbance reduced tree diversity and increased the proportion of lower wood density and small-seeded tree species in study plots.…”

Large carbon sink potential of secondary forests in the Brazilian Amazon to mitigate climate change

“…Undisturbed, old-growth forests not only serve to maintain the current carbon sink but also act as key sources of seeds for regeneration. However, disturbances to both old-growth and secondary forests have increased the proportion of low wood density and small-seeded tree species 51 . Identifying the proximity of secondary forests to disturbed versus undisturbed forests could potentially be another driving variable impacting the regrowth rates we have calculated in this study.…”

“…The drivers used in this study to assess regrowth potential can be developed further to include other important variables that influence regeneration and regrowth. This includes variables such as the proximity to other forest landscapes, both young and old and disturbed and undisturbed 51 , 54 as well as the type of previous land-use practices (livestock, agriculture and forestry) and the period of active land use before abandonment 53 . For instance, secondary forests regrow 38% faster on land used for agriculture than those for cattle pastures 44 , 63 .…”

Secondary forests offset less than 10% of deforestation‐mediated carbon emissions in the Brazilian Amazon

“…However, it is likely that proximity to old‐growth forest will be more important later in succession, as they are essential for providing the diverse seed sources required to establish resilient, biodiverse and high‐biomass secondary forests (e.g. Hawes et al, 2020). Furthering our understanding, these relationships will be key to designing effective restoration programmes within landscapes where there is little old‐growth forest remaining.…”