Abstract
Secondary forests originate from natural regeneration after fallow (succession) or restoration. Species assembly in these communities, which can affect ecosystem functions and successional trajectories, is very unpredictable. Trait-based trajectories can shed light on the recovery of ecosystem functions and enable predictions of how the regenerating communities will change with forest age. Regeneration communities are affected by initial conditions and also by canopy structure and functional traits that alter dispersers' attractiveness and coexistence mechanisms. Here we evaluated how community functional traits change over time and tested if functional diversity and composition of the established canopy, as well as the structure of the canopy and forest age, influence the functional structure of regenerating tree communities when compared to their reference forests. For this, we calculated dissimilarity in trait composition (community-weighted means) and in functional diversity of regenerating communities of each succession/restoration stand, using the tree stratum of nearby mature forests as baseline values. Functional trait information comprises leaf, wood density, and reproductive traits from tree species. Our community data contain information from natural successional forests and restoration sites, in the South-Brazilian Atlantic Forest. Predictor variables of functional dissimilarities were forest age, canopy structural variables, canopy functional composition, and functional diversity. Results showed leaf traits (leaf dry matter content, leaf nitrogen content, leaf nitrogen-phosphorus ratio) and seed mass varying with forest age. Canopy functional composition based on leaf traits and total basal area significantly predicted multiple trait functional dissimilarity between the regeneration component of secondary forests and their reference community values. Dissimilarity increased when the canopy was composed of species with more acquisitive traits. Difference in functional diversity was only influenced by forest age. Mid-stage secondary forests showed lower functional diversity than early-stage forests. Our results indicated the importance of canopy traits on the natural regeneration of secondary subtropical forests. If functional similarity with reference forests is a desired objective in order to recover ecosystem functions through natural regeneration, leaf functional traits of canopy trees that establish or are planted in degraded areas must be considered in the successional processes.
Highlights
Secondary forests are important for biodiversity conservation and ecosystem services, such as biomass stocks and water cycling, given the widespread deforestation and forest degradation processes in the tropics and subtropics (Chazdon et al, 2009)
A great portion of current subtropical and tropical forest coverage comprises secondary forests, which increases the role of these forests for biodiversity conservation and the provision of ecosystem services (Chazdon et al, 2009; Martin et al, 2013; Pichancourt et al, 2014)
Understanding whether functional composition and diversity of regenerating tree communities increase in similarity when compared to reference forests is essential in order to evaluate the potential return of ecosystem functions and services from these secondary forests
Summary
Secondary forests are important for biodiversity conservation and ecosystem services, such as biomass stocks and water cycling, given the widespread deforestation and forest degradation processes in the tropics and subtropics (Chazdon et al, 2009) These forests are originated from natural regeneration processes after the abandonment of anthropogenic land-use types (succession) or after intentional actions to assist the recovery of ecosystems (restoration). Species composition when compared to structural parameters or species richness, is the most unpredictable factor along succession, taking centuries to recover or even not recovering to similar pre-disturbances patterns at all (Chazdon, 2008; Liebsch et al, 2008; Rozendaal et al, 2019) Considering this and the importance of species characteristics and assemblies to ecosystem functions (Diaz et al, 2007), understanding and predicting the recovery of plant functional traits along the successional process of secondary forests is of most importance. This is especially important in tropical and subtropical forests, where the number of rare species (with potential distinct and unique traits) is high when compared to the amount of common, abundant species
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