Woody species richness drives synergistic recovery of socio-ecological multifunctionality along early tropical dry forest regeneration

Abstract

Secondary tropical forests offer critical ecosystem services such as regulation of climate, soil and water resources, which are frequently traded off against the provision of forest products for human use or repeated clearing for agriculture. While some evidence also suggests potential synergies between regulating and material contributions of regenerating forests to people, the ecological mechanisms of multiple synergies remain poorly understood. We assess tradeoffs and synergies by testing for cascading effects of tropical dry forest age and vegetation drivers on key ecosystem properties that underpin multiple regulating, material and non-material contributions to people. To do so we first compiled published evidence to propose a conceptual framework of the causal dependence among variables. Then, we tested which direct or indirect effects of this a priori conceptual model are supported by structural equation models of measured data from a chronosequence of secondary tropical dry forest plots. We tested whether individual density, taxonomic or functional diversity, community-weighted mean in wood specific gravity, or composition of the woody vegetation best explained synergies or tradeoffs among multiple key ecosystem properties. We show a synergistic, positive effect of observed woody species richness on all four key ecosystem properties, including total basal area, litter layer carbon stocks, soil penetration resistance and availability and versatility of socioeconomically useful plants. A similar synergistic effect of linear age-dependent changes in species composition suggests that the simultaneous recovery of multiple functions is not only driven by absolute woody species accrual, but also by temporal woody species turnover as secondary succession proceeds. However, local farmers reported uses of only a small fraction of available plant biodiversity that has previously been documented in the literature to be socioeconomically useful. In synthesis, we found that observed woody species richness and successional turnover along tropical dry forest regeneration are synergistic drivers of biodiversity, ecosystem functioning and the availability and versatility of currently underutilized plant products in Western Mexico. Such observed synergy between a range of key regulating, material and non-material contributions to people highlights untapped socioecological potential for multifunctional tropical forest restoration through sustainable use.