Using large‐scale tropical dry forest restoration to test successional theory

Abstract

Microclimatic conditions change dramatically as forests age and impose strong filters on community assembly during succession. Light availability is the most limiting environmental factor in tropical wet forest succession; by contrast, water availability is predicted to strongly influence tropical dry forest (TDF) successional dynamics. While mechanisms underlying TDF successional trajectories are not well understood, observational studies have demonstrated that TDF communities transition from being dominated by species with conservative traits to species with acquisitive traits, the opposite of tropical wet forest. Determining how functional traits predict TDF tree species’ responses to changing environmental conditions could elucidate mechanisms underlying tree performance during TDF succession. We implemented a 6‐ha restoration experiment on a degraded Vertisol in Costa Rica to determine (1) how TDF tree species with different resource‐use strategies performed along a successional gradient and (2) how ecophysiological functional traits correlated with tree performance in simulated successional stages. We used two management treatments to simulate distinct successional stages including: clearing all remnant vegetation (early‐succession), or interplanting seedlings with no clearing (mid‐succession). We crossed these two management treatments (cleared/interplanted) with two species mixes with different resource‐use strategies (acquisitive/conservative) to examine their interaction. Overall seedling survival after 2 yr was low, 15.1–26.4% in the four resource‐use‐strategy × management‐treatment combinations, and did not differ between the management treatments or resource‐use‐strategy groups. However, seedling growth rates were dramatically higher for all species in the cleared treatment (year 1, 69.1% higher; year 2, 143.3% higher) and defined resource‐use strategies had some capacity to explain seedling performance. Overall, ecophysiological traits were better predictors of species’ growth and survival than resource‐use strategies defined by leaf and stem traits such as specific leaf area. Moreover, ecophysiological traits related to water use had a stronger influence on seedling performance in the cleared, early‐successional treatment, indicating that the influence of microclimatic conditions on tree survival and growth shifts predictably during TDF succession. Our findings suggest that ecophysiological traits should be explicitly considered to understand shifts in TDF functional composition during succession and that using these traits to design species mixes could greatly improve TDF restoration outcomes.

Assisted restoration interventions drive functional recovery of tropical wet forest tree communities

“…Higher FRic observed in the assisted restoration treatments was likely influenced by observed dispersal of more seeds of more species to these treatments (Werden et al, 2021), and by the presence of more suitable safe-sites for tree establishment and persistence (e.g., Norden et al, 2009). In particular the higher canopy cover, which has been observed to increase seed-to-seedling transition rates for specific species across our sites (Werden et al, 2020a). Importantly, while FRic differed considerably between assisted and natural restoration interventions at the end of the study, functional dispersion (FDis) did not (Table 2).…”

“…A variety of factors operating on local to regional scales influence tropical forest revegetation rates (Arroyo-Rodríguez et al, 2017). These include the intensity of prior land use (e.g., Meli et al, 2017), the dominance of invasive species (Ostertag et al, 2009;Holl, 2012), and plant dispersal and establishment processes at a given site (Holl, 1999;de la Peña-Domene et al, 2017;Werden et al, 2020a). In cases where natural recovery is slow, rapidly increasing canopy cover by planting trees can shade out invasive forage grasses, attract dispersers, and ameliorate microclimatic conditions for seedling establishment (Lamb, 2005;Holl, 2012).…”

Throughfall exclusion and fertilization effects on tropical dry forest tree plantations, a large-scale experiment

“…Before Horizontes was incorporated into Área de Conservación Guanacaste (ACG), the lands were used for grazing and crops (Werden et al, 2018b). Since 1989, Horizontes has served as a large-scale ecological and forestry research laboratory, and the ~7500 ha area encompasses a mosaic of TDF at different successional stages (0-80 years), 64 ha of timber plantations trials of native TDF species (Gutiérrez-Leitón, 2018), restoration trials (Werden et al, 2020), a Mesoamerican TDF arboretum (http://www.arbnet.org/morton-register/arboretum-del-bosque-seco-tropical), as well as seed orchards of endangered precious wood species (M. Gutiérrez-Leitón personal communication). During the study period total annual rainfall averaged ~1547 mm, with annual totals as follows: 1439 mm (2016), 2201 mm (2017), 992 mm (2018), 919 mm (2019), and 2186 mm (2020), and median temperatures were 26.5 ± 1.6 °C during the dry season and 25.6 ± 1.5 °C during the wet season (Fig.…”

Especies con potencial para sistemas agroforestales en el Departamento del Magdalena, Colombia

“…Ceiba (Pachira quinata) madera, medicinal, leña, construcciones y fuente de alimento para murciélagos (polinizadores) e insectos esfíngidos Werden et al, (2020) Trupillo (Prosopis juliflora)…”