Local tropical forest restoration strategies affect tree recruitment more strongly than does landscape forest cover

Abstract

Summary1. Developing restoration strategies that accelerate natural successional processes and are resource-efficient is critical to facilitating tropical forest recovery across millions of hectares of deforested lands in the tropics. 2. We compared tree recruitment after a decade in three restoration treatments (natural regeneration, applied nucleation/island tree planting and plantation) and nearby reference forest in the premontane rain forest zone in southern Costa Rica. The study was replicated at 13 sites with a range of surrounding forest cover, enabling us to evaluate the relative influence of local restoration treatments and landscape forest cover on tree recruitment. 3. Density of small-seeded (<5 mm), animal-dispersed recruits was lower in natural regeneration than in applied nucleation, plantation or reference forest plots. Species richness, species density and density of medium (5-10 mm)-and large (>10 mm)-seeded, animal-dispersed recruits were greatest in reference forest, intermediate in applied nucleation and plantation and lowest in natural regeneration plots. 4. Recruit composition differed substantially between reference forest and all restoration treatments. In general, plantation recruit composition was more similar to reference forests and natural regeneration least similar; however, there was high within-treatment variation. 5. Models suggested weak support for the effect of surrounding forest cover on tropical tree recruit density and composition, as compared to restoration treatment and site conditions (e.g. elevation), in this intermediate forest cover landscape. 6. Synthesis and applications. Applied nucleation appears to be a cost-effective strategy as compared to plantation-style planting to accelerate tropical forest recovery regardless of the amount of forest cover immediately adjacent to the site. However, even with active restoration interventions, forest recovery is a multidecade process that proceeds at highly variable rates.

Composition and Diversity of Woody Plants in Tree Plantations Versus Secondary Forests in Costa Rican Lowlands

“…found differences in species composition between tree plantations and secondary forest at 10 and 15 years old (Butler et al, 2008;Holl et al, 2017), although a study of 5-year-old sites did not (Gilman et al, 2016). Although regeneration in tree plantations is often dominated by early successional species (Cusack & Montagnini, 2004;Zahawi et al, 2013), it has been shown to resemble the composition of mature forest more than secondary forest does .…”

International principles and standards for the practice of ecological restoration. Second edition

“…One combined approach is applied nucleation , which involves planting small patches of vegetation (often trees) that attract dispersers and facilitate establishment of new recruits, expanding the forested area over time. Applied nucleation has shown promise in restoring landfills (Corbin et al ), Mediterranean woodlands (Rey Benayas et al ), tropical forests (Corbin & Holl ; Holl et al ), and other ecosystems. Deciding on an appropriate approach or combination may not be self‐evident.…”

Litterfall and nutrient dynamics shift in tropical forest restoration sites after a decade of recovery

“…This result is consistent with the limited woody recruitment and aboveground biomass quantified in these plots, which is most likely due to competition with pasture grasses (Holl & Zahawi , Holl et al . ); a possible alternative is slower growth rates at our premontane wet forest sites. Brown and Lugo () conclude that litterfall is highest at an intermediate ratio of temperature to precipitation; however, our sites have comparatively lower temperature to lowland sites where most tropical secondary forest litterfall studies have been conducted ( e.g ., Ewel , Ostertag et al .…”

“…, Holl et al . ), but at least in the short‐term results in less aboveground biomass (Holl & Zahawi ).…”

“…We predicted that litterfall biomass differences in the island and plantation treatments would diminish between the two sampling periods due to the establishment of naturally recruiting trees in the island treatment (Holl et al . ). We also anticipated that there would still be substantial differences in plantation nutrient inputs, as compared to the island treatment and reference forests, given that the majority of the woody biomass in plantations is comprised of the four planted tree species (Holl & Zahawi ), two of which fix nitrogen.…”