Habitat edges aﬀect stand diversity more than biomass regeneration in a wet neotropical secondary forest Nicholas Medina Ecology and Evolution, University of Michigan Biology and Environmental Studies, Brandeis University; Land Stewardship, Osa Conservation HIGHLIGHTS - Old plantations may facilitate wet tropical secondary forest regeneration - Aboveground biomass and light were resilient to edge eﬀects across 300 m, while wood and stem density tended to increase across 300 m habitat edge - Diversity lowered non-linearly and community composition varied notably - Taxa associated with early- and late-stage succession tended to lose biomass - Future forests likely show some resilience in functions but not biodiversity INTRODUCTION Secondary forest regeneration - Forest and landscape restoration is a key international conservation and climate change adaptation strategy (De Pinto et al. 2020), and while tropical forests speciﬁcally store most land biomass (Pan et al. 2013), most are now secondary (FAO 2020) and regenerating degraded functions (Hubau et al. 2020) amid increasing climate stressors (Anderegg et al. 2022) yet insuﬃcient policy support (Robin L. Chazdon 2018) via skewed priorities (Pyron and Mooers 2022). - Secondary forests can regenerate relatively quickly compared to old-growth forests in some ways, but in other ways remain distinct. - Neotropical secondary forests can grow quickly enough to accumulate biomass >10x faster than old-growth forests (Finegan 1996; Poorter et al. 2016), and substantially oﬀset carbon emissions, with estimates ranging from ~10% from Amazonian deforestation (Smith et al. 2020) to a decade of fossil fuel emissions from all of Latin American and the Caribbean (R. L. Chazdon et al. 2016). - They also recover taxonomic richness and biomass quite quickly, as well as tree height, averaging 80% of old-growth forest levels in just 20 years, especially in wetter regions (Rozendaal et al. 2019). - The recovery of species richness alone is beneﬁcial in that it also tends to correlate with the recovery of some ecosystem services (Guariguata and Ostertag 2001; Stanturf, Palik, and Dumroese 2014) like biomass and carbon storage (Liu et al. 2018). - However, secondary neotropical forests diverge widely in taxonomic composition (Norden et al. 2015), potentially taking over a century to recover (Poorter et al. 2021) with added variability (Atkinson et al. 2022). - Despite being one of the slowest ecosystem properties to recover, restoring recovering community composition is often important for preserving rare taxa (Carlo and Morales 2016), which can be keystone to locally-adapted food webs, including birds (Maas et al. 2016). - Understanding secondary forest regeneration is key for global biodiversity conservation at the global scale, yet local management remains the strongest driver of tropical forest carbon stores (Pyles et al. 2022). Edge eﬀects - Secondary forest regeneration is often aﬀected by edge eﬀects, or changes near an ecosystem boundary, as well as land-use history, especially in heterogeneously-managed landscapes (Perfecto, Vandermeer, and Wright 2009; Melo et al. 2013). - About 70% of all forests have been estimated to be within a km of their edge (Haddad et al. 2015), resulting in tropical forests having been estimated to lose ~22% aboveground carbon along heavily-managed edges >100m, in part due to shortening trees and lighter leaf mass (Ordway and Asner 2020). - Edge eﬀects also have the potential to shape community composition, based on the local dispersal kernel patterns of existing taxa (Wandrag et al. 2017), which while complicated (Muller-Landau and Hardesty 2009), can also correlate with simpler plant traits like height and seed mass (Thomson et al. 2011; Tamme et al. 2014). - The traits of existing taxa also depend on land-use history and previous management (Omeja et al. 2012), which historically has favored tree taxa that tend to pioneering, or be faster-growing, have lower wood