Regrowing natural forests is a prominent natural climate solution, but accurate assessments of its potential are limited by uncertainty and variability around carbon accumulation rates. To assess why and where rates differ, we compiled 13,112 georeferenced measurements of carbon accumulation. Climate explained variation in rates better than land use history, so we combined field data with 66 environmental covariate layers to create a global, 1-km resolution map of potential aboveground carbon accumulation rates for the first 30 years of forest regrowth. Our results indicate that on average default forest regrowth rates from the Intergovernmental Panel on Climate Change are underestimated by 32% and miss 8-fold variation within ecozones.Conversely, we conclude that previously reported maximum climate mitigation potential from natural forest regrowth is overestimated by 11% due to the use of overly high rates. Our results therefore provide a much needed and globally consistent method for assessing natural forest regrowth as a climate mitigation strategy. BackgroundTo constrain global warming, we must reduce emissions and capture excess carbon dioxide (CO2) in the atmosphere 1,2 . Restoring forest cover, defined here as the transition from < 25% tree cover to > 25% tree cover where forests historically occurred, is a promising option for additional carbon capture 3 and has been prioritized in many national and international goals 4,5 . It is deployable, scalable, and provides important biodiversity and ecosystem services 6 . Yet the magnitude and distribution of climate mitigation opportunity from restoring forest cover is poorly described, with large confidence intervals around estimates 2,3 . To evaluate the appropriateness of forest cover restoration for climate mitigation, compared to the multitude of other potential climate mitigation actions, countries, corporations, and multilateral entities need more accurate assessments of its potential 7 .Mitigation potential from restoring forest cover (reported here in terms of MgCO2 yr -1 ) is determined by the potential extent and location of new forest ("area of opportunity") and the rate at which those forests remove atmospheric CO2 (reported here in terms of MgC ha -1 yr -1 ). While there are now multiple estimates of area of opportunity based on diverse and often heavily debated criteria (e.g., references 3,8-11 ), we lack spatially explicit and globally comprehensive estimates of accumulation rates. This is especially true for natural forest regrowth, defined here as the recovery of forest cover on deforested lands through spontaneous regrowth after cessation of prior disturbance or land use. Many countries do not have nationally specific forest carbon accumulation rates and instead rely on default rates from the Intergovernmental Panel on Climate Change (IPCC) 12,13 . Although these rates were recently updated 8,12 , they nonetheless represent coarse estimates based on continent and ecological zone, and do not account for finer scale variation in rates due to mor...

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We currently have the opportunity to restore one of the most threatened tropical ecosystems on the Pacific coast of Panama as a consequence of land use change. Factors that influence succession must be understood in order to capitalize on natural regeneration mechanisms. In this study, we determined the effects of exotic grass removal, cattle removal, proximity to forested riparian zones, and topography (upslope vs. downslope) on the initial stages of forest regeneration from pasture in a dry tropical region. After 3 years, basal area, stem density, and species richness of plants (trees, shrubs, vines, and herbs) were significantly and positively affected by exclusion of cattle, presence of exotic grass (no herbicide application), and presence of adjacent forested riparian zones (p < 0.01). Interactions between factors were not significant. Cattle foraged and stomped on vegetation, whereas herbicide application, although effectively removing grass, also killed tree and shrub sprouts, the major source of regrowth. Proximity to forested riparian zones had the greatest effect on species diversity. Shannon's index for diversity (H) equaled 3.23 in plots adjacent to forested riparian zones as compared to 2.78 in plots not associated with these areas. Our recommendations during the early stages of forest succession are to (1) exclude cattle, (2) make site-specific decisions about herbicide application based on the presence or absence of forested riparia and prevalence of coppicing, and (3) actively conserve and protect riparian zones, which function as a critical source of diverse propagules.

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Small vertebrates were inventoried within three habitat types in a degraded dry forest region of Panama. Animals were classified as frugivorous if they were observed foraging on fruit or if fecal samples contained mostly or exclusively seeds. Overall, we found that eight bat species and 21 bird species consumed fruit. The greatest numbers of birds were observed within live fences and bird species richness was greatest within riparian forests. Bat assemblages were not significantly different between habitats. The implication is that ecosystem services such as seed dispersal may still be functional in this landscape.Abstract in Spanish is available at http://www.blackwell-synergy.com/loi/btp.