LETTERS PUBLISHED ONLINE: 28 APRIL 2014 | DOI: 10.1038/NCLIMATE2200 Cheap carbon and biodiversity co-benefits from forest regeneration in a hotspot of endemism James J. Gilroy 1 * † , Paul Woodcock 1,2 , Felicity A. Edwards 3 , Charlotte Wheeler 4 , Brigitte L. G. Baptiste 5 , Claudia A. Medina Uribe 5 , Torbjørn Haugaasen 1 and David P. Edwards 6,7 * Climate change and biodiversity loss can be addressed simultaneously by well-planned conservation policies, but this requires information on the alignment of co-benefits under different management actions 1–3 . One option is to allow forests to naturally regenerate on marginal agricultural land: a key question is whether this approach will deliver environmental co-benefits in an economically viable manner 4–7 . Here we report on a survey of carbon stocks, biodiversity and economic values from one of the world’s most endemic-rich and threatened ecosystems: the western Andes of Colombia. We show that naturally regenerating secondary forests accumulate signifi- cant carbon stocks within 30 years, and support biodiverse communities including many species at risk of extinction. Cattle farming, the principal land use in the region, provides minimal economic returns to local communities, making forest regeneration a viable option despite weak global carbon markets. Efforts to promote natural forest regeneration in the tropical Andes could therefore provide globally significant carbon and biodiversity co-benefits at minimal cost. As the financial resources available to tackle climate change and biodiversity loss are limited, there is an urgent need to identify actions that simultaneously address both issues 1,2 . Carbon- based payments for ecosystem services (PES) can fund such actions, although current economic pressures are tending to shift priority towards maximizing carbon gains at the lowest cost 2,3 . With weak carbon markets, there is a danger that biodiversity will be left behind in the drive to make schemes economically viable 4–7 . A critical challenge at the interface of climate change and ecosystems science is to identify points of convergence between carbon storage, biodiversity protection and the economic viability of conservation actions, allowing PES co-benefits to be maximized 1,7–9 . One possibility is to allow forests to naturally regenerate on marginal agricultural lands, although this option has been overshadowed by a focus on avoiding further deforestation, for example in the literature discussing the United Nations’ programme for reducing emissions from deforestation and forest degradation (REDD+; refs 2,5–7). An important question is whether natural forest regeneration represents a cost-effective tool to combat climate change and biodiversity loss, particularly in the hyperdiverse tropics 5–7 . Here we examine the alignment of carbon and biodiversity co- benefits from natural forest regeneration in one of the world’s most threatened ecosystems: the tropical Andes. Global assessments highlight this region as an unparalleled centre of biological endemism 10,11 , housing one of the highest concentrations of threatened species worldwide 12,13 . Andean landscapes have a long history of deforestation for agriculture (Supplementary Fig. 1), suffering the highest predicted extinction rate of all biodiversity hotspots 13,14 . Recently, however, there are signs of land abandonment and rural depopulation associated with low economic returns from agriculture, followed by a wave of natural forest regeneration 15 . We conducted field studies across three regions in Western Colombia, a zone where prior research has been scant owing to political and social unrest 14 , despite exceedingly high conservation priority 12,13 . We performed in situ carbon assessments in primary forest, naturally regenerating secondary forest and cattle pastures (Supplementary Fig. 2 and Table 1), combining these with biodiversity surveys (birds and dung beetles) and economic analyses to examine whether carbon-based PES can provide cost-effective conservation benefits. Carbon assessments indicated that non-soil carbon stocks accumulated at a rate of 4.29 t C ha -1 yr -1 (±0.56 s.d.) in naturally regenerating secondary forests, with stocks reaching approximately half the levels found in primary forests within 15–30 years (Fig. 1a and Supplementary Table 2). We calculated the cost of payment initiatives to encourage forest regeneration (for example, REDD+ for carbon enhancement) by estimating the opportunity cost of taking agricultural lands out of production, as well as managing and implementing a PES project (Fig. 1b). We focus on cattle farming, which accounts for 75% of agricultural land and 49% of total land in the Colombian Andes (Supplementary Table 3). We estimated the median net present value (NPV) of cattle pasture in the region to be US$149.83 ha -1 (Fig. 1d), with a 95% credible interval (CI) ranging from -US$51.81 ha -1 to US$383.81 ha -1 , accounting for uncertainty in economic parameters (Methods). Over a 30-year time horizon, the median market price for viable forest regeneration under a long-term certified emissions reduction scheme (lCER; ref. 16) was US$1.99 t -1 CO 2 (CI $0.59–$3.66, Fig. 1c). Under a temporary credit accounting system, where each credit is re-issued at five-year intervals (tCER; ref. 16), the median price was US$0.80 (CI $0.25–$1.67, Supplementary Fig. 3). As forest regeneration is a riskier investment than avoided deforestation, willingness to pay for temporary credits may be lower than for permanent credit schemes that apply to standing forests 16 . Consequently, the market value of tCERs may be several times lower than that of permanent credits, whereas lCERs are more directly comparable 16 . Globally, permanent credits traded at a mean of US$7.80 t -1 CO 2 in 2013 17 , suggesting that both lCERs and tCERs for natural forest regeneration should be economically 1 Department of Ecology and Natural Resource Management, Norwegian University of Life Sciences, Ås, 1430 Norway, 2 School of Environment, Natural Resources and Geography, Bangor University, LL5 2UW, UK, 3 School of Biology, University of Leeds, LS2 9JT, UK, 4 Department of Geography, UCL, WC1E 6BT, London, UK, 5 Instituto de Investigación de Recursos Biológicos Alexander von Humboldt, Bogota Calle 28A # 15-09, Colombia, 6 Department of Animal and Plant Sciences, University of Sheffield, S10 2TN, UK, 7 School of Marine and Tropical Biology, James Cook University, Cairns, QLD 4811, Australia. † Present address: School of Environmental Sciences, University of East Anglia, Norwich NR47TJ, UK. *e-mail: james.gilroy1@googlemail.com; david.edwards@sheffield.ac.uk NATURE CLIMATE CHANGE | ADVANCE ONLINE PUBLICATION | www.nature.com/natureclimatechange 1 © 2014 Macmillan Publishers Limited. 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