Natural regeneration of new forests has significant potential to mitigate greenhouse gas emissions, but how strong is the potential biodiversity co-benefit? We quantified carbon accumulation and biodiversity gain during secondary succession of two New Zealand lowland forests. The rate of carbon sequestration was the same for the kanuka-red beech succession as for the coastal broadleaved succession (c. 2.3 Mg C ha(-1) year(-1)) over the first 50 years of succession. Mean above-ground carbon stocks were 148 +/- 13 Mg C ha(-1) for kanuka-red beech forests and 145 +/- 19 Mg C ha(-1) for tall coastal broadleaved forests after at least 50 years of succession. Biodiversity gain was investigated through the quantification of 'ecological integrity', which comprises dominance by indigenous species, occupancy of indigenous species or a group of species fulfilling a particular ecological role, and gain in representation of lowland forests within each ecological region. All components of ecological integrity increased with carbon accumulation for both successions. In addition, above-ground carbon stocks were correlated with the Shannon and Simpson diversity indices and species richness for both successions, suggesting that conventional metrics of diversity also show biodiversity gain with above-ground carbon during succession of recently non-forested lands to secondary forest.
