Search

Abstract Background New Zealand’s planted forest area is dominated by radiata pine (90%), but also includes Douglas-fir (6%), and a range of minor species including eucalypts and cypress. Carbon sequestration in planted forest is currently estimated using yield tables from the Forest Carbon Predictor (FCP), which was designed to estimate dry matter in live biomass and dead organic matter pools in radiata pine stands. Stand variables required as model inputs include basal area, mean top height, stocking, and tending regime. In addition, wood density needs to be measured or estimated. When the FCP is applied to plantation species other than radiata pine, dry matter estimates may need to be adjusted to remove bias. Methods To test for and remove bias, existing biomass studies were compiled and additional biomass data collected to fill gaps. Measured dry matter stock estimates were compared with predictions from the FCP model. Species assessed included Pseudotsuga menziesii (10 stands), Cupressus lusitanica (2), Eucalyptus regnans (7), E. nitens (5), E. saligna (7), E. botryoides (2), E. fastigata (2), and Acacia dealbata (2). Results Stem bark and crown components were higher in Douglas-fir than predicted by the FCP, whereas crown components were appreciably lower in hardwood species than predicted. Root biomass estimates in Douglas-fir and hardwood species were similar to predictions from the FCP. Dead organic matter stock estimates were similar in Douglas-fir to predictions from the FCP. Dry matter predictions from the model were adjusted by species or species group, to help reduce model prediction error when the FCP is applied to these species. Model bias for Douglas-fir averaged 4.1% for aboveground live biomass, with a root mean square error of 12.9%. Model bias for hardwood species averaged − 0.11% for aboveground live biomass, with a root mean square error of 16.1%. Owing to data limitations, model bias was poorly estimated for dead organic matter pools. Conclusions This study has shown that forest carbon models that have been developed for well-studied plantation species can be adapted with some degree of certainty and applied to other species with suitable, albeit limited, biomass data in order to improve the accuracy of predictions of stand biomass and carbon sequestration.

Species-specific and mixed-species volume and above ground biomass allometric equations were developed for 15 indigenous tree species and four tree fern species in New Zealand. A mixed-species tree equation based on breast height diameter (DBH) and tree height (H) provided acceptable estimates of stem plus branch (>10 cm in diameter over bark) volume, which was multiplied by live tree density to estimate dry matter. For dead standing spars, DBH, estimated original height, actual spar height and compatible volume/taper functions provided estimates of dead stem volume, which was multiplied by live tree density and a density modifier based on log decay class from field assessments to estimate dry matter. Live tree density was estimated using ratio estimators. Ratio estimators were based on biomass sample trees, and utilized density data from outerwood basic density surveys which were available for 35 tree species sampled throughout New Zealand. Foliage and branch ( < 10 cm in diameter over bark) dry matter were estimated directly from tree DBH. Tree fern above ground dry matter was estimated using allometric equations based on DBH and H. Due to insufficient data, below ground carbon for trees was estimated using the default IPCC root/shoot ratio of 25%, but for tree ferns it was estimated using measured root/shoot ratios which averaged 20%.