MITIGATING AN ORGANIZATION'S FUTURE NET CARBON EMISSIONS BY NATIVE FOREST RESTORATION

Abstract

Forest establishment has been proposed to moderate recent rises in atmo- spheric CO2 concentration. This study investigated the long-term feasibility of undertaking forest restoration to balance an organization's net carbon emissions. Native forests were chosen because they can retain high levels of carbon biomass under a wide range of environmental conditions. For a site near Christchurch, New Zealand (latitude 43.32° S, longitude 172° E), an individual-based forest model (LINKNZ) predicted, in the absence of large-scale disturbance, newly established conifer-dominated forest would store 400 Mg C/ha after 350 yr, gradually declining to 300 Mg C/ha as succession proceeded. Future net carbon emissions, initialized at 250 Mg C, were examined under four scenarios: 1%/ yr growth; constant level; decline to an asymptote; and 1%/yr decline. Depending on the scenario, the minimum area needed to balance accumulated forest carbon biomass against net carbon emissions doubled from 65 ha to 138 ha, time to attain a balance extended from 28 yr to >300 yr, and the period in surplus lasted from 4 yr to 70 yr. The forest model showed that, by taking the forest dynamics into account, the timing and duration of a positive carbon balance could be markedly improved. For example, under net emission growth of 1%/yr, a 5% increase in area from the minimum needed to reach a balance prolonged the surplus sixfold and shifted the balance date from year 28 to year 17. The nonlinear relationship between the minimum forest area and the balance date gave an optimal choice under each scenario. Management of the organization's carbon emission levels large- ly determined the long-term viability of establishing forest to balance net emissions. To balance emissions by year 100, assuming a 1%/yr growth from 250 Mg C/ha, required restoring >230 ha in forest; in comparison <90 ha would suffice if emissions could be reduced 1%/yr. Over longer periods the analysis suggested an organization would have to restrain or reduce net carbon emission levels to avoid diverting considerable resources into forest restoration. In general, the results supported global-scale predictions on the viability of establishing forests to reduce carbon levels.