Mitigating an organization's future net carbon emissions by native forest restoration

Forest establishment has been proposed to moderate recent rises in atmosphe ric CO2 concentration. This study investigated the long-term feasibility of undertaking forest restoration to balance an organization's net carbon emi ssions. Native forests were chosen because they can retain high levels of c arbon biomass under a wide range of environmental conditions. For a site ne ar Christchurch, New Zealand (latitude 43.32 degrees S, longitude 172 degre es E), an individual-based forest model (LINKNZ) predicted, in the absence of large-scale disturbance, newly established conifer-dominated forest woul d store similar to 400 Mg C/ha after 350 yr, gradually declining to similar to 300 Mg C/ha as succession proceeded. Future net carbon emissions, initi alized at 250 Mg C, were examined under four scenarios: 1%/yr growth; const ant level; decline to an asymptote; and 1%/yr decline. Depending on the sce nario, 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 dyn amics into account, the timing and duration of a positive carbon balance co uld 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. T he nonlinear relationship between the minimum forest area and the balance d ate gave an optimal choice under each scenario. Management of the organizat ion's carbon emission levels largely 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 reduce d 1%/yr. Over longer periods the analysis suggested an organization would h ave to restrain or reduce net carbon emission levels to avoid diverting con siderable resources into forest restoration. In general, the results suppor ted global-scale predictions on the viability of establishing forests to re duce carbon levels.