Potential effects of climate and land use change on soil carbon and CO2 emissions from New Zealand's indigenous forests and unimproved grasslands
Present understanding of the relative sensitivity to climate change of the natural and managed land systems of New Zealand, and feedbacks to the atmosphere, is generally poor and largely qualitative. This paper describes the development and application of a process-based ecological simulation model to estimate increases in soil CO2 emissions resulting from human-induced ecosystem modifications in New Zealand's indigenous forests and unimproved grasslands under current climates, and future climate warming. For these New Zealand land uses at steady state, plant residue carbon inputs of 53 and 73 Mt C y-1 respectively, are needed to maintain standing stocks of 547 and 671 Mt C (soil carbon) to 23 cm depth. Lower inputs resulting from ecosystem degradation could result in significant net CO2 emissions. An additional source of soil CO2-C of about 0.52 and 0.76 Mt y-1 from forests and grasslands could result from accelerated decomposition of soil organic matter. These simulated releases of CO2 from decomposing soil organic matter, resulting from the combined effects of ecosystem degradation and climate change, would accelerate the buildup of atmospheric CO2, further enhancing the warming trend.