Successional Changes in Carbon Stocks After Logging and Deforestation for Agriculture in Interior Alaska: Implications for Boreal Climate Feedbacks

The large boreal carbon (C) stocks in Alaska are vulnerable to losses from disturbance, such as clearcut logging and deforestation for agricultural development. Here we investigated impacts of logging in uplands and agricultural deforestation in lowlands on C and nitrogen (N) stocks in Interior Alaska, using chronosequences, and synthesized results from other studies in the boreal region. Two years after logging, ecosystem C stocks in upland forests were reduced by 11 kg m−2 (46% of the original ecosystem C stock), mainly as a consequence of stem removal. Soil C and N stocks increased over the first few years after logging, but returned to pre-harvest levels during the following decades to century. Studies across the boreal region showed that mean initial C loss was four times greater, but long-term C cycling was similar in logged as compared to burned forests. Agricultural development in Alaskan lowlands permanently reduced ecosystem C stocks, reaching losses of 11 kg m−2 (34% of the ecosystem C stock) on non-permafrost soils after several decades and 31 kg m−2 (69%) on permafrost soils over 6 years. These C losses are much more rapid than the 5–6 kg m−2 over 500 years that models project to be lost by warming or warming-plus-wildfire in lowland boreal forests. If economic incentives and climate warming augment boreal land-use change in lowlands because of improved agricultural opportunities and performance, this could magnify warming-induced C loss and amplify climate warming. These impacts can be reduced by conserving permafrost-dominated sites for C storage and focusing agriculture on permafrost-free sites.