• Hollinger, David Y.
  USDA Forest Service
  

Forestry may yet play an important role in policy responses aimed at reducing climate-warming greenhouse gases. This is because when forests grow they remove from the atmosphere the principal greenhouse gas, carbon dioxide, and store it as carbon in wood and other biomass.

Payment for carbon storage has been discussed as a potential incentive for forest owners to manage their lands to take up and store carbon. There are many unresolved scientific and policy issues relating to such schemes and how they might affect present forest management practices.

A recent scientific concern relates to the consequences of afforestation and the decrease in the reflectivity (albedo) of a forested land surface compared to crops or grassland, and the impact that these changes in albedo may have on the climate system. In essence, snow covered fields reflect away more winter sunlight than evergreen forests, so planting forests could lead to the absorption of more solar energy and further warming of the climate system. However, the climate models that are used to estimate the impact of forests on the climate system rely on often outdated estimates of albedo and do not consider the effects of management on forest albedo, even though these impacts can be significant and many forests are managed. We assembled estimates of albedo based on shortwave radiation data obtained at AmeriFlux sites to evaluate the estimates used in climate models. We found that albedos used for grassland and needle-leaf deciduous conifers were in need of revision. We also carried out measurements of albedo in managed conifer forest in central Maine, focusing on comparing shelterwood harvest forest with intact forest. We found that the more open canopy of a shelterwood had a slightly higher albedo than closed coniferous forest, especially in the winter. This means that in addition to potentially high rates of carbon sequestration, such shelterwood systems will lead to reduced climate warming compared to unmanaged forest but climate model simulations indicated limited change in surface temperatures to such slight changes in albedo.