Early tree regeneration is consistent with sustained yield in low-input boreal forest management in Alaska

The boreal forest of Alaska has experienced a small area of forest cuttings, amounting to 7137 ha out of a total of 256,284 ha of timberland in the Fairbanks and Kantishna area of state forest land. Low product values and high costs for management have resulted in a low-input type management with heavy reliance on natural regeneration. Because of increasing demand for wood biomass energy which may reduce rotation ages, understanding post-harvest regeneration is crucial. Harvested areas must meet stocking standards within seven years under the state Forest Resources & Practices Act (FRPA). We evaluated whether state forest harvest units are adequately regenerated up to 40 years following harvest based on FRPA standards in terms of stem density and biomass accumulation. We measured density of all tree size classes, and DBH and height of tree species in 726 plots from 30 representative harvest units, distributed according to harvest and treatment types, harvest year, unit size, and the geographical location of harvests. The majority of regenerated tree stems came from natural regeneration, even on planted units (77%). White spruce (Picea glauca) natural regeneration appears to continue for a few decades (seed crops) following harvest. Stem density was below the standard in most units surveyed during the FRPA 7-year period, but far exceeded the standard when resampled in this study (average 16 years later), suggesting either seven years is too early to evaluate tree regeneration, or that a different standard is needed for early surveys. We found a major peak in white spruce stem density (45,000 ha−1) in units harvested in 1987 (an historically large spruce seed crop year), suggesting that where possible, foresters need to adjust management plans according to spruce mast years. Post-harvest and post-fire successional patterns are similar, involving rapid establishment and growth of hardwoods and slow growth of white spruce, but post-harvest white spruce recruitment appears to continue longer than post-fire. By 2014 all measured harvest units met FRPA standard under low-input management, but some issues of uniformity of regeneration may remain. Although regeneration density varied among species and by management practices, biomass accumulated steadily over time (60 t ha−1 after 40 years), largely composed of hardwoods, indicating that short-rotation forest management must utilize hardwoods. Our results are based on relatively small harvest units within a matrix of natural forest, and similar results might not occur in landscapes dominated by stands originated from more extensive and intensive management.