- Smith, Charles Tattersall Jr.
College of Forest Resources, University of Maine, Orono
Whole-tree harvesting in the spruce-fir type has been studied cooperatively at the Weymouth Point Study Area by the Cooperative Forestry Research Unit at the UMO College of Forest Resources; the U.S. Forest Service, Forestry Sciences Laboratory, Durham, N.H.; and Great Northern Paper Company Millinocket, Maine. The objectives were to estimate the biomass and nutrients removed or redistributed during whole-tree harvesting; and to evaluate the harvesting and three residue management alternatives with respect to long-term site fertility and soil water quality. The three residue management alternatives studied were l) complete removal of residue' 2) residue chipped and scattered on the site, and 3) residue scattered intact on the site to simulate chainsaw delimbing.
The nutrients present in the top 54 cm of the glacial till soil of the study area and quantities removed by harvest were estimated (Table 1). The proportion of nutrients removed by a bole-only and whole-tree harvest provide ratios useful in estimating the number of rotations of equivalent harvest removals that the soils could sustain without additions of nutrients from other sources (Table 2).
For example, the ratios (Table 2) indicate that whole-tree harvesting might deplete total soil nutrient reserves of N after 21 rotations, Ca after 25, K after 52, P after 60, and reserves of Mg after 829 rotations. However on the basis of exchangeable soil nutrient, reserves, whole-tree harvesting would deplete K after O.8 rotations, Ca after 0.9, Mg after 5, and reserves of P after 5 rotations. The supply of exchangeable K and Ca may be limited in the next rotation. Exchangeable nutrient reserves are replenished by weathering of soil minerals, decomposition of organic matter, and by atmospheric deposition. These replenishment sources are important in suppling future rotations with nutrients.