- Perry, Thomas
University of Maine
- Seymour, Robert
University of Maine
- Wagner, Robert
University of Maine
As part of their mandate to report on the condition of Maine’s forests, the Maine Forest Service (MFS) commissioned the University of Maine to develop an approach for classifying harvests and assessing the resulting silvicultural outcome. The objective was to develop an approach and sampling method that was objective, scientifically based, consistent, and cost-effective. In addition to the silvicultural outcomes component, the MFS commissioned the Manomet Center for Conservation Sciences to develop a second module that could be used to assess the biodiversity impact associated with forest harvests. This Multi-Resource Harvest Assessment (MRHA) was designed as an add-on to the existing Regional Water Quality Best Management Practices Protocol currently used by the MFS to assess the water quality outcomes on recently harvested sites.
The MRHA relies on the Forest Harvest Classification System developed by a Maine Society of American Foresters Task Force (Wagner et al. 2007). This system classifies a recent harvest based on the residual basal area of a harvested stand and the proportion of the original stand that was removed by the harvest. Five residual basal area classes (A to E) based on increments of 30 square feet are combined with five classes of removal intensity (1 to 5) based on the percentage (approximately 20% classes) of the pre-harvest stand basal area that was removed. Basal area measurements of the residual stand and stumps are used to determine the harvest classification for a specific site. For example, a clearcut would be classified as an E5 while 50% basal area removal of a stand with a pre-harvest basal area of 100 square feet would be classified as a B3. Since the basal area of the residual stand (or overstory) remaining after harvest determines how much light and other environmental resources are available to the understory to stimulate regeneration, it is possible to estimate the likely silvicultural outcome of the harvest. Depending on the degree of overstory removal and stocking of advanced regeneration surviving a harvest operation, there are three possible silvicultural outcomes from a harvest operation:
• Release – The harvest removed a sufficient amount of overstory to release abundant advance regeneration in the understory. Future development of the stand will be determined primarily by the released advance regeneration.
• Establishment - The harvest removed a sufficient amount of overstory to stimulate the establishment of a new cohort of tree seedlings and/or sprouts. Future development of the stand will be determined primarily by development of this new cohort of regeneration. Advance regeneration was not present in high enough density to meet minimum stocking standards at the time of harvest.
• Tending – Removal of the overstory was insufficient to release advance regeneration or promote establishment of new regeneration. Trees in the residual stand are likely to reoccupy most of the open canopy space created by the harvest and future development of the stand will determined primarily by trees in the residual stand.
Of course, a single harvest may produce various combinations of these three outcomes within a harvested stand. Thus the silvicultural outcome classification includes various combinations of the three (e.g., Release / Establishment).
It is important to recognize that the silvicultural outcome for purposes of the MRHA protocol is intended to provide an objective silvicultural description of the harvest. It is not intended to reflect the intention of the forester and/or logger that prescribed and/or implemented the harvest. The silvicultural outcome also is not intended to be used as a value judgment about what was created, nor whether the harvest was a success or failure (or “good” or “bad”) in achieving any particular stand management objective. The classification is intended to be used only an objective assessment of what the harvest did to the stand in a strict silvicultural or ecological sense, and to provide only a general indication of how the future stand may develop and what management options may become available to the landowner.
Since harvesting produces other potential conditions and/or risks to the stand, the MRHA protocol presented here also includes a classification of post-harvest stand characteristics. Measurements of the residual forest stand are used to assess current conditions of the stand and identify other important attributes. These assessments include: 1) susceptibility of the residual stand to windthrow, 2) damage to residual stems and regeneration, 3) future susceptibility of the stand to spruce budworm, 4) proportion of the harvested area occupied by trails, and 5) potential proliferation of American beech.
During the summer of 2007, fourteen recently harvested sites were randomly selected from across the state of Maine to test and refine the MRHA protocol. The sampling approach proved reliable under a wide range of harvested stand conditions.