Silvicultural Systems And Management
Silvicultural systems are integrated activities designed to establish, tend, protect, and harvest crops of trees. Activities associated with silvicultural systems are carried out on particular sites. However, the spatial and temporal patterns of those sites on the landscape must also be designed, and this is done using a management plan appropriate to that larger scale. The landscape-scale management plan is typically detailed for the first five years, but it should also contain a 25-year forecast of objectives and activities. The design and implementation of silvicultural systems and management plans are among the most important activities undertaken by modern foresters.
The primary goal of forestry is generally to achieve an optimized, sustainable yield of economically important, tree-derived products from the landscape. In places where the mandate of forestry is focused on the economic resource of trees, the silvicultural system and management plan will reflect that priority. However, in cases where society requires effective management of a range of resource values (that is, not just trees), then integrated management will be more prominent in the system and plan.
As with the individual harvesting and management practices described in the preceding section, silvicultural systems can be quite intensive, or much less so. An example of an intensive system used in North America might involve the following series of activities, occurring sequentially, and beginning with a natural forest composed of a mixture of native species of trees: (1) whole-tree, clear-cut harvesting of the natural forest, followed by (2) scarification of the site to prepare it for planting, then (3) an evenly spaced planting of young seedlings of a narrow genetic lineage of a single species (usually a conifer), with (4) one or more herbicide applications to release the seedlings from the deleterious effects of competition with weeds, and (5) one or more thinnings of the maturing plantation, to optimize spacing and growth rates of the residual trees. Finally, the stand is (6) harvested by another whole-tree clear-cut, followed by (7) establishment, tending, and harvesting of the next stand using the same silvicultural system. If the only objective is to grow trees as quickly as possible, this system might be used over an entire landscape.
In contrast, a much softer silvicultural system might involve periodic selection-harvesting of a mixed-species forest, perhaps every decade or two, and with reliance on natural regeneration to ensure renewal of the economic resource. However, even a system as soft as this one might pose a risk for certain non-timber resource values. For example, if certain species dependent on old-growth forest were believed to be at risk, then an appropriate management plan would have to include the establishment of ecological reserves large enough to sustain that old-growth resource value, while the rest of the land is "worked" to provide direct economic benefits.
Because silvicultural systems can differ so much in their intensity, they also vary in their environmental impacts. As is the case with agriculture, the use of intensive systems generally results in substantially larger yields of the desired economic commodity (in this case, tree bio-mass). However, intensive systems have much greater environmental impacts associated with their activities. The challenge of forestry is to design socially acceptable systems that sustain the economic resource, while at the same time accommodating concerns about the health of other resources, such as hunted and non-hunted biodiversity, old-growth forests, and ecologically important, but non-valuated goods and services that are provided by forested landscapes.
See also Deforestation.
Freedman, B. Environmental Ecology. 2nd ed. San Diego: Academic Press, 1995.
Kimmins, H. Balancing Act. Environmental Issues in Forestry. Vancouver: University of British Columbia Press, 1992.
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