Old-Growth Forests

Because of their great quantities of large-dimension timber of desired tree species, old-growth forests are an extremely valuable natural resource. However, old-growth forests are rarely managed by foresters as a renewable, natural resource. Usually, these forests are mined by harvesting, followed by a conversion of the site to a younger, second-growth forest, which is only allowed to develop into a middle-aged forest before it is harvested in turn. This management strategy is pursued because old-growth forests sustain little or no net production of new biomass, since the growth by living trees is approximately balanced by the deaths of other trees through senescence, disease, or accident. Because the primary objective of forestry is to optimize the productivity of tree biomass, it is economically preferable to harvest the secondary forests soon after their productivity starts to decrease. However, this occurs long before they become old-growth forests.

Because of this forestry practice, old-growth forests have been greatly fragmented and diminished in area. Consequently, threats of further losses of this natural ecosystem engender great controversy. To conserve some of the important qualities of old-growth temperate forests, including some of their dependent species, socalled "new forestry" harvesting systems are being encouraged in some areas. Compared with clear-cutting and plantation establishment, these new systems are relatively "soft" in terms of the intensity of the disturbance caused, and the physical integrity of the forest remains substantially intact after the harvest. For example, a system being encouraged in old-growth forests of western North America is selection-cutting with some degree of snag retention, followed by natural regeneration of trees instead of planting.

However, even the new forestry practices cause substantial changes in the character of the forest. If the societal objective in some areas is to preserve the special, natural values of old-growth forests, this can only be done by setting aside large, landscape-scale, reserves in which commercial forestry is not practiced. Only natural ecological dynamics and disturbances are allowed to occur in those ecological reserves. The landscape perspective is important to the preservation of old-growth forests because particular stands of this ecosystem cannot be preserved forever, since they are inevitably subject to the effects of unpredictable, catastrophic disturbances and/or environmental changes. However, if the ecological reserve is large enough, these stand-level dynamics can be accommodated, because a continuum of stands within the natural, old-growth successional dynamic can be sustained over the longer term.

Old-growth forests are a unique type of natural ecosystem, with great intrinsic value. If old-growth forests are to always be a component of Earth's natural biodiversity, then human societies will have to preserve them in large ecological reserves, even if this means there will be some short-term economic losses.