The landscape approach to ecosystem management provides multiple forest values by maintaining a range of forest structures across the landscape and through time.
Stand structure is the spatial arrangement of all of the individual trees, and their stems, branches, and leaves, within the stand. Stand structure is influenced by processes both within the stand (i.e., autogenic) and from outside of the stand (i.e., allogenic). Autogenic factors include recruitment, growth, and mortality, which are affected by the life-history traits of each species (e.g., seed dispersal, shade tolerance, maximum growth rate). Allogenic factors include climatic change and disturbance. Disturbances may be either chronic (e.g., air pollution) or acute (e.g., tornado, fire, insect outbreak).
Stand development is the change in a stand's structure (e.g., density, tree diameter, height, branch size, presence of woody debris) through time. Different stand structures provide different values. For example, newly regenerated stands provide habitat for certain species of small mammals and birds, but have little current timber value. As a stand develops the values it provides change. Creating and maintaining a diversity of stand structures within a landscape over time ensures a diversity of forest values (habitats, wood products, water and soil protection, etc.) over time.
Landscape management attempts to maintain all forest structures within the landscape by mimicking, avoiding, and recovering from natural disturbances as the forest changes through natural population processes. In the process other forest values, such as the values outlined by the Montreal Process Working Group described above, can be maintained as well.
Mimic disturbance: Silvicultural manipulations of forest stands can mimic a range of disturbances, from individual treefall gaps to stand-replacing events, by removing trees of certain species, sizes, or canopy positions. However, some disturbances, such as chronic air pollution or climate change, do not have a silvicultural analog.
Avoid disturbance: Susceptibility to disturbance is a consequence of stand structure. For example, dense stands of trees that are tall and relative narrow for their height (i.e., high height/diameter ratios) can be highly susceptible to windstorms. Silvicultural actions can mitigate potential risk from catastrophic disturbances at the stand scale by increasing individual tree vigor and stability. Early thinning of dense stands can improve diameter growth in the leave trees, thereby lowering the average height/diameter ratio of the stand and making it more windfirm.
Silvicultural actions can also mitigate potential risk from catastrophic disturbance at the landscape scale by ensuring that no one stand structure dominates the landscape. In effect, landscape management treats the landscape as an asset portfolio in which each stand has a set of associated values and risks that changes through time. By distributing the risks among many stands across the landscape and over, the potential for a catastrophic disturbance, and consequent loss of many forest values, is minimized.
Recover from disturbance: A widespread catastrophic disturbance, such as a wildfire or a hurricane, may create an excess of a particular structure. Silvicultural actions, coordinated across the landscape, can accelerate the process of development towards a variety of other stand structures. Early and repeated thinning in dense stands could promote rapid development towards the understory reinitiation and complex stand structures, particularly on high quality sites. In contrast, where disturbance has been excluded from a forest, silvicultural actions coordinated over the landscape could facilitate the development of pre-exclusion stand structures.
Several silvicultural pathways are developed for each stand within a landscape. Technical tools such as the Landscape Management System (LMS) allow the resource manager to test various combinations of these pathways as different management options for the landscape to determine how they provide different mixes of forest values.
Different values, such as those of sustainable forestry (see Montreal Process Criteria), are achieved at different scales. For example, protecting biodiversity may be a regional- or global-scale forest management concern, while creating nesting habitat for a locally endangered bird species may be a stand- or landscape-scale management issue. Ultimately, however, protecting regional and global biodiversity is achieved by maintaining biodiversity at smaller scales, such as the stand and landscape. Setting aside large reserves in one part of a region may meet regional criteria for total area of reserves, but flora and fauna in unprotected areas within the same region may continue to be threatened.
Silvicultural operations such as harvesting, pruning, site preparation, prescribed burning, and planting are short-term activities that directly influence individual trees within a stand. At the stand scale, silvicultural pathways (or regimes) are the set of unique changes in stand structure that occur over many decades and arising from the interaction of growth, mortality, and recruitment of trees within the stand and the specific silvicultural operations that are applied to individual trees within the stand.
Intensive plantations and reserves have been proposed as an alternative means for providing the range of forest values. Including these approaches within the context of the landscape management approach could help maintain particular types of stand structures on the landscape.
Two different approaches to implanting ecosystem management approach have been proposed:
The relative advantages and disadvantages of each have been discussed (Oliver 1999).
A central tenet of the landscape management approach is "management" of the entire landscape. However, it is important to define "management" to avoid potential confusion. In the context of the landscape management approach, management of the landscape does not imply actively harvesting the entire landscape. Rather, it means that forest managers should have a detailed knowledge of the current values provided by each stand within the landscape, as well as the potential future values, and that when decisions to harvest trees are made they are made within the context of the entire landscape, not the individual stand. Given the relative lack of complex forest structures on most landscapes it would be important to maintain the existing stands, but at the same time employing a variety of silvicultural pathways (e.g., thinning, mixed species stands) to develop similar complex forest structures from more abundant stand structures.
Oliver, C.D. 1999. The future of the forest management industry: Highly mechanized plantations and reserves or a knowledge-intensive integrated approach? Forestry Chronicle 75(2): 1-17.