14. Implications of Patch Dynamics for Forested
Ecosystems in the Pacific Northwest
G.A. Bradshaw, Frederick J. Swanson, and
Maria R. Fiorella
It is not possible to discuss ecosytem processes and functions without
explicit reference to the relevant scales of analysis. Although the concepts
of heterogeneity and patchiness have been used for nearly twenty years
(e.g., Pickett, 1991; Wiens, 1976) terms such as " pattern" , "hierarchical",
and "scale" appear with increasing frequency in journals from disciplines
as disparate as geophysics, ecology, and oceanography (e.g., Grant,
Swanson, & Wolman , 1990; Moloney, Morin, & Levin, 1991; Powell,
1989). Two current approaches to understanding patterns in the ecosystem
are patch dynamics and hierarchy theory (O'Neill , DeAngelis, Wade, &
Allen, 1986; Pickett and White, 1985; Steele et al., 1992; Wiens, 1976).
The concepts of patch dynamics and hierarchy theory focus on relationships and phenomena across spatial and temporal scales. Hierarchy theory
views the system as organized into levels by its intrinsic structure, where
flux between levels is regulated by regionalized variables. On the other
hand, patch ,dynamics has focused attention on the heterogeneous nature
of the landscape , where the landscape evolves as a mosaic of patches. In
ecosystems, this heterogeneity or variability is expressed as patterns in
the distribution of plants, animals, and abiotic processes. More recently,
these concepts have been incorporated into conservation design and forest
and stream management plans (e.g., U.S.D.A., 1993; Swanson et al.,
1994).
283
Ecosystems in the Pacific Northwest
G.A. Bradshaw, Frederick J. Swanson, and
Maria R. Fiorella
It is not possible to discuss ecosytem processes and functions without
explicit reference to the relevant scales of analysis. Although the concepts
of heterogeneity and patchiness have been used for nearly twenty years
(e.g., Pickett, 1991; Wiens, 1976) terms such as " pattern" , "hierarchical",
and "scale" appear with increasing frequency in journals from disciplines
as disparate as geophysics, ecology, and oceanography (e.g., Grant,
Swanson, & Wolman , 1990; Moloney, Morin, & Levin, 1991; Powell,
1989). Two current approaches to understanding patterns in the ecosystem
are patch dynamics and hierarchy theory (O'Neill , DeAngelis, Wade, &
Allen, 1986; Pickett and White, 1985; Steele et al., 1992; Wiens, 1976).
The concepts of patch dynamics and hierarchy theory focus on relationships and phenomena across spatial and temporal scales. Hierarchy theory
views the system as organized into levels by its intrinsic structure, where
flux between levels is regulated by regionalized variables. On the other
hand, patch ,dynamics has focused attention on the heterogeneous nature
of the landscape , where the landscape evolves as a mosaic of patches. In
ecosystems, this heterogeneity or variability is expressed as patterns in
the distribution of plants, animals, and abiotic processes. More recently,
these concepts have been incorporated into conservation design and forest
and stream management plans (e.g., U.S.D.A., 1993; Swanson et al.,
1994).
283