Structure in Upland Areas of Watersheds

The physical form of the uplands in watersheds can vary greatly, in ways beyond the scope of this discussion. Here we focus only on the distribution of and variations in vegetation and land use, which together create the element of watershed structure called landscape pattern. Vegetation and land use patterns in watersheds are known to have many significant influences on the condition of the water bodies they drain into; this topic is explored in greater detail in the Watershed Academy Web module on Watershed Change.

Landscape patterns
Landscape ecology offers a simple set of concepts and terms for identifying basic landscape patterns: matrix, patch, and mosaic. The ecological term matrix refers to the dominant (> 60%) land cover, while a patch is a non-linear area that is less abundant and different from the matrix. A mosaic is a collection of different patches comprising an area where there is no dominant matrix. Various patch types have been described. Basically, the most obvious landscape patterns are formed by combinations of native vegetation communities, unvegetated areas, and land use patterns.

Landscape pattern change. The individual patches in a landscape can change, and so can the entire landscape change in pattern and/or composition. Disturbances and various landscape processes maintain a constant dynamic, referred to as a shifting mosaic. Some landscapes remain in a "dynamic equilibrium" and, although changing steadily from place to place, retain an important quality called mosaic stability. A well-managed forestry operation, for example, would exhibit over the long term a constantly shifting set of locations where mature forest occurred, but at the same time sustains the relative proportions of forested and nonforested land in the area. Or, a landscape may evolve toward a new type of pattern and composition (e.g., via timber clearcutting, suburban sprawl, abandonment and succession of agricultural lands back to forest, or landscape change due to disease, fire, or climate change). It is always important, when analyzing landscape pattern and landscape change, to remember that the spatial resolution of your information (how small a landscape feature you can detect) may or may not be sufficient to detect all the landscape changes of possible significance that may be occurring.