River Ecology and Restoration - River Dynamics and Integrated River Management - page 626

2. Patch—a nonlinear area (polygon) that is less abundant than, and different from, the matrix.
3. Corridor—a special type of patch that links other patches in the matrix. Usually, a corridor is linear
or elongated in shape, such as a stream corridor.
4. Mosaic—a collection of patches, none of which are dominant enough to be interconnected throughout
the landscape.
Fig. 10.1 A river ecosystem consists of the terrestrial ecosystem and the aquatic ecosystem, which is affected by
and impacts on the landscape ecosystem through input and output (after FISRWG, 1997)
Figure 10.2 shows examples of a forest matrix, a city patch, a stream corridor, and a mosaic consisting
of a lake, island, forest and hills. One may see a matrix of mature forest, cropland, pasture, clear-cuts,
lakes, and wetlands on a landscape scale. However, on a river reach scale, in a matrix of less desirable
shallow waters, a trout may perceive pools and well sheltered, cool, pockets of water as preferred patches
and in order to travel safely among these habitat patches, the stream channel may be its only alternative.
The matrix-patch-corridor-mosaic model is a very useful, basic way of describing structure in the
environment at all levels. When planning and designing ecosystem restoration, it is very important to
always consider multiple scales.
The stream corridor is an ecosystem with an internal and external environment (its surrounding
landscape). Stream corridors often serve as a primary pathway for the aforementioned movement of energy,
materials, and organisms in, through, and out of the system. This may be accomplished by connecting
patches and functioning as a conduit between ecosystems and their external environment. Movement in,
through, and out of the ecosystem may be dictated by spatial structure, especially in corridors; conversely,
this movement also serves to change the structure over time. Thus, the end result of past movement is the
spatial structure, as it appears at any point in time. In order to work with ecosystems at any scale it is
paramount to understand the feedback loop between movement and structure.
Many of the functions of the stream corridor are strongly interlinked with drainage patterns. So, many
people commonly use the term 'watershed scale', and it will also be used in this chapter. A watershed is
defined as an area of land that drains water, sediment, and dissolved materials to a common outlet at
some point along a stream channel (Dunne and Leopold, 1978). Watersheds, therefore, occur at many
different scales, ranging from the watersheds of very small streams that measure only a few km 2 in size
to the largest river basins, such as the Yangtze River watershed. The matrix, patch, corridor, and mosaic