A third principle about ecosystems is that ecosystem bounds are human constructs. For ease of conversation, each ecosystem we designate is bound by a theoretical line that is the "end" and the "beginning" of the system. In a perfect world, these boundaries would be unmistakable, impenetrable, and static. Water and soil would not cross from a higher to a lower elevation, animals would not carry plant seeds from one county to the next, and laws would not apply on one side of the fence and not the other. However, ecosystem boundaries are fluid, porous, and often unrecognizable in the same way to more than one person.
The significance of spatial boundaries to ecosystem projects is in selecting the appropriate project area. The area must be:
· Sufficiently large to accommodate the ecological processes of interest.
· Not too large to be able to grasp and accomplish objectives.
One simple suggestion for selecting the right boundaries is to work at one level up or out from the area of immediate attention. If you are looking at a pond, add a buffer zone around it. If you are looking at the pond and its buffer, add the tributary that supplies water to the pond.
Another suggestion is to consider the forms of disturbance that operate to maintain a community and work at a scale that allows the disturbance to do its job. For example, the longleaf pine community in the Southeast is a fire-driven system.
The project area necessary to maintain that community must be large enough to allow burns of a portion of the system each year, meaning that other portions are in some stage of recovery.
Cottonwood stands along a river respond to flooding and rely on water to move their seeds downstream to establish new stands. Maintenance over time of a viable cottonwood community on a 100-mile stretch of stream will not be possible without adequate variability in the flooding regime.
