The Natural Systems Concept

Thus far, you have been introduced to the physical template from which watersheds develop, and the biological setting which then becomes established upon and integrated with the physical template. The interactions and natural processes that link these abiotic and biotic components of watersheds (note here the similarity to the definition of ecosystem) exhibit what can be called system-like behavior.

The dictionary defines a system as "a group of interrelated, interacting, or interdependent constituents forming a complex whole." We have seen that natural systems such as watersheds have interacting components that together perform work (e.g., transport sediment, water, and energy) and generate products (e.g., form new physical structures like floodplains or channels, and form biological communities and new energy outputs). In a natural system, interactions make the whole greater than the sum of its parts -- each of the physical and biological components of watersheds if they existed separately would not be capable of generating the work and the products that the intact watershed system can generate.

The natural systems concept is key to watershed management because it emphasizes that a watershed, as a natural system, is more than just a variety of natural resources coincidentally occurring in one place. Severely degraded watersheds may have lost several of their components and functions and provide fewer benefits to human and natural communities as a result. Thus it is clear that recognizing the natural system and working toward protecting the system's critical components and functions are key to sustainable watershed management. Other ecological concepts and theories help explain the idea of natural systems. These include spatial and temporal scale, disturbance theory, and the river continuum concept, all discussed below.