aggressive term "aliens." Some invade only disturbed areas; others invade healthy and normally functioning ecosystems. An example of the former is cheatgrass, which typically invades overgrazed rangelands. The knapweeds are examples of the latter, which are capable of moving into high quality rangelands and deteriorating the range condition.
Aggressive nonindigenous plants are well-adapted to a variety of sites and are resilient to disturbance. Invasions of nonindigenous species are among the most pervasive influences on the biodiversity of ecosystems (Coblentz 1990). Among some of the alien plants affecting nonfederal forestland are scotch broom, gorse, kudzu, haole koa, melaleuca, Australian pine (Casuarina), poka vine, cogon grass, pampas grass, and ivy. Most are well-adapted to fire, and wildfire often results in their continued spread. These problems are likely to increase. Management controls are often ineffective because nonindigenous plants are so well-adapted to disturbance, often more so than indigenous plants. As effective strategies to control some aliens are implemented, others will continue to be introduced.
Ecologically healthy watersheds located within nonfederal forests are maintained by natural disturbance processes (Naiman et al. 1992). A dynamic, rather than a steady-state, equilibrium is characteristic of resilient and productive watersheds. Changes in riparian forests, wildlife habitat, water quantity and quality, and sediment are all part of healthy watersheds from the headwaters to the estuaries. As the watershed increases in scale, more landowners are likely to be involved in the improvement, maintenance, or degradation of watershed quality. State regulations and voluntary Best Management Practices (BMPs) are almost always associated with watershed quality, and federal cost-share programs. Watershed integrity has been of concern to programs administered through the USDA and have often focused on watershed restoration (Agricultural Conservation Programs [ACP] and Conservation Reserve Program [CRP]), as well as the programs of the U.S. Environmental Protection Agency, the U.S. Army Corps of Engineers, the U.S. Fish and Wildlife Service, the National Marine Fisheries Services, and the Bureau of Reclamation. Watershed integrity includes more than just chemical measurements of water quality (Box 5-4).
The cyclic nature of natural disturbances of the past have set into motion complex sediment routing patterns from smaller to larger-order streams (Benda 1990). One of the primary lessons from this behavior is that watershed maintenance and restoration must include a long time frame, whether the focus is for natural forests, transitions from natural forests to plantations, subsequent rotations of trees, conversions of old fields to new forests, or conversions of forests to agricultural or urban uses. Each of those uses will affect watershed integrity in positive or negative ways, and some effects might have considerable time lags, particularly in large-order watersheds (Swanson et al. 1992). The value of watershed