A watershed is an "entire geographic region in which all surface and groundwater flows downhill to a common point, such as a river, stream, pond, lake, wetland or estuary". Rivers most often are the focal points in a watershed, but clearly, watersheds are not just water. A single watershed may include combinations of forests, glaciers, deserts, or grasslands. A small stream in the Bigelow range, or a major waterway like the Kennebec or Penobscot Rivers can define watersheds.
Adjacent watersheds may be part of the same ecosystem based on similar rainfall, flooding patterns, soil structure, and other physical characteristics. A larger ecosystem or biome may include numerous watersheds that comprise a major regional community of plants and animals with similar life forms and environmental conditions. These systems rarely follow political boundaries, nor are they equal in the diversity of the species that dwell within their natural systems. It is this diversity through which the biological richness of watersheds is judged.
Protecting open space in watersheds is key to maintaining the biodiversity of plants and animals throughout Maine. The two biggest threats to biodiversity are the destruction and fragmentation of wildlife habitats and the introduction of invasive non-native species of plants and animals. Regardless of its size, each natural community includes plants that capture sunlight for their own growth, animals that forage and consume these plants, and other organisms and fungi that help to decompose dead matter into nutrients as part of the carbon cycle.
Watersheds within Maine provide a richness of biological diversity, including many different species of birds, mammals, amphibians and reptiles. Thousands of species of trees, shrubs, flowers, and ferns also exist within the state. But that is not all. There are literally thousands of invertebrates, fungi, algae, and other organisms that also play important roles as actors in the biologic communities of watersheds.
Biological diversity is not necessarily stable and there is a continued risk of losing species, especially through elimination or fragmentation of habitat. As this occurs, the disruption of the interaction between species can upset the balance of the natural system. Land is connected to water, and both are connected to plants, animals, and the atmosphere. Once these connections are broken, species and diversity becomes stressed and often disappear, and the loss of a single species can often affect the entire community.
Urban sprawl away from our cities and suburban population centers has accelerated the destruction and fragmentation for all species. This occurs not only as homes and commercial properties are built and roads paved, but also because of the dramatic decrease in the physical area it takes to sustain a species. Each species requires a certain minimum area to survive, and when this area is lost or fragmented, a species must adjust to the changes in order to sustain themselves. Hence, the whitetail deer have become the "four-legged urban pigeons" in many suburban areas, causing vehicle accidents and damage to gardens and landscaping. Coyotes now abound in backyards, preying on domestic pets and terrorizing small children, and bears now regularly visit neighborhood bird feeders.
Although not as obvious or dramatic as development or land fragmentation, the insidious encroachment of invasive species proceeds at a much slower pace. Non-native introductions displace and destroy native species slowly, without notice, until they lose habitat area or disappear entirely. Some ecosystems in watersheds are threatened or destabilized by new species or changing physical factors. Damaging species like zebra mussels or purple loosestrife clog streams and wetlands, crowding out native species. Sometime native species such as phragmites, which used to be found only in coastal marshes, have become so widespread through human disturbance; they now expand along rivers and into interior wetlands. Insects from Europe carrying fungi infected our stately elms with Dutch elm disease, and the Mediterranean fruit fly causes severe damage to many of our domestic fruit crops every year. With no natural predators our native species are at risk from all invasives.
Not all ecosystems in the different watersheds across Maine are created equal, nor are they endowed with equal number of species. No two ecosystems are identical and some will have more species than others. Some regions like the Maine coast and the islands or the western mountains of the state contain more endangered plants and animals than other areas in the state. While significant populations of species like squirrels and sparrows exist in urban areas, it is because they have adapted more readily than others, but expanded diversity is extremely inhibited. Many areas now have difficulty and will not support unique species.
One could ask, "Are some watershed ecosystems more important than others"? All else being equal, any system exhibiting unusual habitats, or because human activities have eliminated similar habitats, are likely to have more biodiversity and species not found in other areas. Because the restoration of a species is a slow, expensive, and difficult process, it is important to protect open space as part of watershed management plans. Existing habitats may never achieve the biological criteria critical to reintroduction of a species without special protection.
Protecting biodiversity does not mean halting development, but it does mean planning agencies should strongly consider impacts on the biological resources of our communities. Land management based on the concept of protecting watersheds provides a scientific understanding of the impacts of human activities. It should be a major goal to protect biodiversity as part of ecosystem management, as well as placing consideration on the social and economic variables attached a community’s perception of values.
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