Our present understanding is inadequate to quantify all the important differences among natural communities. Consequently, some types are rather broadly defined and serve as catchall categories, while others are more precise. Natural community types are usually defined in terms of plants because they are easy to study, often compose the physical structure to which most other organisms respond, and are sensitive indicators of physical and biological factors that influence many types of organisms. Since plant assemblages often correspond closely to other groups of organisms, they can be used as coarse filters that include many of the species and processes in a naturally community, even if they have not been specifically identified. Classifying natural communities enables ecologists, land managers, and others to communicate effectively and to make management decisions regarding ecological systems.
Many classifications exist that define vegetation or other land units.
The classification of natural communities in New Hampshire is based on data from more than ten years of ecological research by ecologists with NH Heritage and The Nature Conservancy, plus extensive reviews of scientific literature. These data have been compiled and arranged into natural community types in part through the use of ordination and other statistical methods. Most state natural heritage programs continually update their classifications and cooperate with The Nature Conservancy's regional and national ecologists to define natural community types that are comparable across state lines. The names of natural community types generally begin with the dominant or most characteristic plant species, and may include the name of a landscape feature or vegetative structure that is typical of that community type. High-quality natural communities have greater potential to contain or achieve natural dynamics that are characteristic of the original community types and are useful for recognizing areas of high biodiversity significance today.