What Are Natural Communities?
Natural communities are recurring assemblages of plants and animals found in particular physical environments. Three characteristics distinguish natural communities: 1) plant species composition, 2) vegetation structure (e.g., forest, shrubland, or marsh), and 3) a specific combination of physical conditions (e.g., water, light, nutrient levels, and climate). Each natural community type occurs in specific settings in the landscape, such as wind-exposed rocky summits at high elevations, or muddy coastal river shores flooded daily by tides. Natural community types vary with changes in physical settings, resulting in predictable patterns across the landscape.
New Hampshire is a mosaic of natural communities, encompassing habitats as varied as alpine meadows, riverbanks, forests, tidal marshes, ponds, and cliffs. Communities range from common and widespread types that cover hundreds or thousands of acres across broad areas of the state, to uncommon or rare types that are small and restricted to a specific part of the state such as the White Mountains or Seacoast region. Across much of the landscape, a few forest natural community types form a matrix, with other natural community types occurring as patches embedded within that matrix.
Different communities may have considerable overlapping species and other characteristics, but each contains distinct and diagnostic combinations of species and physical characteristics. For example, the northern hardwood - spruce - fir forest natural community has considerably more red spruce in the overstory, and is generally higher in elevation than the standard northern hardwood forest community (sugar maple - beech - yellow birch forest) despite the fact that many species occur in both.
Classification of Natural Communities
Classifying natural communities enables ecologists, land managers, and others to communicate effectively and to make sound management decisions by providing a framework for evaluating the ecological significance of pieces of the landscape. This in turn allows for sound and effective biodiversity conservation. Understanding the rarity of a natural community within both the state and region, and knowing the quality of each example, is critical to informed conservation planning. As landscape units that share physical and biological characteristics important to many species, natural communities help focus management and conservation attention, particularly since our knowledge of individual species is often incomplete. Natural community classification can also help us understand how ecological processes in one community affect neighboring communities.
The New Hampshire Natural Heritage Bureau (NH Heritage) created a classification of the state's natural communities. The effort was an outgrowth of natural community classification work undertaken in the northeastern United States by The Nature Conservancy, and ties into similar classifications by other state natural heritage programs across the country. It is based on data from more than thirty 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 used to define natural community types in part through the application of ordination and statistical classification techniques.
The names of natural community types generally begin with the dominant or most characteristic plant species, and may include the name of a specific landscape feature or vegetative structure typical of the community type. For example, black gum - red maple basin swamp refers to a basin swamp with abundant black gum and red maple in the tree canopy. Hyphens offset by a space indicate different species or characteristic groups of plants. For example, in pitch pine - heath swamp, pitch pine is in the tree canopy and the heaths are in the shrub layer. Hyphens without spaces are an inherent part of some species names, such as twig-rush, or are word modifiers. Slashes represent and/or combinations, such as with herbaceous riverbank/floodplain, in this case indicating the community occurs on both riverbanks and floodplains.
NH Natural Heritage bases its natural communities on plant species, the structural layers that these species collectively form, and the specific physical environment. Several species of trees are indicators of subtle differences in their environments. A number of natural communities can be distinguished based largely on trees, and in some instances, a difference in tree composition is the main difference between two community types. Conversely, trees such as white pine or red maple are so broadly adapted that their presence does not necessarily indicate unique site conditions. Similarly certain species of shrubs and herbs have a narrow range of ecological tolerances and are found in only a few types of natural communities. Other shrub and herb species, such as black huckleberry and rough goldenrod, are generalists similar to white pine and red maple.
Relationship of NH Natural Communities to Other Classification Systems
Exemplary Natural Communities
NH Natural Heritage evaluates the ecological significance of individual natural communities and assigns a quality rank. Quality ranks are a measure of the ecological integrity of a community relative to other examples of that particular type based on size, ecological condition, and landscape context. Natural disturbances such as ice storms, blow downs, and fires, are a critical component of natural system processes and do not diminish a community occurrence ranking. NH Natural Heritage designates most occurrences of rare natural community types (such as northern white cedar – balsam fir swamps), and high quality examples of more common community types, as exemplary. Exemplary natural communities represent the best remaining examples of New Hampshire's biological diversity (a.k.a. biodiversity). NH Natural Heritage identifies and tracks exemplary natural community occurrences to inform conservation decisions.
Now Available: The Nature of New Hampshire: Natural Communities of the Granite State. NH Natural Heritage has created this beautiful and informative 341-page book describing the state's natural communities and environment. You can order it on the publisher's website.
Natural Community Systems
NH Heritage has also created a classification of the state's natural community systems. Natural community systems are associations of natural communities that co-occur in the landscape, linked by a common set of driving forces, such as landform, flooding, soil, and nutrient regime. Systems can be useful units for a variety of conservation planning and mapping purposes.