Natural communities are assemblages of species that recur together in particular environmental conditions. These groups of plants and associated animals can be classified and described by their dominant biological and physical features. Named types of communities have structure (such as being forested or not forested), characteristic species that usually occur in that type of community, and dominant species that control or strongly influence the growth of other species (for example, hemlock trees shade the ground so thoroughly that they limit what other species will be present). Physical conditions influence the types of communities that can occur in particular areas: degree of wetness, abundance of nutrients, presence of salt, and many other physical factors control the species that occur and therefore the community type. Red Maple Swamps and Level Bogs are types of Palustrine (wetland) natural communities where the presence of water controls the species present and, therefore, the community type. Sandplain Grasslands occur in dry conditions on sandy soils. Natural communities are not discrete units with neat boundaries; there is overlap among and between communities in their composition, structure, and physical characteristics. Large and mobile animals often include multiple community types in their habitats.
Natural communities may be restricted or widespread in their distribution across the state. NHESP gives conservation priority to types of natural communities that have limited distribution in the state and, of course, those with restricted global distribution (together considered to be Priority Types of Natural Communities for Conservation or “Priority Natural Communities”). NHESP also identifies Massachusetts’ best examples (exemplary occurrences) of more common community types that are otherwise Low-Priority for conservation or “Low-Priority Community types”: these are very important for conserving the biodiversity of the state.
The Massachusetts Natural Heritage & Endangered Species Program actively inventories and tracks the distribution and status of NHESP Priority natural communities and exemplary occurrences of more common types across the state. In June 2016 the NHESP natural community datalayer on MassGIS was updated to include the current mapped and described Priority and Exemplary Low-Priority Natural Communities in the NHESP database. The updated GIS layer uses the revised names and attributions from the 2016 Classification of Natural Communities of Massachusetts, Version 2.0. Along with the revised Classification, NHESP produced new fact sheets, one per defined type of natural community that include photos and distribution maps.