If a map of Acton eliminated all the buildings and roads and other human structures on the surface, what would be left is what is called “Open Space”: woods, meadows, marshes, streams, ponds, and rivers. Some of that Open Space is protected in various ways, including (in order of increasing strength of protection):

Current Use Some land has no legal protection, and just happens not to be built on right now.
Zoning Some land is zoned “ARC” (agriculture, recreation, and conservation), and some kinds of development are prohibited unless zoning is changed.
Article 97 protection Article 97 of the MA Constitution, guaranteeing the right to clean air and water and other environmental protections, has been interpreted in courts, legislation, and state agency policies to provide high levels of protection to land managed by conservation commissions, or bought by Towns with certain protective language in the deeds or votes. Usually, moving land out of Article 97 protection requires votes by state and local bodies, and the protection of compensating protection for land elsewhere.
Conservation Restriction A conservation restriction (CR), or conservation easement, is a way to provide a perpetual restriction on development of a parcel of land. The language is in the deed, and in paperwork reviewed and approved by local and state agencies. Land bought by Community Preservation Act money for Open Space purposes is supposed to have a CR placed on it, but in Acton this process has been slow.

Protecting Open Space is an important aspect of protecting environmental values in Acton and elsewhere.