The Basin is a geologically distinct area that encompasses many of the municipalities that comprise so-called "Metro-Boston." It is underlain by sedimentary rock that erodes more easily than the metamorphic bedrock that surrounds it, creating a ‘basin’ with low, rolling topography. Though largely developed, there are remaining patches of oak-white pine forest, as well shrubland and salt marsh along the coast. The urban heat island effect makes this area warmer than it would be otherwise, which affects the plant species that thrive there.
This coastal lowland is dominated by sand and silt from glacial outwash, and is now covered by extensive salt marshes, mudflats, and sandy coastal shrublands. Inland areas are primarily oak forest. It is significantly colder than coastal areas just to the south, in part because of the shielding effect of the Cape Cod peninsula.
Northeast Coastal Plain
This plain is part of a larger region that extends downward from the inland area of the Gulf of Maine. It is slightly higher in elevation than the coastal areas, and is dominated by secondary growth (post agricultural) oak-white pine forests growing on nutrient-poor, acidic soils. Several large rivers drain in the area, creating pockets of floodplain forest.
Southeast Coast and Islands
This region has two distinct zones: the inland coastal plain that extends down into Rhode Island; and the pine barrens of Plymouth, the Cape and the Islands. Both were shaped by the movements and deposits of receding glaciers. The coastal plain lowland is dominated by oak-pine forest, and the barrens by pitch pine and scrub oak woodlands. The latter community is underlain by coarse, sandy, low-nutrient soils and dotted by acidic wetlands and kettle holes. This region has a long growing season for New England— the climate is moderated by its low elevation and extensive water bodies.
This is the northernmost part of a much larger region that covers the southeastern hills and plains of both Connecticut and Rhode Island. That region extends into Massachusetts around the Blackstone River. It is lower in elevation than the area directly to the north, with a somewhat milder climate. There are abundant glacial moraines, and the forest cover is primarily oak-pine, with a few areas of hardwoods that include sugar maple.
The land on this plateau is at a higher elevation than the coastal area to its east and the valley to its west, and therefore much colder, particularly at its northern end. It is dominated by transitional hardwood forests, with a mixture of the more northern beech-maple-birch communities, and oak-hickory woods of warmer southern climes. The northern part of the plateau features several glacial monadnocks, as well as acidic wetlands and peatlands.
Connecticut River Valley
In this valley, the terrain is much flatter and covered in rich alluvial soils. The area has a milder climate than the surrounding upland and all these characteristics make it quite favorable to agriculture. It is dominated by oak-hickory forests, and by silver-maple and cottonwood in floodplain areas.
The forest communities of the Berkshires range from oak-hickory at lower elevations, to transitional hardwoods, and then northern hardwoods as we ascend further. Finally, at the highest elevations, we find the cold-loving spruce-fir forests that characterize northern New England. Though the underlying bedrock is primarily acidic, there are areas of calcareous limestone in the northeast part of the region.
Taconic Mountains and Marble Valleys
The Taconic hills and the valleys that separate them are marked by an underlying geology that is vastly different from other areas of the state. There are marble valleys, limestone outcrops, and calcareous glacial deposits found here, creating rich soils that support plant communities not found elsewhere in Massachusetts. Similar to the Berkshire Hills, the forests here vary with elevation, and from the northern to southern ends of the long region.