Ecological dynamics

[Caveat: The vegetation information contained in this section and is only provisional, based on concepts, and future projects support validation through field work. *] The vegetation groupings described in this section are based on the terrestrial ecological system classification and vegetation associations developed by NatureServe (Comer et al., 2003) and localized associations provided by the New York Natural Heritage Program (Edinger et al., 2014), Maine Natural Areas Program (Gawler and Cutko, 2010), New Hampshire Natural Heritage Program (Sperduto and Nichols, 2011), and Massachusetts Division of Fisheries and Wildlife (Swain, 2020).

The information contained in the State and Transition Model (STM) and the Ecological Site Description were developed using archeological and historical data, professional experience, and scientific studies. The information presented is representative of a very complex set of plant communities. Not all scenarios or plants are included. Key indicator plants, animals and ecological processes are described to inform land management decisions.

The historic reference plant community phase of this site is perceived to be an uneven-aged mixing of temperate deciduous and boreal species, called the “Acadian Forest”. This forest consisted of long-lived, shade-tolerant species with small gaps and relatively infrequent severe disturbances. Due to the multiple (8) biophysical regions involved and the history of land use and management, which involved over 95 percent of the MLRA land area, a least disturbed climax plant community phase will be considered the reference state for this ecological site description. The least disturbed climax state is a mixed conifer-hardwood forest.

Before European settlement, which occurred in the early 1600s, the plant community phase on this site consisted of an uneven-aged mixing of southern temperate deciduous and northern boreal species. This forest consisted of long-lived, shade-tolerant species with small gaps and relatively infrequent severe disturbances, from 0.6 to 1.0 percent per area per year. Dominant tree species were hemlock and spruce with a scattering of pines and cedar with some ash and oak according to early settlement survey records (Barton et al., 2012). In forested wetlands along the mid- and downeast coast, dominant tree species included spruce, birches, and alder with smaller amounts of pine, fir, maple, oak, beech, and hemlock, which is similar to present-day vegetation composition (Barton et al., 2012). The pre-settlement forest stands were generally between 104 to 203 years old in the oldest stands. Presettlement natural disturbances were usually small, single-tree mortality events caused by wind or insect damage, rather than stand replacing events. Stand replacing events include huge fires on average every 1,461 years and major wind storms, such as hurricanes, on average every 3,289 years. Extensive insect outbreaks, such as the spruce budworm infestation, were recorded as occurring every 60 to 70 years (Barton et al., 2012). During present day times, these natural disturbances still occur within these intervals of time.

The reference state (1.1), northern white cedar/three-seeded sedge (Thuja occidentalis/ Carex trisperma) is forested. Because of the constant harvesting of the forest and the composition of the data collected from representative sites, it was not possible to differentiate between a possible more mature and younger phase. The reference plant community phase has many of the same attributes, including species composition and structure, as the historic reference plant community phase. The site has a moderate to dense canopy cover, 75 to 95 percent, of a stratified mixture of even-aged conifer and northern hardwood tree species. Northern white cedar (Thuja occidentalis) is the major tree component with other codominant or intermediate species such as red spruce (Picea rubens), which occurs as a dominant tree on coastal sites. Red maple (Acer rubrum) and balsam fir (Abies balsamea) are usually in the suppressed understory. Some sites may contain black spruce (Picea mariana), and tamarack (Larix laricina). Some sites contain only red spruce and/or red maple depending on the geographic location within the MLRA and previous forest management.

The understory vegetation is very sparse due to the dense overstory cover except for very small open areas, less than a 0.1 of an acre, where a wide variety of forbs, ferns, and shrubs grow. The ground cover occurs within a typical pit and mound microtopography. Under the dense conifer overstory, only small scattered shade-tolerant and moisture-loving plants grow. Many species of feather-moss grow over the ground, on dead wood, and the bottoms of trees. Tall shrubs are virtually non-existent in this dense, shady, understory. In the small open areas, taller shrubs, such as common winterberry (Ilex verticillata) and speckled alder (Alnus incana) are present along with small shrubs such as dwarf red raspberry (Rubus pubescens) and wild sarsaparilla (Aralia nudicaulis), which occurs on the mounds. Seedlings and saplings of red maple and balsam fir are typically found in small patches. Clumps of cinnamon fern (Osmunda cinnamomea) as well as sensitive fern (Onoclea sensibilis) are also commonly found. Forbs usually found include starflower (Trientalis borealis) and blue-bead lily (Clintonia borealis) on the mounds. Very few grass or grass-like plant species were found on this site. There were more sedges than grasses and both appeared in small clumps scattered sparsely throughout. Threeseeded sedge (Carex trisperma) was common to abundant. Leafy liverworts were prevalent in the pits and feather mosses were common at most sample sites on the mounds. On one site skunk cabbage (Symplocarpus foetidus) was abundant in the pools of water.


Natural disturbances include ice and wind storms, and insect infestations that cause small gaps in the canopy. These small open areas in the forest provide an abundance of small herbs, grasses, sedges, and shrubs as well as tree regeneration for a brief period of time. Many species of medium and small sized mammals, birds, and insects can have significant influence on the plant communities in terms of pollination, herbivory, seed dispersal, and creation of local disturbance patches, all of which contribute to plant species diversity.

Human disturbances are primarily restricted to timber harvesting due to the very poor drainage. Harvesting of this reference state has been continuous over the years since European settlement, with all harvesting occurring in the winter months due to the very poorly drained nature of the soil. spruce and pine were the desirable species to harvest, mainly for timber up until about 10 years ago, although northern white cedar was used for house roofs and siding because of its resistance to decay. Presently all types of trees, including standing dead trees, are harvested for their best use depending on their size and grade. Best use includes timber, pulp, cordwood, firewood, and biomass. The ponded state (2.1) is a result of natural disturbances from beaver activity, which causes frequent ponding for long durations. This is considered a state and not a plant community phase of the reference state because the long duration would realistically be considered permanent. The nature of beaver and the particular laws regarding their control in Maine make the ponded state permanent. Beaver control has been on-going for multiple decades, but control has never been achieved. The hydrology is permanently altered to favor open areas of shrubs such as alder, grasses, and grass-like plants, such as tussock sedge. Yellow pond-lily (Nuphar lutea spp advena) was found at one sample site in a permanently ponded area.

A typical harvested state (3.1) consists of young red maple with a few gray, birch, balsam fir and sometimes black ash. Any larger trees remaining are of poor grade and some younger looking trees are actually older suppressed trees that may not respond to release. This state is usually harvested in the winter when the soil is frozen and is typically allowed to regenerate naturally back to the reference state over a long time period or may become a red maple swamp.

Reference, ponded, and harvested states may become infested with invasive plants such as purple loosestrife and Japanese knotweed. The flooded state (2.1) is particularly vulnerable to invasion from these two species. Brush management multiple times and planting of desirable native plants would be required to restore to a reference state.

A State and Transition Model for the Marine Terrace Depression Ecological Site (F144BY002ME) follows this narrative. Thorough descriptions of each state, transition, plant community, and pathway follow the model. Experts base this model on available experimental research, field observations, professional consensus, and interpretations. It is likely to change as knowledge increases.

Plant communities will differ across the MLRA because of the naturally occurring variability in weather, soils, and aspect. The Reference Plant Community is not necessarily the management goal. The biological processes on this site are complex. Therefore, representative values are presented in a land management context. The species lists are representative and are not botanical descriptions of all species occurring, or potentially occurring, on this site. They are not intended to cover every situation or the full range of conditions, species, and responses for the site.

The following diagram suggests some pathways that the vegetation on this site might take. There may be other states not shown on the diagram. This information is intended to show what might happen in a given set of circumstances. It does not mean that this would happen the same way in every instance. Local professional guidance should always be sought before pursuing a treatment scenario.