Habitat description
Mature forests develop when older forest and woodland natural communities have vegetation (species composition, age classes, structure) and associated ecosystem processes (including, but not limited to, fire, hydrology, disease, wind, and ice) that are relatively stable. In mature forests and woodlands, this occurs when the majority of trees exceed 80 years old. While most of the habitats MassWildlife identifies are defined by assemblages of plants and animals that co-occur across the landscape, mature forests and young forests are age classes of forest habitats, such as northern hardwood and conifer forests and oak forests and woodlands. These age classes have unique habitat qualities that may require special management considerations.
Although mature forests and woodlands are relatively stable, natural processes are always at work at many different levels that help shape forests as they age. Climate, soil composition, nutrient cycling, fauna, and both small- and large-scale disturbance interact in determining forest composition and structure, sometimes precluding the establishment of a steady state mixture of late successional species. Because mature forests and woodlands vary so significantly in composition and structure, and because of the variety of factors that continue to shape them, they are important to biodiversity conservation and to helping us better understand how different types of forests and woodlands evolve in response to natural disturbances, increasing climate stressors, and evolving human land uses.
Terms such as “old growth” or “primary forest” usually refer to the subset of mature forests where people have not harvested trees or otherwise substantially altered the forest, and that are minimally influenced by fire. In Massachusetts, mature northern hardwood and conifer forests are typified by mostly closed canopies with scattered older and larger trees, multiple canopy layers of trees of mixed ages and species, small gaps and openings in the canopy, complex horizontal and vertical structure, litter accumulation, well-developed organic soil horizons, and large woody material in various stages of decay. Regeneration of trees, shrubs, and other vegetation occurs primarily in the gaps caused by individual or small-group mortality of trees. Some lichens and fungi also grow only on old, large trees.
In addition, mature fire-influenced forest and woodland natural communities In Massachusetts can be described as having “old-growth characteristics.” These mature forests and woodlands are typified by older and larger trees of varying density, but where periodic fire reduces litter accumulation, maintains sandy mineral soils often with a shallow duff layer, and regularly resets the composition and structure of understory vegetation. The term “climax forest” refers to a forest where ecological succession has altered the species composition to the point where it is relatively stable despite, or in some cases because of, ongoing natural disturbance processes. Indeed, in dry woodland and barren, as well as some oak forest and woodland natural communities, periodic fire is necessary to maintain old-growth characteristics. Mature oak survives the fire because of its thick bark, and by reducing shrubby vegetation in the understory, fire reduces the potential for canopy fires that can kill even the most fire-adapted oaks.
Many mature forests and woodlands occur in remote or difficult to access sites, where human impacts have been lower than in forests adjacent to other human land uses. However, depending on the underlying natural community, mature forest habitat can be encouraged using specific management practices that accelerate the development of old-growth characteristics.
Characteristic natural communities
In MassWildlife’s habitat classification, forest habitats can be further subdivided into distinct natural communities. Any of the upland or wetland forest habitats of Massachusetts, and their associated natural communities, may develop into mature forest. In Massachusetts, with its long history of human landscape alteration, northern hardwood and conifer forests and oak forests and woodlands represent the majority of currently existing mature forests.
Mature forests may also occur within dry woodlands and barrens, acidic peatlands, riparian and floodplains, forest swamps and seeps, and maritime forests and shrublands.
Characteristic plants and animals
While there are no known species in Massachusetts that are old-growth obligates, mature forests can provide important habitat for species such as the Jefferson salamander, marbled salamander, broad-winged hawk, cerulean warbler, scarlet tanager, and wood thrush. This is in addition to species, such as bobcat, that frequently use mature forest habitat and numerous plant species found predominantly in mature forest, such as black cohosh.
Associated habitats
Mature forests may be associated with upland forests of various ages, including young forest, as well as wetland habitats, such as forest swamps and seeps, riparian and floodplains, and vernal pools. Mature forests also support many riverine habitats, especially cool and cold streams, by providing shade, filtering, and inputs of large woody material.
Ecological processes
Mature northern hardwood and conifer forests are dominated by relatively stable species composition, uneven distribution of tree ages, and high horizontal and vertical structural complexity, with frequent windthrow and other single-tree and small gap disturbance events that open the canopy to provide light for growth of patches of herbs, shrubs, and tree seedlings/saplings. Less frequent, larger natural disturbance events, including hurricanes, tornados, ice storms, and insect and disease outbreaks, create larger gaps or even stand-replacing disturbance.
On the other hand, in oak-dominated systems like oak forests and woodlands, oak hickory forests, and dry woodlands and barrens, periodic wildland fire is a natural process that is frequently excluded due to habitat fragmentation and nearby human land use. Where prescribed fire is used as a habitat restoration and management tool to simulate this natural process, it favors the growth of fire-associated trees such as oaks and hickories while reducing generalist species like red maple and eastern white pine. Because of this, mature oak forests tend to have more widely spaced, larger canopy trees and a more open understory dominated by heaths and other fire-associated shrubs.
Threats
Development results in habitat loss and fragmentation of mature and maturing forests. Recent census data shows that Massachusetts is the fastest-growing state in the Northeast, and development continues to convert forest and agricultural sites to residential and suburban developments and solar arrays. Approximately 30,000 acres of forested land in Massachusetts were lost between 2012 and 2017 (Losing Ground: Nature’s Value in a Changing Climate; 2020; Sixth Edition, MassAudubon).
Invasive species, including exotic plants, insects, and pathogens, are also a significant threat. Hemlock wooly adelgid, emerald ash borer, and Asian long-horned beetle directly impact tree species common in mature northern hardwood-conifer forests, and spongy moth has dramatically altered the trajectory of most oak-dominated forest types in Massachusetts. Invasive exotic earthworms increase nutrient cycling and loss of forest floor organic material, which reduces or prevents the regeneration of many native plant species in mature forests and benefits invasive exotic plant species, such as Japanese barberry, glossy buckthorn, stilt grass, or garlic mustard.
White-tailed deer abundance and browsing intensity can be influenced by landscape-scale land use changes (natural systems modification). The impact of deer herbivory on understory vegetation can be significant not only on the biodiversity of native herbs, shrubs, and tree seedlings, but also on forest-breeding birds.
Climate change: Predicted increases in summer temperature, fall droughts, and winter freeze-thaw cycles are expected to further increase stress on shade-tolerant and high-elevation tree species. This is likely to impact the stability of mature forests in the northern hardwoods and conifer regions of the state. Increases in drought may increase frequency, severity, and extent of wildfire in mature forests, leading to conflicts with other human uses and favoring the regeneration of grasses, forbs, and shrubs over trees. Increasing drought also interacts with pests and pathogens to limit the survival of overstory trees.
Conservation actions
- Proactive habitat protection. Protect mature forests and other associated, interconnected habitats to maintain healthy and resilient landscapes for people and biodiversity conservation. Prioritize sites supporting state-listed animals and plants and other SGCN, as well as other protection priorities identified in BioMap and other conservation planning tools (e.g., municipal open space plans).
- Habitat restoration and management. See recommendations below.
- Law and policy. Incentivize the protection and maintenance of forest on private and public lands. Regulate and limit the impacts of development and consider innovative approaches to incentivizing compatible development, and farm and forest preservation where applicable. Some mature forests make excellent candidates for forest reserves.
- Conservation Planning. Include mature forests in conservation planning efforts at multiple spatial scales. (See BioMap as an example.)
- Monitoring and research. Monitor the health and trends of SGCN populations, plant communities, and other wildlife. Monitor the effectiveness of habitat management efforts and conduct targeted research to improve habitat and population management.
- Public outreach. Include information about the role mature and maturing forests play in biodiversity conservation, flood mitigation, water filtering, and climate resiliency as part of broader communication strategies.
Restoration & management recommendations
The history of extractive timber harvesting with inadequate attention to biodiversity and species regeneration in many Massachusetts forests has altered their composition by preferentially removing tree species with high monetary value without ensuring regeneration of those species. This history has also led to the removal of many of the healthiest and fastest-growing individuals of harvested species, leaving behind poorly formed stems that may have the least-well-adapted genetics for the site. Combined with decades of fire exclusion and lack of other disturbance, many mature forests in Massachusetts are compositionally and structurally far less diverse then they could be. For example, in the absence of appropriate management, many of our mature oak forests and woodlands are poised to be replaced by already ubiquitous red maple, white pine, birches, and other common tree species.
Planning phase
Before undertaking a project, it is important to complete a thorough planning process that establishes clear goals that are compatible with site conditions, as well as other conservation goals that may be relevant to the site. When considering whether passive or active management may be most appropriate, it will be important to consider the health, growth rate, composition of, and threats to the current forest. More information on those considerations can be found below. In addition, careful consideration should be given to the underlying natural community type and its ecological condition.
The publication “Restoring Old-Growth Characteristics to New England’s and New York’s Forests” (D’Amato and Catanzaro, 2022) provides an in-depth look at both passive and active management approaches to restoring the ecological characteristics of mature forests in the region, and we refer to that publication as the most complete and current set of specific recommendations. Dynamic Forest Restoration (Jones, 2022) is a developing method of combining mature forests with inclusions or adjacent stands of varying aged forests. This approach diversifies forest age classes and provides food and cover resources in younger stands for species that use mature forests for one or more life stages (for example, interior-forest-nesting birds that rely on open habitats during the post-fledging/pre-migration period).
Mature forest and woodland habitat is most valuable at sizes larger than 50 acres, especially as part of a larger, landscape-scale mosaic of related habitat types. Keeping forests as forests and protecting additional adjacent forest from development are among the most important steps to take for mature forests, and careful consideration should be given to whether additional areas have the potential to become mature forests through active or passive management or whether they should form part of a working landscape buffer. Forests that abut developed areas (including roads, houses, and other fragmenting features) are less likely to provide all the interior forest resources of an intact mature forest. Finally, since mature forests can vary substantially in species composition and structure, the underlying natural community must be considered. For example, some natural communities within the oak forest and woodland continuum may need periodic fire and or other management to restore and maintain appropriate mature forest characteristics and the full suite of species associated with them.
Evaluating and controlling established invasive species within mature forests should be included in a management plan, and regular monitoring and rapid response to pioneering invasive species before they begin to impact habitat should be a priority. Herbicide may be required for effective control, particularly in areas with widespread infestations.
Management approaches
Management approaches can and should vary based on the on the habitat type and underlying natural community. Below are some high-level examples of management approaches; however, more specific recommendations are available in each habitat’s “restoration and management” section.
Management approach: Passive management
In New England, mature forest characteristics in northern hardwood and conifer forests begin to develop in unmanaged stands through natural stand dynamics between 80-100 years of age, with large-tree benchmark conditions reached around year 200, and development continuing thereafter. This approach is suited mostly for large areas of forest that have healthy overstory and understory vegetation of the appropriate species, have not been managed in at least 50-100 years, that are not highly invaded by invasive species, and that are not fire dependent. Passive management may limit the landowner’s ability to respond to future stressors or disturbance events brought about by climate change.
Areas intentionally set aside for growth without active management are sometimes considered “forest reserves,” although that term has numerous meanings for different landowners. If landowners choose this approach, it is important to establish up front what actions will and will not be allowed, and what events would trigger those actions. For example, if there is an invasion of exotic insects, will that be allowed to proceed unimpeded, or will mitigation efforts take place? If exotic invasive plants become a problem, will the landowner attempt to remove them through mechanical or other means? How will trespass by off-highway vehicles be reduced or eliminated? What are the guidelines for prescribed fire in fire adapted ecosystems to help build resiliency? If carbon sequestration is an explicit goal, how will this be measured, and will any actions be taken if the accumulation of carbon declines or reverses?
Management approach: Active management and restoration
Management and restoration actions to promote structural complexity and other old-growth characteristics may help move some forests and woodlands in the direction of mature forest habitat, enhance carbon storage, and provide the habitat characteristics of mature forest earlier than in forests without such restoration. Any active management of mature forests and woodlands must carefully consider the underlying natural community type, how close the current forest/woodland is to achieving the vegetative composition and structure of that natural community, and what management or restoration actions are needed.
If mature forest or woodland is the primary goal, active management in stands that are already providing high quality mature forest habitat may be limited to addressing invasive exotic plants and animals and their impacts, reducing human impacts, such as off-road vehicles, or taking actions to enhance old-growth characteristics or restore carbon accumulation.
On the other hand, fire-influenced mature forest and woodland natural communities, from oak forests and woodlands to dry woodlands and barrens, depend on periodic fire to help maintain healthy ecosystems and their unique old-growth characteristics. Many fire-influenced forests and woodlands are currently fire suppressed, and even older trees are vulnerable to being killed by intense, catastrophic fires. In those cases, mature and old forest conditions would never be reached, and dense thickets of pitch pine or white pine may establish in the wake of intense wildfire. Depending on the underlying forest or woodland natural community type, reintroducing prescribed fire every few years or decades thins shade tolerant species in the understory, reduces the risk of ladder fuels spreading fire into the tree canopy, and allows larger, fire adapted trees to grow with less competition for light and moisture over time, making them more resistant to subsequent fires. These trees have higher rates of growth, thicker bark, and higher canopy base heights. The periodic renewal of understory vegetation structure and composition in these systems contributes to species diversity, as well as carbon sequestration and storage. In short, prescribed fire contributes to developing and maintaining the unique old-growth characteristics of fire-influenced forests and woodlands. In addition, prescribed fire also reduces the risk of extreme fire behavior and exposure to firefighters and surrounding human communities and built environments. For more information, see the restoration and management recommendations for oak forests and woodlands and dry woodlands and barrens.
Additional resources
Chandler, Carlin C.; King, David I.; Chandler, Richard B. 2012. Do mature forest birds prefer early-successional habitat during the post-fledging period?. Forest Ecology and Management. 264: 1-9. https://doi.org/10.1016/j.foreco.2011.09.018
D’Amato, Anthony and Paul Catanzaro. 2022. Restoring Old-Growth Characteristics to New England’s and New York’s Forests. Amherst: University of Massachusetts.
Dunwiddie, Peter, D. Foster, D. Leopold, and R.T. Leverett. 1996. Old Growth Forests of Southern New England, New York, and Pennsylvania. Pages 126 – 143 in M.B. Davis (ed.) Eastern Old Growth Forests. Island Press, Washington, D.C.
Ford, Sarah E. and William S. Keaton. 2017. Enhanced carbon storage through management for old-growth characteristics in northern hardwood-conifer forests. Ecosphere 8:4. https://doi.org/10.1002/ecs2.1721
Hagan, J. M., and A. A. Whitman. 2004. Late-successional forest: a disappearing age class and implications for biodiversity. Brunswick, ME: Manomet Center for Conservation Sciences.
Jones, Benjamin C. 2022. Dynamic Forest Restoration. RGS & AWS Magazine, Winter 2021.
Martin, P., Jung, M., Brearley, F. Q., Ribbons, R. R., Lines, E. R., & Jacob, A. L. 2016. Can we set a global threshold age to define mature forests?. PeerJ, 4, e1595. https://doi.org/10.7717/peerj.1595
Mathis, C.L., McNeil Jr, D.J., Lee, M.R., Grozinger, C.M., King, D.I., Otto, C.R. and Larkin, J.L., 2021. Pollinator communities vary with vegetation structure and time since management within regenerating timber harvests of the Central Appalachian Mountains. Forest Ecology and Management, 496, p.119373.
Oliver, Chadwick Dearing and Bruce A. Larson. 2016. Forest Stand Dynamics (New York: John Wiley & Sons, Inc.)
Raybuck, D.W., Larkin, J.L., Stoleson, S.H. and Boves, T.J., 2020. Radio-tracking reveals insight into survival and dynamic habitat selection of fledgling Cerulean Warblers. The Condor, 122(1), p.63.
Rushing, C.S., Rohrbaugh, R.W., Fiss, C.J., Rosenberry, C.S., Rodewald, A.D. and Larkin, J.L., 2020. Long-term variation in white-tailed deer abundance shapes landscape-scale population dynamics of forest-breeding birds. Forest Ecology and Management, 456, p.117629.
USDA Forest Service. 2020. Forests of Massachusetts, 2019, Resource Update FS-239, https://doi.org/10.2737/FS-RU-239.