Habitat description
Young forests (less than 20 years of age) occur where a natural or human disturbance has resulted in removal of a closed tree canopy within a forest. Disturbances may include tornados, severe hurricanes, beaver activity, forestry, or other land-clearing events. While most of the habitats MassWildlife identifies are defined by assemblages of plants and animals that co-occur across the landscape, young forests and mature forests are age classes of forest forest exhibiting distinct characteristics that are important for certain species. Young forests are characterized by regenerating stands of young trees, accompanied by shrubs, grasses, and flowering plants. Young forests can eventually develop in old fields and other open areas over the course of many decades. In the absence of additional disturbance, young forests transition to mature forests, which have much lower woody stem density and larger trees.
Characteristic natural communities
Young forests may occur in any forest type, including wetlands, and are typically within the natural communities associated with oak forests and woodlands, northern hardwood conifer forests, and maritime forests and shrublands. Depending on the surrounding landscape, site conditions, forest type within which they originate, and the specific practices or events leading to its creation, plant species composition and structure vary considerably. At some sites, tree sprouts, seedlings, and understory shrubs from the formerly more mature forest play a dominant role; while at other sites, pioneer species, such as aspen or gray birch, may be prevalent. As young forests mature without additional management, they become dominated by more shade-tolerant tree species characteristic of the site and the surrounding landscape.
Characteristic plants and animals
Young forests are ephemeral, lasting for approximately 20 years or until the regenerating forest is dominated by overstory trees and the understory plants no longer provide dense cover. The preliminary phase of young forest development, “stand initiation,” usually lasts about 10 years and is characterized by densely growing plants without a substantial young-tree canopy. Seedling trees, deciduous tree stump sprouts, and native shrubs that previously occurred in the forest will flourish. In the early years, native flowering plants and understory shrubs may be a significant component of the young forest patch. During this time, young forests provide particularly important cover and food for migrating and breeding SGCN songbirds, including chestnut-sided and mourning warblers, and for foraging SGCN snakes, such as North American racer and eastern ratsnake.
Between 5 and 10 years of age, when dense cover and fruiting shrubs are available, young forest patches continue to provide critical food and cover–particularly during spring and fall migration–for fledgling and adult songbirds, including those that breed in mature forest habitats such as scarlet tanager, wood thrush, and black-and-white warbler. Patches with dense cover also provide nesting habitat for American woodcock and are particularly valuable when they are adjacent to forested or shrub swamps, where they forage, and grasslands, where they roost. Young forests at this stage also provide breeding habitat for prairie warbler, brown thrasher, blue-winged warbler, and eastern towhee, as well as important foraging habitat for large mammals, including black bear, moose, and bobcat. Vertebrate species diversity peaks when the regenerating young forest is around 10 years old.
The shading from the dense young tree canopy causes flowering plants and shrubs on the forest floor to die back, and competition for light and nutrients results in a decline in the number of young trees; this is referred to as the “stem-exclusion stage.” Patches of 10-20 year old young forest are important for the winter survival of New England cottontail and are particularly valuable when adjacent to deciduous dominated forest swamps and seeps, which also offer dense understory shrubs as critical source of food and cover. Ruffed grouse also favor 10-20 year old young forest for cover or forage, especially stands that offer birch catkins and aspen buds as a winter food source.
Eventually, gaps in the young forest canopy form as a result of non-competitive mortality, including root rot and wind, facilitating the establishment of the understory, including shade tolerant trees, as the next forest development phase—the “understory reinitiation stage.” In more generalist forest types, tree species composition will most often resemble that of the forest within which the young forest patch occurs , with some shade-tolerant shrubs remaining in the understory. Once the trees are greater than about 15-feet tall, the site usually lacks the densely growing understory required by young forest-dependent species and is no longer considered young forest.
Associated habitats
Young forests are an age class that can be found within or adjacent to any forested habitat types in Massachusetts. As described above, many species of plants and animals benefit from habitat diversity at a landscape scale, including access to young forest and other relatively open canopy habitats. Ideally, these patches of more open habitats comprise a matrix alongside mature and maturing forests.
Ecological process
Natural disturbances, such as severe hurricanes, ice-storms, fires, tornados, severe flooding, beaver activity, and, in some cases, tree pathogens or insect infestations, drive the creation of young forest habitat. The scale of these natural disturbances varies greatly. While the hurricane of 1938 and the tornado of 2011 resulted in thousands of acres of young forest being created, it may be more than 100 years between events of this scale. Patches of young forest created by more frequent flooding, wind, or ice events, downbursts, and annual flooding typically result in much smaller young forest patches. Many of the natural disturbances that drive young forest creation have been curtailed by human settlement: beaver activity, flooding, and fire are intentionally limited to protect public health, safety, and property; and wind events, ice damage, and mortality from pests and pathogens are often “cleaned up” for safety or aesthetics. Tree removal or harvest by humans for a variety of purposes has also led to the creation of young forests and is an especially important tool for establishing this ephemeral habitat today.
Land use history plays an important role in current ecological processes. Forests were cleared for agriculture after European settlement and then broadly abandoned after the onset of the Industrial Revolution (particularly in the late 1800s and early 1900s) within a relatively short period. This has created an unnaturally evenly-aged forested landscape that lacks the structural and species diversity that would have characterized our forest landscapes before European settlement, which would have had more extensive old forests. Until Massachusetts forests age and redevelop their natural structural and species diversity, creating young forests in appropriate locations across the landscape is an important conservation tool for some wildlife species.
Threats
Development is a threat to Massachusetts forests, including young forest. 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). A lack of landowners and managers conducting forestry and/or young forest management is also a threat tied to changing land uses.
Human development, beaver control, fire suppression, flood control, and response to pathogens and insect infestations are all natural system modifications that disrupt ecological processes maintaining young forest on the landscape.
Invasive species, such as multiflora rose, common buckthorn, Asiatic bittersweet, and autumn olive, often thrive after disturbance and can disrupt the natural process of young forest succession. Invasive shrub species also reduce the quality of young forest as a food resource for certain species, including songbirds. Invasive species can also complicate habitat management projects related to young forest.
Although climate change is expected to increase the extent and frequency of natural disturbances, such as flooding, wind events, wildfire, and tree pathogens or insect infestations, it is unclear whether these changes are increasing or decreasing the production of young forest habitat. Changes in the frequency and severity of droughts could also have adverse impacts.
Conservation actions
- Proactive habitat protection. Protect forests on both public and private lands as a critical part of efforts to maintain healthy and resilient landscapes for people and biodiversity conservation. Forest protection is also an important part of the Commonwealth’s climate adaptation strategy. In many cases, land protected for conservation includes disturbed forest, or forest that has recently been harvested, which create outstanding opportunities for young forest without the need to impact more mature forest. In addition, a ctive management on private lands provides an opportunity to create young forest, sustainably produce local wood products, and incentivize forest preservation, as opposed to land conversion for development and other purposes.
- Habitat restoration and management. See recommendations below
- Law and policy. Incentivize the protection and maintenance of forest on private and public lands. Ensure local infrastructure and incentives for the sustainable harvest and production of wood products, with an emphasis on long-lived products that store more carbon. Regulate and limit the impacts of development.
- Conservation planning. Include forests, and young forest in particular, in conservation planning efforts at multiple spatial scales. See BioMap as an example.
- Monitoring and research. Implement and support research on the habitat values of young forest to plant and animal species, including rare species. Monitor the health and trends of SGCN populations that depend on young forest and other similar habitats. Monitor the effectiveness of habitat restoration efforts and conduct targeted research to improve habitat and population management.
- Public outreach. Include information about the role of young forest and other similar habitats for biodiversity conservation and climate resiliency as part of broader communication strategies. Provide context that this is part of a holistic approach that includes protecting mature forest and reserves, and that young forest, and other similar open canopy habitats, should comprise a relatively small percentage of the overall landscape.
Restoration & management recommendations
Planning
Creating and maintaining young forests can be either a long- or a short-term commitment, depending on the size of the parcel, landowner capacity and goals, and current forest condition. The landscape context of the proposed project is also important, as many species require a variety of habitat types to thrive. For example, many bird species that breed in mature or interior forests benefit from access to nearby young forest patches during the post-fledging period for food and cover to prepare for migration. Species such as eastern ratsnake and North American racer benefit from young forest patches near their overwintering sites. Since some young forest species are associated with specific forest types, it’s important to provide young forest in a variety of forest habitat types, including northern hardwood and conifer forests, oak forests and woodlands, and maritime forests and shrublands. Young forest can be managed “in place” with repeated treatments over time to maintain the habitat, or as a shifting mosaic across the landscape.
On private, conservation, or municipal lands, forest stands selected for creation of young forest often consist of diseased, poorly formed, or commercially undesirable tree species. Removing these trees to regenerate young forest may not only meet habitat management goals but can also address long-term forest management objectives, provide an opportunity to generate income or offset habitat management costs, and enable landowners to keep their land as forest rather than developing it. These stands can also be managed to create a more diverse regenerating stand that encourages trees species with favored sources of nuts or berries. Income generated from a timber harvest may also provide private landowners with funds to conduct other habitat restoration and management activities.
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. For example, it is important to:
- identify unique and/or otherwise sensitive species and natural communities that should be avoided;
- evaluate key threats, such as invasive species;
- secure key resources required to implement the project, as well as subsequent monitoring and adaptive management; and
- secure community, stakeholder, and institutional support.
- A variety of practices can be implemented to create young forest patches depending on the type of mature forest where management will occur.
It is important to note that species that breed in young forests, including prairie warbler, eastern whip-poor-will, and blue-winged warbler, generally require patches greater than 5-acre patches to accommodate territories of multiple pairs, food, and cover requirements. Patches greater than 25 acres may be necessary to maintain viable populations of other area-sensitive species.
Implementation
Young forest patches can be established through selective mechanical tree removal (in accordance with the MA Forest Cutting Practices Act and other regulations). Delineate patches in regularly shaped circles or squares with rounded edges and corners to maximize inside area and minimize outside edge, as most young forest-associated birds prefer to nest greater than 250 feet from edges . If patches greater than 10 acres can be created, irregularly shaped edges will result in differences in light and temperature throughout the patch, resulting in increased plant species diversity. Avoid steep slopes and adhere to Massachusetts Forestry Best Management Practices Manual stream and wetland filters, as well as other harvesting and Forest Cutting Practices Act requirements.
Conducting a silvicultural clear cut, clear cut with reserves, seed tree cut, or the second phase of a shelterwood cut can result in young forest features consisting of densely regenerating young trees and shrubs depending on the initial stand conditions. Cut trees greater than four inches in diameter at breast height, unless being retained as seed trees, and then allow the site to regrow naturally. Retaining “biological legacies” as single elements or as patches/groups within the project area will be important. These legacies can include mature red oak, black cherry, yellow birch, and American beech, which are preferred sources of nuts and berries along with low-branching conifers or evergreen shrubs for cover. Retain large diameter cavity trees, snags and downed logs. If large dead logs are limited within the project area, then plan to add them as part of the project using trees of low or no value. Retain tree species that are not well represented in the project area for future seeding. Ensure slash is distributed in accordance with guidance and requirements included in the Massachusetts Forestry Best Management Practices Manual.
Addressing invasive species in managed young forest habitat patches is a priority, as invasive plant species are often able to colonize and spread in response to increased light availability and soil disturbance. Evaluating and controlling established invasive species prior to creating young forest habitat—and monitoring and treating invasives after canopy tree removal has taken place - should aways be included in a management plan. Protocols to prevent the introduction or spread of invasive species during forest management, such controlling potential vectors (contaminated soil, equipment, etc.) by powerwashing equipment prior to arriving on site, should be implemented to the greatest extent practicable. Finally, regular monitoring and rapid response to pioneering invasive species before they begin to impact habitat should be a priority. Herbicide is usually required for effective control, particularly in areas with widespread infestations prior to the initial treatment and canopy thinning.
Aspen regeneration
Aspen, often referred to as poplar, is a short lived and shade intolerant tree important for numerous wildlife species, especially when it occurs in dense young forest stands of saplings where it provides cover and food resources for most species associated with young forests such as chestnut-sided warbler, ruffed grouse, yellow bellied sapsucker, and moose. In Massachusetts, quaking aspen and bigtooth aspen grow in various densities within deciduous forests. Though under the right conditions it can regenerate from seed, aspen is a clonal species that responds to being cut by sending up hundreds of saplings from its roots if adequate sunlight is available. Large acreages of aspen are rare in the Commonwealth, but small pockets can be found in areas of recent disturbance, such as agricultural field edges, old clearcuts, or abandoned beaver ponds. Due to its importance to wildlife and limited availability on the landscape, where found, aspen should be maintained, at least partially in a young forest stage.
To promote dense regeneration of aspen forests that contain aspen even as minor component, remove most of the overstory and even the midstory through a timber harvest of at least five acres to get sunlight on the ground and maximize root suckering. If possible, cut all stems over two-inch diameter at breast height (dbh) during leaf off conditions. If there are adequate numbers of aspen in the overstory, retain some in clumps near the edge of the harvest, as the buds of mature aspen are an important winter food source for ruffed grouse. Also retain scattered mast producing overstory trees, such as cherry or oak, along with cavity trees, snags, and large downed logs. If there are dense young conifer patches within the harvest area, retain those for thermal cover. Aspen regeneration following a timber harvest is prolific and will quickly fill the opening, sometimes reaching four feet in height by mid-summer.
Prescribed fire can also be a beneficial management tool for maintaining and promoting aspen on the landscape. Aspen responds to fire much like cutting, by sending up thousands of shoots from the root system. Fire removes competitors to aspen and burns up suppressing ground cover, allowing the soil temperatures to increase further promoting the growth of aspen. Use of fire for aspen management is very site specific and requires detailed planning and evaluation before applying. For example, retention of coarse woody debris should be minimized during initial harvest to facilitate later prescribed fire implementation.
Once established, young aspen stands under eight-inch dbh can be managed using mechanical treatments with mulching/mowing machines. To maximize habitat benefits to wildlife, maintain aspen stands of 20 acres or larger on a 40-year rotation, mowing 25% of the area once every 10 years to promote four age classes (0-10, 10-20, 20-30, 30-40). Even where there are only small patches of aspen next to fields or other openings, they can be expanded through management and should be maintained on the landscape as much as possible.
Additional resources
Managing Grasslands, Shrublands, and Young Forests for Wildlife