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Active stewardship of forests is critical for creating healthy, sustainable ecosystems. This chapter covers the qualities and benefits of health forests as well as a range of management opportunities and challenges.
A healthy forest or woodland has well developed structural layers including the canopy, subcanopy, shrub, and herbaceous or herb layers (the latter two comprising the understory), each with a high level of plant diversity. A multi-layered diverse forest provides a range of habitat niches and fosters resilience to pathogens and environmental stresses such as drought and high winds. Brush piles and dead and downed trees provide additional habitat and replenish soil nutrients as they decompose.
The goal of forest stewardship should be to create a healthy forest ecosystem with trees of mixed ages and to minimize the influence of ecological stressors like introduced invasive species, pests, and other effects of human development. While Pennsylvania supports over 17 million acres of forest, much of it is considered second-growth because of widespread clearcutting over 100 years ago. There are only a handful of locations that support old-growth or “original” forest. Undegraded forests contain trees of a variety of species and age classes, and this diversity results in higher resilience and less vulnerability to catastrophic disturbance or disease. A variety of tree ages within a forest also provides a range of habitat types for wildlife.
Forests in the eastern United States can generally be grouped into four age classes: young (less than 30 years), maturing (30 to 75 years), mature (75 to 150 years), and old-growth (greater than 150 years). Young forest develops where there has been a disturbance (e.g., naturally occurring fires or high wind events) or a management activity (e.g., timber harvest) that results in the removal of a significant portion of the canopy. Shortly after such a disturbance, the area begins to transition from an open-canopy community (meadow or shrubland) to a tree-dominated community characterized by many small trees growing close together with a sparse shrub and herb layer. As the forest matures, some trees die and some grow into prominent positions in the canopy. The more widely spaced trees allow shrubs and herbs to become established. In a mature forest each structural layer or stratum (canopy, subcanopy tree, shrub, and herb) is well developed. Old-growth forests are characterized by a multi-aged canopy (scattered large canopy trees interspersed with canopy trees of younger age classes), a multi-layered understory, and abundant down and standing dead wood. Maturing and mature age classes show different degrees of development of those traits.
For greatest resilience (ability to withstand physical and biological stresses) a forest should have high diversity of native plants in each structural layer. Biodiversity fosters resilience by ensuring there are multiple plant species that provide similar ecological functions, including food and shelter for wildlife, nutrient retention, and erosion control. If a plant species is struck by a pest or disease, other species will still be present to supply similar functions.
Natural disturbances like fire or storms can reset the forest to an earlier age class or to early successional habitat. This means that the sequence of forest age is often not linear but is instead a back-and-forth progression. The disturbance return interval varies greatly among different forest types and is influenced by topography, wind exposure, solar aspect (which can affect flammability), and random weather events.
Under ideal conditions, a forest is able to recover naturally from disturbance. However, introduced invasive plants and high deer populations can prevent natural regeneration of native species and halt forest succession. Active management is needed to control these stressors, including invasive plant species control (see Invasive Plants chapter) and deer population management (see Deer Management chapter). Restoration or enhancement activities may be used to augment the suitability of the habitat for specific wildlife species. Planting trees to encourage transition to older forests, planting shrubs and understory trees to build out structural layers, or even creating early successional habitat are examples of forest augmentation or enhancement. All are based on the current conditions and also driven by management goals.
A note about early successional habitat: It is declining in the region due to development of abandoned pasture and farmland to residential, commercial, and industrial use and loss of natural disturbance from fire. Early successional habitat dominated by native plant species is critical habitat for some wildlife, particularly certain bird species.
Healthy forests have a variety of age classes and diverse, resilient landscapes include a variety of stand ages—early successional habitat, mature or old-growth, and everything in between. This helps build resilience, as different forest ages vary in their resilience. A patchwork of age classes increases the likelihood that at least some areas of the forest will withstand a given disturbance event. Even-aged forests are not healthy forests.
Large areas of healthy forest can also provide forest interior habitat—the area of a forest that is more than 100 meters (roughly 330 feet) from an edge, the boundary between forest and non-forest. Forest interior adds value for wildlife, particularly migratory songbirds, as they are protected during the breeding season from predators and nest parasites that favor forest edges, such as raccoons, feral cats, and brown-headed cowbirds. Forest interior habitat is declining due to forest loss and fragmentation. An unfragmented forest is not just large in area but also has a low edge-to-area ratio, that is, the shape of its footprint is compact rather than narrow or with sinuous edges.
In addition to wildlife habitat, forests provide many benefits for landowners, local residents, and recreationists. Forest vegetation improves air quality by filtering dust and other pollutants, absorbing carbon dioxide, and releasing oxygen. Healthy forests with high structural diversity are extremely effective in capturing precipitation and their soils are able to absorb high volumes of water, which helps to recharge groundwater supplies and minimize sediment-laden runoff to small streams. Forests also provide recreational opportunities such as hiking, birdwatching, nature photography, and hunting and offer a welcome visual relief from sprawl development for motorists.
Palustrine forests, or forests in wet areas, protect water quality by filtering sediments and pollutants before they reach surface water. They also slow surface water flow, protecting streambanks and promoting infiltration that maintains groundwater levels. Palustrine forest stands along streams and rivers are known as riparian buffers (see Water Resources chapter). Depending on the frequency and intensity of flooding, palustrine forests may experience more disturbance than terrestrial forests, which can affect tree age distribution and decrease vegetation density.
All healthy forests aid in moderating climate. An intact canopy provides shade for lower layers, reducing temperatures and maintaining moisture. Trees absorb and store carbon in leaves, woody stems, and soil, preventing it from contributing to the greenhouse effect and global climate change(see Addressing Climate Change on Natural Lands chapter). By absorbing carbon and releasing oxygen, trees also contribute to sustaining a breathable atmosphere.
Key features of a healthy forest include:
Inventories can be carried out to monitor the health of the forest and identify issues. This will help with determining management goals and actions. An effective inventory should seek to assess the above key features and identify possible issues. While inventories are important, they can be resource intensive. The following categories, Good, Better, and Best outline three different levels of inventories. While the Best category can be considered the “gold standard,” any of the three options can provide valuable insights into forest health and sustainability.
More information on inventorying and how it fits into stewardship planning and management can be found in the Preparing a Stewardship Plan chapter.
The size of a forest and how it relates to the surrounding landscape are important factors in understanding what kinds of management may be most effective. A key a metric is the amount of forest interior. Forest interior is defined as the forest at least 100 meters from a non-forested edge. Generally, the closer a forested area’s shape is to a smooth-edged circle, the more interior it has. Narrower, more sinuous, pinched in the middle, or jagged-edged forest areas have smaller interiors and may have none at all. Larger patches of interior can support a wider diversity of plants and animals because they support larger populations, they are likely to contain a broader range of habitat diversity, and forest species are more isolated from the disturbances and intrusions (invasive species, predators, noise, etc.) typical of the forest edge. Also, the kinds and extents of land uses that surround any given patch of forest can greatly influence the quality of a forest and its ability to support certain functions, habitats, and species. Managing a forest can also mean managing surrounding land uses to minimize impacts to the forest patch of concern.
Good
Better (in addition to Good)
Best (in addition to Good and Better)
Both condition and age of a forest are difficult to assess in a quantitative way. The Floristic Quality Index, which is a tool to determine the quality of a native plant community based on a numerical ranking, is one approach to providing a comparative (to other forests) indicator of the quality of a given patch of forest. However, experience and expertise are needed to take full advantage of the tool. More subjective, qualitative approaches can also be of value and provide enough information to allow management decisions and stewardship practices to go forward. Knowing the age of a forest helps to guide management, and if old-growth management is a goal, a determination of age and the factors that go into that determination can serve as a baseline for management.
Good
Better (in addition to Good)
Best (in addition to Good and Better)
A forest's composition reflects geology, topography, hydrology, disturbance, and other aspects of site history. It can also suggest age and successional trajectory. Many forests are managed with a compositional plan in mind, meaning that there is a goal for what species are present. Sometimes certain wildlife management goals suggest the choice of species, although most often the key factor in goal-setting is forest structure—establishing and maintaining full and diverse canopy, subcanopy, shrub layer, and herbaceous layer. Having an idea of the general composition and patch diversity of a forest provides a way to frame and discuss basic stewardship needs.
Good
Better (in addition to Good)
Best (in addition to Good and Better)
Cities, boroughs, and townships can benefit by conducting tree inventories along streets and roads and throughout the public areas within their borders. This can help indicate where more trees are needed, which trees may die off in the near future, and which species are successful. Factors to monitor include:
Monitoring can be done on a rotating basis with each tree inventoried every 2-3 years. Hazard tree assessments should be conducted annually and after each severe storm.
The adaptive management approach is a way of comparing promising alternative methods for achieving goals as a part of routine management, without high-cost research. It is evidence-based stewardship in which a management team is accountable for the results. Monitoring and analyzing trends over time generates practical new knowledge that is promptly put to use. It is in essence a performance evaluation—a systematic, disciplined approach to measure and improve the effectiveness of management. Monitoring is vital to improve consistency, rigor, and efficiency in measuring progress toward achieving and sustaining desired conditions. The following steps outline the adaptive management process:
Not all land stewards have the staff and volunteer capacity, available expertise, or funding to monitor as thoroughly as might be considered ideal. The level of monitoring will depend on the resources available and the level of priority. If endangered species or ecological communities of high conservation significance are involved, the most stringent level of monitoring is appropriate and necessary. In more ordinary situations, a simpler and less demanding set of monitoring methods may be all that is needed.
Under Management Opportunities (below) we suggest options for what indicators to monitor in various land stewardship situations.
Having a sustainable and resilient forest means that the forest should persist into the future with diminishing management demands. Fostering a sustainable forest requires maintaining high diversity of native species, full development of forest layers as appropriate for the forest age, low to no pressure from introduced invasive plants, and deer browsing at a level that allows persistence and reproduction of diverse native trees and other native forest plants. This will ensure that the forest layers remain intact over time and continue to provide important ecosystem benefits like water protection and provision of habitat for wildlife.
At the landscape level, the goal is a mixed age forest with young, maturing, mature, and old-growth forest areas. Having the full range of age classes helps prevent widespread forest loss and supports the cycle of younger forests maturing to replace older forests as the older forests succumb to natural disturbances and age (see Qualities and Benefits of a Healthy Forest, at the beginning of the Forest Management chapter).
Beyond this main goal, landowners and managers can determine more specific goals. Examples of goals include supporting wildlife in general or a particular species or set of species, protecting water quality, and providing recreational opportunities. Landowners will have to decide what their priorities are and what goals will help them achieve their priorities (see Preparing a Stewardship Plan chapter).
Common threats to forest health and management goals include deer overabundance, introduced invasive species, fragmentation, development, and poor harvesting practices. Climate change is a looming threat that can have widespread impacts on forests. These threats are described in greater detail in their respective sections.
Key strategies for forest management include:
The goal of forest stewardship should be to foster healthy, sustainable forests as a mosaic of mixed tree ages to increase resilience and provide a range of habitat types for wildlife. Resilient landscapes include a diversity of forest ages, ranging from young to old-growth, which makes the landscape less vulnerable to widespread forest loss from disturbance or disease. Pennsylvania forests typically consist of only one or two ages. Few old-growth forests or mosaics of multiple forest ages remain.
Historically, forests were shifting mosaics of different ages, created by natural disturbances affecting different forests patches over time. Patchy treefalls, windthrows, and wildfires resulted in a mix of early successional, maturing, mature, and old-growth forest. However, due to the suppression of natural disturbances like fire, the prevalence of other stressors such as deer and introduced invasive plants, and even-aged growth after clearcutting and farmland abandonment, the shifting mosaic of different forest ages has been disrupted. Vast areas of regrowth are now even-aged, with trees of similar size spaced so closely together that little light penetrates to the subcanopy, shrub, and ground layers.
To support varied forest ages, multiple approaches can be taken. One option is to create early successional forest patches by fostering forest regeneration after natural disturbance or by intentionally creating disturbance using prescribed fire or selective cutting. To support regeneration after natural disturbance, introduced invasive plants and deer need to be managed to allow native plants to thrive, and selected tree species can be planted to enhance long-term forest resilience. If taking a more proactive approach, such as prescribed fire, projects should be carefully planned and managed to:
Older forest ages can be supported through activities such as:
For greatest resilience (ability to withstand physical and biological stresses) a forest should have a wide diversity of plant species, the majority of them natives, with any nonnatives being relatively scarce and of non-invasive species. Native biodiversity creates resilience through redundancy. Where multiple native plant species co-occur that are similar in ecological function, if one species is impacted by a pest or disease, other species will still be present to fulfill a similar ecological role. A forest stand should have all structural layers characteristic of the stand age with a range of plant species in each layer. This should include natural regeneration of native species to replace existing plants as they die.
Good—For forests that are predominantly native plants with low introduced invasive plant pressure, manage deer and introduced invasive plants (see respective sections).
Better—For forests with a moderate diversity of native plants, low introduced invasive plant pressure, and some mix of forest ages, manage deer and introduced invasive plants (see respective sections) and protect areas with native regeneration and plant additional native plants to bolster diversity and add density to structural layers.
Best—For forests with a high diversity of native plants, low to no introduced invasive plant pressure, all forest ages represented at a landscape scale, and natural regeneration occurring, follow recommendations in the Better scenario and create a landscape plan assessing current forest ages and determine methods to support a mix of forest ages (see above).
Although often viewed as unsightly and messy, dead wood is the foundation of the forest food chain and also provides shelter to many animal species. In addition, fallen logs and limbs serve as a water reservoir in times of drought. They soak up water and can retain it for long periods of time, providing nursery sites for seedlings (especially during dry spells) and moisture for small animals like salamanders and tiger beetles. Logs also help control erosion by slowing surface water flow and by absorbing water in place. Mycorrhizal filaments reach up from tree roots into fallen wood to extract valuable nutrients.
Individual standing dead trees—“snags”—are also important to leave, when they do not pose a hazard to humans or structures, because they are used as dens by many animals and harbor insects and microorganisms that provide food for many birds and small mammals. These, in turn, are food for larger mammals and birds of prey.
Where is this a low abundance of snags, land managers can create snags. According to the Washington Department of Fish and Wildlife, this can be done by girdling the trunk or branches, removing the top third of the tree and half of the remaining side branches, or removing a majority of the tree’s side branches. Consultation with a certified arborist can help determine which trees and approaches may be appropriate to use when creating snags (see Related Items of Note).
Leave snags and downed wood where not a hazard or nuisance.
Create snags where lacking.
Interior forest —forest that is at least 100 meters from an edge in large, contiguous tracts— is important habitat for wildlife because certain species, such as migratory songbirds, need interior habitat for shelter and protection from predators (raccoons, feral cats) during the breeding season. Interior forest is declining throughout the state due to fragmentation of large, forested areas by roads, rights-of-ways, and development. Trails are not as great of a concern in terms of fragmentation, as they are often narrow enough to maintain a closed canopy.
Large tracts of forest should be protected to preserve interior forest habitat. This includes preventing full loss from harvesting or development and preventing incursions into the forest through roads or isolated structures like well pads. Common forest management practices like deer management and introduced invasive plant control can be used to improve the health of existing interior forest. New interior forest can be created by planting fields or other low cover/vacant areas with trees adjacent to existing areas of forest. This is not to say that all meadows, shrublands, and grasslands around large forest tracts should be converted to forest to increase interior forest habitat. These vegetation covers have their own value as habitat. Careful consideration of the benefits of various cover types should be considered when deciding where to expand forests to create interior forest.
Good—Avoid development or other conversion of large forest tracts.
Better (in addition to Good)—Actively manage forests in large forest tracts to support sustainability and resilience.
Best (in addition to Good and Better)—Expand forest tracts to create new interior forest habitat (see Afforestation/Reforestation below).
Forests may be created adjacent to established forest, along streams, and in open areas that provide little habitat value by allowing an area to naturally transition over time (noting that many open areas like grassland and meadows do provide high habitat value). However, this may take an extended period of time and natural regeneration may be suppressed by deer overbrowsing and competition from introduced invasive plants. If this is the case, landowners should lower deer impact and control introduced invasive plants (see Wildlife Management and Habitat Enhancement and Invasive Plants for more information). After controlling for stressors, natural tree regeneration can be augmented by planting seedlings or saplings if necessary. Choose trees that are appropriate for the location based on site conditions including hydrology, climate, and soils. Naturally occurring plant communities can be used as reference to determine which species grow well together. Information on Pennsylvania’s native plant communities can be found in the Pennsylvania Natural Heritage Program’s Plant Community Classification resource (naturalheritage.state.pa.us/Communities.aspx as of 2024).
Trees should be planted in a grid pattern which allows mowers and maintenance staff to more easily move between trees for maintenance. Within the grid, trees should be planted in 10 x 10’ squares. The spacing can be increased, up to 20 x 20’, if larger trees are planted.
Fencing, tree shelters, or tree guards should be used to deter deer from browsing on planted and naturally regenerating seedlings and saplings. Competition, particularly from introduced invasive plants, can be reduced by mowing between trees and selectively applying herbicide as needed. The base of tree shelters should be kept clear of tall vegetation to minimize damage from small mammals like voles. Herbicide applied around the outside of a shelter in a 3-foot-wide ring twice a year will eliminate competition from herbaceous plants and increase tree growth significantly. Mowing should continue until the canopy reaches 60% cover. Herbicide should be applied in targeted areas in subsequent years to control introduced invasive species. Native shrubs can then be planted as needed to establish the shrub layer and deter introduced invasive plants.
Continued maintenance to address introduced invasive plants, pests, and deer will be needed throughout the lifespan of the forest, though it should decrease over time.
Good—Allow areas to naturally regenerate over time, controlling deer and introduced invasive plants.
Better (in addition to Good)—Plant and maintain trees until they are large enough to be self-sustaining.
Best (in addition to Good and Better)—Support infill by shrubs over time, controlling deer and introduced invasive plants.
Urban forests are also destinations—providing recreation areas within communities that provide residents with a chance to connect with nature. The presence of well managed and maintained forests has been linked to higher property values and increased human health—both physical and mental.
Urban forests come in a variety of forms, but are unified by their definition as densely wooded areas located in a built environment. Urban forestry is defined as the planting, maintenance, and care of trees in urban settings.
No forest is truly without human influence, but urban forests may differ from forests in more remote natural areas, far away from cities or suburban centers, in that they are exposed to more direct human-caused stressors. Forests in agricultural areas share many of these anthropogenic stressors. Often, ecological stressors are magnified in urban forests due to small patch size, trash, poor air quality, and recreational impacts. Urban forests are variable in nature, composed of many different species, and have considerably variable origins. Urban forests are sometimes unplanned, where, in the absence of landscaping and maintenance activities, forest communities have grown in a strip of unmaintained ground. Stewardship activities can greatly improve the quality of these areas for plants and wildlife, improve resilience and adaptation to climate change, and be managed to maximize environmental services.
Deer management is a critical issue for forest management. When deer populations are too high, they overbrowse native vegetation, particularly seeds and seedlings. This reduces native plant diversity and prevents healthy levels of native plant regeneration, creating forests with little to no native understory and no young trees in place to replace canopy trees as they die. This can affect forest structure and sustainability. Management of deer populations to sustainable levels is important for protecting forest health across the state. Additionally, protecting plantings and sensitive species from deer can help mitigate their impact.
Good—Protect plantings with staked wire mesh cylinders or tree tubes to allow plants to reach a height where they are less susceptible to browsing and rubbing. Plant species that are more resilient to deer. Monitor for deer impacts.
Better (in addition to Good)—Fence sensitive areas or areas with natural regeneration. Arrange for doe hunting by land manager, owner, or other licensed hunters. Monitor for deer impacts.
Best (in addition to Good and Better)—Carry out a managed hunting program focused mainly on doe harvest. This can include permitting hunting, arranging for hunting by a select group, or obtaining a culling permit from the Pennsylvania Game Commission and contracting with sharpshooters. Alternatively, fence entire property. Monitor for deer impacts.
More detailed information is available in Deer Management.
Introduced invasive plants, species brought accidentally or intentionally from another continent that proliferate aggressively, outcompete native species, and provide little or no food for native wildlife, threaten many of Pennsylvania’s forests. As the introduced invasive plants outcompete native plants, they reduce plant species diversity and crowd out plants crucial to the food web that wildlife depend on. Some species, like garlic mustard (Alliaria petiolata), even give off allelopathic chemicals that interfere with tree seedlings’ and other native plants’ growth. Invasive vines like oriental bittersweet (Celastrus orbiculatus) and English ivy (Hedera helix) are a significant issue for forests as the vines can girdle young trees and overtop their canopies, weakening or killing them by shading their leaves. Vines also add weight to mature tree canopies, making the trees more susceptible to wind throw. English ivy in particular, as a broadleaf evergreen, can trap snow and ice and add tons of weight to a tree, greatly increasing the likelihood of toppling. Some introduced invasive vines also can transmit diseases to the trees they climb.
When prioritizing among different forest areas for invasive plant control, the highest quality areas should be managed first to protect the existing ecological quality. Another high priority is to control species that are toxic to people and animals, like poison hemlock (Conium maculatum) and giant hogweed (Heracleum mantegazzianum), to reduce risk. Land managers should monitor for new introductions of invasive plants as it is easier to control small populations compared to large, established colonies of invasive plants. From there, the general rule of thumb is to control invasive plants that affect canopy tree species first. This includes vines growing on trees and introduced invasive trees. Control efforts should then work their way down the forest layers—canopy, understory, shrub and vine, and herbaceous layers.
Good—Control introduced invasive plants in the highest quality areas. Control invasive plants that pose a risk to humans or animals. Prevent introduction of new invasive species.
Better (in addition to Good)—Control introduced invasive plants in areas of moderate quality, as well as the highest quality areas. Control invasive plants that pose a risk to humans or animals. Prevent introduction of new invasive species. Educate visitors about invasive plants.
Best (in addition to Good and Better)—Systematically control introduced invasive plants throughout entire property, following prioritization strategies. Prevent introduction of new invasive plants. Work with nearby landowners to collectively manage invasive plants.
Forests are currently facing, and will continue to face, challenges to resilience as climate change occurs (also see main Climate Change section). Key impacts will vary based on location within the state, elevation, current health, size, connectivity, and species composition. Impacts to forests include:
Temperature and precipitation changes are causing plant hardiness zones to shift over time, affecting habitat suitability. In general, as temperatures increase in a region, hardiness zones shift north and upward in elevation. Species that are already at the southern end of their habitat zones at a particular location are generally the most vulnerable to habitat changes, which reduces survival of current trees and their ability to regenerate. Species that are in the northern or central sections of their habitat zones may be more resilient as their habitats shift north.
The ongoing shift in plant hardiness zones should be taken into consideration when choosing species for planting projects. One option is mainly to use those species already present in the area that are projected to be more resilient to climate change. Another option is incorporating plants from areas similar to what the climate is predicted to be like at the planting location in 20-30 years. This can be done either by introducing more southern species or by using species that are already present at the location but sourcing the plants or seeds from more southern regions. When carrying out planting projects, these new southern U.S. species or southern ecotypes of Pennsylvania-native species should only be a portion of the total plants used. Of course, species introduced from other regions and continents should still be avoided.
DCNR’s Climate Change Adaptation and Mitigation Plan includes a list of common tree species for each Pennsylvania region and the modeled impact of climate change on each species. This can help inform which tree species that are currently present could be favored or used less frequently in plantings.
Climate change is causing the growing season in Pennsylvania to start earlier in the spring and continue later into the fall. According to the Pennsylvania Department of Environmental Protection, Pennsylvania may see a 50% increase in growing degree days. This may allow for more tree growth through the season. However, it can also support introduced invasive plants and pests, which can be major stressors. A longer growing season may also affect timing of plantings, shifting the start and end of the spring planting season earlier and the start and end of the fall planting season later. However, late frosts may be a concern with earlier spring plantings. Projected increases in temperature and drought through the growing season may stress trees, affecting plantings and counteracting the growth benefits of a longer growing season.
Overall, forests will be exposed to more stress due to climate change. This is from a range of factors, including increased severity and frequency of droughts, storms, and flooding, and reduced snow cover. These effects stress plants, increasing their risk of mortality. Such stressors also make plants generally more susceptible to pests and disease, further increasing risk of mortality. Compounding this is the fact that introduced invasive plants may benefit from longer growing seasons and higher temperatures, making them a greater threat to forests.
According to scientific studies, some of the negative impacts to forests may be counteracted by a positive effect from CO2 fertilization on forest growth, at least for the short term (Zhu et al. 2016). Higher levels of CO2 can increase photosynthesis, resulting in increased growth for forests. This effect is already occurring globally. CO2 fertilization may increase forest growth in the short term, improving the health of the forests and making them more resilient. Given enough time though, the CO2 fertilization effect is likely to plateau, and the negative risks linked to climate change may have a greater impact. Therefore, it is important to take advantage of the positive effects now by continuing planting efforts.
Forests are a main source of carbon sequestration (pulling carbon from the atmosphere) and carbon storage (retaining carbon within biomass, such as within roots, stems, and branches). As explained by Penn State Extension, different forest ages all contribute to carbon storage and sequestration. Young forests have a high rate of carbon sequestration with a lower level of carbon storage, as the carbon has not had a chance to accumulate in the forest over time. Maturing and mature forests still sequester high amounts of carbon as older trees continue to grow and young trees fill in canopy gaps and lower levels, thereby sequestering carbon at the fast rate of young trees. They also have accumulated more stored carbon than young forests. Old-growth forests have a large amount of stored carbon which has accumulated over the years, both in living and dead wood. The rate of sequestration is slower as there are fewer individual trees overall and fewer younger trees growing in these forests. However, disturbance of old-growth forest, such as logging, can release large amounts of stored carbon. The best way to keep their high carbon reserves in storage is to maintain them as healthy old growth.
Young, maturing, and mature forests can be managed to maintain and increase carbon sequestration and storage capacity. Mature trees, with their high level of carbon storage, should be retained. Increasing forest resilience by promoting tree species diversity and planting only species predicted to have high resilience will also increase carbon sequestration and storage capacity. Dead and downed trees should be retained as they continue to store carbon as they slowly decompose.
The following management strategies are recommended as general approaches to helping forests adapt to and survive climate change.
Good—
Better (in addition to Good)—
More climate change information is included in the main Climate Change section.
There are many pests and diseases threatening forests across Pennsylvania. The following are key pests and diseases currently affecting forests as of 2024. It is important for land managers to stay aware of new pests and diseases that may be moving into the area.
Emerald ash borer (EAB), an exotic pest from Southeast Asia, is killing ash trees in the midwestern and northeastern United States. The first sighting within the United States occurred in Michigan in 2002. The pest subsequently spread east to Pennsylvania, and by 2019, EAB had spread to every county in the state. EAB larvae feed on the inner bark of ash trees and kill them essentially by girdling, stopping nutrient flow from leaves to trunk and roots. Trees typically die within 3-4 years of infestation.
EAB infestations are typically identified through the symptoms they cause. Signs and symptoms of an infestation include crown dieback, epicormic branching, bark splits and flaking, “D” shaped exit holes, and sinuous larval galleries under the bark.
Control Methods
Ash Harvest/Removal
Ash trees should be cut or removed if a tree is a potential hazard or if a dense stand can be harvested. An ash tree could be a hazard if it is near a road, trail, or other gathering area where people or property may be damaged if the tree were to fall (see Hazard Tree chapter for more information on hazard trees). In most cases, the tree can simply be cut and left to add to the down dead wood. Removal might be necessary if it is within a residential area. A timber harvest can be considered in areas where high numbers of ash trees are easily accessible to heavy equipment. However, harvesting is becoming less viable over time as the health and marketability of the trees decline. Ash tree harvests are not recommended in sensitive areas where erosion or introduced invasive plant incursion is a major concern. An arborist should be consulted to address hazard trees. A professional forester should be engaged if a timber harvest is being considered.
Insecticide Treatment
Ash trees can be injected with an insecticide such as Arborjet™ to protect the tree from EAB. However, treatment is expensive and repeated applications are necessary. Treatment should be considered for specimen trees in highly visible areas or female trees that have heavy seed production to maintain a seed source if the EAB is eventually controlled. An arborist should be consulted about which trees should be treated. (Note: Where trade names are used no endorsement is implied; the authors of this document are not liable for problems associated with the use of herbicides described therein.)
No Action
Ash trees can be left to die in place in forests and other natural areas where they are not a hazard. The debris can be left in place to provide habitat for wildlife. The die-off will result in a change in forest composition, particularly in areas dominated by ash.
Multiple control options can be used, based on the desires of the landowner. Regardless of the method chosen, native trees should be planted to reestablish a canopy after ash tree die-off or removal. This will reduce canopy gaps and help prevent establishment of introduced invasive plants. Additionally, land managers should be careful doing any work or activities in an area with ash trees due to their susceptibility for breakage.
Management Objectives
Good—
Better (in addition to Good)—
Best (in addition to Good and Better)—
The spotted lanternfly (SLF) is an exotic pest that originated in China, India, and Vietnam. Adult SLF feed on smooth-barked trees and then lay their eggs on smooth surfaces in large masses covered with a mud-like substance. They generally prefer tree-of-heaven (Ailanthus altissima) for food but will also feed on northern cork-tree (Phellodendron amurense) and some native trees including birches, willows, maples, tuliptrees, and ashes. They can cause weeping sap, but it has not yet been determined if they cause tree mortality. Adult SLF can be identified by their bright red hind wings with black spots, yellow abdomen with black bands, and black legs and head. Egg masses can be identified through their gray mud-like casing and oblong shape. Symptoms of SLF infestation include mold around the base of the tree and weeping sap wounds. The eggs are laid from late September through late November/early December. The eggs then hatch in late April to mid-May.
It has been observed that SLF goes through an initial boom period with an overwhelming number of SLF that lasts for a couple years. Numbers then decline in subsequent years, though the SLF is still present. Due to the relatively recent introduction of SLF, it is unclear if this will become a cyclical cycle or if populations will remain low after the initial boom period.
By wounding and feeding on their host trees, the SLF can potentially affect forest composition and habitats. Loss of smooth-barked trees will cause a range of issues including canopy gaps, increased area for introduced invasive species, and reduced feeding and shelter sites for wildlife. In addition to forest trees, the SLF’s preferred hosts include agricultural crops such as grapes, apples, and stone fruits. Loss of these trees or crops would hurt Pennsylvania farmers and lumber mills, which are major components of the economy.
The first confirmed sighting of the SLF in the United States was in Berks County in 2014. By 2024, the pest had infested 52 Pennsylvania counties. To mitigate the spread of the SLF, a quarantine was imposed on all counties with confirmed sightings. For a current map, see Related Items of Note.
The quarantine restricts movement of all products within the area that can harbor the spotted lanternfly including timber products, lawn waste, and outdoor household items with smooth surfaces. According to the Pennsylvania Department of Agriculture, “SLF quarantine strictly prohibits the movement of any SLF living stage including egg masses, nymphs, and adults and regulates the movement of articles that may harbor the insect. Intentional movement of SLF is expressly prohibited and is a serious offense. Violations could result in criminal or civil penalties and/or fines.”
Control Methods
There are several methods of control recommended by the Department of Agriculture. The methods can be jointly implemented. The extent of control needed will vary based on the population size of SLF in an area.
Trap Trees (mid-May-August)
SLF can be efficiently killed using trap trees and insecticide. Trap trees are created by reducing the number of tree-of-heaven in an area, as they are the preferred host for SLF, and leaving approximately 10% of the original population that are then treated with insecticide. By restricting the number of host sites, there are fewer trees to treat with insecticide and a higher probability that SLF will feed on the treated trees. Male trees with a diameter at breast height (dbh) of approximately ten inches should be left as trap trees. Female trees should not be used as trap trees as they can produce seeds and increase the population of tree-of-heaven. Recommended methods for tree-of-heaven removal can be found in Invasive Plants.
Egg Mass Scraping (October-late April)
Egg masses can be scraped from their host sites. A hard, flat surface like a credit card should be used to scrape the waxy coating and eggs off the surface. The eggs should then be deposited in a container with rubbing alcohol or hand sanitizer. This will kill the eggs, whereas only scraping them off the tree is not known to be effective.
Circle Traps (May-July)
Another option is a circle trap that poses less of a risk to non-target species. Based on designs by Penn State Extension, these traps use insect screens around a portion of the tree to funnel SLF into a plastic bag at the top where they are collected. Circle traps are most effective on trees with smooth bark. Directions for making this trap can be found on Penn State Extensions website.
Sticky bands around trees are no longer recommended as they endanger non-target species.
Management Objectives
Good—
Better (in addition to Good)—
Best (in addition to Good and Better)—
The hemlock woolly adelgid (HWA) pest originated in Asia and was first found in the United States in 1924 in the Pacific Northwest. The first sighting in Pennsylvania occurred in 1967. HWA feeds on the fluid at the base of the hemlock needle and causes defoliation. Over time, possibly as quickly as four years, the pest can kill hemlock trees. This is a significant issue as hemlocks are considered a keystone species within eastern forests. Signs of HWA infestation include defoliation, white fibrous material at the base of needles, and a gray cast to the bark.
Control Options
Note: Where trade names are used no endorsement is implied; the authors of this document are not liable for problems associated with the use of herbicides described therein.
Soil Drenching or Injection
Insecticide can be added to the soil where it will be taken up by hemlock roots and spread throughout the tree. This will then kill HWA feeding on the branches. For drenching, a shallow trench can be made around the base of the tree, and the insecticide is then poured into the trench. After application, the trench should be covered over with soil and organic debris. For soil injections, insecticide should be injected about 2-5 inches deep around the base of the tree. Insecticides containing imidacloprid or dinotefuran such as Safari 20 SG© can be used for soil drenching or injection. Treatment should be applied in the spring or fall when trees are actively taking up water. This method is not recommended in areas with poor soils, particularly rocky soils, or near waterbodies.
Trunk Injection
Insecticides containing imidacloprid can be injected into the trunk to treat HWA. This is best used in areas where other treatment options can result in unintended spread of the insecticide, such as on cliffs, near waterways, or in rocky soils. This option can be costlier, cause wounds, and be less effective. If this is chosen as a treatment option, a certified arborist should be engaged to do the injections.
Trunk Spray
Trunk insecticide sprays can be utilized where soil drenching or injections are not appropriate, such as areas with poor soils. Insecticide is sprayed starting at the base and up to 4.5 feet above the soil level. Trees should be sprayed in the spring or fall using an insecticide such as Safari 20 SG©. Spraying can quickly treat many trees.
Foliar Treatments
Foliar insecticide treatments are applied to leaves and stems between July and October, before HWA develops its woolly covering. Recommended products include Safari 20 SG©4, or those containing imidacloprid or bifenthrin. When applying a foliar treatment, it is important to cover both the top and underside of the branches. Foliar treatments are effective on trees under 30ft tall or in hedgerows. The lower branches of taller trees can also be sprayed with a foliar insecticide treatment if they are heavily infested. It is important to note that foliar treatments can result in an increase of spider mites and hemlock rust mites.
Horticultural oils can be used as an alternative to insecticides for single trees. Horticultural oils are non-toxic and therefore more appropriate for areas near homes or people, particularly children. These oils kill pests by smothering them as the oils dry and have no residual effect after application. They can be applied anytime between August and when it becomes too cold to spray.
The effects of chemical treatments may not be noticeable until the trees leaf out again. The trees should be monitored for needle growth. Follow up treatments will likely be necessary. As it can be expensive and resource intensive to treat large stands, trees that are important seed producers should be prioritized for treatment.
Biological Control
The Department of Conservation and Natural Resources (DCNR) and the US Forest Service are implementing biological controls within the infected area. Natural predators from the HWA’s native habitat are being raised and then released in affected areas. The intent is that these predators will become established and feed on the HWA. The two beetles being used (Pseudoscymnus tsugae and Laricobius nigranus) feed only on HWA and similar invasive pests. This method can provide long-term control and eliminate the use of chemicals. However, it can take 5-10 years for a population to become established, necessitating additional control methods for infected trees in the intervening 5-10 years. Additionally, this can be an expensive treatment. As such, this is only appropriate for large stands of hemlocks. If interested, contact DCNR for further information.
Management Objectives
Good—Monitor for hemlock woolly adelgid.
Better (in addition to Good)—Treat infected trees utilizing the options above as appropriate. If needed, plan for replanting of the area if hemlocks are dying off.
Best (in addition to Good and Better)—For large stands, work with DCR to determine if biological controls are an option.
Beech leaf disease (BLD), associated with the nematode Litylenchus crenatae mccannii, was first detected in Pennsylvania in 2016 in Erie County. Since then, it has spread across all 67 counties. BLD is generally fatal for younger beech trees, particularly saplings. In Rhode Island, BLD has caused 90% mortality in infected saplings. Clonal colonies are also more susceptible, likely because of the root connections between trees. The effect on mature beech trees is still being studied, but it appears that mature trees are also susceptible but will take longer to die. Symptoms of beech leaf disease include crispy, dry leaves and dark bands between leaf veins. As of 2023, there is no known treatment or cure, through research is being conducted. Some research indicates that there may be effective pest control for large, specimen trees.
As there are currently no proven control methods, management options are limited. Land managers should monitor beech trees for any sign of BLD. This will at least alert the landowner if beech die off should be expected. The landowner can then plan for how to best support the forest, such as planting a diversity of understory trees that can replace the beech over time.
Management Objectives
Management objectives are currently limited as there is no known treatment.
Good—Monitor for beech leaf disease. Stay aware of new treatment options.
Best (in addition to Good)—Create plans for replanting areas if needed.
Oak wilt is currently moving through Pennsylvania. This disease is a vascular wilt that is caused by the Bretziella fagacearum fungus. The disease affects all oak species, but it is more aggressive for species in the red oak group. Red oak group species can die from infection in a matter of weeks whereas white oak group species may last for years. Oak wilt is spread through underground root grafts between oak trees and through insects. Root graft spread creates more localized infestations while insects can create wide-spread infestations. Vector insects are drawn to fresh wounds and then cause infection of the wounded tree. Uncleaned equipment can also transmit oak wilt from infected to uninfected trees.
Symptoms of oak wilt include brown and dull leaves. For red oak groups species, brown/dull leaves first appear in the outer and upper branches and then move inward. For white oak group species, leaf browning and dullness appear more scattered.
There is no cure, but propiconazole can be used to suppress oak wilt before a tree is infected. Trees need to be treated every other year. Oak trees should not be pruned during the growing season to avoid creating fresh wounds that will attract vector insects. If pruning is needed or wounds occur through damage, wound dressing can reduce the likelihood if infection. The only other treatment is removal of infected trees. Root grafts should be cut prior to removal of infected trees to avoid spreading infection. Any infected trees that are removed should be destroyed. No wood should be stacked for use as firewood or transported.
Management Objectives
Good—Monitor for oak wilt. Dress any wounds during the growing season as feasible. Stay current with treatment options.
Better (in addition to Good)—Remove infected oak trees, being careful to sever root grafts and dress wounds. Destroy wood from infected trees. Create plans for replanting areas if needed.
Best (in addition to Good and Better)—Choose a select number of oak trees that are not infected to treat with propiconazole.
Other pests and diseases are affecting or may affect Pennsylvania forest to varying degrees. The Pennsylvania Department of Conservation and Recreation website includes a list of such species (dcnr.pa.gov/Conservation/ForestsAndTrees/InsectsAndDiseases/OtherInsectsandDiseases/Pages/default.aspx, as of 2024)
Management Objectives
Stay current with what pests and diseases are moving into the area and what can be done to mitigate their damage as possible.
Monitoring Suggestions
Historically, land use in the region was dominated by agriculture and logging. Those uses, coupled with recent residential and commercial development, have effectively removed or disturbed most of the native vegetation in the region and, through subdivision and clearing, added countless miles of edge (the zone where forest meets a non-forested area) to the fragments of forest that remain. Edges allow light and drying winds to penetrate the forest, which fosters the proliferation of introduced invasive plants that crowd out native flora. Edges also provide easy access to the forest by predators (feral cats, raccoons) and nest parasites (cowbirds) that consume or displace forest interior animals, especially birds.
Fragmentation of our forests is second only to outright destruction and conversion of forestland to other uses as a cause of degradation of ecosystem function, habitat quality, and biodiversity. Forest fragmentation results in the local extinction of species and can lead to far lower overall species diversity than would occur if the same total area of forest were to remain as a single contiguous block. The level of impact on the original forest ecosystem depends on the number, size, and shape of resulting forest fragments.
Fragmentation has at least four components:
Conventionally, in temperate eastern North America, the part of the forest that lies more than 100 meters (a little over 300 feet) from the closest edge is considered as functional forest interior for most species. It follows that, in two forest blocks with identical areas but different “footprints,” the one with the higher edge-to-area ratio (more sinuous edge or narrower overall shape) is more fragmented. A circle is the two-dimensional shape with the lowest edge-to-area ratio and hypothetically the optimal shape for conserving forest diversity in a fragment, but smaller circles have higher edge-to-area ratios than larger circles. Any part of a forest block whose width is 600-700 feet or less has little or no functional interior. Cutting a road or other linear non-forest feature through a forest fragment may not decrease total forest area by much, but each of the two fragments so created has a much smaller area, a much higher edge-to-area ratio, and far less (or no) functional interior than before.
For many animal species, the area of contiguous habitat in a forest fragment must be above some threshold size for a population to sustain its long-term viability. Minimum-area requirements vary greatly among species, but the total area of forest in a fragment is not all that matters. Many plants as well as animals are forest-interior specialists, unable to utilize the outermost zone of forest near the edge as habitat. The area inside a forest but near its edge is vulnerable to a host of detrimental outside influences, including increased wind, light, and heat, decreased humidity, and the influx of seeds of introduced invasive species. In general, fragmentation favors invasive species and works against native species.
Furthermore, the threshold size of a forest block required to sustain a population of a forest-interior species is larger with greater isolation from other forest blocks, because there is less movement of individuals between blocks. Consequently a long-established population in a forest fragment may die out even if the habitat remains intact, if enough nearby forest fragments are further fragmented or destroyed. Put another way, in a neighborhood in which most of the forest is gone, the remaining forest fragment must be larger to sustain the same level of species diversity than if it were near other large forest blocks.
Decreasing the edge-to-area ratio and increasing the area of functional forest interior can be accomplished by afforesting selected “peninsulas” and “islands” of non-forested land that presently intrude into the main body of a contiguous forest.
Edge effects are conditions in and near the forest/non-forest transition zone that foster the growth of introduced invasive plants, provide access for nest predators (e.g., raccoon) and parasites (e.g., brown-headed cowbird), and repel forest-interior animal species. In Pennsylvania, edges with a southern, southeastern, or southwestern exposure are usually most degraded by invasive plants taking advantage of the greater amount of sunlight to creep into the forest. Dense, healthy mid-canopy and shrub layers at the forest edge can help prevent edge effects from moving into the forest interior by intercepting seeds and blocking sunlight and drying winds. A forest edge that has existed for many decades often has a well-developed wall of leaves and branches extending from near the ground to the upper leaf canopy. Remediation is often required at more recent edges, particularly on a southerly exposure where trees have been cut down within 20 years, and at edges where landscape maintenance practices restrict new growth. Such edges are said to have high permeability. Native trees and shrubs of species appropriate to specific site conditions should be planted along forest edges with high permeability (see Native Plant Materials). Mixtures of evergreen and deciduous species should be used where the natural community would include evergreens, in order to enhance impermeability in all seasons. Construction and maintenance practices should be avoided that would damage understory and mid-canopy vegetation at the forest edge and increase its permeability to sunlight, air movement, and the influx of seeds.
The ecological and environmental conditions of forested areas within natural lands are protected and enhanced by contiguous forest on neighboring properties. Together they minimize edge effects and create a larger unfragmented forest. For this reason, it is best to engage adjoining landowners to discuss the benefits of coordinated management.
Good—Avoid fragmentation by protecting the current extent of forest.
Better (in addition to Good)—Reduce edges through planting (see Afforestation/Reforestation above).
Best (in addition to Good and Better)—Work to expand interior forest (see above Interior Forest section). Work with surrounding landowners to reduce edge and fragmentation at a landscape scale.
As this guide focuses on management options for natural areas that emphasize ecological stewardship, and, to a lesser extent, compatible recreational use, timber harvesting is generally beyond its scope. Land managers should consult qualified foresters who specialize in sustainable and ecologically healthy forest management. The Pennsylvania Department of Conservation and Natural Resources’ Bureau of Forestry is a good starting resource. Key recommendations are to avoid clearcutting as this causes significant ecological damage through vegetation removal and soil exposure and to actively restore areas if no longer used for timbering
If a link is broken, try searching on the keyword string preceding the link.
Landowner Resource Center: Conserving the Forest Interior, a Threatened Wildlife Habitat (lrconline.com/Extension_Notes_English/pdf/forInterior.pdf, as of 2024)
Floristic Quality Assessment (https://library.weconservepa.org/guides/33-floristic-quality-assessment, as of 2024)
Freyman, W.A., L.A. Masters, and S. Packard. 2016. The Universal Floristic Quality Assessment (FQA) Calculator: an online tool for ecological assessment and monitoring. Methods in Ecology and Evolution 7:380-383. (universalfqa.org, as of 2024)
PennState Extension, Conducting a Community Tree Inventory (https://extension.psu.edu/conducting-a-community-tree-inventory, as of 2024)
Pennsylvania Natural Heritage Program: Pennsylvania Conservation Explorer (for PNDI data; conservationexplorer.dcnr.pa.gov, as of 2024)
U.S. Forest Service: Forest Inventory and Analysis (research.fs.usda.gov/programs/fia, as of 2024)
Washington Department of Fish and Wildlife, Living with Wildlife: Snags—the Wildlife Tree (wdfw.wa.gov/species-habitats/living/snags, as of 2024)
Penn State Extension: Dead Wood for Wildlife (extension.psu.edu/dead-wood-for-wildlife, as of 2024)
Zhu, Z., S. Piao, R. Myneni, et al. 2016. Greening of the Earth and its drivers. Nature Climate Change 6:791-795. doi.org/10.1038/nclimate3004
Penn State Extension: How Forests Store Carbon (extension.psu.edu/how-forests-store-carbon, as of 2024).
FPenn State Extension: Stay Alert for Oak Wilt! (extension.psu.edu/stay-alert-for-oak-wilt, as of 2024)
Penn State Extension: Beech Leaf Disease (extension.psu.edu/beech-leaf-disease-in-pennsylvania, as of 2024)
Under the canopy: Penn State researchers study beech leaf disease in PA forests (psu.edu/news/agricultural-sciences/story/under-canopy-penn-state-researchers-study-beech-leaf-disease-pa-forests, as of 2024)
Pennsylvania Department of Agriculture: Spotted Lanternfly Quarantine (agriculture.pa.gov/Plants_Land_Water/PlantIndustry/Entomology/spotted_lanternfly/quarantine/Pages/default.aspx, as of 2024)
Penn State Extension: How You Can Comply with the Spotted Lanternfly Quarantine Regulations (extension.psu.edu/how-you-can-comply-with-the-spotted-lanternfly-quarantine-regulations, as of 2024)
Pennsylvania Department of Conservation and Natural Resources: Emerald Ash Borer (https://www.dcnr.pa.gov/Conservation/ForestsAndTrees/InsectsAndDiseases/EmeraldAshBorer/Pages/default.aspx, as of 2024)
Pennsylvania Department of Agriculture: Emerald Ash Borer Survey Program (https://www.agriculture.pa.gov/Plants_Land_Water/PlantIndustry/Entomology/EABSP/Pages/default.aspx, as of 2024)
Penn State Extension: Emerald Ash Borer (https://extension.psu.edu/emerald-ash-borer, as of 2024)
Climate Change Projections for Individual Tree Species in Pennsylvania (forestadaptation.org/learn/resource-finder/climate-change-projections-individual-tree-species-pennsylvania as of 2024).