Habitat description
Oak Forests and Woodlands are a broad category that is primarily characterized a tree oak (Quercus spp.) overstory that ranges from a mostly open canopy, called woodlands, to closed or nearly closed canopy, called forests. They occur on a wide range of settings, but most often are found in areas with frequent disturbance, dry soils, and/or exposed slopes. Oak dominated habitats often occur in areas that regularly burn.
Aside from the oak overstory, there are several other characteristics of oak ecosystems. The understory tends to contain deep oak leaf litter with slow decomposition. Because oak systems tend to have a more open canopy relative to conifer or mixed hardwoods, more light reaches the ground than other types of forest. As a result, a lush ground cover of Pennsylvania sedge (Carex pennsylvanica) and numerous other sedges, grasses, ferns, mosses, and forbs (particularly legumes) is common. In dry and acidic settings huckleberry (Gaylussacia baccata) and lowbush blueberries (Vaccinium angustifolium and V. pallidum) are often present. American chestnut (Castanea dentata), which was once a common dominant tree, now survives as stump sprouts scattered in the midstory. In somewhat richer sites, oak often co-occurs with hickories (Carya spp.), sugar maple (Acer saccharum), and/or hop-hornbeam (Ostrya virginiana). Bunch grasses such as little blue stem (Schizachyrium scoparium) may be a dominant feature in forest openings where there are few or no trees.
Associated habitat types
Oak Forests and Woodlands are disturbance dependent habitats, historically maintained by periodic fires, wood cutting, and other disturbance. In areas of extremely dry soils and/or frequent or severe disturbance, communities can grade into Barrens such as Pitch Pine – Oak Woodland/Forests, Pitch Pine – Scrub Oak Community, and other barrens habitats. With infrequent disturbance, the type grades into a variety of forests including Northern Hardwood – Hemlock – White Pine Forest and Successional White Pine Forest. Moist areas near oak woodlands, such as north and east facing slopes, drains, and low elevation zones are often conifer forests like Spruce – Fir – Northern Hardwood Forest, Rich, Mesic Forest Community, or Hemlock Forest.
Characteristic communities and species
More information on the specific natural communities (Swain 2020) within this habitat type is available from the following fact sheets:
- Black Oak – Scarlet Oak Woodland (S3S4)
- Chestnut Oak Forest/Woodland (S4)
- Coastal Forest/Woodland (S4)
- Dry, Rich Oak Forest/Woodland (S4)
- Hickory – Hop Hornbeam Forest/Woodland (S2)
- Oak – Hickory Forest/Woodland (S4)
- Open Oak Forest/Woodland (S3)
- Sugar Maple – Oak – Hickory Forest (S3)
- Yellow Oak Dry Calcareous Forest (S1)
- White Pine – Oak Forest (S5)
- Red Oak – Sugar Maple Transition Forest (S4)
A wide range of animals use Oak Forests and Woodlands, particularly when acorns are abundant. As one of the most prevalent forest types, oak ecosystems support most common wildlife and many rare species found in the commonwealth. Characteristic animals may include white-tailed deer, opossums, Eastern box turtles, towhee, vireo, bluebird, Whip-poor-will, wild turkey, mice, voles, red squirrel, gray squirrel, black bear, garter snakes, black racer, black rat snake, Frosted Elfin (Callophrys irus), and oak hairstreak (Satyrium favonius). Oak and hickory woodlands support a rich diversity of plants on the forest floor including many rare and uncommon species.
Ecological processes
Oak Forests and Woodlands most often occur on dry, nutrient-poor soils, but can persist in a wide variety of conditions with periodic disturbance. Fire is the primary mechanism for promoting regeneration, reducing competition, and maintaining the typical ground cover. The highly flammable leaves of oaks and hickories, along with grasses and sedges in the understory, create conditions favorable to frequent low-intensity fires. Wood cutting, insect damage, storms, and other types of disturbance also play an important role in creating canopy openings in which the next generation of oaks can grow into the overstory. In healthy forests and woodlands, oak and hickory seedlings and saplings are in place to take advantage of increased light when overstory trees die or are removed. In the absence of fire, fire-intolerant shrubs and trees such as red maple, beech, birches, and white pine become established, shading out the grasses, sedges, and oak seedlings. Over time, a dense mat of moist flat leaves replaces the more flammable understory and the other tree species overtake oaks for dominance.
Threats
Even though oak trees are very common in Massachusetts, the overall health of oak forests and woodlands is in decline. Numerous oak and hickory natural communities such as Yellow Oak Dry Calcareous Forest, Hickory – Hop Hornbeam, and Open Oak Forest/Woodlands are quite rare, and once common communities such as Oak-Hickory Forest/Woodland and Sugar Maple – Oak – Hickory Forest are disappearing. Oak woodlands in general have become quite scarce. Across the Commonwealth, there is a dearth of oak regeneration. Decades of fire exclusion and lack of other disturbance have facilitated the expansion of red maple, white pine, birches, and other trees that are poised to take over canopy dominance when the oak overstory dies. Mature oaks are a favorite target of many non-native insects including spongy moth (Lymantria dispar formerly Gypsy moth) and winter moth (Operophtera brumata). Recent outbreaks following droughts have caused massive oak die-offs. Because the moths prefer oaks, other tree species such as white pine and red maple are left with minimal damage, allowing them to replace the dead oaks in the canopy. Non-native pest and pathogen outbreaks are distinct from native insects and diseases that cause periodic mortality events.
The failure of oak regeneration has two main causes, a lack of disturbance and over-browsing by white-tailed deer. Oak seedlings need copious sunlight to thrive. Disturbances that create or maintain canopy and mid-story openings such as wood-cutting, grazing, and most importantly fire have declined in the region, and as a result fewer seedlings have become established. Deer prefer oak seedlings over most other tree species, so in areas where deer densities are high, oak regeneration is often absent. Species which do establish on the forest floor are those which deer do not readily prefer such as white pine and ferns.
Other stressors include non-native plants, animals, and diseases. Invasive, exotic plants often dominate the midstory preventing regeneration. Exotic earthworms accelerate the speed at which leaves are decomposed, causing increases the nutrients available for invasive and moisture loving plants while reducing the fuel available to support fire. Oak Wilt (Bretziella fagacearum) is an exotic disease that severely impacts oaks and has been detected in New York and Connecticut. Once established, it could cause widespread mortality, especially in combination with other stressors. Development threatens Oak Forests and Woodlands directly through destruction and fragmentation, and indirectly by reducing the ability of managers to apply prescribed fire because of concerns about smoke impacts. Invasive plants can dominate the understory in some areas preventing regeneration and pushing out native understory species.
- Climate Change: Under a climate change scenario of increased drought, oak forests and woodlands may not fare well. Despite being associated with dry sites, oaks are more likely than other tree species to die during droughts. Furthermore, increased droughts may cause more frequent and severe outbreaks of spongy moth, a non-native insect that can decimate oaks. A wetter climate, however, would likely exacerbate the ongoing process of oak forests and woodlands becoming moister and would help facilitate the conversion from oak overstory to other trees. A warmer climate is expected to make Massachusetts more suitable for the exotic disease Sudden Oak Death (Phytophthora ramorum), which is a major threat to oaks. Additionally, because many Oak Forests and Woodlands are dependent on management for their health and existence, the impacts of climate change will in part be tied to the ability to effectively manage. In both scenarios of higher and lower precipitation, storm events are expected to be more extreme with large rainfalls and longer droughts in between. This may reduce the total number of days suitable for prescribed fire implementation, an important management activity.
Restoration & management recommendations
Oak Forests and Woodlands are found on a continuum from open to closed canopy in a patchwork distribution across a fire-influenced landscape. Woodlands occur as open canopy areas within larger forest systems and as partially closed-canopy areas within open grasslands and barrens, linking habitats and sites over large and small scales. Depending on site conditions and management, woodlands may occur as stable communities maintained through regular fire occurrence, in which rich ground cover supports fire intensity adequate to prevent the overstory from becoming too dense. Alternatively, woodlands may occur as a temporary stage in a shifting mosaic of oak habitats where fire (or a fire surrogate) prevents most fire-intolerant trees and shrubs from establishing, and periodic woodcutting and episodic natural disturbance create openings as other areas fill in with maturing trees. Oak forests are essentially oak woodlands matured to a nearly closed canopy. Although matured, most oak forests need periodic management to promote regeneration and prevent conversion to other species. Goals for the site will drive the management actions.
- Planning Phase: Several factors should be considered when setting the goals for a restoration project. Oak Forests and Woodlands can take many forms and vary greatly depending on site conditions and the type and intensity of management activities. If an oak forest is in good ecological condition and is going to be managed as a mature forest, it will require less intensive management than a site managed as woodland or for oak regeneration. Oak systems can be managed for specific species or suites of species. A site managed for deer and turkey may differ in management from a site managed for rare plants and insects, however there is much more in common than there is different. Timber income may be a priority for some landowners, in which case the cutting prescriptions will differ from an area managed primarily for wildlife values. When deciding on specific goals, consider the surrounding lands. If there is something missing such as young forest, mature forest, or woodlands, consider filling that need. Alternatively, a site could be managed similarly to a nearby property to expand the footprint of a desired habitat type. Simply having oak in the canopy is not always enough to ensure that a restoration or regeneration project will be successful. Sometimes threats must be addressed before large scale management begins. Understand the specific elements of the oak natural communities within the restoration site and prioritize retaining and encouraging both the oaks and complimentary species like hickory, hop hornbeam, or sugar maple. Work with a forester and other natural resource specialists to help ensure your plan is designed to meet your goals.
If possible, oak restoration planning should begin years prior to starting forestry operations. The extra time allows for better selection of retention trees, and treatment of invasive species. Prior to starting management, the site should be evaluated by an experienced fire practitioner to determine the feasibility of prescribed fire implementation. This should be done early on because it may help shape other parts of the planning process such as timber harvests or other mechanical treatments. Harvest areas, skid roads, firebreaks, and burn units should be established in coordination to limit conflicts and reduce overall cost. Fire is often not feasible, but sites that cannot be burned can still be effectively managed for oak and hickory with other management techniques such as mechanical and chemical treatments.
Tree cutting or forestry should be done in consultation with a forester. A forester can help create tailored plans, accounting for the unique characteristics and goals for each site. Oak needs open conditions with copious sunlight to regenerate. If you plan to use timber harvesting to regenerate oak, you should identify areas where regeneration is viable. Look for at least 10 mature oaks or hickories per acre, and more than 100 seedlings and saplings, called advanced regeneration, per acre. If there are not adequate overstory trees, the amount of advanced regeneration should be at least double to ensure enough oaks will be present to take advantage of the conditions following harvest. Seedling establishment can be helped by thinning around mature oak and hickory trees, which will increase acorn and nut production. The soil disturbance associated with tree cutting will facilitate seedling establishment.
If adequate overstory trees are present but there is not regeneration, consult with a deer biologist to see if deer are eating the seedlings. If deer predation is not the problem, deep leaf litter, light competition, or other factors that can be remedied through management may be preventing seedlings from becoming established. If deer populations are too dense, without population management, oak regeneration is likely to fail. Generally, larger harvest areas will distribute the impacts of browsers such as deer and moose more widely, potentially allowing more seedlings to mature. In areas managed as a static oak woodland, regeneration is not necessarily a top management priority, however if deer are over-browsing the oak seedlings, they are probably also damaging the populations the desirable herbaceous plants found in open woodlands. Population control is generally the best solution for deer over-browsing. Large fencing exclosures are effective, but expensive and difficult to maintain, and slash walls are problematic in areas where prescribed fire will be part of restoration and management.
Invasive species infestations should be mapped and prioritized for treatment. Trees to be retained should be selected individually for desired characteristics. If time permits, mark trees that are highly productive for acorns and tree nuts. If possible, time the harvest with mast years (years with copious acorn production) because the disturbance caused by logging equipment will greatly benefit seedling establishment. In red oaks, acorns can be detected one year in advance because they take two growing seasons to develop, whereas white oak acorns and hickory nuts develop in one growing season. Planning should account for additional overstory mortality following harvest caused by blowdown because of reduced wind sheltering, disease, damage from logging, and prescribed fire. Use an estimate of 10-25% mortality based on site conditions. Areas with drier soils and/or more exposure to wind will likely experience higher rates of mortality, but it may be reduced by delaying harvest and fire during drought or insect/disease outbreaks. Keep up to date on the distribution of Oak Wilt and follow all best management practices as appropriate. - Initial Restoration: The first step in restoration is to control invasive species that may be released by disturbance and light exposure. For sites without recent disturbance, overstory thinning is usually next. Cutting creates patches of young forest, which is valuable habitat, and creates diversity in the forest structure. Forests with different aged trees are more resilient to disturbances such as diseases and storms. A tree cutting plan should be based on the target community type and soil characteristics. In areas with a diversity of age classes and a healthy understory, the restoration phase may be skipped and maintenance activities could be initiated.
The following recommendations for oak regeneration may be altered based on target natural community, aspect, goals, and other factors. Work with a forester to create a plan for each forest stand to be cut. Drier sites generally regenerate oak more easily and with fewer trees cut, while moist sites require a more heavy-handed approach. Sites on moist and rich soils should average 60’-70’ spacing between trees of 20” diameter or larger. This will allow for enough light to reach the seedlings. Leave groups of trees and large open areas. Some sugar maples occurring in drains or toe slopes should be retained. Dry and nutrient-poor sites can have more trees retained, with ~15” diameter trees spaced every 30’-35’. Consider retaining any pitch pines. Intermediary sites should retain trees of ~17” diameter every 40’-50’. Non-native and undesirable species should be removed as the overstory is thinned to the desired cover. Whole tree removal is preferred to leaving treetops on the ground because the dead material can change soil characteristics and cause problems for prescribed fire implementation. Mowing or mulching should be minimized, when possible, for the same reasons. Prescribed fire should be applied as soon as vegetation is able to carry fire, usually 2-4 years after harvest. Oaks and hickories that establish shortly after a fire are more likely to survive subsequent fires because the rootstock is contained mostly in the soil rather than leaf litter or duff. Following the initial mechanical treatment and prescribed fire, expect a flush of herbaceous vegetation, expansion of heath, and establishment of tree seedlings in the understory. Mowing and/or herbicide treatments may be required to control undesirable resprouting trees, shrubs, and invasive plants. In all sites, but especially wet and moderately dry sites, if fire is not an option or not able to control competition, mechanical or chemical control of generalists (i.e., beech, birch, red maple, white pine) will probably be needed to ensure oaks are dominant at canopy closure. Consider keeping or creating pockets of open, grassy areas nested within the oak forest/woodland matrix. Openings managed like grasslands (with fire, mowing, and/or scarification) are important habitat for many plants and animals. - Maintenance: Prescribed fire should be the primary maintenance tool in Oak Forests and Woodlands when feasible. Where prescribed fire cannot be used, other mechanical and/or chemical treatments may be needed to manage competing vegetation. Woodlands require frequent fires, at least every 10-15 years to establish and maintain their typical herbaceous plant diversity. More frequent fires promote grasses, heaths, sedges, and forbs, whereas longer intervals allow trees and shrubs to proliferate. Open woodlands with warm-season grasses or a heath understory may burn as frequently as every 2-3 years. Fire return intervals less than five years will reduce the ability of oak seedlings to mature, maintaining a more open canopy. Hickories are generally able to reproduce under a more frequent fire regime than oaks. Except on very dry sites, or under very frequent fire regimes, oak woodlands will eventually become oak forests.
In woodlands, burning during a variety of seasons will help promote open structure and plant diversity. Spring fires can be used to help establish native grasses and sedges, however once they are established, growing season burns should be incorporated to help control woody stem proliferation and promote a diversity of herbaceous plants. Prescribed fires during periods of stress such as drought or insect outbreaks may cause high oak mortality, especially during late spring when temperatures are rising, but vegetation has not yet greened-up. Burning in masticated or mechanically treated fuels during dry periods, particularly during summer or fall, may cause high intensity, extended smolder, and overstory mortality. Periodic mowing and/or herbicide treatments may be needed if fire alone does not achieve desired results. In a shifting mosaic of woodlands and forests, rotational harvest may be used to “reset” a forest to an open woodland once the overstory closes. Cordwood can be selectively harvested every 20-30 years, with low quality trees and undesirable species removed and the highest quality trees left behind. An open woodland is unlikely to produce quality timber because direct sunlight on tree boles promotes epicormic branching.
If managing for forest regeneration, after the initial one or two burns within the first 8-10 years, a fire-free period of roughly 8 years is often needed to allow some oak seedlings to grow large enough to be resistant to low-intensity fire (4-6"). A fire-free period of 10-15 years may be required to maximize the number of oaks that will survive a fire, but the long interval may open opportunities for competitors to become established in the overstory. Just two or three burns may be enough to favor oaks and hickories to the point where they are the dominant overstory forest trees. When trying to establish oak forest, early spring is generally the preferred season to burn because it encourages vigorous resprouting and minimizes impacts to roots. Periodic fires in oak forests, including growing season fires, help maintain diversity, provide food for wildlife, and encourage the next generation of oaks. In areas where fire is not feasible, selective thinning and herbicide treatments should be used to reduce competition from undesirable species. Cutting or herbicide treatment of competing stems should be done before they overtop the oaks, usually around 10-15 years after cutting. What is in the canopy at the time of crown closure will dominate the forest for decades.
Examples
- Quaboag WMA : Ongoing project at Quaboag WMA to restore oak forests, woodlands, and grasslands.
- Herman Covey WMA: Ongoing project at Herman Covey WMA to restore oak forests, woodlands, grasslands, and barrens.
- Squannacook River WMA: Restoration site for oak and oak-hickory woodlands and forests. Read about the project here.
- Quabbin Reservoir: Contains an array of oak, hickory, and barrens habitats. Quabbin Hill has oak forests, oak-hickory forests on slopes, and oak-pitch pine forests. Gay’s Hill in New Salem and Junket Hill in Belchertown are examples of chestnut oak forest. A video about forest management in the Quabbin can be see here.
- Mt. Toby WMA: Oak forest that was overgrown with hemlocks, birches, maples and other trees. A wildfire killed many of the non-oak trees in favor of oaks.
- Freetown – Fall River State Forest: Coastal oak forest and woodland mixed with pitch pine and huckleberry understory. Portions of the site are under prescribed fire management.
- Blue Hills Reservation: Oak-hickory forests and woodlands that grade into ridgetop barrens. The site has a long history of frequent fires.
Additional resources
- Coming soon