20 minute read
Forest Ecology
Photo: Tim Stout
Vision Statement for Vermont Forests: “The forests of Vermont will consist of healthy and sustainable ecosystems, a prosperous and sustainable forest products industry, abundant recreational opportunities and a combination of ownership patterns supporting a working forest landscape and large, unbroken forest tracts. Citizens, government and businesses understand their proper roles, responsibilities and rights, and work together to support the values of forests for this and future generations.” (Vermont Forest Resources Plan, 2010)
Regional Forests
Vermont has been primarily forested since glaciers last receded around 15,000 years ago. When colonists arrived, Vermont was 95% forested. They cut many trees for agriculture, pasture, and fuel, and by 1840 the state was only about 25% forested (Thompson 18). Since the late 1800s, agricultural fields have been reverting to forest. The state is currently 76% forested, though a recent increase in development has caused a slight decline in forest cover since a peak in the 1990s (Vermont Forest Resources Plan 2010). Vermont’s forests are threatened by fragmentation, or the division of larger parcels into smaller parcels. These parcels may then be developed or simply create more divided forest management choices because of the greater number of property owners.
The New England/Acadian Forest type blankets the region. These forests contain many subtypes of forest communities, which vary from coastal pine scrub to subalpine Krummholz. Southern New England typically features oak-hickory forest, while the central and northern parts of the region are typically northern hardwood, and the northernmost areas are considered boreal forest. Vermont lies in a transition zone between northern hardwood and spruce fir forests, and features many acres of each forest type.
Montane forest types found at higher elevations support many animal species that require cooler temperatures, such as the Blackburnian warbler, endangered Bicknell’s thrush, American marten, and Canada lynx (Kimball, 2011). Farm & Wilderness’ property at the Ninevah Area includes higher elevation forests with montane communities. As temperatures warm in Vermont, these higher elevation ecosystems will shrink, hardwoods will migrate upslope, displacing the species that have niche habitat requirements. Farm & Wilderness’ property is at the southern edge of the montane spruce-fir forest type, which is already relatively uncommon in Vermont. Protecting the southerly range of this forest type and maintaining connectivity corridors with nearby similar habitat will allow mobile species to shift regionally northward. Farm & Wilderness already has this part of their property protected in perpetuity, adding to important regional connectivity. NORTHERN HARDWOOD FOREST
Map: The Nature Conservancy
Figure 1. Northern hardwood forest covers much of inland New England, including many acres at Farm & Wilderness (location in red).
MONTANE FOREST
Map: The Nature Conservancy Figure 2. Montane forest is found throughout New England at elevations above 2,300’ and supports niche species of plants and birds.
Current and projected forest suitability, 2100
Figure 3. Habitat suitability for New England forest types will shift by the year 2100. Based on two Intergovernmental Panel on Climate Change scenarios, this map reflects habitat suitability, but not necessarily what forest types will actually be inhabiting the areas shown. Adapted from Rustad et al, 2012.
CLIMATE CHANGE PRESSURES ON REGIONAL FORESTS
As climate change shifts the dynamics of forests in Vermont, many changes are anticipated. Increased droughts are expected to alternate with increased precipitation; with warming temperatures and more frost-free days per year, the landscape will be greatly affected (Rustad et al., 2012). Large storm events may create sudden and visible alterations like those seen from Tropical Storm Irene, but slow shifts in forest ecology will be harder to detect without careful observation.
White-tailed deer feed on tree saplings and herbaceous understory plants. Currently the deer population on Farm & Wilderness property is not large, but habitat conditions are projected to become more favorable for white-tailed deer as temperatures warm and winter conditions become less harsh (Weiskopf et al., 2010). A growing deer population will increase browse pressure on the forests, in turn affecting the regeneration of young trees. With fewer saplings able to grow beyond the reach of deer, the mix of tree ages will be disrupted, creating a less-diverse age range of trees. As older trees die, there will be fewer young trees ready to take their place (Côté et al., 2004). Additionally, deer prefer to eat certain species of tree saplings (e.g., eastern hemlock, northern white cedar, maples, and oaks) and leave others uneaten, further contributing to an unbalanced matrix of growth (UMN Extension, 2020).
Spruce and fir, which are typical of northern regions and higher elevations, are particularly vulnerable to climate change (D’Amato, 2015). Habitat suitable for montane forest is expected to decline significantly, and oakdominated forests will expand (Rustad et al., 2012). Tree species’ ranges move slowly—an acorn can only be carried so far from the tree—and the rapid pace of climate change is likely to be faster than tree species can keep up with. In some cases, assisted migration, sometimes called adaptation planting, can be a helpful tool to equip forests with the ability to recompose with climate-resilient species.
A deer browse line is the highest deer nibble, and is visible here in a stark example of an over-browsed forest.
Assisted Migration: also referred
to as adaptation planting, is the human-assisted movement of plant and tree species in response to climate change. Moving trees northward whose current range is at a lower elevation or more southerly latitude could help forests move toward climate resiliency.
Photo: Susan Day, UW Madison Arboretum
Photo: USDA
Emerald ash borer, Agrilus planipennis, is a foreign beetle whose larvae eat through the cambium of ash trees. Once the ash borer infests a forest, ash trees typically die within 5 or 6 years, with a mortality rate upwards of 97%. Invasive jumping worms disrupt the forest ecosystem by devouring the layer of leaf litter on the forest floor, leaving behind crumbly soil and few nutrients for plants to grow (top). The worms have a pale band encircling the darker body (below).
Photo: Susan Day, UW Madison Arboretum
REGIONAL PESTS AND PATHOGENS
Pests and pathogens put additional stress on forests undergoing climate change, and problematic insects are already numerous in New England. Hemlock woolly adelgid, beech bark disease, emerald ash borer, spotted lanternfly, and longhorn beetle all threaten the forests of the Northeast.
EMERALD ASH BORER Farm & Wilderness is particularly concerned about the emerald ash borer (EAB). EAB infests all types of ash trees and causes widespread mortality relatively quickly, creating a major disturbance in the forest life cycle. There is a high concentration of ash in parts of the property, and the beetles have been confirmed in other areas of Vermont.
Forests grow rapidly, and New England forests typically regenerate quickly after disruption. However, if the majority of ash trees die within a short time span, that will open up the tree canopy and allow light to reach the forest floor. This stimulates the growth of new saplings and other forest understory plants, but also creates opportunities for invasive plant species to proliferate if they are present (James et al., 2012). On rich soils like those at the southern end of Woodward Reservoir, the growth of unwelcome species can be further accelerated.
JUMPING WORMS Earthworms are not native to New England, but most species are lauded for their soil-enriching qualities. There are three species of invasive worms, Amynthas agrestis, Amynthas tokioensis, and Metaphire hilgendorfi, that have been present in the region for years but have recently proliferated and spread rapidly. Inhabiting just the top few inches of soil, they devour leaf litter and nutrient-rich organic matter that plants need to thrive, leaving behind loosened soil resembling coffee grounds.
Collectively termed “jumping worms”, they are popular as fishing bait because they thrash and wriggle, attracting fish. Sometimes sold as compost worms, these worms are moving around the region rapidly. Both these uses accelerate their distribution. Their small eggs, called cocoons, are easily transported on garden tools or muddy boots as well as in soil from potted plants. Once they enter a forest ecosystem, they greatly alter the forest floor, increasing the amount of nitrogen in the soil, lowering the carbon/nitrogen ratio (Price-Christenson et al., 2020). Jumping worms can devour up to 95% of the leaf litter in one season (Sever, 2020).
While it is too early to know their long term effects on an ecosystem, it may be prudent to avoid their introduction where possible. Diligent cleaning of boots and tools, as well as prohibiting the use of jumping worms as fishing bait or compost worms can help slow their expansion and reduce the chances of the worms being introduced to soils at Farm & Wilderness.
FOREST CARBON
Carbon sequestration is the process in which trees, grasses, and other plants remove atmospheric carbon to use for photosynthesis. Carbon storage refers to that carbon remaining captured in the biomass of trees and forests (Fig. 4). Temperate and boreal forests in North America could sequester and store a greater amount of atmospheric carbon if the trees are allowed to grow to maturity (Moomaw et al., 2019). Some recent studies show that trees continue to sequester carbon even as they grow to maturity; Stephenson et al. state that a large mature tree can sequester in one year the entire amount of carbon stored in a medium-sized tree (2014). Other studies assert that growth patterns and biomass accumulation of large trees are still not certain and more research is needed on sequestration patterns of individual trees as they age (Sheil et al., 2017).
Regardless, temperate forests have a high capacity for carbon storage because of the relatively slow decay rate from cooler temperatures but a fairly warm growing season that consumes atmospheric carbon (Moomaw et al., 2019). Forests that have not been harvested for timber are incredibly biodiverse and are the most carbon-dense terrestrial ecosystems in the world (Moomaw et al., 2019). Areas in Maine that have been harvested consistently contain two-thirds less carbon than the forests of Southern New Hampshire and Vermont that have experienced less frequent logging (Moomaw et al., 2019).
The practice of proforestation, or allowing a forest to continuously grow without active timber management, increases the carbon stored in a forest (D’Amato and Catanzaro, 2019). Carbon credit programs incentivize this practice by selling carbon credits for companies to offset their carbon pollution. However, if timber harvesting in a region is ceased altogether, that timber must be cut elsewhere to meet the demand for wood previously sourced locally. Harvesting timber thousands of miles away and then transporting it consumes fossil fuels and pushes deforestation on other communities.
Most of New England was logged and turned into sheep pasture in the 1800s, but much of this old pasture has been reforested over the last century. Currently, New England’s forests average around 75 years old, which is quite young considering that many regional tree species have a lifespan of around 300 years (Moomwaw et al., 2019). These relatively young forests will have a much higher capacity to sequester carbon if trees are allowed to grow to an older age (Moomaw et al., 2019).
50%
OF THE WEIGHT OF DRIED WOOD IS STORED ATMOSPHERIC CARBON Proforestation: Growing an existing forest intact toward its full ecological potential, allowing continuous forest growth without interruption from active management or timber harvesting. (Moomaw et al, 2019)
CARBON SEQUESTRATION
is the active process of carbon being removed from the atmosphere, such as when trees take up carbon to use in photosynthesis.
CARBON STORAGE
is carbon that is kept out of the atmosphere. In a forest setting, it can be stored in living plants, dead wood, and in the soil. CARBON RELEASE
occurs as organic matter decays. Dead wood and leaf litter slowly release carbon as bacteria and fungi break down the material.
Figure 4. Atmospheric carbon in forest biomass.
STORED CARBON PER ACRE IN NORTHERN HARDWOOD FOREST 80-100 YEARS OLD
84 U.S. TONS
30 TONS/ACRE ORGANIC SOIL MATTER 36% 36%
30 TONS/ACRE LIVING MATTER ABOVE GROUND
Figure 5. Adapted from Catanzaro and D’Amato, 2019 12 TONS/ACRE LEAF LITTER
14% 7% 7%
Forests at Farm & Wilderness
Farm & Wilderness’ 4,500 acres contain a diverse range of forest types and support many tree species and herbaceous understory plants. The property elevation ranges from its lowest point of 1,341 feet at the shores of Woodward Reservoir to 3,159 feet near the peak of Salt Ash Mountain.
WOODWARD AREA
At the Woodward Area, the forest type is predominantly northern hardwood and rich northern hardwood with a large percentage of sugar maple. Red oak-northern hardwood forest and a large stand of hemlock-red spruce forest runs north-south along the ridge that rises to the east of Woodward Reservoir. Red oak, which thrives in areas with a history of fire disturbance, is not common in this part of Vermont but is anticipated to be a climate-adapted species that can withstand fluctuations in temperature and moisture levels (Clark et al., 2022). Encouraging the growth of red oak may provide greater climate resiliency in the face of increasing temperatures and precipitation extremes. At the southern end of Woodward Reservoir, where richer limestone soils are prevalent, the forest has a very high density of white ash trees, and other species that prefer rich soils such as basswood. These richer limestone soils also support less-common understory plants such as green spleenwort, summer sedge, stout goldenrod, back’s sedge, and wood millet.
NINEVAH AREA
The Ninevah Area sits at a higher elevation than the Woodward Area, with the shores of Lake Ninevah at 1,778 feet in elevation. Here the forests have more conifers mixed in with the hardwoods, with many more spruce and fir living at this elevation. Sugar maples, beech, and white ash are the predominant hardwood species. Salt Ash Mountain (elevation 3,286’) hosts a large stand of beech trees, which are an important mast tree for black bears.
Many acres of deep forest at the Ninevah Area have no trails, creating undisturbed forest habitat. Farm & Wilderness already carefully stewards this forestland, and its oversight protects the biodiversity featured here.
Figure 6. Adapted from field data collected by B. Engstrom, 2016-2018.
Forest Ecology
|
37
Forest Types at
Northern Hardwood Forest: This is a dominant forest community within Vermont and occurs at middle-elevations (less than 2,700 feet). It includes beech, sugar maple, and yellow birch, and can also contain hemlock, red oak, red maple, and white pine (Thompson, 94). It holds some of the most diverse variety of plant species of any forest community in the state. Most of Farm & Wilderness’ property contains this forest type. Rich Northern Hardwood: A variant of northern hardwood forest, characterized by sugar maple and white ash, and hosts a richer variety of plants that require mineral-rich soils. These forests are found where mineral-rich bedrock or downslope movement of minerals from rich bedrock occurs (Thompson, 138-139). There are areas of rich northern hardwood forest at both the Woodward Area and the Ninevah Area.
Mesic Red Oak-Northern Hardwood: Similar to northern hardwood forests, but these forests have a significantly higher amount of red oak present. These communities mostly occur on dry, south-facing slopes below 2,500 feet in the southern portion of Vermont, and below 1,500 feet in the northern portion of the state. Large whorled pogonia is a rare, acid-loving orchid that can be found in this forest community (Thompson, 142-143). A small section of forest in the Woodward Area along Wilderness Ridge is considered Red Oak-Northern Hardwood forest. Hemlock-Northern Hardwood: A common community in Vermont ad New England, occurring at elevations less than 1,800 feet. Hemlock make up less than 25% of the otherwise dominant hardwood communities within this forest. Hemlocks are shade-tolerant and can survive under the shade of tall hardwood trees. Hemlocks can be found growing alongside hardwoods in many parts of the Ninevah Area.
Farm & Wilderness
Hemlock-Red Spruce: A variant of a Hemlock Forest, this community occurs at elevations below 1,800 feet, and is identified by the hemlock and red spruce trees that dominate. Hemlock trees are capable of living up to 1,000 years. They cover only about 5% of Vermont’s forests (Thompson, 145-146). This forest type is found at the Woodward Area, along wilderness ridge to the east of the reservoir.
Montane Spruce-Fir: Occurs at elevations above 2,500 feet and contains red spruce and balsam fir, and is the preferred habitat of Bicknell’s thrush, a rare and vulnerable bird in Vermont. Some high elevation slopes of the Ninevah Area are Montane Spruce-Fir forest. Montane Yellow Birch-Red Spruce Forest: This forest community occurs at elevations between 2,200 and 3,000 feet. Dominated by yellow birch and red spruce, the understory species include hobblebush viburnum, striped maple, and mountain maple (Thompson, 107, 119). This forest type is found in the north west portion of the Ninevah Area.
Spruce-Fir-Northern Hardwood Forests: A forest community that can be found at a range of elevations and up to 3,500 feet, where trees reach their threshold of survival in New England. Plants suited to cold, harsh weather conditions thrive in these forests. Many acres at the Ninevah Area feature this forest type.
Current Practices
TIMBER HARVESTING & FOREST HEALTH
Farm & Wilderness practices uneven aged management, long harvest cycles, and small patch cuts (½ to 2 acres in size) to mimic the disturbances experienced by natural forest systems. Uneven aged forests have range of tree ages, with younger trees interspersed with older trees. This age diversity offers resilience in the case of a disturbance event such as a wind storm or pest infestation that may impact a certain tree size or age more than others.
Because much of the land had been cleared for agriculture in the recent past, the forests growing now are relatively young and careful management equips the forests to continue to return to their natural patterns of death and regeneration. Farm & Wilderness has expressed interest in reducing their timber harvesting even further than their current practices. While reducing harvesting would increase carbon storage in the forest, ceasing it altogether would require continued careful planning and further management to help the forest develop the diverse structure and age composition that were stripped from it when it was cleared centuries ago. Farm & Wilderness does not harvest timber above 2500’ elevation as shown in the map on the facing page. In Vermont, harvesting above this elevation requires a permit. By not cutting here, these montane areas, typically slower to recover after disturbance, remain unstressed from harvesting. See Figure
In 1998, an ice storm damaged many trees in southern Vermont, but Farm & Wilderness did not carry out any salvage cutting after the storm. Many landowners remove downed trees to recoup some of the monetary loss from the fallen timber following a disturbance, but allowing woody debris to remain in place continues to store carbon as the trees slowly decay and cycle nutrients back into the soil.
Within the acres at the Woodward Area that are managed for timber harvesting, there are some stands of forest along Wilderness Ridge that are electively not harvested; this is where the landscape is particularly steep. The forest here has not been logged in at least 80 years. This is also a deer wintering area, which provides important habitat beneath spruce and hemlock trees that shield the ground from deep snow, allowing the deer to move around without expending precious energy in the winter months.
Farm & Wilderness does not harvest any oak on the property, which is present only around Wilderness Ridge. Oak is expected to be a climate resilient tree in future forests. By leaving oaks in place, Farm & Wilderness hopes to promote continued seeding and growth of new oak trees.
UNEVEN-AGED FOREST
EVEN-AGED FOREST
AREA ABOVE 2,500’ ELEVATION
Smith Peak 3,204’
Burnt Mountain 2,804’
Bear Mountain 3,088’
Salt Ash Mountain 3,286’ Wilderness Ridge 2,200’
State Forest
Figure 7. Area of 2500’ elevation or higher shown in orange. 287 acres of forest at the Ninevah Area are above 2500’ and are not harvested for timber.
Forest Ecology
|
41
ASH TREE DENSITY AT NINEVAH AREA
Ash Trees Other Tree Species State Forest
Figure 8. Density of ash trees at the Ninevah Area, calculated from forest management statistics on the percentage of tree species growing in mapped forest stands. Because the count of trees per acre is not known, this map assumes a uniform density of growth across all acres.
ASH TREE DENSITY AT WOODWARD AREA
WHITE ASH
With the threat of emerald ash borer looming, many landowners have been preemptively harvesting ash trees before they become damaged by the beetles. Trees compromised from insect damage are less valuable as timber and can break and fall in unpredictable ways, endangering loggers. Farm & Wilderness’ forester has not been preemptively cutting ash trees beyond the amount they normally cut.
With such a high quantity of ash trees on the property, Farm & Wilderness has an opportunity to see if any individuals survive infestation and may therefore offer a genetic resistance to the beetles. Withholding from interference in the face of emerald ash borer presents the opportunity for a large-scale experiment to see what might happen following the arrival of the beetles. Because Farm & Wilderness holds such a large acreage, research institutions may be interested in monitoring the site before, during, and after infestation and studying the findings. Seeking partnerships with organizations interested in conducting research on Farm & Wilderness property could contribute to regional strategies for dealing with impacts from the emerald ash borer.
Ash Trees Other Tree Species State Forest
Figure 9. Density of ash trees at the Woodward Area, calculated from forest management statistics on the percentage of tree species growing in mapped forest stands. Because the count of trees per acre is not known, this map assumes a uniform density of growth across all acres.
