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The Rise and Diminishment of Oak Forests in Connecticut

By Emery Gluck, Retired State Lands Forester, and Pitch Pine Enthusiast


🌳 Oaks have been in Connecticut for thousands of years. It is hard to overstate their importance to the forest ecosystem. Their acorns provide a highly nutritious source of plant-based protein for over 80 animals. They host the greatest number of species of caterpillars (462 in Connecticut) which provide the most important source of protein for birds to feed their nestlings. One study found that it took 6000 to 9000 caterpillars to raise a brood 🐛! The abundant caterpillar resource is a major contributor to why oak forests have a greater abundance and diversity of birds when compared to maple forests. Unfortunately, red maple has surpassed red oak as the most abundant tree in Connecticut. This is part of a downward trend that oaks have been experiencing in most of the eastern U.S. for at least a half century. Younger oaks are scarce as oaks are not sustaining themselves under current natural conditions except on very sandy or shallow soils.


One key factor in their inability to sustain new generations is that the forest has grown shadier, mainly due to the large influx of birch, beech, maple and shrubs in the absence of fire. Though their seedlings can survive in the shade for a while, oak seedlings will stagnate or die if they do not eventually get a fair amount of sunlight. Even with global warming being beneficial to oaks, the shadiness of the forest and other impediments will likely still stymie young oaks from growing into the overstory.

Oak overstory with typical dense black birch and ironwood understory - photo by Emery Gluck
Oak overstory with typical dense black birch and ironwood understory - photo by Emery Gluck

Oaks have historically seeded in after fires, and after fields were abandoned, or both. Most of Connecticut was once cleared for farmland. As the fertile farmland of the Midwest became available, most of Connecticut’s rocky farmland was abandoned in the last half of the 19th century and first part of the 20th century. Fires were also prevalent in days gone by. An average of over 30,000 acres reportedly burned in Connecticut annually from 1905 to 1925. For a point of reference, the size of the average Connecticut town is around 21,000 acres. The fires often killed or severely damaged thinned-bark birch, beech and maple and sometimes even the thick-barked oaks. Thick bark provides some protection from the lethal heat to the tree’s cambium, the living layer of cells under the bark. Recently, only a few hundred acres usually burn annually and the fires are generally much less intense than those a century ago as the shadier forest does not dry out as fast and is transitioning to less flammable vegetation. 🔥


Historically, clearcuts have increased the proportion of American chestnut and oaks as both are prolific sprouters after being cut or top-killed by a fire. Since the chestnuts outgrew and overtopped the oaks, the chestnut blight was boon for the latter. A large portion of the state was repeatedly clearcut for firewood and charcoal, especially from the late 19th to early 20th century. These products were in high demand as they, in addition to water power for mills, were a major source of energy at that time.


It was often more efficient to produce charcoal in the woods, as it was lighter than firewood to transport. The slow burning of wood in piles covered with dirt without much oxygen drove out the moisture, leaving a pure form of carbon.

CT Colliers on charcoal mound circa 1905 - photo courtesy of Connecticut Agricultural Experiment Station
CT Colliers on charcoal mound circa 1905 - photo courtesy of Connecticut Agricultural Experiment Station

Charcoal was used by the iron furnaces in northwest Connecticut, and by gun manufacturers, as wood fires were not hot enough to smelt iron. It is estimated that over 20 square miles of forests were clearcut annually to provide charcoal for the iron furnaces at their peak production. Some forests would be clearcut again every 20 to 40 years once the trees reached a 4” to 6” diameter. The extensive amount of logging slash likely increased the size and intensity of wildfires. The high frequency and severity of wildfires was a disincentive for forest landowners to allow their forest to grow for a longer time as it increased the risk of their assets going up in smoke. Widespread overcutting and excessive fires led to the beginning of Connecticut’s State Forests in1903, as the Legislature authorized the State Forester to purchase land for up to $4/acre under “An Act to Reforest Barren Lands”. Some cutover land was purchased for $.50/acre.


Many of today’s forests were born from the widespread farm abandonment, clearcutting, and fires that occurred 100 to 140 years ago. This gave rise to a relatively uniform forest landscape, as most of the overstory trees are roughly the same age and relatively evenly spaced out. It wiped out the patchwork and mosaic of different-aged forests that arose after thousands of years of natural disturbances on multiple scales. These included blowdowns from severe storms, mortality from droughts and infestations, flooding by beavers, and Native American fires. It is worthwhile to note that some ecologists consider Indigenous land management techniques, such as their burning, as part of the natural disturbance regime.


Today’s oak forests face many aggregating challenges that deter new generations and are causing the deterioration of the old guard. Deer preferentially browse on oak seedlings, allowing other species to grow taller and cast more deadly shade on the oaks. This wasn’t a problem a century ago when today’s forests were getting started, as deer were then very uncommon. In some places, ferns have formed a dense carpet keeping out or inhibiting oak seedlings. Exotic invasive plants exacerbate the problem of the killing shade that dense shade-tolerant native plants cast on oak seedlings. Successive Spongy moth (previously known as the Gypsy moth) defoliations, drought, and the two-line chestnut borer have killed many oaks. Selective harvests often select mostly the valuable overstory oaks for removal, accelerating the transition to less ecologically valuable and shade-tolerant birch, beech and maple forests.


For oak forests to be sustainable, new trees must at least occasionally be recruited to the overstory as replacements for the fallen ones. This is not happening, as historic events that gave oaks the breath of life are rarely occurring today. The crucial disturbance that is now effectively absent is fire. This has opened the floodgates for fire-sensitive shade-tolerant trees and shrubs to seed in, making the forest much more dense than it has historically been.


The thoughtful cutting of small trees can serve as a partial proxy for fire. This will allow extra light to existing oaks seedlings and may promote oak germination.

Oak seedling after surrounding small trees are cut - photo by Emery Gluck
Oak seedling after surrounding small trees are cut - photo by Emery Gluck

When oak seedlings are an adequate size and number, some to most mid-story and overstory trees generally also need to be harvested to allow a new generation of oaks to start their journey to the upper canopy.

Thriving oak saplings after a group of overstory black birch was cut - photo by Emery Gluck
Thriving oak saplings after a group of overstory black birch was cut - photo by Emery Gluck

Cutting a substantial amount of medium and large trees can usually provide some revenue. It is usually best if a forester plans a treatment to meet the landowner’s objective and works in conjunction with a logger. Additional cutting of small trees is usually needed after a commercial harvest to free up young oaks from faster growing hardwoods that will likely overtop them. This may need to be repeated until the oaks are likely to outgrow their competitors in height or when they are “big enough to make it on their own”. Unless done by the landowner, cutting small trees can be a substantial expense, but necessary to sustain oaks. Federal cost-sharing funds might be available to do such work.


🦉 Connecticut Audubon’s publication “Managing Forests for Trees and Birds in Connecticut” views the logging slash as beneficial to many insects, birds, and other animals. To improve habitat quality, the publication encourages “leaving it messy” by leaving at least 2 cords and up to 12 cords per acre of down wood at least 5” in diameter clustered together. Leaving enough tall logging slash can provide oak seedlings shelter from deer browse.


Even though seemingly counterintuitive, forest management can promote old growth characteristics into the tree cutting process. These characteristics include canopy gaps; multi-layered forests; large live, large dead standing and fallen trees that are left. Significant development of these characteristics have historically accumulated from natural disturbances over time when the trees are about a century older than today’s forest.


Among the methods suggested in the publication “Restoring Old Growth Characteristics to New England’s and New York’s Forests” is cutting the main competitors of healthy overstory trees to accelerate their diameter growth. This reduces the time for them to reach old-growth-like sizes. Some or all of these trees can be retained in perpetuity as legacy trees. Cutting and leaving sizable trees would increase the large down wood trait. This would create small gaps and eventually multiple canopy layers. Creating sizable gaps (at least an acre) in the canopy potentially allows tree species that require substantial sun for their development (oaks, cherry, ash, poplar, white birch) to be part of the mix of the future forest. The subsequent cutting of small trees overtopping young oaks would still likely be needed. Reserves or skips where no tree cutting occurs on part of the forest is also an important trait when managing for old growth characteristics.


It is not easy to be a young oak. Most die before they make it too far. With so much ecological value at stake, the current trend of slowly losing our oaks makes thoughtful action essential.


This article is one of a pair by retired State Lands Forester Emery Gluck. They first appeared in local CT publications and are re-printed here.

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