The Forests of Spring Creek: A Tale of Change
Dr. James Finley, Emeritus Professor of Forest Resources, Department of Ecosystem Sciences and Management. Penn State University.
Today, forests cover just under 17 million acres (56%) of Pennsylvania’s 28 million acres. While forests are the dominant land cover, this forest is in many ways very different from the forests first encountered by Europeans as they settled across the state. Then forests would have seemingly spread unbroken across the landscape. Forest-buffered rivers and streams ran cold and clear. Threats to the forest were limited. Native Americans had lived on the land for at least 12,000 years, yet their impact was little apparent. The ecological health of the forest was in balance; threats brought to the forest by future generations were inconceivable.
This “Tale of Change” explores general changes to forests across Pennsylvania and imply how
these changes affected and will affect forests in the Spring Creek Watershed. The decisions that were made and the decisions that will be made, extend across large landscapes. It is nearly impossible to anticipate how seemingly small decisions or actions create large and significant changes to our interconnected natural resources and all the communities that depend upon them. We all have a duty to the health and vitality of our natural systems as Aldo Leopold (1949) stated when he wrote of our duty to the ecological community.
“All ethics so far evolved rest upon a single premise: that the individual is a member of a
community of interdependent parts. The land ethic simply enlarges the boundaries of the
community to include soils, waters, plants and animals, or collectively the land.” The Land Ethic. A Sand County Almanac.
The Forests Primeval
In the late 1700s when settlers first arrived in the Spring Creek Watershed, how did they perceive the forests they encountered? Likely, they saw the forest as both an asset and a challenge. Here was the raw material to meet individual and community needs. There was ample wood for fuel, shelter, and commerce. At the same time, these forests may have seemed overwhelming, as settlers considered the need to clear the land for planting, transportation, and community building.
For the most part, the forest the first Europeans witnessed was minimally changed by human
disturbance; it had developed and grown for millennia, since the retreat of the late Wisconsinan glaciation, which ended about 12,000 years ago. The Spring Creek Watershed had not experienced the direct impact of those ice sheets; however, periglacial (i.e., relating to or denoting an area adjacent to a glacier or ice sheet or otherwise subject to repeated freezing and thawing) conditions did impact the watershed. During this and earlier glaciation events, much of Pennsylvania would have supported tundra vegetation such as various grasses, scattered spruce, and low shrubs. As the ice sheets covered the land and periglacial climate dominated, many plant species would have retreated south. Bear Meadows, south of State College, still supports a mix of periglacial tree species (e.g., black spruce, balsam fir, eastern hemlock, yellow birch). More apparent evidence of the glaciation is the relatively common talus slopes (i.e., block or boulder fields on the sides or bottom of slopes) on the mountains in and near the Spring Creek Watershed. These were formed by the repeated freeze-and-thaw cycles that caused frost riving (splitting caused by freeze and thaw cycles) of exposed rocks of the Ridge and Valley physiographic province.
The succession of plant communities or associations from periglacial conditions to today’s mixed species forest of hardwoods and conifers was slow although predictable, as tree and plant species extirpated by the glaciation advanced north and recaptured the warming landscape. Species such as willow and aspen with light windblown seeds were among the first to appear, followed by species with larger wind dispersed seeds such as maple, ash, black birch, and white pine. At the same time, mast [i.e., old English word for food, commonly used to describe forest food such as hard-mast (e.g., acorns, hickory nuts) or soft-mast (e.g., berries, thornapples)] producing species such as oak, hickory, cherry, and others dependent on returning avian, rodent, and mammal populations would eventually establish footholds. Regardless of how they moved, the process of moving north took centuries!
As the post-glacial forest established and matured, it would have developed what today we call old-growth structure. Where “structure” encompasses two dimensions: vertical and horizontal. Vertical structure relates to the arrangement of plants from the forest floor to the top of the canopy. The amount of light, which drives photosynthesis, reaching vertically into the forest decreases as vertical structure increases. As a result, individual plant species “tolerance” for shade influences the plant community. In some forests, so little light reaches the forest floor that few understory plants can germinate or persist.
Horizontal structure describes how forests vary across the land. Conditions across the state and even within the watershed differ from place to place depending on site [e.g., bedrock, soils, drainage, slope, aspect (i.e., compass direction a slope faces), altitude], species composition (e.g., seed source, competition, vertical structure), and natural and cultural history (e.g., amount of disturbance). Site condition often dictates the successional pathway for various plant species relating to their ability to establish and compete with other plants.
Disturbance events are an important forest process as they influence horizontal and vertical
structure. Large disturbances such as a tornado or hurricane can change plant communities across a forest involving various sites resetting the successional process. For example, a hemlock forest with a tight canopy supports little vertical structure and allows little light to reach the forest floor – after a large wind event, the increased light on the forest floor can drive a whole new species mix. On the other hand, the loss of a few trees from natural mortality or small wind disturbances might create a small canopy opening that marginally increases light to understory plants. In this case small local changes in vertical structure occur. As a result, over time and location this type of disturbance creates old-growth structure with trees of all ages, lots of dead down and standing trees, rich in diversity, and where the forest can absorb disturbance and continue to replace individual trees across large landscapes.
The first Spring Creek settlers would have encountered this old-growth forest that in some places was nearly impenetrable because of accumulated detritus on the forest floor, which was a “jackstraw” mix of large and small stems, some having laid there for decades, if not centuries. Below the high canopy, the vegetation layers would have varied. In some places it contained trees, shrubs, and herbaceous plants that could sustain growth in increasing lower light levels. In some places, the forests would have contained dense areas of apparently young trees among the remnants of fallen stems. The conditions across the landscape reflected site conditions and levels of disturbance. Some parts of the forest may have been somewhat open as the result of Native American management, which had declined considerably in the 50 to 100 years before the Europeans arrived in the Spring Creek Watershed.
Wind was perhaps the most common disturbance type. Research has shown that most of
Pennsylvania experiences a forest replacement wind event every 1,000 years. That is not to say that the entire forest falls; rather, areas from one to several trees to thousands of acres
topple from wind. Ice is another common disturbance in the region’s forests; however, while it can involve large landscapes, it seldom fells large areas of forest. Instead, it breaks crowns and disfigures trees, many of which reinitiate crown development. Natural fire events were uncommon in Pennsylvania. Unlike in the West, lightning strikes in the East most often occur with rain. As well, prevailing climate conditions tend to support high humidity conditions that keep fine fuels on the forest floor moist and less likely to sustain fire across large areas; however, in the spring and in the fall, either before leaf-out or after leaf fall, fire can occur.
Native American Influence on Forests
Native Americans were present in the Spring Creek Watershed when it was under the periglacial climate. Evidence suggests they moved throughout the area traveling in small family bands as hunters-gatherers. As the forests returned and the plant and tree composition began to reflect that which is common in the watershed today, Native Americans had little impact on the developing forest as they hunted and collected seasonal plant foods. Likely they repeatedly visited areas in search of seasonal seeds, nuts, berries, and medicinal and other useful plants. They might have concentrated in some areas in larger groups and for longer times depending upon available resources, such as spawning fish or migrating American eels, which were seasonally available.
Artifacts suggest that between 1000 BC and 1600 AD, Native American use of the area changed. For example, there is evidence such as clay potshards, and plant seeds and animal bones in middens (e.g., refuge heap) suggesting year-round encampments. In this period, some Native Americans engaged in agriculture such as planting squash, beans, and later corn. These sites are often found on floodplains and along small streams where tillage using sticks and stone, or bone hoes was easiest. On the Allegheny Plateau, to the north of the Spring Creek Watershed, there is evidence that Native Americans planted and nurtured white and red oak, American chestnut, and various trees and plants bearing small fruits (e.g., shrub cherries and Amelanchier or Juneberry) and berries.
Around 1600 there was a sharp decline in Native American populations. The likely cause was
exposure to European diseases, which decimated previously unexposed Native American
populations along the Eastern seaboard.
It is difficult to fully understand the role Native Americans played in shaping the forested
landscape; however, some of the best white pine stands harvested for ship masts from the early 1800s and through the 1850s commonly occurred on floodplains. Early Native American efforts at agriculture may have played a role in preparing seedbeds for this species. Recent research suggests that Native American activities had a critical role in the development and maintenance of the oak-hickory forest type through their use of fire. They used fire to create open landscapes to improve hunting, encourage food producing plants, and increase localized deer populations, which may have affected forest structure where open forest conditions may have persisted. In wetter areas, lacking fire, maple forests may have shifted to oak forests over 100 to 150 years. In localized areas, Native Americans may have introduced various minor species (e.g., hawthorns which benefit from open disturbed sites) and may have affected tree species composition as they killed by girdling trees competing with desired mast producing trees
The Forest of the Late 1700s
As discussed earlier, site conditions influence forest composition. Fike (1999) describes forest community types for terrestrial and palustrine (i.e., non-tidal wetlands) forests across Pennsylvania. Fike defines a plant community as “as an assemblage of plant populations sharing a common environment and interacting with each other, with animal populations, and with the physical environment.” She recognizes that identifying and describing these communities is somewhat artificial and not very precise as plant assemblages will vary based on site, history, and interactions. The community types shown in Table 1 represents those identified by Fike that occur in the Spring Creek Watershed.
Table 1 also lists the dominant tree and shrub types occurring in these respective forest community types according to occurrence frequency in today’s forests. While it may not be precise, these do provide an approach for estimating the relative distribution of tree species encountered in the late 1700s. The current forest cover (Figure 1) in the Spring Creek Watershed occurs mostly on the Bald Eagle, Mount Nittany, and Tussey Ridges 1 . Depending on the slope and aspect these ridges contain Community types 2, 5, 6, 10 and 11 (Table 1). Near the northwest corner of Figure 1 another large block of forest which connects to the Toftrees development contains Community types 3, 7 and 10. Just north of the Arboretum at Penn State is Harley Woods, a documented residual old-growth forest which is mostly Community type 7. From the Toftrees patch past the Arboretum and toward Bellefonte, another “finger” of woods connects to Dry Hollow and then to Spring Creek, This,
forest, too, would be a mix of Community types as it moved along the valley floor, represented in that reach are Community types 1, 4, 7, 8, 9, and 10.
Using the residual forests composition and the Community types as a blueprint, it is possible to reconstruct a picture of the 1790s forests in the Spring Creek Watershed. Tree species composition on the forested ridges that remain today is little changed. Though missing from the mix is American chestnut that would have thrived on the acid soils. On the other hand, red maple now listed as a more important species was likely less common in the past. Its success ties to the loss of fire, likely set by Native Americans in the past, and increased pressure from white-tailed deer as they prefer oak browse over red maple. Throughout the watershed, white pine and hemlock were likely more common. Although they are shown as high in occurrence in several of the types, they have had more of a presence in the old growth forest based on hemlock’s shade tolerance and white pine’s ability to attain height above other less competitive tree species.
Across the watershed, hemlock and white pine were likely common even on some of the dry sites, especially if Native Americans had not burned the area. Oaks as a group were likely very common and depending on the site, different species would dominate. On the soils either farmed or developed, where limestone derived soils occur, red oak, black oak, and white oak were common. On the more xeric (i.e., dry sites) chestnut oak, scarlet oak, and black oak occurred. Mixed with the oaks were one or more hickory species, again relating to moisture availability. On the very best sites the species mix was reflected by species such as tulip poplar, white ash, sugar maple, basswood, yellow birch, American beech, and cucumbertree. You might note that sweet birch is listed in most of the Community types. It is much more common today as it takes advantage of harvest disturbance that creates ideal light conditions, and the species has low browse preference.
Forest Tree Use in the late 1700s
Each of the myriad tree species occurring in the Spring Creek Watershed forests had a purpose to the early European settlers. An early imperative was to clear agricultural land and construct homes and farm structures.
Tree species would have guided land clearing decisions. The occurrence of red oak, white oak, hickory, ash, American elm, tulip poplar, black walnut, butternut, sugar maple, and white pine would have provided insights into soil fertility and moisture. As a result, early clearing would have focused on areas with these trees. Nearly all these species were easily worked with hand tools and would have provided opportunities for early building, manufacturing, and transportation.
Oak was easily split to make boards and shingles. Red oak made loose-cooperage barrels for
shipping dry goods and white oak barrels made tight cooperage barrels for shipping liquids. Hickory found use where strength and flexibility were required and worked well for wagons and tool handles. Ash was easily split and worked for handles and fuel. Elm had special uses because of it was difficult to split ended up in stable floors and wagon hubs. Walnut, butternut, tulip poplar, and maple were more highly prized for furniture, flooring, and finer goods. White pine was easy to shape and relatively light, it yielded wood for building, furniture, and finish carpentry. Hemlock bark was used for leather tanning, and the wood was used for construction and shingles. Everything they found would have provided fuel for heating and eventually iron production and forging.
As settlements moved out of the valleys and land clearing moved to the slopes, other species found uses. Black gum, chestnut oak, black oak, scarlet oak, and red maple, along with the mix more common on better sites were sourced for various needs. Fuelwood, which was originally common and easy to obtain, became increasingly more difficult to source especially as the iron industry grew and the demand for charcoal increased dramatically. Straka (2014) estimated that in the 1860s an acre of forest converted to charcoal would yield between 6 to 8 tons of pig iron. If the furnace produced 1,000 tons annually, this required clearing between 125 and 160 acres of forest annually.
Today’s Forests: Social, Ecological, and Economic Challenges
Tree Species Composition
The earlier discussion about the forests of the late 1700s drew upon Community types (Fike 1999) to back cast tree species occurrence. To describe the forest composition in the watershed today, it is useful to again consider Community types. The U.S. Forest Service conducts surveys and publishes data from periodic inventories for each state, and recently, they have instituted annual reports that provide data useful for understanding statewide forest conditions. Unfortunately, data at the county level, because of sample size issues, are not reliable.
Table 2 provides a 2019 statewide summary for the 25 most common tree species one inch in stem diameter and larger. Red maple has held the statewide top position since the 1970s. Sweet birch continues to increase across the state as it is a prolific seed producer, does well under partial shade conditions and deer browse it infrequently. American beech is an interesting case because Beech Bark Scale, a complex involving a scale insect and a nectria fungus, is killing beech trees across northern Pennsylvania. As these trees die, they produce large number of root suckers (i.e., shoots that originate from buds on the root system). Unfortunately, there is little evidence that these beech suckers will mature into desirable trees. Black cherry is gaining numbers outside its traditional range because of selective deer browsing. Expectations are that Eastern hemlock numbers will decline in the future because of Hemlock Woolly Adelgid and Elongated Scale infestations. Black gum continues to increase because of cutting practices that leave unwanted stems and its ability to produce root suckers (i.e., shoots that emerge from dormant buds on lateral roots).
Interestingly, over time, all the major mast producing oak species have moved down in the list due to regeneration challenges. The value of oak economically and ecologically was mostly positive until the mid-1930s when the Gypsy moth crossed the Delaware River into Pennsylvania. Relatively quickly it spread across the state and devastated the oak forest with regular, heavy defoliation. Mortality, especially on better sites was higher than expected. In the mid-1970s, the Oak-leaf Roller killed large swaths of oak in the north-central oak forest. Fortunately, this event was short-lived, unlike the state’s extended experience with Gypsy moth. Along with this loss, oak species are difficult to regenerate, and regeneration failures are common, allowing red maple and sweet birch to take over many sites. Among the challenges to oak regeneration is selective browsing by white-tailed deer. In the past 15 years, many resource managers have found that fire is helpful in promoting successful oak regeneration.
Table 2. US Forest Service 2019 Pennsylvania annualized report
showing the 25 most common trees species and number of trees (thousands)
1 inch and larger at diameter breast height (DBH)
Other tree species are facing significant threats from insects and pathogens introduced by
international trade. For example, the Asian longhorned beetle imported to the East coast in shipping pallets and dunnage (i.e., loose wood, matting, or similar material used to keep a cargo in position in a ship's hold) threatens a suite of tree species including birch, ash, elm, maple, poplar, willow, and others. It is already in Massachusetts, New York, Ohio, and South Carolina. One pest already in Pennsylvania is the Spotted Lanternfly that feeds on most fruit trees, maples, oaks, pine, poplar, sycamore, walnut, and willow. American beech is another common Pennsylvania tree reduced to root sprouts across much of its range as an aphid and fungus complex destroys overstory trees and encourages dense clumps of root-sucker origin saplings. The list of potential threats to forest species composition is ever increasing and warrants continuing attention.
Forests, if they are stewarded well, have the potential to sustainably supply goods and services to future generations. Ensuring diverse and healthy forests will not occur without care and focus. In the mid-1800s the forests across the United States seemed limitless. The philosophy was to cut and move on. The abandoned forests in Pennsylvania, cut hard from 1885 to 1920 were abandoned and left to recover on their own. Circumstances were different then and a diverse, high-quality forest self-renewed across the state. As that forest began to mature, foresters working in the in the 1950s and 1970s recognized that regeneration problems were occurring across the state.
Recent U.S. Forest Service annualized surveys and assessments in Pennsylvania find that when harvesting reduces canopy cover to a level where natural forest tree regeneration should occur, new tree stocking is inadequate. Nearly half of the forests studied fail to meet seedling number guidelines for achieving successful regeneration of desirable tree species. If the list of tree species is increased to include all commercially used species (e.g., American beech, sassafras, elm, and others) the likelihood of achieving regeneration success increases somewhat, but not enough.
There are numerous recognized reasons for these regeneration challenges. One of the most common ones is the role of white-tailed deer. Deer density numbers have since the 1960s
exceeded ecological carrying capacity (i.e., deer density that does not impact undesirably on the surrounding ecosystem(s)) across much of the state’s forested lands. At ecological
carrying capacity, deer would not adversely affect habitat function; however, their referential feeding has shifted tree, shrub, and herbaceous species composition. This has led to conditions where light and competitive plant conditions across forests suppress desirable tree seedlings. Ferns, striped maple, and beech sprouts are examples of these competitive plants.
Beyond native plants competing for light and other resources and affecting forest regeneration, there is an explosion of non-native plants in our woodlands. The U.S. Forest Service annual survey finds that 61% of their inventory plots has one or more of these exotic plants present. This is a long list with multi-flora rose leading the pack; others are Japanese stiltgrass, Japanese barberry, Russian olive, bush honeysuckle, and Oriental bittersweet among many others. Not only do these plants challenge forest regeneration, but there is also evidence that they reduce native insect populations and subsequently affect songbird brooding success.
Land Use Decisions and Planning
The forests in the Spring Creek Watershed are in many ways different from those that supported Native Americans and in the 1700s the first Europeans. We have brought large changes to our forests, which we anticipate will continue to change.
In the 1600s the forest was nearly continuous from ridge top to ridge top, broken only by rivers and streams. The 2003 Phase II, Centre County Comprehensive Plan on Forests, states that about 71% of the county is forested; however, in the Centre Region that includes much of the watershed, only 51% is forested. Concerns cited in the report are fragmentation (large forest patches broken into smaller parcels), deforestation (agriculture, industrial, commercial, and residential), forest regeneration, forest in transition (age and structure), and parcellation (different from fragmentation in that ownership reduces parcel size). The concern is that these shifts will and are affecting forest-based economic development and jobs, water quality, and forest health and vitality. A review of the plan provides approaches for reducing these and other impacts on forests.
Forests have an important role in addressing climate change as they absorb and sequester carbon. The process of managing forests as carbon sinks poses yet another challenge and involves everything from planning to execution of plans with a long-term vision that extends across landscapes and generations. The decisions we are making today about the care and stewardship of forests involves understanding the past as well as the present and giving due consideration to changing conditions. Already, there are indications that climate change will require long-range thinking to implement management strategies. For example, it may be necessary to use migration assistance to move southern species north, or low elevation species to higher elevations. Entire plant communities may change and affect dependent species. It will take careful observation, risk taking, and adaptive practices to care for forests as our climate impacts playout.
Forests dominate our landscape. In many ways, we take them for granted. We have used them in the past with little thought about their future. Today, hopefully, we are learning that we have an obligation to our forests and all components of our environment. We are part of the ecosystems we depend on; they more than ever clearly depend on us. We are on the cusp of big changes. Returning to Aldo Leopold,
“A thing is right when it tends to preserve the integrity, stability, and beauty of the biotic community. It is wrong when it tends otherwise.”
Clearly, we need to take this admonition to our hearts and our heads.
Dr. James Finley always wanted to be forester. His career took him from the field to education and research. His research and education interests involved working at the intersection of people and forests. He started the PA Forest Stewards volunteer program, was co-chair of Penn State’s dual title intercollege degree program in Human Dimensions of Natural Resources and the Environment, co-founder of the Center for Private Forests at Penn State. His research involved human dimensions, forest management, forest
sustainability, and forest regeneration.
Editor’s note: Dr. Finley passed away a few days after submitting the final version of this article. The Atlas Project volunteers extend our sincere sympathies to Dr. Finley’s family.
1 The forest cover found in the Spring Creek Watershed today strongly relates to the underlying geology and its influence on agricultural development. On the ridges and side slopes of the watershed soils derived from sandstone and shale rock were less fertile. Lower valley sites with limestone soils were less fertile, best favored for agricultural uses.
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