Is global climate change real? Is it human caused? The arguments advanced by both sides of the debate are complex and divisive. However, whether you believe the climate is changing or if humans are causing change is not important. If you are a woodland owner or just enjoy woods for their many values, know that our forests are truly under stress.
Some historic and current forest stressors occurring in Pennsylvania are clearly human-caused. Consider how insects and diseases brought to our forests from other places have, in a relatively short time, taken from us important tree species and threaten others. A hundred years ago, chestnut blight from China began extirpating American chestnut across its range. American elm was soon added to the list of species impacted by an imported disease. Then, in the 1930s, gypsy moth began to take its toll on our oak forests.
In recent years, other problems have come to our forests. Pennsylvania's state tree, the Eastern hemlock struggles with hemlock wooly adelgid and elongate scale, which in a few short years will greatly reduce the presence of this important species that shades our streams and provides important habitat. Similarly, emerald ash borer is rapidly extending itself across our forests and will likely eliminate all native ash species. The next major threat to myriad tree species is the Asian long horned beetle, which will play havoc with oak and maple species. In sum, there are mounting issues affecting individual tree species.
The invasion of exotic competitive plants adds to the mix of issues affecting forests. In much of Pennsylvania, it is difficult to remember or to imagine what our woodlands looked like without multiflora rose, bush and Japanese honeysuckle, autumn and Russian olive, barberry, and privet adding their touches of green and, occasionally, colorful flowers. Canopies, especially along woodland edges, are filled with native grapes and Oriental bittersweet. Invasive tree of heaven, paulownia, mulberry, and buckthorn are not uncommon, especially along forest edges, roadsides, in old fields, and even sometimes, they make up many of the stems in our native woods.
Consider how our spring woods now take on displays of color that only a few years ago were uncommon. There is the white of garlic mustard flowers, the purples and lavenders of dames' rocket, and the soft greens of Japanese stilt grass. Later in the year, other shades of green compete for light and space with native plants. Increasingly Japanese knotweed and mile-a-minute, or tearthumb, fill in forest openings and provide little but aggravation.
In sum, the loss of native trees, competition from native and non-native plants, and changing weather conditions - think about warmer summers in the past few years, shifting rainfall, storms - are affecting the composition of our forests and their health. Clearly, the complexity of native plants is changing because of the aforementioned threats. In the end, this leads to a simplification of forests - there are fewer native species.
Simplicity may mean that some plants will move into voids left by the loss of a given species. Consider that in the early 1970s red oak was the most common tree in Pennsylvania. Then, because of myriad reasons, red maple took over number "one" in the most common tree species. Over time, as species composition becomes simpler and these fewer species dominate more of the landscape, resilience changes. An insect, for example Asian long horned beetle, comes to the forest. Its opportunity to wreak havoc is high; and overall resilience declines as yet another species enters a spiral of decline and there are fewer species to fill-in the niche that has opened.
As we look at forests, it is apparent that to maintain their health it is important to adapt to changing conditions. Clearly, there are many imposed change agents affecting forests - insects, diseases, competitive plants and maybe climate change. All of us will have to adapt to a landscape that will be imposed upon us and consider how we can, through our management and actions, help forests adapt to change. What can we do to help threatened species, how might we guide the replacement of one species with one or more native species that fit into our changing conditions? If one of the variables is climate change, what species, maybe one on the edge of its range, might be introduced to the forest?
Active participation in adaptation logically leads to making mitigation decisions. In the forests, some activities will mitigate some threats - leading to better conditions and increase resilience. The mitigation activity might focus on a specific threat. Eastern hemlock decline might provide a mitigation scenario. To protect streams losing hemlock cover and threatened with increased water temperatures and detritus from non-native plants, which do not "feed" native stream insects, a mitigation step would be to increase native white pine regeneration, maybe introducing another species such as rhododendron to provide cover and shading for streams.
Mitigation might extend further by making social decisions about how you might reduce your carbon footprint to address climate change, even if you are uncertain about its reality. Your individual decision might not seem to make much of a decision, but it could be simply a statement about your stewardship of the forests and the environment. Stewardship, in its simplest form, is living in a way today that you help conserve resources and options for future generations.
Hopefully, as you consider this discussion you can think about our forests, your relationship to them, and begin to make decisions that help them adapt to change. To learn more about sustaining forests, contact the Renewable Natural Resources Extension Office (contact information below) and ask for a copy of Forest Stewardships Principles for Landowners.
The Pennsylvania Forest Stewardship Program provides publications on a variety of topics related to woodland management. For a list of free publications, call 800-234-9473 (toll free), send an email to RNRext@psu.edu, or write to Forest Stewardship Program, Forest Resources Extension, The Pennsylvania State University, 416 Forest Resources Building, University Park, Pa. 16802. The Pennsylvania Bureau of Forestry and USDA Forest Service, in Partnership with Penn State's Forest Resource Extension, sponsor the Forest Stewardship Program in Pennsylvania.
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Jim Finley is a professor of Forest Resources at Penn State University.