Enumerate the problem facing the maintenance of forest
Answers
The conversion of forests to agricultural land, overgrazing, unmitigated shifting cultivation, unsustainable forest management, introduction of invasive alien plant and animal species, infrastructure development (e.g. road building, hydro-electrical development, urban sprawl), mining and oil exploitation, anthropogenic ...
"Insects and diseases brought to Eastern forests from other places have, in a relatively short time, taken from us important tree species and threaten others," he said.
"One hundred years ago, chestnut blight from China began extirpating American chestnut across its range. Soon, American elm was added to the list of species impacted by an imported disease. Then, in the 1930s, the gypsy moth began to take its toll on our oak forests."
In recent years, other problems have come to our forests, Finley said. Pennsylvania's state tree, the Eastern hemlock, struggles with hemlock wooly adelgid and elongate scale, which in a few years will greatly reduce the presence of this important species that shades streams and provides important habitat.
"Similarly, emerald ash borer is rapidly extending itself across our forests and likely will eliminate all native ash species," he said. "The next major threat to many tree species is the Asian longhorned beetle, which will play havoc with oak and maples. In sum, there are mounting issues affecting individual tree species."
The invasion of exotic, competitive plants adds to the mix of issues affecting forests, Finley said. Across much of the East, 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 now common, especially along forest edges, roadsides and old fields. They even make up many of the stems in some forested tracts, Finley said.
"Consider how our spring woods now take on displays of color that only a few years ago were uncommon," he said. "There is the white of garlic mustard flowers, the purples and lavenders of dame's rocket, and the soft greens of Japanese stiltgrass.
"Later in the year, other shades of green compete for light and space with native plants. Increasingly, Japanese knotweed and mile-a-minute weed, or tearthumb, fill in forest openings and provide little but aggravation."
Together, Finley noted, the loss of native trees, competition from native and non-native plants, and changing weather conditions are affecting the composition of our forests and their health. Clearly, the complexity of native plants is changing because of these influences. 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, Finley explained. For example, in the early 1970s, red oak was the most common tree in Pennsylvania. Then, for a myriad of reasons, red maple took over as the No. 1 tree species.
"Over time, as species composition becomes simpler and these fewer species dominate more of the landscape, resilience changes," he said. "An insect -- for example, Asian longhorned beetle -- comes to the forest, its opportunity to wreak havoc is high, and overall resilience wanes as yet another species enters a spiral of decline and there are fewer species to fill the niche that has opened."
Even the weather and seasons seem to be changing, opening one more front in the battle to keep forests healthy, Finley suggested. Climate change may well be one more factor influencing forest health and species diversity.