Last week Deborah and I finished our Friday classes and office hours by noon and then planned to spend a couple of hours out on the campus Nature Trail. It was still quite cold (about 20 degrees) with a strong wind between 15 and 20 mph. After we got back from the hike, I entered the temperature and wind speed data into an on-line wind chill calculator and came up with a 4 degree F wind chill. We were a bit more sheltered from the wind down in the woods, but now I know why our hands and feet felt so numb!
There was a light, cloud cover (what we call “Pennsylvania sunshine”) so we headed out with our camera to try to re-take some of the pictures that have illustrated our winter hike on the Virtual Nature since 2001. The sunlight, though, failed us and the pictures turned out too dark to use on the web site.
To get to the entrance of the Nature Trail we had to cross the new soccer practice field. The snow on the field was about ten inches deep, well packed down by freeze-thaw cycles, and covered with a hard, thick, icy crust. Each step we took broke through the ice and sunk our boots a couple inches down into the Styrofoam-like snow. The noise of each of these steps was an impressive set of crashes and crunches. The two of us sounded like an army marching down a gravel road.
We wanted to watch and listen for birds along the trail, so we had to stop frequently to get relief from the walking noises to try to catch hints of the bird songs around us. By the time we got to the trail I realized that my binoculars were safe and warm back on my desk in my office. Oh, well. We did see and hear chickadees and titmice in the low branches around us and spotted a solitary, white-breasted nuthatch high up in the branches of a sugar maple tree. There were also some small groups of sparrows flitting around in the low undergrowth, but without binoculars I couldn’t tell if they were white-throated sparrows or song sparrows. We also heard the faint rappings of woodpeckers (downies?) back in the woods far off of the trail. We saw a lot of evidence of woodpecker activity, too (more on that later).
The snow on the trail was as crusted and as deep as it had been out on the soccer field, so walking was difficult. The snow surface in the woods was also covered with rabbit tracks! In the winter the eastern cottontail forages around looking for woody plants to consume (including the twigs, bark, and buds of oak, dogwood, sumac, maple and birch). Usually these rabbits hunt for food by themselves in the winter, but the density and pattern of the tracks made it look like a good sized group of rabbits had been collectively active out on the trail in some kind of a rabbit rumpus! It looks like we have a robust population of eastern cottontails this year!
Our boot crunching scared up a white-tailed deer (a doe) that had been hunkered down in the brush of the oak and poplar section of the trail. She leaped on ahead and was down the slope of the ravine before we could even point the camera in her direction.
I had descriptions of the web site photographs we were trying to upgrade, and it was very interesting looking at the trail from a “year 2001” perspective. For example, we wanted some shots of wild raspberry canes sticking up through the snow and of barberry bushes with their little red berries still attached, but these plants were not as abundant as they had been fourteen years ago. Instead, almost all of the plants growing along the trail were multiflora rose! This invasive plant, which I have written about many times before, apparently, has outgrown and out competed the native raspberry and also the exotic barberry and has greatly changed the floral composition along the trail.
Several trees have come down across the trail this winter. A white ash has fallen across the Entrance Trail, a yellow poplar is blocking the end of the Red Pine Trail, and a tall, sugar maple has fallen across the Wildflower Trail. The size of the maple forced us to detour high up into the woods as we were hiking on the blocked trail up from the bridge over the lower stream. Clean-up Day this spring will require a chain saw or two to clear the paths.
The most significant thing we saw on this snow hike, though, was up beside the pavilion at the beginning of the trail. Along the Entrance Trail are a number of white ash trees. These trees are interesting for a number of reasons including the rich growth of lichens that cover their ridged, diamond-patterned bark. Students in past years have mapped these lichens and evaluated the preference of the lichens for the complex surfaces of these trees. Today, however, the bark of all of the white ash trees along the trail were scratched and scarred with woodpecker holes. The woodpeckers (probably the downy or the hairy from the relatively small sizes of the bark tears) were in search of larvae of beetles living just beneath the bark. It was an ominous sign. It indicated that these white ash trees were infested with emerald ash borers.
The emerald ash borer (Agrilus planipennis) is an exotic invasive beetle from Asia (eastern Russia, northern China, Korea and Japan). It was first detected in the United States in 2002 in a stand of ash trees near Detroit, Michigan, but it has probably been in North America since the 1990’s. The beetle has subsequently spread to twenty-four states and two Canadian provinces. There are 7.5 billion ash trees in the United States and nearly all of them (green ash, black ash, white ash, and blue ash) are threatened by this beetle. So far, 50 million ash trees in the United States have been killed by the emerald ash borer.
The adult, ash borer beetle is quite striking in appearance: it is about a half and inch long and is a bright, metallic green. Adult females lay eggs on the ridged bark of ash trees and the hatching larvae then eat their way through the tough outer bark into the living tissues of the tree. The phloem (the sugar/sap transporting vascular tissue) and the actively growing, cambium layer of the tree are consumed by the developing larvae. The larvae can so effectively destroy the sap flow of the tree that entire limbs or even the main trunk of the tree can be effectively “girdled” (or severed) thus causing limb systems or the entire tree to die.
In June 2007 the emerald ash borer was found in Cranberry Township in Butler County just to the west of Penn State New Kensington. In June 2009 it was found in Westmoreland County (the county where our campus is located) in nearby Allegheny Township. Now we know that it is here in Upper Burrell Township, too. To date, fifty-five counties in Pennsylvania have been infested by the emerald ash borer.
Sadly, these white ash trees will die. There are white ash trees all across the long ridge on which Penn State New Kensington sits and many more down in the wooded valleys that surround us. These trees are also probably infested and are dying.
Think of the carnage that has hit our forests because of exotic, pest species! The impact of the emerald ash borer may remove an entire group of tree species from our eastern forests. It may be even more devastating than the Chestnut Blight or Dutch Elm disease, two other exotic, invasive diseases brought to North America by human activity. And, remember the gypsy moth and their devastation of our oak trees? There is a large, fallen white oak out on the campus nature trail that is testament to the gypsy moth population explosions of the 1990’s! And, let’s not forget about the Asian long horned beetles that are plaguing our maples and many other hardwood species or the wooly adelgids that are destroying our state tree, the Canadian hemlock. And, most sadly, there are many more! Our forests have been and continue to be under terrible assaults by agents we have transported from afar.