The Value of Aging Trees

A big red oak on top of Sapsucker Ridge

A big red oak on top of Sapsucker Ridge

On a hot July day, I sit beneath a large red oak, nestled into a deep buttress, one of several that flare out from this 200-year-old tree. The ground beneath the tree is littered with old acorn remnants as are the bases of the other elders in this stand of deciduous trees.

Protected as a picnic spot by the previous owners, the trees were allowed to prosper even as other portions of our property were cut over in the nineteenth and even twentieth centuries. Instead of fencing a young forest, such as that last 120-acre cutover piece we acquired back in the 1990s, we put up our three-acre deer exclosure in March 2001 around these mature trees.

Now, as I gaze around, I see dozens of oak seedlings and saplings filling in the forest floor. Most are red oaks, but some are offspring of the enormous white oak beside the exclosure gate.

Technically, this is not an old-growth forest but one that is becoming old-growth. Still, it and much of the rest of our property consists of an aging forest. Not long ago, old trees were seen as useless and were harvested so that young trees would grow in their place. But in the last few decades scientists have been discovering that old trees in an old forest are incredible absorbers of carbon dioxide. And red oaks, with their dense wood, are particularly good at absorbing impressive amounts of carbon.

One study, in Massachusetts’s Harvard Forest, found that at 50 years of age, their trees, both oak and maple, were absorbing 0.8 tons of carbon per acre every year. After 15 years, the rate of carbon uptake had doubled. Researchers studying old-growth forests in the West discovered that those forests too absorbed more carbon as they aged.

One of those researchers, Bev Law, of Oregon State University, told a journalist that, “Across forest types, globally, we find that the amount of carbon stored is high in older forests, and that live carbon continues to accumulate for centuries.” This carbon is held not only in the trees themselves but in their fallen leaves and branches as well as in the fertile soil of old forests.

Law is director of the AmeriFlux Network, an international collaborative project founded in 1996 to measure the carbon dioxide, water vapor, and energy in all kinds of major ecological community types or biomes in North, Central, and South America. Using a variety of sophisticated tools, scientists are able to track carbon in any ecosystem. Here in our eastern forests, studies have been done in several states including the aforementioned Massachusetts.

Old trees in an old forest have other uses too. They provide large hollow trees for a variety of birds and animals that use them for nesting, food, and shelter. For instance, sycamore trees are the most massive trees in the eastern United States. They can grow over 100 feet tall and 10 feet wide and live up to 500 years. When they are very old, they have a cavity at ground level large enough, in one recent case, to house a maternity colony of 100 Indiana bats, researchers discovered back in 1993.

A giant eastern hemlock tree in Central Pennsylvania

A giant eastern hemlock tree in Central Pennsylvania

Large, hollow trees also appeal to children of a certain age. I was reminded of Jean Craighead George’s book My Side of the Mountain which my husband Bruce read aloud to all of us when our three sons were young. They were all entranced by the 12-year-old hero of the story, Sam Gribley’s large, hollow tree home in the wilds of the Catskill Mountains. In his case it was a hemlock tree. Remembering the many old-growth hemlocks we have (or had, before the hemlock woolly adelgids killed so many of them in our Pennsylvania old-growth forests), I knew that such trees might have been large enough to house one young boy.

Because our old-growth hemlock trees are mostly in Pennsylvania’s state natural areas, the trees attacked by adelgids have been allowed to die and be reclaimed by the earth as our son, Dave discovered during a recent visit to Snyder-Middleswarth Natural Area. Many people find this wasteful, believing that such trees should be harvested. But Dr. Joan Maloof, who has been writing and speaking about the value of old-growth forests, maintains that “old-growth forests are one of the few land uses where topsoil is created instead of destroyed.”

We like to think that our own younger but mature forest is also creating soil as we allow our trees to fall over and rot, creating, as our young nephew Patrick once cried over and over, “Dirt, dirt, dirt” while sifting the powdery, reddish-brown remains of red oak branches through his fingers. Those powdery remains of the heartwood and sapwood appear to be a nursery for the downy rattlesnake plantains I’ve discovered inside and outside our exclosure. When we first put up the exclosure, I found a large colony of this orchid growing on a slope where several trees had rotted down to heartwood and sapwood. Another plant that we found outside the exclosure and fenced had germinated beneath a stump that was seeping rotted wood at its base.

Then, a couple years ago, I found still another downy rattlesnake plantain plant that had germinated on the decaying remains of a fallen red oak limb. At the same time, I noticed that the fenced plant outside the exclosure was looking poorly. I gathered up more of the “natural” fertilizer from the trunk and sprinkled it over the plant, and once again it is thriving. I haven’t seen any studies that indicate that downy rattlesnake plantain needs this material, but I wonder.

Photographing downy rattlesnake plantain in our deer exclosure

Photographing downy rattlesnake plantain in our deer exclosure

As our forest has aged over the last 41 years we’ve lived here and now nearing one hundred years of age in our hollow area, our forest bird diversity has increased. Fallen trees across our first-order, headwater stream, attract several breeding Louisiana waterthrushes and winter wrens. Barred owls court and nest in our larger, hollow trees. Scarlet tanagers, worm-eating warblers, and red-eyed vireos, among others, are more common than ever. Once we had no nesting black-throated green warblers, cerulean warblers, blue-headed vireos, winter wrens, or Acadian flycatchers, but our aging forest has attracted them. All of these bird species and several more, such as blackburnian warblers — depending on whether species need coniferous, deciduous or mixed deciduous forests — use older, mature forests. And the larger these forests are, the better the chances are for the birds to fledge nestlings.

The same is true for many mammal species. Bears, raccoons, and porcupines, for example, like to den in large, hollow trees. One study of black bear den trees found that in order for red and white oak trees to be big enough, they had to be between 175 and 280 years old, which reminds me of the huge oaks our boys found more than 30 years ago at the steep base of our mountain on a property line with a neighbor. They took some box camera photos of themselves standing in front of them and they looked as if they were as large as California redwood trees. I was amazed and delighted, but before I had a chance to see those trees, our neighbor’s logging operation had cut them down. The boys went to check on them and said that they were all hollow inside, so excellent habitat had been destroyed and not a dollar earned on those trees.

The same den tree study found that raccoons liked tree hollows in trees from 90 to 164 years old, and gray squirrels 65 to 130 years in age. Many bat species, too, like old trees with cavities and loose bark. Other opportunities for denning in older forests include in soil pits created by large root masses of wind-tilted trees, in the root masses themselves, and in stumps, logs, large, horizontal limbs and cavities in standing trees, all of which we have in abundance in our aging forest..

One special kind of older forest that has diminished greatly is that of mixed red spruce and hemlock in the northern tier of Pennsylvania. Such a forest especially appeals to red-backed voles, water shrews, and state-endangered northern flying squirrels. According to researcher Dr. Carolyn Mahan of Penn State, this type of coniferous forest creates a moist microclimate that supports a diversity of fungi, which both the voles and the northern flying squirrels thrive on. They also spread the fungi spores, thereby enriching the soil. Water shrews also seem to prefer such forests, but they like them to be in swampy ravines.

Megalodacne heros beetles feed and mate on varnish shelf fungi, found on an ancient hemlock logs

Megalodacne heros beetles feed and mate on varnish shelf fungi, found on ancient hemlock logs

We also have red-backed voles in our deciduous forest, and Mahan explains that they are not specific to old red spruce/hemlock forests, but more of them are found there than in forests such as ours. Northern flying squirrels are much rarer in our state because they are habitat specialists and their red spruce/hemlock forests have been lost to habitat fragmentation from development of all kinds and to hemlock woolly adelgids. The remaining smaller, patchier coniferous groves next to deciduous forests also attract the more generalist and numerous southern flying squirrels. They are sharing nest sites and even hybridizing with northern flying squirrels, and in the process, passing on a roundworm species, Strongyloides robustus, to which they seem to be immune but which is killing the northern flying squirrels.

Mahan has 600 nest boxes in 21 study sites for the northern flying squirrel, and this year not one northern flying squirrel has been found in any of those boxes. Last year she and other researchers planted an experimental 2500 native red spruce seedlings among the dying hemlocks of a site and others in a recent Game Commission clearcut which was fenced to see if they will grow and thrive and someday produce more red spruce forests. If they do well, they will plant more red spruce seedlings. But think how long it will be before there will be another red spruce forest as magnificent of those we had in Pennsylvania. How much better it would have been if we had saved larger pieces of our older spruce forests.

After talking to Mahan and other researchers, I am more determined than ever to keep growing an older forest. But on this hot summer day, I most appreciate our mature forest for its deep shade that cools not only me but all the creatures large and small that live here.

All photos by Dave Bonta ~ click on images to view larger versions at Flickr

The Longest Autumn

red oak in snow

red oak in snow (all photos in this post by Dave Bonta except where indicated)

Every autumn the first hard frost comes later. Back in the 1970s and early 1980s, when we were engaged in intensive gardening, we could expect a hard frost in the first week of October. Gradually, as the years passed, the hard frost date arrived in the second week. Then, in this century, it moved into the third week. And last October it finally came on October 28.

Just as the date for the first hard frost has advanced year by year, so too has mild autumn weather. Instead of several days of Indian summer weather at the beginning of November, we have stretches of Indian summer weather throughout November and, last autumn, well into December.

Final leaf fall is also later every year. In the seventies and even into the eighties, we could count on a brisk wind at the end of October shaking down every last leaf and leaving us with the bare branches of November. Yet despite last October’s heavy snowstorm, most of our red, black, white, chestnut and scarlet oaks held on to the majority of their leaves until the third week of November.

Remembering the previous year’s mid-October snowstorm that brought down so many trees and branches overburdened with leaves and snow, I was apprehensive when I woke to snow on October 29. As the snow piled up on leaves and branches, I walked down our road, dreading to hear the sound of breaking branches, but I heard only a few. Once I picked up an oak branch, its leaves heavy with snow, and marveled at its weight.

Later in the day, the thermometer slowly rose to 34 degrees. The trees dripped even as it continued snowing, but the warmth saved most of our leafy trees. The one casualty I found was a large, live, black oak along our road. But it was hollow throughout much of its trunk length and would have come down soon in any case.

bottom of the First Field in an October snowstorm

bottom of the First Field in an October snowstorm

By November most of the snow had melted, and we finally had a couple weeks of what is normally “October’s bright, blue weather” and dazzling leaf color after a mostly soggy October. The sugar maples along the Far Field Road were still a blaze of red and gold. The coppery gold of American beeches lit up the hollow. And from Alan’s Bench, I gazed at the oaks of Laurel Ridge, which glowed reddish-gold and burnt orange.

Although I saw an occasional buck during my walks, squirrels, chipmunks, and turkeys were scarce. What few acorns the oaks had produced had been plucked from their branches by blue jays weeks before. I also saw little evidence of hickory nuts. Even our black walnut yard trees hadn’t produced many nuts. After the previous year’s feast, the wildlife was faced with famine. As soon as I put my bird feeders up, in early November, they were mobbed by gray squirrels and chipmunks.

The birds were not as affected even though our wild grape crop had also failed. Berry eaters, such as robins, cedar waxwings, and bluebirds still called most warm days. Carolina wrens caroled back and forth in our yard. The female tapping cardinal returned to our stairwell window. Winter wrens called and bounced up and down beside the stream. Golden-crowned kinglets foraged in the spruce grove. And, in Margaret’s Woods one day, I found dozens of singing, foraging white-throated sparrows, several dark-eyed juncos, a Carolina wren, and at least one fox sparrow in a large hedge of multiflora rose covered with bright red rose hips.

Raptors, too, were plentiful. A male American kestrel sat on his favorite power pole overlooking our First Field. On a hazy warm day in late November a male northern harrier flew silently past me as I sat on Coyote Bench. Driving down our hollow road, I flushed a sharp-shinned hawk. And on Thanksgiving Day our son Steve and his wife Pam watched a barred owl swoop down on a tree branch beside the Far Field Road. Steve also saw a golden eagle migrating along Sapsucker Ridge that day.

Hermit Thrush in Prospect Park, Brooklyn, November 9, 2011

Hermit Thrush in Prospect Park, Brooklyn, November 9, 2011 (photo by Christopher Eliot, Creative Commons Attribution-Noncommercial licence)

But I had the most unexpected sighting of Thanksgiving. As I circled the Far Field on Pennyroyal Trail, I flushed a hermit thrush. Never had I seen one so late in the season. When I checked McWilliams’s and Brauning’s The Birds of Pennsylvania, it reinforced my belief that hermit thrush migration peaks during October, which is when we usually see them. By the second week in November most hermit thrushes have moved south. A few winter over at low elevations in Pennsylvania, particularly in the Piedmont area. But more surprising than my sighting occurred three days later, on a warm November 27, when our son Dave heard a singing hermit thrush on Laurel Ridge. Since we rarely hear one singing here during spring migration, we were especially surprised to hear one so late in the autumn.

Whether it was the acorn failure or merely the lure of our birdseed, we had many excellent views of southern flying squirrels at our feeder area. Because it was still warm and some bears were no doubt still about, I brought in my feeders every night throughout November and December. On Thanksgiving evening I turned on the back porch light before going out to retrieve the feeders. A flying squirrel was busily scarfing up seeds on the porch floor. So intent was it that my husband Bruce was able to take several photos of the creature through the storm door. It only fled down the steps when I went out to get the feeders.

My next sighting was the first of December when I watched one flying squirrel chase off another on the birdseed-covered ground below the back step. The victor continued eating, even burying most of its body beneath the grass and seeds in its quest for food.

A full moon illuminated the sky on the tenth of December when Bruce startled a flying squirrel on the back porch. It zipped up the porch railing and sailed over near the juniper tree where it made a rough landing and disappeared down slope. The next evening I surprised the flying squirrel on the back porch steps, and it performed the same maneuver as it had for Bruce the previous night.

flying squirrel on a black locust tree in Plummer's Hollow

flying squirrel on a black locust tree in Plummer’s Hollow

We saw at least one flying squirrel at our feeder area throughout December, and we thought it was only fair that we should feed flying squirrels at night since we hosted at least 11 gray squirrels by day.

Whether or not the flying squirrels were affected by the unusual warmth, at least one woodchuck was. Below the back porch a fat male woodchuck continued to emerge from his hole every afternoon to eat the fresh greenery on the slope into December. The last time I saw him was mid afternoon on December 22, again a record breaker here for a woodchuck. Usually, they are tucked into their hibernation dens by mid-November and we don’t see any until the following February when the males are busy visiting female dens.

Plants also responded to the continual warmth. Several so-called green immigrant flowers, those that came from over seas, bloomed later than I could remember. On November 27 I found a pearly everlasting (Anaphalis margaritacea) blooming beside Alan’s Bench. A member of the Composite family, it was once dried and used in making memorial wreaths and for decorating vases and wall brackets. Today it still appears in dried flower arrangements. Its small, white, globular-shaped flowers grow in clusters atop a cottony stem with thin, toothless leaves that are sage-green above and woolly-white beneath. Other names for it are silverleaf, cottonweed, lady-never-fade, Indian posy and ladies’-tobacco. Since it came from Europe, Indian posy seems inappropriate and I doubt whether ladies smoked it. But they did use it for coughs and as a poultice for bruises in pioneer days. Its latest blooming month, according to Rhoads’s and Block’s The Plants of Pennsylvania, is October, which was why I was amazed to find it flowering in late November.

On that same day several forsythia flowers blossomed on a scattering of branches. Forsythia originated in South China where it grew wild. The Chinese called it golden bell. Robert Fortune, a young Scot, was sent into China to collect new plants for the Royal Horticultural Society of London in 1845, three years after the Opium War, when westerners were resented and mistrusted. So Fortune, disguised as a Chinese man, dressed in native garb and wearing a pigtail, explored the South China coast with a crew of Chinese workmen in springtime. There he found the countryside filled with forsythia. Although he later named it for the second curator of London’s Chelsea Gardens—William Forsyth—who was also a Scot, golden bell is a more evocative name that was quickly forgotten.

Dandelions also thrived in our driveway and during this longest autumn, I found a dandelion blooming on Butterfly Loop on December 5. It too came over with the colonists who used it as a cleansing herb and pot herb. It probably originated in Asia Minor long before anyone thought to notice it because both the Greeks and the Romans cultivated it. The Chinese called it earth nail and used its long taproot and green leaves for food and medicine while in Japan it was grown as a decorative plant. In Britain, the Celts used it for both food and wine and the Anglo-Saxon tribes that settled in the British Isles after the Romans left valued it as cure for scurvy and as a laxative and diuretic. Here in Pennsylvania, the Germans grew dandelion in their gardens and even today the Amish value and use the plant in early spring. Years ago, I too harvested the leaves every spring and served them with an Amish bacon dressing that I devised.

dandelion seedhead

dandelion seedhead

As the warm weather persisted, so too did Lyme disease ticks and I continued to pick them off my pants throughout December. Even on December 15 it was 54 degrees late in the day.

It rained on the winter solstice and the following day. But it was back to Indian summer the next two days before winter weather finally settled in, at least for a short time. What changes I have seen during my 41 years here on our central Pennsylvania mountaintop. Never in my wildest dreams could I have imagined, back in the 1970s, when autumn began at the beginning of September and ended at the end of November that the seasons would shift and autumn would become the longest season of the year.