What the numbers from all the studies tell us is that nature-shaped forests are far more diverse woodlands than those manipulated by humans. The complexity of old-growth environments may turn out to be their most important attribute in terms of being self-regulating autopoietic forest systems.
–Robert Leverett, “Old-Growth Forests of the Northeast,” in Wilderness Comes Home: Rewilding the Northeast, C.M. Klyza, ed., Middlebury College Press, 2001
A couple weeks ago, my mother gave a short walking tour to a couple of guests who were seeing our woods for the first time. “It looks like something out of the Lord of Rings!” they exclaimed. I guess if you’re used to looking at younger forests, the portions of Plummer’s Hollow that have avoided lumbering since the mid- to late-19th century might look pretty impressive by comparison. Our forest doesn’t yet meet even the most minimal definitions of old growth — for example, a median age of half of the dominant tree species’ maximum longevity in the majority of stands — but it does exceed by several decades the average age of private or public forests in Pennsylvania, and is beginning to acquire a number of standard old-growth characteristics that add up, perhaps, to a general impression of enchantment.
The older trees get, the more character they develop. And even apart from the age of its individual members (or at least their aboveground portions), a more mature forest is qualitatively different from a younger one. More and more species of lichens, fungi, insects and other key organisms form increasingly complex food webs. Though foresters are wont to think of old growth in terms of individual stands of large old trees, forest ecologists will tend to stress the age of the over-all forested landscape. The longer a forested landscape goes without being clearcut, or completely leveled by a catastophic disturbance such as a large tornado or a canopy-destroying fire, the more structural complexity it acquires. Icestorms, diseases, strong winds and insect invasions take their toll, while shade-tolerant tree species bide their time in the understory, waiting for a gap to open in the canopy.
Young forests tend to consist of trees of just two to three species, all about the same size, and with very few rotting logs or standing dead trees (snags). In the northeast United States, natural stand-clearing disturbances are quite rare, but the dominance of industrial forestry has made this kind of forest the norm, and more diverse forests like ours the exception. However, it would also be very unnatural for extensive sections of a Pennsylvania forest to resemble Mirkwood in The Hobbit, or Fangorn in The Lord of the Rings. In J.R.R. Tolkien’s imagination, an old forest seems to have consisted almost entirely of old trees, but in most places around the world, some kind of landscape-level patchiness would develop as various small-scale disturbances create openings of various sizes. The nature and frequency of these disturbances — what ecologists call the disturbance regime — is as important as climate, soil, and species mix in determining the character and compostion of the forest.
Our over-riding management goal for the wooded portions of the property — close to 600 acres — is to grow an old-growth forest. But what will future old-growth look like? Chances are it will not resemble the forests that covered Pennsylvania in 1600 to any significant degree. Several species of keystone ecological importance are extinct, such as the passenger pigeon; regionally extirpated, such as the cougar and the gray wolf; or reduced to a pitiful remnant by an introduced disease, such as the American chestnut. Like most upland forests in the Appalachians, our mountain was once covered by these tall, slow-growing, long-lived trees; now their sprouts (as in the above photo) are lucky to reach 30 feet before succumbing to the blight. The loss of their nut crop — more copious and far more dependable than acorns and hickories — must’ve had a huge impact on many species of wildlife.
And that’s just one example. Many other native tree species are falling victim to introduced diseases and insect pests, including dogwood, eastern hemlock, butternut, American beech, and various species of ash. The composition of the shrub and forest herb layers are changing dramatically as new, exotic plant species move in. The soil itself has been fundamentally altered in many if not most parts of Penn’s Woods, first by massive erosion following the wholesale clearcutting of the 19th and early 20th centuries, and then by acid deposition and, most significantly of all perhaps, the introduction of non-native earthworms.
I’m increasingly reluctant to dwell on these issues with first-time vistors to Plummer’s Hollow, though, just as I haven’t blogged about them very much. I think it’s better to let people be inspired by a vision of something special and enchanted, even if that vision might seem a little naí¯ve, than to try and give them a crash course in unpleasant environmental realities. I do tend to stress the impact of white-tailed deer, because that’s something we have at least a chance of ameliorating, and our 15-year-old deer hunter program in Plummer’s Hollow is beginning to show some dramatic and positive results.
Why manage for old growth? A survey of available literature suggests that, while every forest is different, generally speaking, large tracts of old-growth forest in Pennsylvania should be unexcelled providers of:
- Breeding habitat for a wide range of birds whose populations reach their greatest density in old growth, including winter wren, Acadian flycatcher, black-throated green warbler, Blackburnian warbler, magnolia warbler, Swainson’s thrush, brown creeper, and blue-headed vireo
- Habitat for embattled native fish and other organisms endemic to forested, cold-water environments, including the prized brook trout as well as a number of state threatened and endangered species
- Habitat for the federally endangered Delmarva fox squirrel (now absent from PA), and possibly optimal conditions (especially with the spatial patchiness characteristic of old growth) for two other endangered species–small whorled pogonia and Indiana bat–and cerulean warbler, a candidate for listing as threatened on the federal Endangered Species List
- Excellent, perhaps optimal habitat for species in danger of extirpation or facing steep declines in Pennsylvania such as northern flying squirrel, green salamander, sugar maple longhorn beetle, yellow-bellied flycatcher, and eastern woodrat
- Optimal habitat for many sensitive, slow-dispersing wildflowers that may require over 150 years to fully recover from the effects of clearcutting
- Optimal habitat for top carnivores such as northern goshawk, barred owl and (arguably) fisher, plus some presently absent or of uncertain occurrence in Pennsylvania: pine marten, gray or red wolf, eastern cougar, and lynx
- Optimal conditions for salamanders (top carnivores and likely keystone species in the forest litter) and essential refuges for these logging-sensitive organisms
- Optimal conditions for some forest-dwelling bats such as eastern red, big brown, silver-haired and hoary bats
- A full complement of native ferns, mosses and liverworts
- A full complement of native forest lichens
- A full complement of fungi, including mycorrhizae and other soil microorganisms essential for forest health, nutrient uptake by trees, and recovery after a disturbance
Structural diversity, including pit-mound microtopography, nurse logs for tree seedlings, habitat and runways for small mammals and herps, and standing snags
- Superior masting by many trees, such as white oak, red oak and American beech
- A full complement of native forest insects and other arthropods
- Functional and genetic resistance to insect pests
- Functional and genetic resistance to disease
- Formation of unique biogroups of trees–interspecific communities with distinct physical and physiological traits–through root grafting and and the formation of fungal bridges (shades of Tolkien!)
- Seed banks with a full range of genetic variables for commercially desirable tree species
- Timber of unparalleled quality
- Baselines for scientific research, including on strategies for successful recruitment and stand replacement
- A full range of natural soundscapes
- A source of aesthetic and spiritual values unattainable elsewhere
- The creation of optimal forest soils through accumulation of humus in the O and A horizons, periodic mixing of horizons by uprooting, and the formation of macropores
- Groundwater purification and storage (old trees use less water for growth)
- Flood control through maximal absorptive capabilities and stream bank stabilization
- A dependable source of coarse, woody debris essential to the ecological functioning of streams in forested ecosystems
- Clean rivers, bays and oceans though maximal prevention of siltation
- Drought prevention through transpiration to the atmosphere
- Sequestration of carbon dioxide
- Amelioration of local, regional, and global warming
For more on Pennsylvania old growth, see here.