University of Pittsburgh
OP-10: Biodiversity

The original research site for the University of Pittsburgh's Pymatuning Laboratory of Ecology since 1949 is situated on Sanctuary Lake, a protected waterway. It as well as the associated researcher housing site are on the shores of Pymatuning Lake and are completely surrounded by Pymatuning State Park. The Pymatuning Lab also manages Tryon-Webber Woods, an old growth forest owned by the Western Pennsylvania Conservancy.

The impact of deer on relationships between tree growth and mortality in an old-growth beech-maple forest
Zachary T. Long *, Thomas H. Pendergast IV, Walter P. Carson

White-tailed deer have been at high levels in the northeastern forests of the United States for decades and have strongly influenced forest dynamics. In this long-term study, we found that the composition of the overstory and understory assemblages of an old-growth beech-maple forest differed significantly. We used exclosures to test the hypothesis that deer contributed to these differences by differentially influencing the
relationship between growth and mortality among seedlings of the six most abundant tree species. In the absence of deer, we found that the mortality of the six species decreased with increased growth and that interspecific differences in the relationships between growth and mortality coincided with previously observed shade-tolerance rankings. In the presence of deer, mortality decreased with growth only for the browse tolerant species (American beech, black cherry, and sugar maple). Mortality did not decrease with growth for preferred browse species (oak species, ash species, and red maple), rather, this relationship was eliminated in the presence of deer. The changes in growth and mortality relationships in the presence of browsing generally corresponded to observed changes in seedling density following the removal of deer. Sugar maple, ash, black cherry, and total stem density increased in the absence of deer. Our results suggest that the relationship between survival and growth in the understory, a metric of shade tolerance, is a fairly plastic response that varies depending upon the presence and absence of herbivores. Our results indicate that deer have contributed to the differences between understory and overstory vegetation, with browse tolerant species increasing in abundance at the expense of preferred browse species.

The legacy of deer overabundance: long-term delays in herbaceous understory recovery
Thomas H. Pendergast IV, Shane M. Hanlon, Zachary M. Long, Alejandro A. Royo, and Walter P. Carson

Decades of white-tailed deer (Odocoileus virginianus (Zimmermann, 1780)) overpopulation have dramatically homogenized forests across much of the eastern United States, creating depauperate forest understory communities. The rate at which
these communities recover once deer browsing has been reduced remains an open question. We evaluate overbrowsing legacy effects by examining how forest herbaceous layers respond in terms of biodiversity, density, and community composition over
11 years using exclosures and control plots within a mature beech–maple forest. Although little recovery occurred in the first 5 years, total density and preferred browse density rebounded substantially during the final years of the study. Although
community composition began to diverge between exclosure and control plots after 5 years, diversity failed to recover even after 11 years of excluding browsers. Our findings show that vulnerable species can increase after excluding browsers but only if those
species were initially present. Biodiversity recovery may be extremely slow because preferred browse species have been nearly extirpated from many forests and thus are unable to recruit into refugia. We empirically demonstrate the extent of the ghost of
herbivory past or legacy effect of browsing, i.e., the substantial time delay between herbivore abatement and community response after decades of high deer densities.

Tryon-Weber Woods Species List

Common Name Scientific name
Multiflora rose Rosa multiflora
American hophornbeam Ostrya virginiana
Apple Malus sp.
Arrowhead viola Viola hastata
Black cohosh Actaea racemosa
Ash Fraxinus sp.
American beech Fagus americana
Perfoliated bellwort Uvularia perfoliata
Blueberry Vaccinium sp.
Black birch Betula lenta
Black cherry Prunus serotina
Blackgum Nyssa sylvatica
Buttercup Ranunculus sp.
American cancer-root Conopholis americana
Cherry Prunus sp.
Christmas fern Polystichum acrostichoides
Cinnamon fern Osmunda cinnamomea
Cleaver Galium sp.
Clubmoss Huperzia lucidula
Gooseberry Ribes sp.
Flowering dogwood Cornus florida
American elm Ulmus americana
False Solomon's seal Maianthemum racemosum
Garlic mustard Alliaria petiolata
Grapevine Vitis sp.
Grass Poaceae
Hawthorne Crataegus sp.
Hay-scented fern Dennstaedtia punctilobula
Hickory Carya sp.
Jewelweed Impatiens capensis
Jack-in-the-pulpit Arisaema triphyllum
Japanese barberry Barberis thunbergii
Common clubmoss Lycopodium clavatum
Mapleleaf viburnum Viburnum acerifolium
Mayapple Podophyllum peltatum
Canada maylilly Maianthemum canadense
Cucumber magnolia Magnolia acuminata
New York fern Thelypteris noveboracensis
Devil's walkingstick Aralia spinosa
Partridgeberry Mitchella repens
Poplar Populus sp.
Broad-leaved plantain Plantago rugelii
Poison ivy Toxicodendron radicans
Red maple Acer rubrum
Red oak Quercus rubra
Raspberry Rubus sp.
Sassafras Sassafras albidum
Sedge Cyperaceae
Sensitive fern Onoclea sensibilis
Serviceberry Amelanchier sp.
Sessile bellwort Uvularia sessilifolia
Solomon's seal Polygonatum pubescens
Spicebush Lindera benzoin
Sugar maple Acer saccharum
Trillium (at least 3 species) Trillium spp.
Tulip poplar Liriodendron tulipifera
Canada white violet Viola canadensis
Roundleaf yellow violet Viola rotundifolia
Common blue violet Viola sororia
Virginia creeper Parthenocissus quinquefolia
White oak Quercus alba
American witch hazel Hamamelis virginiana
Wood fern Dryopteris sp.
Fourleaved yam Dioscorea quaternata

Eastern Newt Notophthalmys viridescens
Northern Dusky Salamander Desmognathus fuscus
Mountain Dusky Salamander Desmognathus ochrophaeum
Northern Two Lined Salamander Eurycea bislaneata
Redback Salamander Plethodon cinereus
Slimy Salamander Plethodon glutinosis
Northern Red Salamander Pseudotriton ruber
Wood Frog Lithobates sylvaticus
Spring peeper Pseudacris crucifer
Green frog Lithobates clamitans
Eastern American Toad Anaxyrus americanus
Four-toed Salamander Hemidactylium scutatum
Spring Salamander Gyrinophilus porphyriticus
Spotted Salamander Ambystoma maculatum
Fowler's Toad Anaxyrus fowleri
Gray Treefrog Dryophytes versicolor

Wood Duck Aix sponsa
Wild Turkey Meleagris gallopavo
Turkey Vulture Cathartes aura
Red-tailed Hawk Buteo jamaicensis
Red-shouldered Hawk Buteo lineatus
Mourning Dove Zenaida macroura
Yellow-billed Cuckoo Coccyzus americanus
Black-billed Cuckoo Coccyzus erythropthalmus
Eastern Screech-Owl Megascops asio
Great Horned Owl Bubo virginianus
Barred Owl Strix varia
Chimney Swift Chaetura pelagica
Ruby-throated Hummingbird Archilocus colubris
Red-bellied Woodpecker Melanerpes carolinus
Downy Woodpecker Picoides pubescens
Hairy Woodpecker Picoides villosus
Northern Flicker Colaptes auratus
Pileated Woodpecker Dryocopus pileatus
Eastern Wood-Pewee Contopus virens
Acadian Flycatcher Empidonax virescens
Eastern Phoebe Sayornis phoebe
Great Crested Flycatcher Myiarchus crinitus
Blue-headed Vireo Vireo solitarius
Red-eyed Vireo Vireo olivaceus
Blue Jay Cyanocitta cristata
American Crow Corvus brachyrhynchos
Black-capped Chickadee Poecile atricapilla
Tufted Titmouse Baeolophus bicolor
White-breasted Nuthatch Sitta carolinensis
Brown Creeper Certhia americana
House Wren Troglodytes aedon
Blue-gray Gnatcatcher Polioptila caerulea
Wood Thrush Hylocichla mustelina
Veery Catharus fuscescens
Swainson’s Thrush Catharus ustulatus
American Robin Turdus migratorius
Gray Catbird Dumetella carolinensis
Brown Thrasher Toxostoma rufum
European Starling Sturnus vulgaris
Cedar Waxwing Bombycilla cedrorum
Ovenbird Seiurus aurocapillus
Louisiana Waterthrush Parkesia motacilla
Black-and-white Warbler Mniotilta varia
Blue-winged Warbler Vermivora pinus
Tennessee Warbler Oreothlypis peregrina
Nashville Warbler Oreothlypis ruficapilla
Hooded Warbler Setophaga citrina
American Redstart Setophaga ruticilla
Black-throated Blue Warbler Setophaga caerulescens
Magnolia Warbler Setophaga magnolia
Blackburnian Warbler Setophaga fusca
Yellow Warbler Setophaga petechia
Yellow-rumped Warbler Setophaga coronate
Chestnut-sided Warbler Setophaga pensylvanica
Black-throated Green Warbler Setophaga virens
Blackpoll Warbler Setophaga striata
Eastern Towhee Pipilo erythrophthalmus
Chipping Sparrow Spizella passerina
Song Sparrow Melospiza melodia
Northern Cardinal Cardinalis cardinalis
Scarlet Tanager Piranga olivacea
Rose-breasted Grosbeak Pheucticus ludovicianus
Indigo Bunting Passerina cyanea
Common Grackle Quiscalus quiscala
Red-winged Blackbird Agelaius phoeniceus
Brown-headed Cowbird Molothrus ater
Baltimore Oriole Icterus galbula
House Finch Carpodacus mexicanus
American Goldfinch Carduelis tristis
House Sparrow Passer domesticus

On April 19, 2017, the Western Pennsylvania Conservancy (WPC) announced the protection and addition of 18 acres of land in Sadsbury Township, Crawford County, to one of the most ecologically important forested areas in the region.

These acres are now part of the Conservancy’s Tryon-Weber Woods Natural Area, which is a remote 108-acre reserve that is open to the public for nature walking, exploring, and hunting. Students from the University of Pittsburgh’s Pymatuning Laboratory of Ecology have been using the natural area for years for a variety of research projects, including learning about the effects of deer browsing on forest health.

Protected in May 1976, the natural area consists primarily of upland forest and a small stream valley with hillsides flecked with trillium, violets, bellwort, and wild geranium in spring. A tributary to the stream enters from the east and along the southern border where there is an area of forested wetlands, including vernal pools that provide temporary habitat for some unique plants and animals.

The area also contains a 40-acre stand of old-growth American beech-sugar maple forest, thought to be the last remaining mature stand of beech-sugar maple in western Pennsylvania and the easternmost stand in the national range. Accordingly, these woods were recently incorporated into the national Old-Growth Forest Network, which recognizes the locations of and organizations from across the country that protect these special forest types. Some of the trees in this forest are around 100 feet tall and at least 90 to 120 years old.

Funds from the estate of Helen B. Katz were used to purchase this property. In 2008, the Conservancy received her bequest that remains the largest contribution to date from an individual to WPC.