Source: Joel McNeal
This plant, Aquilegia canadensis L. (wild columbine), is included in the floristic survey conducted by Daniel Laughlin, Penn State graduate student in ecology.


The Arboretum at Penn State
Special Publication No. 1

Floristic Inventory of The Arboretum at Penn State
Daniel Laughlin
July 2001

Introduction

The objective of this study was to conduct a floristic inventory of The Arboretum at Penn State. The mission of the Arboretum is "to promote the quality of human life by seeking, through scholarship, research, and education, collaborative solutions to growing demands on the natural landscape and its resources." One of the first steps in accomplishing this goal is to fully assess the land on which the future Arboretum is to take root and become familiar with its biological richness so that our activities will not compromise "the quality of human life" or "the natural landscape and its resources."

Since one of the goals of the Arboretum is to preserve native plant communities and develop heavily used public areas, it is of utmost importance to inventory the existing flora and to identify particularly unique and sensitive areas. Many native plants require specialized environments for their survival. Future management activities in the Arboretum may either enhance or degrade these environments and will affect the survivorships of high quality native species. This study will not only be valuable as a benchmark by which the effects of Arboretum development can be monitored, its information will also be important for decisions about Arboretum development in the near future.

Methods

For the purpose of this study, the Arboretum was divided into eleven sections that represented plant community or land use categories as shown in the aerial photograph in Figure 1. This partitioning was important to facilitate the documentation of where each species was found so they may be located at a later date. The names of the sections were created to correspond to either their current status (i.e., Oak Forest) or their future status (i.e., Flower Gardens) in the Arboretum. Brief descriptions of the sections are provided in Table 1.

Comprehensive inventories of each section were conducted from June 1, 2000 through May 31, 2001. The large and diverse oak and conifer forests demanded more effort than the species-poor pastures and agricultural fields. These forests were visited once every 2-3 weeks throughout the summer and fall of 2000 and 5 times in May 2001. The pastures and agricultural fields were visited once a month throughout the summer and fall of 2000 and twice in May 2001. Preliminary surveying in each section was concentrated near human and animal trails to identify the most common species. More detailed investigative searching was conducted in more isolated areas after the preliminary surveys yielded few new species. The sections were explored using zigzag transects with a visual scanning radius of ~5 meters in each direction. Each section was thoroughly searched until new species were no longer discovered.

One or two specimens were collected of every species found in the Arboretum, except for uncommon species represented by only a few individuals (e.g, Platanthera orbiculata, the large round-leaved orchid). All specimens were pressed, dried, and identified to species or stored as unknowns. Specimens were then mounted on herbarium sheets, labeled, and stored in the Herbarium of The Pennsylvania State University (PAC). The labels include a map of the Arboretum and a dot signifying where the specimen was collected (see Figure 2). Species were also categorized according to their relative abundances in each section of the Arboretum. Descriptions of the relative abundance rankings are listed in Table 2.

Table 1.
Descriptions of the section designations in The Arboretum at Penn State used for this study. Section titles reflect either their current or future status.
 
Section Title and description
A Agricultural Fields. Severely disturbed areas dominated by exotic, weedy plant species. Constitutes a considerable portion of the total area of the Arboretum
B Barrens. Future site of the restored pine barrens. Currently used as pasture. Heavily grazed and dominated by exotic species.
C Conifer Forest. Diverse, upland, acidic woods that contains seven conifer species and a rich herbaceous flora.
F Flower Gardens. Future site of the flower gardens. Currently used as a hay field and dominated by exotic plants.
G Grassland. Future site of restored native grassland. Currently used as hay fields and dominated by exotic plants.
H Horse Paddocks. A mixture of old fields, horse paddocks, and a cornfield. Dominated by exotic plants.
M Mesophytic Forest. Small patch of forest along Big Hollow Road.
O Oak Forest. Mature and diverse upland forest with a white oak canopy, a red maple understory, and a rich herbaceous flora.
P1 Red Pine Plantation. Large stand of red and white pines with surprisingly diverse mixture of native herbs in the understory.
P2 Scotch Pine Plantation. Young stand of Scotch pine and associated landscape.
R Railroad Bed. Historic Bellefonte Central Railroad bed. Currently maintained by frequent bikers and runners.

Figure 1.
The Arboretum at Penn State and the eleven sections used for this inventory. A - Agricultural Fields, B - Barrens, C - Conifer Forest, F - Flower Gardens, G - Grassland, H - Horse Paddocks, M - Mesophytic Forest, O - Oak Forest, P1 - Red Pine Plantation, P2 - Scotch Pine Plantation, R - Railroad Bed. 

Figure 2.
Example of the herbarium sheet labels designed for the voucher specimens found in the Arboretum. Quercus alba, white oak, is the signature tree species of the oak forest. The map represents the outline of the perimeter of the Arboretum and the dot signifies where the specimen was collected. 

Table 2.
Qualitative species abundance rankings used in Appendix 1 (html, pdf).
 
Number Description
1 One to few individuals in entire section
2 Patchy distribution throughout the section
3 Frequent throughout the section
4 Very abundant to ubiquitous throughout the section

In order to quantitatively assess the floristic quality of a natural area I adopted a method developed by Wilhelm and Ladd (1988). Each species found in the Arboretum was assigned a coefficient of conservatism found in Andreas and Lichvar's (1995) floristic index for northern Ohio. A coefficient of conservatism is a numerical quality rating from 0 to 10. Weedy species that are adapted to human disturbances like roadsides and old fields are assigned low values and conservative species that only grow in mature forests (or other high quality natural areas) are assigned high values. For example, heath aster (Aster pilosus), a weedy native species found abundantly in old fields, has been assigned a coefficient of 1, whereas spikenard (Aralia racemosa), which is only found in rich woods, is assigned a coefficient of 8. According to Andreas and Lichvar (1995), "The natural quality of an area is reflected by its richness in conservative species." All non-native taxa are assigned zeros and a few species in the present study did not receive a coefficient because they are not listed by Andreas and Lichvar. Because Andreas and Lichvar's list is most applicable to "31 counties in northern Ohio", and because "the numerical values included in [their] report become less valid outside [their] study area", caution is warranted to not take the quantitative results presented here too seriously. However, since most species involved have similar autecological requirements in both Ohio and Pennsylvania (e.g., heath aster is found most abundantly in disturbed old fields in both states) and since no index has been developed in Pennsylvania or other nearby states, my results are useful indications of which sections in the Arboretum have the highest floristic value.

The floristic quality assessment index (FQI) was calculated for each section in the Arboretum by dividing the sum of the coefficients of all plants in each section by the square root of the number of native species found in each section. See Wilhelm and Ladd (1988) and Andreas and Lichvar (1995) for a discussion about the methods of assigning coefficients and the calculation of the FQI.

Historical information about the occurrence of rare plant species in the Arboretum has kindly been provided by the Pennsylvania Natural Diversity Inventory (PNDI). Nomenclature follows Rhoads and Block (2000) in all cases except for the fern families. Gleason and Cronquist's (1991) fern family systematics were adopted, but fern genera and species epithets follow Rhoads and Block (2000).

Results

The 395-acre Arboretum is a pastoral landscape with a mixture of upland forests, rock outcrops, horse and cattle pastures, hayfields, old fields, hedgerows, and cornfields. No streams or wetlands are found within the Arboretum. A few fields contain drainage depressions that are seasonally moist, but no native wetland plants reside in them. Regardless, the diversity of habitats within the Arboretum begets a rich flora.

A total of 410 plant species representing 77 families were documented as occurring in The Arboretum at Penn State, and 402 taxa were identified to species. A list of the species organized by family is included in Appendix 1 (html, pdf). All species in bold print are not native (exotic) to Pennsylvania. An exotic species is defined as a plant from another part of the world that arrived in Pennsylvania "since the period of earliest European settlement" (Rhoads and Block 2000). The coefficient of conservatism (CC) for each species is listed in the column following the common name and the relative abundances of each species in each section in the Arboretum are also included. Wetland codes developed by the U. S. Fish and Wildlife Service are listed according to Rhoads and Block (2000) and are described in Table 3. Unfortunately, not every plant has yet been assigned a wetland code. Finally, the habit (growth form) of each species is recorded and these codes are described and tallied in Table 4.

Table 3.
Description of the U.S. Fish and Wildlife Service wetland codes used in Appendix 1 (html, pdf) (from Rhoads and Block (2000)).
 
Wetland code Description Probability of occurring in wetlands under natural conditions
OBL obligate wetland species 99%
FACW facultative wetland species 67-98%
FAC facultative species 34-66%
FACU facultative upland species 1-33%
UPL upland species 1%

Table 4.
Description of plant habits used in Appendix 1 (html, pdf) and total number of species of each kind found in The Arboretum at Penn State.
 
Code Total Description
W-TREE 50 Woody plant that is large and arboreal when mature
W-SHRUB 43 Woody plant the size of a shrub when mature
W-VINE 8 Woody plant that trails through and climbs up other vegetation
H-VINE 4 Herbaceous plant that trails and winds through other plants
A-HERB 52 Annual herbaceous plant that germinates, produces seed and dies in one year
B-HERB 21 Biennial herbaceous plant that forms a rosette the first year and produces fruit the second year
P-HERB 166 Perennial herbaceous plant with underground perennating structures that allow it to live for many years
A-GRS 11 Annual grass (Poaceae)
P-GRS 26 Perennial grass (Poaceae)
P-SDG 15 Perennial sedge (Cyperaceae)
P-FERN 14 Non-flowering, spore producing perennial ferns

The total ratio of native to exotic (N:E) species in the Arboretum is 1.68 (Figure 3 and Table 5). This ratio corresponds well with Pennsylvania's overall ratio of 1.67 (2076:1242) (Rhoads and Klein 1993). Therefore, the Arboretum as a whole represents the regional flora rather well in this respect. Within individual sections, the Conifer (C) and Oak (O) Forests have the highest ratios of native to exotic plant species (>2.5). Five sections, Barrens (B), Agricultural Fields (A), Horse Paddocks (H), the future site of the Flower Gardens (F), and the Grassland (G), all have native to exotic ratios that are less than 1.0. Figure 3 illustrates a general decline in species richness as the native to exotic species ratio declines.

Figure 3.
Total numbers of native and exotic plant species in each section of The Arboretum at Penn State. Sections are ordered from highest to lowest ratios of native to exotic species. 

The floristic quality assessment index was calculated for each section. Not surprisingly, the Oak (O) and Conifer (C) Forests have the highest FQI's, and the Mesophytic Forest (M) and the Red Pine Plantation (P1) have the third and fourth largest FQI's (Table 5). An FQI for the entire Arboretum is not reported because the FQI is most appropriately applied to individual habitats rather than an entire landscape with a mosaic of plant communities (Wilhelm and Ladd 1988).

Botanists have studied this landscape for many decades. Their collections have left valuable records of plants that still persist on the site and a few that have been extirpated. Four rare plants have been documented here in the past but were not found in the present study. Hairy rockcress (Arabis hirsuta [L.] Scop.) was last collected in 1943, Sprengel's sedge (Carex sprengelii Spreng.) was last collected in 1930, Indian paintbrush (Castilleja coccinea [L.] Spreng.) was last collected in 1921, and rigid goldenrod (Solidago rigida L.) was last collected in 1943. These plants are now listed in Pennsylvania as either endangered, threatened, or of special concern. The exact locations in which these collections were made are unknown. However, according to habitat preferences it is likely that hairy rockcress and Sprengel's sedge occurred near the limestone outcrops in the Oak Forest. Rigid goldenrod and Indian paintbrush likely occurred either near the Railroad Bed or on the southwestern edge of the Conifer Forest where other common plant associates like whorled rosinweed (Silphium trifoliatum), nodding onion (Allium cernuum), and northeastern beard-tongue (Penstemon hirsutus) still persist.

Table 5.
Floristic quality assessment indexes and native to exotic species ratios for the entire Arboretum and its individual sections. The sections are listed in order of decreasing FQI.
 
Section FQI Native to Exotic Ratio
Entire Arboretum n/a 1.68
Oak Forest 51 2.65
Conifer Forest 46 2.53
Mesophytic Forest 30 1.60
Red Pine Plantation 30 1.77
Railroad Bed 24 1.55
Barrens 22 0.74
Scotch Pine Plantation 21 1.13
Agricultural Fields 19 0.68
Horse Paddocks 15 0.58
Grassland 11 0.33
Flower Gardens 7 0.40

The Sections of the Arboretum

Agricultural Fields.
FQI = 19; N:E = 0.68.
These open areas take up almost a third of the area in the Arboretum. Most of these fields are still under cultivation for hay, but some have been left fallow. Four categories of fields exist: grass hay fields, alfalfa fields, corn fields, and old fields (i.e., no longer in use). The old fields harbor the greatest diversity of plants, yet all the fields are dominated by weedy exotics. The pasture grass fields are filled with orchard grass (Dactylis glomerata), fescue (Festuca elatior), timothy (Phleum pratense), and smooth brome (Bromus inermus). The alfalfa fields are dominated by alfalfa (Medicago sativa), giant foxtail (Setaria faberi), barnyard-grass (Echinochloa crusgalli), barley (Hordeum vulgare), and oats (Avena sativa). The old fields are dominated by horseweed (Conyza canadensis), daisy fleabane (Erigeron annuus), curly dock (Rumex crispus), pokeweed (Phytolacca americana), nightshade (Solanum dulcamara), Queen Anne's-lace (Daucus carota), burdock (Arctium minus), oxeye daisy (Chrysanthemum leucanthemum), dandelion (Taraxacum officinale), and buttercup (Ranunculus acris). Wild black cherry (Prunus serotina) and multiflora rose (Rosa multiflora) are common in the hedgerows that divide these fields. The soils in this section are Hagerstown silt loams (Braker 1981).

Barrens.
FQI = 22; N:E = 0.74.
This section is the future site of restored barrens community and was used as a horse pasture during the time of this study. The grazed fields are dominated by weedy exotics. A seasonally wet area is characterized by creeping buttercup (Ranunculus repens), common teasel (Dipsacus sylvestris), and stinging nettles (Urtica dioica). A few mature apple (Malus pumila) and crabapple (Malus prunifolia) trees also grow on this site. A large dead snag stands out in this section and is used as a perch for many birds. A large borrow pit has been excavated for use as fill elsewhere on campus. The soils in this section are mostly Morrison sandy loams (Braker 1981).

Conifer Forest.
FQI = 46; N:E = 2.53.
This forest, situated on a hill, supports the richest assemblage of native plants in the Arboretum, totaling 129 species. The north and east slopes comprise a mature red pine (Pinus resinosa) plantation, though white pine (Pinus strobus) saplings tend to dominate the understory. Mature white pines cover most of the southern slope. A grove of hemlocks (perhaps planted?) graces the summit of the hill and beneath the trees lies a well-used fire pit. Three species of native orchids inhabit this forest: large round-leaved orchid, pink lady's slipper (Cypripedium acaule), and downy rattlesnake plantain (Goodyera pubescens). These three gems are found nowhere else in the Arboretum. Other notable natives include spikenard, aniseroot (Osmorhiza longistylis), yellow-pimpernel (Taenidia integerrima), Joe-Pye-weed (Eupatorium purpureum), whorled rosinweed, field thistle, northeastern beardtongue (Penstemon hirsutus), devil's-bit (Chamaelirium luteum), starry campion (Silene stellata), wild bergamot (Monarda fistulosa), flat-branched ground-pine (Lycopodium obscurum), pipsissewa (Chimaphila umbellata), doll's eyes (Actaea pachypoda), wild columbine (Aquiligia canadensis), hepatica (Hepatica nobilis), early meadow-rue (Thalictrum dioicum), wood anemone (Anemone quinquefolia), and New Jersey-tea (Ceanothus americana). This forest supports seven species of ferns, including sensitive fern (Onoclea sensibilis), ebony spleenwort (Asplenium platyneuron), and purple cliffbrake (Pellaea atropurpurea), and eleven sedges in the genus Carex. The soils in this forest are a combination of Morrison very stony sandy loam and Morrison sandy loam (Braker 1981).

Flower Gardens.
FQI = 7; N:E = 0.40.
This section is currently used as a hay field for pasture grass and a parking lot for football games. It is also a favorite place for local community residents to walk their dogs. Most of the plant diversity was found along the fences and road edges, but most of these plants were weedy exotics that were sprayed in the fall. Some species unique to this section are corn chamomile (Anthemis arvensis), black bindweed (Polygonum convolvulus), spreading orach (Atriplex patula), and clammy ground-cherry (Physalis heterophylla). Interestingly, a few individuals of boneset (Eupatorium perfoliatum), a common wetland plant, were found in a soil pit dug in this field by soil scientists. Boneset does not occur anywhere else in the Arboretum and the closest population is probably along Spring Creek. The soils in this section are Hagerstown silt loams (Braker 1981).

Grassland.
FQI = 11; N:E = 0.33.
The majority of this section is comprised of pasture grasses, shrubs, and small hedgerows. Part of this section runs through Big Hollow, which is widely used by local residents for walking, running, or biking. The Schreyer House (the residence of the University's president) is included in this section but I did not survey this property. The common pasture grasses include orchard grass, fescue, smooth brome, timothy, redtop (Agrostis gigantea), quack grass (Elytrigia repens), and Kentucky bluegrass (Poa pratensis). The common forbs include buttercup, common speedwell (Veronica officinalis), thistle (Carduus acanthoides), crown vetch (Coronilla varia), English plantain (Plantago lanceolata), butter-and-eggs (Linaria vulgaris), burdock, and multiflora rose. Historical documents and a small grassland remnant attest that an impressive prairie opening, known as the Great Plains, existed in Penn's Valley at the time of European settlement. The proposed scheme for this site is to replace the exotic pasture grasses with restored native grassland. The soils in this section are a mixture of Hagerstown silt loams, Nolin silt loams, Opequon-Hagerstown complex, and Opequon rock outcrop complex (Braker 1981).

Horse Paddocks.
FQI =15; N:E =0.58.
This section is comprised of old fields, a large hedgerow, a cultivated cornfield, and horse paddocks. I was unable to thoroughly survey inside the horse paddocks because they were fenced off. Though mostly comprised of weedy exotics, a peculiar stand of switchgrass (Panicum virgatum), a warm season prairie grass, was found on the edge of the cornfield. Switchgrass seeds were likely either stuck on a seed drill or tractor used to plant the corn or seeds blew in from a highway planting. It is highly unlikely that they were part of the native sod. Plants unique to this section are broom-sedge (Andropogon virginicus), common mugwort (Artemisia vulgaris), common cocklebur (Xanthium strumarium), mouse-ear cress (Arabidopsis thaliana), red-stem filaree (Erodium cicutarium), and jetbead (Rhodotypos scandens). The soils in this section are Nolin silt loams and Chagrin soils (Braker 1981).

Mesophytic Forest.
FQI = 30; N:E = 1.60.
Big Hollow Road passes through this section as it drops down into the hollow. Though designated as the future mesophytic forest, it is actually dominated by upland oaks and hickories with several wild black cherry trees. The only occurrence of witch-hazel (Hamamelis virginiana) in the entire Arboretum is found along the edge of the road. As one penetrates the shrubby forest edge and enters the center of the forest, tall oaks and hickories dominate the canopy and native plants such as silver-rod (Solidago bicolor), lowbush blueberry (Vaccinium pallidum), spotted wintergreen (Chimaphila maculata), Solomon's-seal (Polygonatum biflorum), field woodrush (Luzula multiflora) and a fairly uncommon sedge, Carex willdenovii, speckle the forest floor. The soils in this section are mostly Hagerstown silt loams and Opequon rock outcrop complex (Braker 1981).

Oak Forest.
FQI = 51; N:E = 2.65.
The upland oak forest community that is contiguous with Sunset Park is shaded by 170-year-old white oaks (Quercus alba), tall white pines, and pignut hickories (Carya glabra). Sugar maple (Acer saccharum) and the invasive Norway maple (Acer platanoides) are also common trees represented in roughly equal proportions. The forest understory is flooded with exotic shrubs such as Morrow's honeysuckle (Lonicera morrowii), privet (Ligustrum vulgare), and common buckthorn (Rhamnus cathartica) as well as exotic herbs such as garlic mustard (Alliaria petiolata) and lily-of-the-valley (Convallaria majalis). Despite the abundance of exotics, this oak forest claims the highest FQI and the highest native to exotic ratio in the Arboretum. High quality woodland herbs such as Canada lily (Lilium canadense), downy false foxglove (Aureolaria virginica), black cohosh (Cimicifuga racemosa), mountain Indian-physic (Porteranthus trifoliatus), bloodroot (Sanguinaria canadensis), smooth blue aster (Aster laevis), and bunchflower (Melanthium latifolium) persist in small and possibly shrinking populations. Interestingly, flat-topped white aster (Aster umbellatus) and culver's-root (Veronicastrum virginicum), two plants commonly associated with wet meadows and floodplains (Rhoads and Block 2000), harbor small populations on the dry slopes of this forest. An impressive limestone outcrop lies on the northwestern side of the forest where a different suite of high quality species resides. Herbs such as bishop's cap (Mitella diphylla), early saxifrage (Saxifraga virginiensis), and wild columbine (Aquilegia canadensis) and ferns such as northern maidenhair (Adiantum pedatum), fragile fern (Cystopteris fragilis), and walking fern (Asplenium rhizophyllum) thrive on this sheltered slope. The soils in the oak forest are mostly Opequon rock outcrop complex and some Opequon-Hagerstown complex (Braker 1981). The very rocky nature of this substrate is surely the reason this forest has persisted for so long without being cleared and turned over by the plow, as is the case with other small forest patches in the Arboretum.

Red Pine Plantation.
FQI = 30; N:E = 1.77.
At first glance, this pine plantation appears to be devoid of an herbaceous layer. However, upon closer inspection, this forest hosts a few species that are either uncommon or found nowhere else in the Arboretum. Lopseed (Phryma leptostachya) is found in abundance on this northwestern slope and doll's eyes and wild columbine are also frequent throughout. This section hosts the only occurrences of interrupted fern (Osmunda claytoniana) and common polypody (Polypodium virginiana) in the entire Arboretum. The soil on this slope is Opequon-Hagerstown rock outcrop complex (Braker 1981).

Scotch Pine Plantation.
FQI = 21; N:E = 1.13.
The majority of this section is dominated by a relatively young Scotch pine (Pinus sylvestris) plantation. The vegetation between the pine trees is dominated by pasture grass and other exotic forbs. Two young pitch pines (Pinus rigida) and one northern white-cedar (Thuja occidentalis) were found in this section. Norway spruce (Picea abies) is abundant throughout. The soil in this section is comprised of Morrison sandy loam (Braker 1981).

Railroad Bed.
FQI = 24; N:E = 1.55.
This section, currently an overgrown trail maintained by frequent bikers, was the former railroad bed for the Bellefonte Central Railroad. It is becoming overgrown with exotic shrubs and will require management to be maintained. Native species that can be found along the trail include wild black currents (Ribes americanum), thin-leaved sunflower (Helianthus decapetalus), pale jewelweed (Impatiens pallida), and thimbleweed (Anemone virginiana). Multiflora rose is abundant along the edge of the forest corridor. A notable grove of mature black cherry trees is adjacent to the railroad bed and is included in this section. Though isolated populations of mayapple (Podophyllum peltatum) were found in this forest patch, the entire understory is a virtually impenetrable swath of exotic shrubs, mostly privet, barberry, and honeysuckle. The southern portion of the railroad bed is composed of Nolin silt loams and the northern portion runs through the Morrison sandy loams (Braker 1981).

Discussion

The Arboretum at Penn State harbors a rich flora. Though the majority of the area is dominated by aggressive exotics, a few islands of high quality natural areas still exist within the sea of disturbed land. The Arboretum, when considered as a whole, has a large number of native plants. However, most of this floristic richness is found within two forest areas. The FQI for each section gives a clear indication of which sections have the highest natural quality and, therefore, which deserve the most careful stewardship.

Clearly, the Oak and Conifer Forests are the highest quality natural areas in the Arboretum, boasting FQIs around 50. Wilhelm and Ladd (1988) concluded that "areas ranking above 35 possess sufficient conservatism and richness to be of profound importance from a regional perspective. Areas rating in the 50s and above are extremely rare and of paramount importance." Both forests have unique environmental conditions that provide a foundation for two different community types. The Oak Forest is rooted in limestone-derived soil, whereas the Conifer Forest is situated on an acidic, sandy knoll. We are fortunate to have two rich yet strikingly different forest communities represented in the Arboretum.

Other small pockets of plant diversity can also be found in areas like the Mesophytic Forest (M) and Red Pine Plantation (P1), which have the third and fourth highest FQIs, respectively. Though small, these two sections harbor plants found nowhere else in the Arboretum and they could be enlarged and extended to provide a forest corridor between the oak and conifer forests.

The forests should be treated with extreme care and the only major activities within them should be the continued removal of invasive shrubs. Invasive plants are exotic species that display very aggressive growth and pose real threats to native plant community structure and ecosystem function. Species with asterisks (*) after their common names in Appendix 1 (html, pdf) are defined as invasive by the Pennsylvania Department of Conservation and Natural Resources (Gresham 2000). Invasive shrubs, such as privet and honeysuckle, shade out native herbs and out-compete native shrubs. They are rapidly converting once-open woodlands into impenetrable thickets. These shrubs should be removed and kept in check so that the herb layer can rejuvenate in response to the additional light, space, and water that would be available. Besides manual removal, one other promising method of removing exotic shrubs is the prescription of infrequent, low intensity fires. Pennsylvania forests are adapted to ground fires that free the understory from excessive shade. Both the herb layer and forest structure would likely benefit from controlled burns.

Not all exotic species disrupt native ecosystems. Many plants like yellow hawkweed (Hieracium caespitosum) and St. John's wort (Hypericum perforatum) have become naturalized and are not actively displacing the native flora. However, Figure 3 demonstrates that areas with high numbers of exotic species tend to be species-poor overall. The Arboretum will be most successful at restoring and recreating diverse plant communities native to central Pennsylvania if management strategies are implemented to reduce the number of exotic species.

This study has documented where native plant diversity is richest, but it is not meant to belittle the value of the land dominated by exotic species. Cultivated or pastured land within the Arboretum may be of low floristic value, but they maintain a value of a different sort. This bucolic landscape has been a nearby yet isolated source of inspiration and relaxation for generations of people who live in Happy Valley, and these green spaces are an increasingly rare commodity in the State College area. Open spaces and forest edges also provide important habitat for many bird species seen in the Arboretum, including brown thrashers, common yellowthroats, great horned owls, red-tailed hawks, and rufous-sided towhees.

The Arboretum mission statement declares that this landscape is and will be "a place of beauty in a rapidly expanding metropolitan area, an educational facility, and a microcosm of the human-nature continuum in settled landscapes," and "the Penn State Arboretum shall strive to become an interdisciplinary 'institute for land health' of state, regional, and perhaps national significance." The preservation of these 395 acres in the midst of a rapidly developing urban area will provide an essential refuge for native plants and animals and an essential green space for the local community.

Acknowledgements

This research has been funded by an assistantship through The Arboretum at Penn State. I thank Dr. Kim Steiner and Dr. Claude dePamphilis for granting me the opportunity to conduct this botanical survey. I am grateful to Joel McNeal, Dr. Carl Keener, Liane Beggs, Jared Woolsey, and Ben Chemel for their taxonomic assistance in the field and in the herbarium. I also thank Dr. Ann Rhoads and her colleagues from the University of Pennsylvania and the many fine botanists, including Jack Holt and Dr. James Macklin, who attended the Rare Plant Forum 2001 and helped identify unknown species. Finally, my gratitude extends to Dr. Christopher Uhl, Dr. Kenneth Tamminga, Dr. Kim Steiner, Dr. Carl Keener, and Joel McNeal for helpful discussions and reviews of early drafts of this manuscript.

Literature Cited

Andreas, B. K. and R. W. Lichvar. 1995. Floristic index for establishing assessment standards: a case study for northern Ohio. Technical Report WRP-DE-8, U.S. Army Corps of Engineers.

Braker, W. L. 1981. Soil survey of Centre County, Pennsylvania. USDA/ SCS (now NRCS)/ Pennsylvania State University. University Park, Pennsylvania.

Gleason, H. A. and A. Cronquist. 1991. Manual of vascular plants of northeastern United States and adjacent Canada, 2nd edition. New York Botanical Garden, Bronx, New York, USA.

Gresham, C. 2000. Invasive plants in Pennsylvania. Pennsylvania Department of Conservation and Natural Resources Publication No. 8100-PA-DCNR3077.

Rhoads, A. F. and T. A. Block. 2000. The plants of Pennsylvania. University of Pennsylvania Press, Philadelphia, Pennsylvania.

Rhoads, A. F. and W. M. Klein. 1993. The vascular flora of Pennsylvania: annotated checklist and atlas. American Philosophical Society, Philadelphia, Pennsylvania.

Wilhelm, G. and D. Ladd. 1988. Natural areas assessment in the Chicago region. Trans. 53rd North Amer. Wildl. and Nat. Res. Conf.: 361-375.

 

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