Charles E. Williams

Use of turtlehead (Chelone glabra L.) and other herbaceous plants to assess intensity of white-tailed deer browsing on Allegheny Plateau riparian forests, USA

One of the key factors affecting the integrity of forest ecosystems in portions of the eastern United States is heavy browsing by overabundant populations of white-tailed deer (Odocoileus virginianus Zimmerman). Deer impacts to upland forests of the Allegheny Plateau in northwestern PA, USA, have been especially intense: high levels of deer browsing over the past 60 years have strongly influenced forest pattern and process. Riparian forests of the region are rich in herbaceous plant species, but virtually nothing is known about how deer browsing may influence the structure and function of these systems. Moreover, reliable techniques for assessing and monitoring deer impacts on riparian forests are lacking. The goal of this study was to determine whether the common riparian herbaceous plant turtlehead, Chelone glabra L., is a useful indicator species with which to assess and monitor the intensity of deer browsing in the herbaceous layer of Allegheny Plateau riparian forests. The percentage of C. glabra stems browsed by deer was significantly correlated with intensity of browsing on the herbaceous community during one sample period, but stem height, an attribute used widely in other studies of browse indicator species, was poorly correlated with intensity of browsing. Three other herbaceous plant species, Aster divaricatus L., A. prenanthoides Muhl. and Impatiens capensis Meerb., were preferentially browsed by deer and show promise for use as indicators of browsing intensity in riparian forests. Variability in deer browsing intensity on C. glabra across sites and sample periods suggests that use of an assemblage of herbaceous browse indicator species is preferable to sole reliance on C. glabra for assessing and monitoring browsing impact.

Riparian Vegetation Survey of Four Small Streams in Northwestern Pennsylvania

The species composition and richness of the summer riparian vegeta? tion of four small streams in the nonglaciated Allegheny Plateau of northwestern Pennsylvania (Forest, Warren and McKean Counties) were examined. The arboreal stratum (stems > 2.5 cm dbh) of the four streams consisted of twenty species with Fagus grandifolia, Betula alleghaniensis, and Tsuga canadensis dominant (mean number of arboreal species across sites = 9.8 + 0.9 SE). Ninety-nine species were recorded from the ground-layer stratum (all vascular plants < 2 m tall) of the four streams with forbs as the dominant growth form. Four species, Dryopteris intermedia, Maianthemum canadense, Pilea pumila, and Viola blanda, were common to the ground-layer vegetation associated with all streams. Species of upland affinity were more prevalent in the riparian vegetation across streams than werewetland species. Several of the plant species recorded are indicators of rich and/or subacid to circumneutral soils, an edaphic medium of limited occurrence in the region. Mean ground-layer species richness and cover differed significantly among streams and ranged from 3.7 to 10.5 species/m2 (mean number of species/m2 across sites = 7.9 ? 1.5 SE) and 8.3 to 43.0% (mean percent cover across sites = 30.4 + 7.7 SE), respectively. Similarity in ground-layer species composition among streams ranged from 33.3 to 54.1% (mean similarity across sites = 38.9 ? 3.7% SE ). Although compositionally distinct, the small stream riparian flora documented by this study compares favorably in richness to other riparian habitats in northwestern Pennsylvania.

Water Dispersal Potential of Fruits of Dirca palustris L. (Thymeleaceae)

Dispersal of propagules by water, or hydrochory, is a primary or secondary dispersal mode for many plant species that live in or near aquatic habitats. Buoyancy of seeds and fruits is a key attribute in hydrochory; the longer a propagule remains afloat, the greater the likelihood that it will be carried some distance from its source by flowing or pulsing water or by wind-generated surface currents (Shimamura et al. 2007). Studies of hydrochory in plants often initially focus on quantifying the buoyancy of propagules in laboratory settings to assess the water dispersal potential of a species (e.g., Williamson and Costa 2000). Plants that use hydrochory for propagule dispersal often occur in habitats that are flooded at seasonal or daily intervals (Schneider and Sharitz 1998, Williamson and Costa 2000, Moegenburg 2002, Shimamura et al. 2007). In many hydrochorous species, especially those of seasonally inundated habitats, fruit production often peaks during flooding events, which maximizes the potential for dispersal (Williamson and Costa 2000, Moegenburg 2002). Eastern leatherwood or wicopy, Dirca palustris L. (Thymeleaceae), is a shrub that occurs in rich, mesic forests in eastern North America, especially along streams (Nevling 1962, Ward and Horn 1998, Williams and Moriarity 1998). On the Allegheny High Plateau of northwestern Pennsylvania, D. palustris is among the earliest of species to flower in the region, usually in early to mid-April (Williams 2004). The fruit, an ellipsoid, greenishyellow drupe 8 to 12 mm in length, matures in May and is dispersed from shrubs during June. Little is known about the dispersal ecology of the fleshy fruits of D. palustris. Fruits are thought to be dispersed by frugivorous birds and mammals, gravity, and water (Ward and Horn 1998). In this note, I examine the potential for hydrochory in D. palustris based on field observations of shrub spatial patterning and laboratory studies of fruit and seed buoyancy. In the small stream valleys where Dirca palustris occurs in northwestern Pennsylvania (Williams and Moriarity 1998, Williams 2004), peak flows and potential for flooding typically occur after snowmelt in March to early April. Relative to hydrochory, these seasonal high flows are out of synchrony with the June fruiting season of the species, which occurs when most regional streams are beginning to reach base flow. The classic coupling of high flow events and propagule dispersal often seen in ‘‘typical’’ hydrochorous plants is lacking for D. palustris in small stream valleys of the region and likely elsewhere in its range. Our examination of the distribution of individuals of a Dirca palustris population along Sibbald Run (Forest County, Pennsylvania), in the Allegheny National Forest, suggests that proximity of shrubs to the stream could enhance the potential for hydrochory in this species during base flow periods. The population hub of D. palustris in this valley consists of over 50 individuals located along approximately 100 m of stream [see Williams and Moriarity (1998) and Williams (2004) for a description of the study area]. In early April 2000, we measured the distance of all D. palustris individuals (n 5 54) from the stream and noted their flowering status (flowering, non-flowering). We found that 55.6% of individuals in this population occurred within 2 m of the stream bank (Figure 1) and that nearly all individuals (97.0%) were in flower. Much of the potential source of fruits in this *email address: chuckvt89@gmail.com Present address: Western Pennsylvania Conservancy, 40W. Main Street, Ridgway, Pennsylvania 15853. Received 25 August, 2008; Accepted 17 January, 2009. CASTANEA 74(4): 372–375. DECEMBER 2009

Patchy Invasion of Riparian Savannas by Rhamnus frangula L. (Rhamnaceae) in Northwestern Pennsylvania: Is Soil Drainage a Factor?

ABSTRACT   Glossy buckthorn (Rhamnus frangula L. or Frangula alnus Mill.) is a tall shrub to small tree, native to Eurasia and North Africa, which can invade both wetland and upland sites in northeastern and midwestern North America. Invasion by R. frangula is often patchy in riparian savannas of the Allegheny High Plateau of northwestern Pennsylvania: Some sites are heavily invaded, whereas others nearby are sparsely invaded or not invaded at all. Because microtopography in riparian savannas can be diverse, with slightly elevated dry hummocks and wet depressions providing habitats for a range of upland and wetland plant species, we tested the hypothesis that the patchy nature of R. frangula invasion of riparian savannas is determined in part by soil drainage, which may ultimately affect shrub establishment and growth. We used depth to mottling by iron oxides as a primary, indirect measure of soil drainage and inundation and also measured the depth of leaf litter, humus, and A and B horizons in belt transects that were either heavily or sparsely to noninvaded by R. frangula at three riparian savanna study sites in the Allegheny National Forest. Sites with relatively well-drained soils, indicated by greater mottling and B horizon depths, supported significantly greater densities of R. frangula seedlings and shrubs than did sites with apparently wetter soils having shallower mottling and B horizon depths. We suggest that physiological stress associated with wet soils may restrict establishment of R. frangula, explaining in part its patchy invasion patterns in Allegheny High Plateau riparian savannas.

Sweet-scented Indian-plantain, Hasteola suaveolens (L.) Pojark., in riparian plant communities of the Allegheny River Islands Wilderness, Pennsylvania.

Abstract Sweet-scented Indian-plantain, Hasteola suaveolens (L.) Pojark., is a species of special concern in 13 states and jurisdictions in the eastern United States and occurs predominantly in riparian habitats. In the Allegheny National Forest (ANF) of northwestern Pennsylvania, H. suaveolens is considered a species with viability concerns. I surveyed riparian plant communities in the Allegheny River Islands Wilderness (ARIW) of the ANF to provide information on the habitat affinities of H. suaveolens useful for conservation and management needs. Hasteola suaveolens was located within 13 of 42 survey sites on six of the seven islands in the ARIW and occurred in three riparian community types: a floodplain scour community dominated by native herbaceous plants an Acer saccharinum–Platanus occidentalis floodplain savanna community and a Platanus occidentalis–Carya cordiformis (Wang.) K. Koch–Ulmus rubra Muhl. floodplain savanna community. Occurrences of H. suaveolens were largely associated with elevated floodplain geomorphic surfaces having moderately drained to well-drained soils that were located above high energy scour zones.