Eastern white pine establishment in the oak landscape of the Ellicott Rock Wilderness, southern Appalachian Mountains

Castanea, Sep 2003 by Abella, Scott R, Shelburne, Victor B

ABSTRACT

Changing disturbance regimes, particularly decreasing fire frequencies, may result in distributional changes of species across southern Appalachian landscapes. Some researchers have hypothesized that Pinus strobus (eastern white pine) is undergoing a change in site affinity from mesic to xeric sites in southern Appalachian forests, but no studies have evaluated the landscape-level status of P. strobus. We examined the status of P. strobus in a 225-ha old-growth Quercus landscape within the Ellicott Rock Wilderness (ERW) in South Carolina by sampling 80 plots. Pinus strobus exhibited the highest mean density (267 trees ha^sup -1^) of all species in the 1-10 cm diameter class, with 96% of the P. strobus currently in these Quercus forests establishing since 1950. Density of P. strobus in the 1-10 cm diameter class was most highly correlated with P. strobus density >10 cm diameter, and was not strongly correlated with other measured vegetation variables such as total Quercus basal area. Results support the hypothesis that P. strobus is expanding its distribution to upland sites in the southern Appalachians. It is possible that the current P. strobus vegetation type observed in the ERW represents a vegetation type that historically would have occurred more extensively had it not been inhibited by Native American or lightning-caused fires.

INTRODUCTION

There is much current interest in the dynamics of southern Appalachian forests, and specifically in potential changes in the Quercus forests that presently occupy most of the southern Appalachian landscape (Bratton and Meier 1998, Harrod et al. 2000, Rhoades 2002). Disturbance regimes in Quercus forests of the southern Appalachians generally changed from frequent, low-intensity fires in the presettlement forest to infrequent or absent fires through the 190Os (Delcourt and Delcourt 1998, Brose et al. 2001). Current trends indicate long fire-free periods will persist in many areas in the 21st century, possibly resulting in shifts, expansions, or reductions in the distributions of individual species (Lorimer 1993, Harrod et al. 2000, McDonald et al. 2002). The composition and structure of future southern Appalachian forests, and how they may differ from current forests, is uncertain.

A species that some researchers postulate is shifting in site affinity in the southern Appalachians is Pinus strobus L. (eastern white pine). White and Lloyd (1998) and Blankenship and Arthur (1999) hypothesized that P. strobus was confined in the presettlement southern Appalachian forest to mesic sites protected from fire, but is shifting or expanding to dry, upland sites during the present period of infrequent fire. Pinus strobus is geographically widespread in the southern Appalachians, and its native range includes portions of Georgia, South Carolina, North Carolina, Tennessee, and Virginia (Burns and Honkala 1990, Abrams 2001). Pinus strobus occurs from elevations of 370 m to a maximum of 1,220 m in the southern Appalachians, and habitats are typically described as north-facing slopes, coves, and stream bottoms (Ayres and Ashe 1905, Burns and Honkala 1990). No studies, however, have focused on the landscape-level distribution of P. strobus in southern Appalachian forests. To help fill this gap in our knowledge, we undertook a study to evaluate the hypothesis of White and Lloyd (1998) and Blankenship and Arthur (1999) that P. strobus is undergoing a distributional change in the southern Appalachians.

We examined the distributional status of P. strobus in an old-growth Quercus-dominated landscape in the Ellicott Rock Wilderness (ERW) of northwestern South Carolina, near the southwestern terminus of the native range of P. strobus (Burns and Honkala 1990). The ERW was selected for study because it is within the geographic and elevation range of P. strobus and contains large tracts of relatively undisturbed forest. This study sought to 1) determine the current landscape-level distribution and age structure of P. strobus in Quercus forests of the ERW, 2) relate the distribution of P. strobus to measured vegetation variables, and 3) assess potential shifts in species composition on this Quercus landscape.

METHODS

Study Area

The 3,647-ha ERW occupies parts of Georgia and North and South Carolina within the Chattahoochee, Nantahala, and Sumter National Forests (Figure 1). This study was conducted in a portion of the ERW within the Sumter National Forest in Oconee County, northwestern South Carolina. Located in the southern section of the Blue Ridge Mountain physiographic province (Cooper and Hardin 1970), the ERW occupies the first chains of mountains that rise abruptly from the lower-elevation Piedmont region of South Carolina (DuMond 1970). Elevations of the highest ridges in the ERW typically range from 870-1,100 m, and topography consists of undulating hillslopes. Major soil taxonomic units include fine-loamy, mixed, mesic Typic Hapludults and fine-loamy, oxidic, mesic Typic Hapludults of the Edneytown and Evard series (Herren and Law 1985).

Presettlement vegetation in this region was dominated by Quercus spp. and Castanea dentata (Marsh.) Borkh. (American chestnut), with the ERW lying in the extreme southern section of the oak-chestnut forest region of Braun (1950). Dominant understory plants in these forests include Vaccinium pallidum Ait. (low-bush blueberry), Gaylussacia ursina (M.A. Curtis) Torr. & Gray ex Gray (bear huckleberry), Kalmia latifolia L. (mountain laurel), and Quercus seedlings (DuMond 1970). Forests dominated by Tsuga canadensis (L.) Carr. (eastern hemlock) and other non-Quercus species form comparatively minor inclusions along riparian areas in the predominant Quercus matrix (Braun 1950, DuMond 1970). With the exception of the chestnut blight (Keever 1953), major disturbance throughout the ERW has been minimal since the early 190Os. Several sections of the ERW have been identified as old-growth forest with canopy dominants greater than age 100 yr during Forest Service surveys for old growth in the region (Carlson 1995).