White Oak Sinks, GSMNP, TN   Jess Riddle   Apr 17, 2007 18:55 PDT  Ents, Metamorphosed sedimentary rocks, most commonly sandstone, underlie the vast majority of the Great Smoky Mountains, and they tend to weather into acidic soils. Hence, the scattered small areas in the range underlain by limestone, with their circumneutral to basic calcium rich soils and associated assemblages of calcium loving plants, have attracted the attention of naturalists studying the mountains. White Oak Sinks, the largest of those areas now in the national park, sits just inside the park's northern border northeast of Cades Cove. The area's name comes from all the streams flowing into the basin flowing underground once they reach the limestone and the half dozen or so sinkholes in the area. All of the sinkholes occur on the relatively flat floor of the closed basin that drains an area of about 900 acres. To the southwest, steep slopes rising over 800' above the floor of White Oak Sinks make the area feel more like a bowl, and help to generate cold air that pools in the bowl's bottom (assuming the topography functions the same way cold sinks do in the Rockies). As a consequence of that cold air pooling, tuliptrees in the sinks remain dormant when other tuliptrees 1000' higher in elevation and on more acidic substrates, which tend to leaf out later, have already broken bud. The forests in the basin surrounding White Oak Sinks do not hint at the unusual area's existence. Scarlet oaks, white oaks, white pines, and hemlocks cover the gentle slopes along some streams over a patchy understory of rhododendron, mountain laurel, huckleberry and open areas with galax beneath. The steeper northeast facing slopes also suggest only quick draining, acidic conditions since white oaks, chestnut oaks, and tuliptrees dominate. While the limestone generally correlates to the flat land in the bottom of the basin, even where the rock extends up the north side of the basin the canopy belies the bedrock. The white oak, chestnut oak, black oak mix on that south facing slope does not seem unusual for the topography, although the lack of a heath understory might not be expected. However, settlers found the area and recognized in it an excellent farm site. Consequently, determining what species originally dominated the floor is difficult, and well drained acidic forests of white oak with some pines and a dense midstory of hemlock now cover much of the bottom. The limestone under those forests may have little influence on the vegetation due to the depth of the colluvium covering the bedrock, but the rest of the floor, especially around sinkholes and outcrops, still features species mixes unusual for the region. Black walnut with some slippery elm dominates the youngest forests on floor. More mature black walnuts grow amongst cliffs and rock outcrops on the edge of the bottom in association with white oak, chinquapin oak, and some shagbark hickory. Those sites appear the least disturbed, though probably not most representative, in the area, so black walnut appears to be native to the site and not introduced by farmers. Tuliptrees now dominate on the lowest and moistest areas of the bottom, and hemlock also forms a nearly pure stand on one slope with multiple limestone outcrops. Shrubs may be even patchier in distribution on the limestone. Spicebush occurs frequently in the shrub layer and American hazelnut also forms thickets in multiple areas. American plum likewise grows in multiple areas, but forms much smaller colonies, sometimes where calcareous forests interface with acidic forests. Multiple sinkholes supported alternate leaf dogwood on their slopes, and one sinkhole hosts American bladdernut, a rare species in the Smokies. The herbaceous layer similarly contains a mix of common rich site species and species rare or absent elsewhere in the park. The combined spring floral display has attracted enough visitors to establish through use an extensive and well defined trail network in and around White Oak Sinks without any maintenance or publication by the Park Service. More common species contributing to the display include may apples, bishops cap, and bluntleaf waterleaf. A phlox has especially high coverage and, since the air does flow out, strikingly perfumes the forest over multiple acres. Amongst the phlox, grow the rare shooting star and largeleaf waterleaf. Barren strawberry grows under the hemlocks on an adjacent slope, one outcrop harbors dwarf larkspur and green violet, purple cliffbrake clings to other outcrops, and Virginia bluebells cloaks one sinkhole; all rare in the park. Only four trees were measured during our visit; past farming and generally dry site conditions precluded most species from reaching exceptional sizes. On the floor of the basin, slippery elm reaches 6'0" cbh. Along end of the bottom, but still influenced by limestone, mockernut hickory reaches 6'3"cbh x 121.2' tall and chinquapin oak 7'2"cbh x 105.1', a new park height record. The gentle sections of the surrounding basin support many impressively tall scarlet oaks including a 7'4" x 121.1'+ individual. Jess Riddle & Josh Kelly   Home