Coarse woody debris in a Southern Appalachian spruce-fir forest of the Great Smoky Mountains National Park
Spruce-fir forests in the southern Appalachian Mountains receive high atmospheric nitrogen inputs and have high nitrate levels in soil solution and streamwater. High levels of excess nitrogen have been associated with reduced tree vigor. Additionally, the balsam woolly adelgid (Adelges piceae Ratz.) has killed the majority of endemic Fraser fir [Abies fraseri (Pursh) Poir.] trees, resulting in large amounts of coarse woody debris. As part of a biogeochemical study in the Great Smoky Mountains National Park, coarse woody debris was sampled to determine volume, mass, change in density, and change in concentration and content of carbon and nitrogen over the decomposition process. Dead wood volume was highly variable across the watershed, ranging from 4.5 m3 ha-1 to 306.8 m3 ha-1 for standing boles and from 21.2 m3 ha-1 to 402.7 m3 ha-1 for down boles. Wood density decreased significantly for all three major overstory species [red spruce (Picea rubens Sarg.), yellow birch (Betula alleghaniensis Britt.), and Fraser fir] by approximately 60%, from slightly decayed boles to boles in advanced decay. Standing and down dead biomass averaged 39.4 Mg ha-1 and 33.8 Mg ha-1, respectively. Carbon concentrations remained relatively constant and were approximately 47% for all decay classes and all species. Nitrogen concentrations increased sharply between live wood and highly decayed wood. The nitrogen content in live wood, compared to wood in advanced decay, increased by 40% to 118% for the species tested. At the watershed level, live bole wood contained 108.4 kg ha-1 of nitrogen, and dead bole wood contained 101.5 kg ha-1. Total carbon in live and dead bole wood averaged 93.8 Mg ha-1 and 34.9 Mg ha-1, respectively. The magnitude of coarse woody debris in this system is among the highest reported in the literature for the eastern United States, emphasizing the high degree of disturbance that has taken place in this ecosystem.