Published online April 11 , 2005

ep ro du ce d fr om S oi l S ci en ce S oc ie ty o f A m er ic a Jo ur na l. P ub lis he d by S oi l S ci en ce S oc ie ty o f A m er ic a. A ll co py rig ht s re se rv ed . best accomplished through the use of paired designs and SOIL CARBON CHANGES AFTER that the chance of detecting a significant change was 26 YEARS IN A CUMBERLAND enhanced by disturbance and the passage of time. Similarly, Richter et al. (1999) suggest that a paired sampling PLATEAU HARDWOOD FOREST approach in a relatively stone free mineral soil might have a good chance of detecting change, especially if J. M. Kelly* and P. A. Mays the interval between samples is on the order of decades. Abstract The objective of our study was to determine if mineral soil C concentration changed over 26 yr in the oak domConcerns about global warming and discussions of possible mitigainated forest of the Camp Branch Watershed. Camp tion measures have generated a need for information on changes in soil C over time. The objective of this study was to determine if there Branch was the site of a series of nutrient cycling studies was a change in soil C concentration in an aggrading oak forest over during the period 1975 to 1990, the results of which have a 26-yr interval. Using permanently identified points on the Camp been summarized in Kelly (1984, 1988), Johnson et al., Branch Experimental Watershed, soil samples were first collected in (1986, 1988), Kelly and Meagher (1986), and Cronan July of 1976 and archived. During July of 2002, 11 points covering 6 et al. (1990). of the 18 soil series present on the watershed were resampled. The series chosen represent a range in topographic positions and forest Materials and Methods cover types. In both 1976 and 2002, a bucket auger was used to collect samples at depth intervals of 0 to 10, 10 to 30, and 30 to 50 cm. Both Site Description sample sets were analyzed in 2002 using a loss on combustion techSoil samples used for this study were collected from the nique to determine organic C concentration. A bootstrapping data Camp Branch Experimental Watershed (35 38 N lat.; 85 18 W analysis indicated an increase (95% confidence interval) in the concenlong.), which is located within the boundaries of Fall Creek tration of C in the 0to 10-cm depth. No change in C concentration Falls State Park on the Cumberland Plateau in Central Tennesoccurred in the 10to 30or 30to 50-cm samples. Average soil C see. The upland vegetation of the central Cumberland Plateau, concentration in the 0to 10-cm samples increased from a mean of once dominated by white oak (Quercus alba L.), has been 20.8 g kg 1 in 1976 to 35.9 g kg 1 in 2002. Among soil series, concentrareplaced by less productive second growth stands dominated tions ranged from 9.5 to 28.9 g kg 1 in 1976 and 22.1 to 64.7 g kg 1 by scarlet oak (Q. coccinea L.), chestnut oak (Q. prinus L.), in 2002. Although the sample numbers are limited, results indicate white oak, and post oak (Q. stellata L.) mixed with Virginia that average soil C concentration in the top 10 cm of the mineral soil pine (Pinus virginiana L.), shortleaf pine (P. echinata L.) and increased by 73% at this site over a 26-yr interval. red maple (Acer rubrum L.) (Ramseur and Kelly, 1981). Past disturbances associated with agriculture (primarily woodland grazing) and timber harvest have contributed to the diversity T is a growing need to increase our understandof species and age classes found within the current forest. ing of the amounts and patterns of C storage in soils. However, there have been no known disturbances on the This need is driven in part by concerns about global watershed since the Park was established in the late 1930s. warming and the role that forest soils may play in the long-term accumulation and sequestration of atmospheric Soil Sampling and Analysis C (Guo and Gifford, 2002). Since a large portion of terIn 1976, a 100 100 m sampling grid was established across restrial C stocks are in the soil, particularly in forest soils the 94 ha in the watershed and each grid intersection marked (Post et al., 1990), answering many of the science queswith a steel fence post. In July of 1976 samples of the mineral tions being considered in this context is highly depensoil were collected 1-m south of each grid intersection using dent on understanding long-term changes in forest soil a 9-cm wide by 22-cm long stainless steel bucket auger. After C. Attempts to quantify change using traditional soil removing the litter layer, mineral soil samples were collected sampling approaches have been inconclusive in part due from the following depth intervals: 0 to 10, 10 to 30, and 30 to 50 cm. Samples were oven dried at 105 C for 48 h, passed to differences in analytical techniques and the heterogethrough a 5-mm sieve to remove roots, and then ground with neous nature of forest soil C distribution. Gaudinski a mortar and pestle to pass a 2-mm sieve. A 250-g reference and Trumbore (2003) suggest that biometric methods subsample was taken from the sample collected at each depth– that calculate C accumulation through repeated mealocation combination, sealed in a glass jar, and stored in cardsures over extended time intervals might help to address board boxes in a building subject to normal fluctuations in these limitations. While Yanai and colleagues (2003) ambient temperature. concluded that detecting change in forest floor C was During July of 2002, samples were collected from 11 of the permanently marked locations sampled in 1976. Sampling sites were chosen to provide a broad range of soil series, topoJ.M. Kelly, formerly at Natural Resource Ecology & Management Dep., Iowa State Univ.; currently at Virginia Tech, College of Natural graphic positions, and forest cover types (Table 1). New soil Resources, 324 Cheatham Hall, Blacksburg, VA 24061; P.A. Mays, samples were collected 1 m southeast of the grid intersection Tennessee Valley Authority, Knoxville, TN. 37902-1499. Received 14 and were prepared for analysis using the same procedures July 2004. Forest, Range, and Wildland Soils Note. *Corresponding used in 1976. Samples from both 1976 and 2002 were oven author ([email protected]). dried before being analyzed in duplicate for soil organic C concentration using a Model NA 1500 N/C/S Analyzer (CarloPublished in Soil Sci. Soc. Am. J. 69:691–694 (2005). Erba Strumatazione, Milan, Italy). A total of 64 samples were doi:10.2136/sssaj2004.0241 analyzed (2 yr 11 locations 3 depths for all locations © Soil Science Society of America 677 S. Segoe Rd., Madison, WI 53711 USA except Wallen-Ramsey only two depths) in duplicate. Varia-