1. Effects of thinning on soil and forest floor carbon storage of Pinus densiflora stands in central Korea A-Ram Yang 1, Yowhan Son 1*, Nam Jin Noh 1, Sue Kyoung Lee 1, Wooyong Jo 1, Choonsig Kim 2, Sang-Won Bae 3, Sang-Tae Lee 3 and Jaehong Hwang 4 A-Ram Yang 1, Yowhan Son 1*, Nam Jin Noh 1, Sue Kyoung Lee 1, Wooyong Jo 1, Choonsig Kim 2, Sang-Won Bae 3, Sang-Tae Lee 3 and Jaehong Hwang 4 1 Division of Environmental Science and Ecological Engineering, Korea University, Seoul 136-713, Korea *E-mail: yson@korea.ac.kr 2 Department of Forest Resources, Jinju National University, Jinju 660-758, Korea, 3 Forest Practice Research Center, Korea Forest Research Institute, Pocheon 487-821, Korea 4 Division of Forest Tree Improvement, Korea Forest Research Institute, Suwon 441-350, Korea Abstract The objective of this study was to investigate the effects of thinning on soil carbon (C) storage of Pinus densiflora stands in central Korea. Study stands were located in P. densiflora forests of central Korea [15-, 25-, and 55-year-old stands] and thinned in 2008. Each stand was divided into three plots by different thinning intensities based on stand density (control, Ct: 0%, light thinning, L: 30%, moderate thinning, M: 50%, heavy thinning, H: 70%). We measured the C storage of soil (0-30cm in depth) and forest floor in 2009. Soil and forest floor C storage (ton C/ha) were not significantly different among three thinning intensities for all stands: [49.0 for Ct, 59.7 for L, and 44.1 for M in the 15-year-old stand], [55.1 for Ct, 49.1 for L, and 49.4 for M in the 25-year-old stand], and [53.4 for Ct, 52.1 for L, and 59.0 for H in the 55-year-old stand]. C storage of soil and forest floor increased with stand age. We speculated that 1 year was too short to detect any consistent changes in C storage of soil and forest floor by thinning. Long-term observation would be needed to observe changes in soil and forest floor C storage. Introduction Many studies reported that forest management activities may affect C dynamics in forest ecosystems (Johnson 1992; Nilsen and Strand 2008). Especially, thinning affects stand conditions and soil environmental factors such as soil moisture and temperature (Kim et al. 2009; Son et al. 2004). P. densiflora is a major forest species and occupies more than 23.1% of the total forest land area in Korea. The objective of this study was to investigate the effect of thinning on soil and forest floor C storage of P. densiflora stands in central Korea. Materials and Methods Site descriptions Study stands were located in P. densiflora forests, central Korea and they included 15-year-old stand in Gwangneung Experiment Forest, Gyeonggi province, and 25-, and 55-year-old stands in Gangwon province (Figure 1). Each stand was divided into three plots by different thinning intensities: control, Ct: 0%, light, L :30%, moderate, M:40%, heavy, H: 70%. These study stands were thinned in 2008 and the characteristics of study stands are shown in Table 1. Table 1. Characteristics of three P. densiflora stands in 2008. *Thinning intensity was determined by stand density Soil sampling and analysis Fifteen to twenty-seven soil (0-30cm in depth) samples per plot were randomly collected using an improved soil core sampler (Hwang et al. 2001), and analyzed for soil water content (SWC), soil pH, and C concentration and storage of soil. Forest floor samples were randomly collected from five to nine samples per plot within each stand using 30 cm×30 cm quadrats. C concentration of soil and forest floor was measured by a vario Macro Elemental Analyzer (Elementar Analysensysteme GmbH, Germany). Soil C storage was calculated from the soil depth, bulk density, coarse rock content, and soil C concentration. Forest floor C storage was calculated from dry weight and C concentration. Statistical analysis Differences in C concentration and storage of soil and forest floor, and soil characteristics with different thinning intensities were analyzed using analysis of variance (ANOVA) procedure. Duncan’s multiple range test (P < 0.05) was used to separate the means. All statistical analyses were conducted using SAS 9.2 software (SAS Institute Inc., USA). Results and Discussion Soil characteristics SWC, soil pH, soil bulk density and coarse rock content in all stands did not show any consistent tendency according to thinning intensities (Table 2). Soil characteristics may not change by thinning after only 1 year. Changes in soil characteristics to thinning occurred after 3- 4 years (Hwang and Son 2006). Table 2. SWC, soil pH, bulk density, and coarse rock content for P. densiflora stands with different thinning intensities at each soil depth. Small letters indicate significant differences among treatments within each study stand (control: Ct, light: L, moderate: M, heavy: H). C concentration and storage of soil and forest floor C concentration (%) of soil and forest floor were not significantly different among thinning intensities (Table 3). Soil C concentration of 0-10cm depth in two thinned plots were higher than that in control plot of the 25-, 55-year-old stands. It may be due to high organic matter input to soil surface by thinning. Soil C concentration decreased with soil depth. C storage (ton C/ha) of soil and forest floor were not significantly different among thinning intensities in any of the stands (Figure 2). Thinning has been shown to increase (Kim et al. 2009, Lee et al. 2010) or decrease (Nilsen and Strand 2008) C storage of soil and forest floor, however, no change was observed in our study. Although C storage of soil and forest floor did not change by thinning, C storage of soil and forest floor increased with stand age. Generally, changes in C storage of soil and forest floor appeared 3-4 years after thinning, long-term observation would be needed to observe changes in soil and forest floor C storage (Campbell 2009; Kim et al. 2009; McHenry 2006). Acknowledgemet This work was supported by Forest Practice Research Center, Korea Forest Research Institute. References Campbell, J., Alberti, G., Martin, J., Law, B.E. 2009. Carbon dynamics of a ponderosa pine plantation following a thinning treatment in the northern Sierra Nevada. For Ecol Manag 257: 453-463. Hwang, J.H., Son, Y., Kim, J.S. 2001. An improved soil core sampler. J Korean For Soc 90: 788-791. Hwang, J.H., and Son, Y. 2006. Short-term effects of thinning and liming on forest soils of pitch pine and Japanese larch plantations in central Korea. Ecol Res 21: 671-680. Johnson, D.W. 1992. Effects of forest management on soil carbon storage. Water Air Soil Pollut 64: 83- 120. Kim, C., Son, Y., Lee, W.K., Jeong, J., Noh, N.J. 2009. Influences of forest tending works on carbon distribution and cycling in a Pinus densiflora S. et Z. stand in Korea. For Ecol Manag 257: 1420- 1426. McHenry, M.T., Wilson, B.R., Lemon, J.M., Donnelly, D.E., Growns, I.G. 2006. Soil and vegetation response to thinning white cypress pine (Callitris glaucophylla) on the North Western slopes of New South Wales, Australia. Plant Soil 285: 245-255. Nilsen, P., and Strand, L.T. 2008. Thinning intensity effects on carbon and nitrogen stores and fluxes in a Norway spruce (Picea abies (L.) Karst.) stand after 33 years. For Ecol Manag 256: 201-208. Son, Y., Jun, Y.C., Lee, Y.Y., Kim, R.H., Yang, S.Y. 2004. Soil carbon dioxide evolution, litter decomposition, and nitrogen availability four years after thinning in a Japanese larch plantation. Commun Soil Sci Plant Anal 35: 1111-1122. Figure 1. Location of three P. densiflora stands with different thinning intensities. Figure 2. C storage of soil and forest floor for P. densiflora stands with different thinning intensities (control: Ct, light: L, moderate: M, heavy: H). Table 3. Soil C concentration for P. densiflora stands with different thinning intensities and soil depth. Small letters indicate significant differences among thinning intensities within each study stand (control: Ct, light :L, moderate: M, heavy: H). The values in parentheses are standard error.