Forest Ecology and Management 258 (2009) 1437–1441 Contents lists available at ScienceDirect Forest Ecology and Management journal homepage: www.elsevier.com/locate/foreco Assessing the effects of vegetation types on carbon storage fifteen years after reforestation on a Chinese fir site Qinkui Wang a, Silong Wang a,b,*, Jianwei Zhang c a Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110016, PR China b Huitong Experimental Station of Forest Ecology, Chinese Academy of Sciences, Huitong 418307, PR China c USDA Forest Service, Pacific Southwest Research Station, 3644 Avtech Parkway, Redding, CA 96002, USA ARTICLE INFO ABSTRACT Article history: Forest ecosystems play a significant role in sequestering carbon (C) in biomass and soils. Plantations Received 13 April 2009 established in subtropical China since the 1980s, mainly of Chinese fir (Cunninghamia lanceolata (Lamb.) Received in revised form 9 June 2009 Hook) in monocultures, have proved to be major C sinks. However, information is lacking about whether Accepted 27 June 2009 mixing Chinese fir with broadleaved tree species will increase stand growth and C sequestration. We address this question by comparing a pure Chinese fir plantation and two mixed plantations established Keywords: in 1990 at Huitong Experimental Station of Forest Ecology, Hunan Province, China. The mixed Carbon storage plantations include Chinese fir and either Kalopanax septemlobus (Thunb.) Koidz or Alnus cremastogyne Mixed plantation Burk., planted at 4:1 ratios. We found that total C storage was 123, 131 and 142 Mg haÀ1 in the pure Broadleaved tree Coniferous plantation plantation, mixed plantation with K. septemlobus, and mixed plantation with A. cremastogyne, respectively. The mixed plantation with A. cremastogyne increased C storage in biomass relative to the pure Chinese fir plantation (P < 0.05). No significant difference was detected between mixed plantations. Soil C storage did not differ among these plantations, ranging from 67.9 Æ 7.1 to 73.3 Æ 9.1 Mg haÀ1, which accounted for about 55% of the total C pools. Our results indicated that as the mixture of Chinese fir and broadleaved species will increase both biomass C and soil C storage over pure Chinese fir, and will do it, within 15 years of planting. ß 2009 Elsevier B.V. All rights reserved. 1. Introduction C storage in forest ecosystems will be a key factor in the maintenance of the atmosphere’s C balance. Terrestrial ecosystems remove about 30% of all CO2 emissions Globally, many attempts have been made to estimate C storage from fossil fuel burning and deforestation (Canadell and in forest ecosystems because sequestering C in biomass and soil is Raupach, 2008). Forests play a significant role in this carbon widely believed to be an effective method to mitigate an increase (C) sink. It has been reported that forests store about 45% of of atmospheric CO2 concentration (Davis et al., 2003; Hazlett et al., terrestrial C, more than double the amount of C in the 2005; Zhang et al., 2007; Zhou et al., 2008). For example, Davis et al. atmosphere (FAO, 2006). In China, terrestrial ecosystems (2003) reported that C storage in 125-year-old pole stands was absorbed 0.19–0.26 Pg C per year, 28–37% of its cumulative 219 Mg haÀ1 and declined to 192 Mg haÀ1 as the stands matured fossil C emissions, during the 1980s and 1990s (Piao et al., 2009). (>150 years old). Zhou et al. (2008) also reported that the 10-year Forests in southern China, mainly as part of a large-scale reforestation program increased C storage by 41.7 Tg from 1994 to plantation program initiated in the 1980s, contributed about 65% 2003 in Guangdong Province, China. However, most of these of the C sink in southern China terrestrial ecosystems. Therefore, publications were focused on boreal, temperate and tropical forest ecosystems influence significantly the global C cycle; even forests, and few studies were carried out on C storage in the forests a small shift in the balance between photosynthesis and of southern China, some of the most important subtropical forests ecosystem respiration can lead to a large change in uptake or in the world. emission of CO2 from forests to the atmosphere. Thus, enhancing Chinese fir (Cunninghamia lanceolata (Lamb.) Hook), an important coniferous timber species with fast growth and good timber quality, has been widely planted for more than 1000 years. Its planting area has reached over 12 million ha, account- * Corresponding author at: Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110016, PR China. Tel.: +86 24 8397 0344; ing for about 6.5% of all plantation forests in the world (FAO, fax: +86 24 8397 0300. 2006; West, 2006). Therefore, Chinese fir forests should play a E-mail address: [email protected] (S. Wang). significant role in global C sequestration. Since the 1980s, it has 0378-1127/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.foreco.2009.06.050 1438 Q. Wang et al. / Forest Ecology and Management 258 (2009) 1437–1441 been recognized that yield and soil fertility of pure Chinese fir a clay loam. The soil is predominantly derived from slate and shale, stands tends to decline due to successive cropping, short rotation and classified as an Oxisol under the USDA taxonomy. times of about 20 years, and whole-tree harvesting (Chen et al., 1990). Fortunately, some studies have showed that planting 2.2. Overstory and understory biomass mixed forest of Chinese fir and broadleaved tree species could increase productivity and improve soil fertility (Feng et al., 1988; Five 400-m2 plots (20 m  20 m) were established at each Chen et al., 1990). To date, however, little information is available plantation in November 2005. We measured the DBH (diameter at about the impacts of mixed plantations on C storage in Chinese fir breast height at 1.3 m height), tree height, and crown length of all mixed forest ecosystems. trees on the five plots of each stand. We harvested 32 Chinese fir In this study, we measured and compared total ecosystem C trees, 19 A. cremastogyne, and 21 K. septemlobus trees in the three among one pure Chinese fir plantation (PC) and two mixed stands. After a tree was felled, we measured total height with a plantations with Chinese fir and either Kalopanax septemlobus steel tape (accuracy, 0.1 m). Each bole was then cut into 2-m (MCK) or Alnus cremastogyne (MCA). The aim is to determine sections, and each section was separated into stem, bark, leaf and whether mixed plantations will increase biomass accumulation branch. All components were dried at 80 8C to constant weight. The and C sequestration and storage in the 15-year-old plantations. dry weight of standing individuals in the sampling stands was estimated by means of allometric regression equations for 2. Materials and methods individual trees. We then used this equation to calculate the aboveground biomass of each tree and the total aboveground 2.1. Site description biomass for each stand. Roots were also excavated to a depth of 100 cm in these plots. This study was conducted at Huitong Experimental Station of Excavations were centered on the stumps of the harvested trees. Forest Ecology (latitude 268400–278090N and longitude 1098260– Roots from the harvested tree were collected, washed, and dried at 1108080E), Chinese Academy of Sciences, Hunan Province, China. 70 8C until a constant weight was reached. The understory and This experimental Station lies at the transition zone from the herbaceous biomass were determined by destructively harvesting Yunnan-Guizhou plateau to the lower mountains and hills on six randomly located 1 m2 plots in each stand. Forest floor litter the southern side of the Yangtze River at an altitude of 300– was sampled using fifteen 0.25 m2 subplots randomly located 1100 m above mean sea level. The climate of this region is within each 20 m  20 m plot. After sampling, forest floor litter humid mid-subtropical monsoon with mean annual tempera- was transported to the laboratory and then dried to constant ture of 15.8 8C from 1990 to 2005. The mean annual precipita- weight at 70 8C. tion was 1200 mm of which about 67% occurred between April and August. 2.3. Mineral soil sampling After the first-generation Chinese fir forest was clearcut in autumn of 1989, a pure Chinese fir plantation and two mixtures of Volumetric samples of mineral soil were taken for calculating Chinese fir and either A. cremastogyne or K. septemlobus were the soil C storage. Soils were sampled to a depth of 100 cm. In planted in early spring of 1990. Each plantation is about 2.5 ha. The each of the three stands, five points were systematically located. ratio of Chinese fir to A. cremastogyne or K. septemlobus in the At these points, three samples were taken from the following mixed forests was 4:1. Planting density was 2000 tree haÀ1. The depth ranges: 0–10, 10–20, 20–40, 40–60, 60–80, and 80– plantations were established at an altitude of 521–554 m above 100cm, and pooled by sampling point and layer. All samples sea level. were transported to the laboratory and then air-dried for The soil bulk density and texture did not significantly differ determining C. Soils were also assessed for bulk density with a among plantations in 2005 (Table 1). The soil texture is classified as bulk density corer (diameter 5 cm) at the same depth range. Rocks and gravel (>2 mm diameter) were sieved from each soil sample. Table 1 Soil bulk density and texture at different depths collected from a 15-year-old pure Chinese fir plantation (PC) and mixed plantations with K.