Effects of “Grain for Green” program on soil hydrologic functions in karst landscapes, southwestern China
Introduction
The Chinese government initiated a “Grain for Green” program in the late 1990s/early 2000s, and started in 2003 in the Guangxi Province which is a karst area. This program has since been implemented in 25 provinces located in central and western China, and these areas occupy 82% of the total land area of China (Liu et al., 2008). The primary areas targeted by the “Grain for Green” program were the upper and middle areas of the Yellow River, Yangtze River and Pearl River (karst areas). This program has increased the greenness and associated ecological benefits (e.g. carbon sequestration) across China (Song et al., 2014, Lu et al., 2015). Previous studies in China focused on the impacts of the “Grain for Green” programs on soil organic carbon (SOC) stocks and carbon sequestration (Zhang et al., 2010, Deng et al., 2014). Some studies have examined the effects of different vegetation restoration types on the soil hydrology (Li and Shao, 2006, Hu et al., 2009, Hu et al., 2013) and on soil erosion (Wang et al., 2015, Zheng, 2006) but mainly in the Loess Plateau. In karst landscapes of southwest China, research on vegetation restoration is mainly focused on the soil fertility quality (properties of SOC, soil microbiology and soil enzymology) (Liu et al., 2016, Long et al., 2005, Yu et al., 2013), and soil ecological effects but not on soil hydrologic functions (Song et al., 2011, Ouyang, 2010). Some studies focused on soil bulk density, water holding capacity (He et al., 2009, Huang et al., 2009) and soil erosion control (Zeng and Wang, 2005, Luo et al., 2003) of vegetation restoration. However, little is known about how vegetation restoration types affect soil hydrologic functions in karst landscapes. Such regions are characterized by complex terrain with a thin soil layer and underground stream structures.
Due to the special geological nature of karst landscapes, rapid soil and water loss and desertification are widespread and serious problems (Cai, 1996, Deng et al., 2009, Fan et al., 2011). Due to the unique nature of karst, the precipitation infiltrating karst rock percolates to the aquifer below, leaving little moisture at the topsoil, resulting in the natural hazards of floods and droughts to occur frequently. (Liu et al., 2014, Liu et al., 2015). Knowledge of the soil hydrologic function and its influencing factors are therefore crucial to successfully implement the “Grain for Green” program in karst landscapes. Therefore, improving the soil hydrologic function is key to successful ecological restoration. Soil hydrologic function is often influenced by the changes of soil structure due to biological influences (Suwardji and Eberbach, 1998) or compaction (Alakukku, 1996), each of which can be influenced by different vegetation restoration types. Structural and hydrological changes in combination with runoff concentration of sediment in arable cultivation lines, can contribute to erosion of arable soil (Fullen, 1985). Therefore, soil field saturated-hydraulic conductivity (Kfs) which quantifies the soil water infiltration capacity is a most important hydraulic properties. Kfs also controls the hydrologic and soil erosion processes, such as rainfall infiltration, runoff production, aquifer recharge, loss of nutrients to streamflow, pesticides and contaminants through the soil profile (Bagarello et al., 2005, Pirastru et al., 2013).
By measuring soil field saturated-hydraulic conductivity (Kfs), this study aims to examine the effects of different “Grain for Green” measures on soil hydraulic functions.
Section snippets
Site descriptions
The experiment (i.e. soil sampling, in-situ infiltration tests, soil analyses, etc.) was carried out at three research areas: Mulian (24°44′N, 107°51′E), Guzhou (24°54′N, 107°57′E), and at the Mulun national nature reserve (107°54′ to 108°05′E, 25°07′ to 25°12′N). All three sites are associated with the Huanjiang Observation and Research Station for Karst Ecosystems of the Chinese Academy of Sciences (CAS), located in the northwest Guangxi Province, southwest China (Fig. 1).
The climate in this
Basic soil properties
Generally, the soils of zenia insignis, toona sinensis, orchard sites and croplands had a similar texture (clay, according to the USDA classification system) for all three depths. The soils of napiergrass sites were silt loam for both the surface and 10 cm depth and silty clay loam for the 30 cm depth; the soils of natural restoration shrubland were loam for the surface and clay loam for both the 10 and 30 cm depths; the soil of the natural reserve were loam for all the depths. The clay fraction
Effects of vegetation types on Kfs
Many studies have shown that certain vegetation types significantly affect Kfs. Ziegler et al. (2004) found that Kfs of grassland top soil (mean, Kfs = 93 mm h−1, CV = 0.31) was higher than that of abandoned fields (mean, Kfs = 28 mm h−1, CV = 0.36) and young secondary vegetation (mean, Kfs = 32 mm h−1, CV = 0.47). Zimmermann et al. (2006) reported that Kfs of the surface soil of a forest (mean, Kfs = 206 mm h−1) was higher than that of a capoeira teak field land and pasture (mean, Kfs = 201, 69 and 26 mm h−1,
Conclusions
This study examined the effects of different vegetation types on Kfs in karst landscapes. Several conclusions can be made as follows:
- 1)
Our GLM model explains approximately 64.75% of the total variation in Kfs; the vegetation type explained the largest proportion (11.29%) of the Kfs variation.
- 2)
Kfs of artificial grassland was much higher than other vegetation restoration types at both the surface and at 10 cm depths, which suggests that napiergrass is suitable for vegetation restoration of karst
Acknowledgments
This study was supported by the National Natural Science Foundation of China (41471233, 41501042, 41571130073), the Science and Technology Service Network Initiative of Chinese Academy of Sciences (KFJ-EW-STS-092), the Youth Innovation Team Project of ISA, CAS (2017QNCXTD_XXL), and the “100 talents program” (2060299) of the Chinese Academy of Sciences.
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