Abstract
Carbon sequestration of plantations formed by three kinds of forestation (natural forest to plantation (NP), grassland to plantation (GP), and cropland to plantation (CP)) greatly depends on the change of soil organic carbon density (SOCD) compared with its initial SOCD before forestation. However, this dependence was rarely studied, especially in semi-humid/arid regions with strong site variation. This limits the precise assessment and management of SOCD. Therefore, the SOCD variations of 0–100 cm soil layers in these three kinds of plantations were studied in the semi-humid/arid Liupan Mountains in northwestern China. The NP with high initial SOCD showed firstly a decrease and then an increase of SOCD up to 293.2 t·ha−1 at 40 years. The CP and GP with low and relatively high initial SOCD showed negligible and slight SOCD decrease after forestation, but then an increase up to 154.5 and 266.5 t·ha−1 at 40 years. After detecting the main factors influencing SOCD for each forestation mode, statistic relationships were fitted for predicting SOCD variation. This study indicates that besides forest age and biomass growth, the effects of initial vegetation, site-dependent initial SOCD, and SOCD capacity, also precipitation and air temperature in some cases, should be considered for more precise assessment and management of SOCD of plantations.
Highlights
Forestation is usually viewed as an important and effective approach to mitigating climate change by increasing the amount of carbon stored in vegetation and soil pools [1]
The analysis showed an obvious difference in soil organic carbon density (SOCD) among sub-areas and vegetation types (Figure 2)
The lower-altitude-associated lower mean annual precipitation (MAP) and higher mean annual temperature (MAT) in RH and LH lead to more severe drought limit to vegetation growth and less soil organic carbon (SOC) input at one side, and the higher mean annual temperature in RH and LH leads to higher SOCD loss due to accelerated SOC mineralization at another side, which primarily resulted from changes in soil microbial metabolic activity or microbial community composition [30]
Summary
Forestation is usually viewed as an important and effective approach to mitigating climate change by increasing the amount of carbon stored in vegetation and soil pools [1]. In the period from 2000 to 2017, China showed the highest net increase of green leaf-covered area (1351 million km2) and the highest growth rate (17.8%), largely due to forestation [2]. Both the existing plantation area and future potential afforestation area are mainly located at the semi-humid/arid regions of northwestern and northern China, where complex land use, variable site quality, and low precipitation (mostly of 400–800 mm) are important influencing factors of the forest area increase [3], forest growth, and carbon sequestration [4]. The accurate estimates of SOCD dynamics after forestation in the climate-sensitive semi-humid/arid regions were rare, especially due to the lack of data from regional field surveys, and remain a major challenge
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