| Village landscapes, which integrate small-scale agriculture with housing, forestry and a host of other land use practices, are a mosaic of natural environment and human management, and cover more than 2 million square kilometers across China. Village lands tend to be managed at very fine spatial scales (≤30 m), with managers both adapting their practices to existing variation in soils and terrain (e.g. fertile plains vs. infertile slopes) and also altering soil fertility and even terrain by terracing, irrigation, fertilizing and other land use practices. The China’s village landscapes are very important in the global change because of its vast area and great population. However, these intensively managed anthropogenic landscapes are dominated by fine-scale landscape changes that are a challenge to measure by conventional complete coverage remote sensing, even were adequate historical imagery available for this. Here we investigate relationships between fine-scale land management patterns and soil organic carbon (SOC), total nitrogen (TN), and total phoshporusin (TP) in the top 30 cm of village soils. First, the sites (100 km2) and 12 samples (500x500 m) were selected based on analysis of regional Landsat LULC data, and then mapped into ecologically-distinct landscape components (ecotope features) using a field-validated high spatial resolution mapping procedure based on IKONOS imagery, then Soils were sampled within fine-scale landscape features using a regionally-weighted landscape sampling design. Last, sample data were upscaled into regional scale analysis using two upscaling procedures, cluster distance weighting procedure (CDW) and multivariate regional optimization (MRO) procedure.According to the ecotope area and SOC density, SOC stocks in China’s village regions were about 5.5±0.69 Pg C in the top 30 cm of 2×106 km2, representing roughly 3～4% of total SOC stocks in global croplands. The SOC density ranged from 3.45±0.66 kgm-2 in Yangtze Plain to 2.12±0.57kg m-2 in Sichuan Hilly, and the other regions were about 2.7 kg m-2, The TN stocks were about 0.54±0.07 Pg in China’s village regions (2×106 km2), and the TN densities were also highest in Yangtze Plain, and lowest in Sichuan Hilly, and the other three regions had middle value; The TP stocks were about 0.30±0.05 Pg, with highest TP densities of 0.22 kg m-2 in North China Plain and Yangtze Plain,0.19±0.03 kg m-2 in Sichuan Hilly,0.11±0.03 kg m-2 in Subtropical Hilly, and lowest value of 0.08±0.04 kg m"2 in Tropical Hilly. When regional SOC, TN, and TP densities were regressed linearly against the environmental variables, there were no good relationship between macroclimate and SOC and TN densities, while good relationship between the macroclimate and TP density, although without statistically significant relationship. The main reason probobly was that intensive human activities in the densely populated village affected the spatial distribution of SOC and TN, but little effect on the TP, highlighting the degree to which human activities may alter SOC in these regions, though much of the variation in SOC associated with different land use types appears to have resulted from farmer selection of the most naturally-fertile lands for intensive agriculture, and not from changes in SOC caused by land management practices in themselves.SOC, TN, and TP density varied strongly with land use, land cover, demonstrating that land use and land cover are likely significant factors controlling SOC density in village landscapes. The highest SOC and TN densities within landscapes were found in agricultural lands, especially paddy, SOC densities were at their lowest in lands without agricultural, forestry or other productive use, such as fallow land, mined areas, and in areas where variability from natural disturbance precluded regular cultivation (seasonal riverbeds). Forestry lands usually had moderate values. However, the TP density spatial distribution was different from the SOC and TN density. As expected, the highest STP densities were found in areas near buildings and in agricultural lands, and the lowest TP densities were found in forest and fallow. Generally, The SOC, TN, and TP densities in the 0-15 cm layer were higher than that in the 0-15 cm layer, respectively, especially in the paddy soil, and no differences in the forest. While in the areas of land around buildings and roads, the SOC, TN, and TP densities in the 0～15 cm layer were higher than that in one region and opposite results in other region, making it difficult to draw conclusions.As a combined result of these high SOC, TN and TP densities and the predominance of agricultural land use in village landscapes, most village SOC was found in agricultural land, except in the Tropical Hilly Region, where forestry accounted for about a half of SOC, TN and TP stocks. A surprisingly large portion of village SOC, TN and TP stocks, having significant relationship with the population density, were associated with built structures and with the disturbed lands surrounding these, ranging from～20% in the North China Plain to～10% in the Tropical Hilly Region, demonstrating that human residence, not just agricultural practice, is a regionally important control on total SOC, TN, and TP stocks across village landscapes. Across the whole densely populated village landscape, the irrigated land account for the largest portion of SOC, TN and TP stock, followed by the paddy soil and forest.In each village region, SOC, TN and TP densities varied strongly with the fine scale of ecotope, and its spatial distribution within ecotope was much more complicated than within land use and land cover. The SOC, TN, and TP densities were also different with ecotopes although with the same land form, or land use, or land cover. The ecotope type with highest SOC, TN and TP stocks was different across five regions, was FPIAac05 in North China Plain, FPPAri01 in Yangtze Plain, BPRAac04 in Sichuan Hilly, FSPAri01 in Subtropical Hilly, and SLTPob02 in Tropical. The ecotope level analysis can reflect the spatial differences of SOC, TN and TP density at the fine scale.From the results above, we concluded that the land form, land use, land cover, and ecotope had significant effect on the spatial distribution of soil nutrients. By linking soil sampling with high resolution ecological mapping, local variation in soil carbon sequestration associated with intensive land management may be quantified and understood within and across densely populated anthropogenic landscapes, including not only the villages of Asia, but potentially urban and suburban landscapes as well. |
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