2008－2018年拉萨市温室蔬菜地时空变化特征

随着居民对蔬菜消费需求的不断提高，拉萨市温室蔬菜地得到快速发展，但对温室蔬菜地格局变化过程仍缺乏清楚的认识。该研究基于2008－2018年11期拉萨市高清遥感影像，结合实地调研，采用重心转移分析、地统计分析等方法，研究了2008－2018年拉萨市温室蔬菜地时空格局变化特征。结果表明：1）2008－2018年，拉萨市温室蔬菜地面积总体呈波动上升趋势，年均增长率为6.93%。研究时段内，温室蔬菜地变化经历了发展、调整、稳定三个阶段，各阶段年均变化率分别为11.08%、-2.13%和0.77%。2）研究时段内，拉萨市城关区和堆龙德庆区温室蔬菜地比例下降56.2%，达孜区和曲水县温室蔬菜地比例上升51.58%，温室蔬菜地分布重心向远离城区的城郊转移，向东南方向迁移了约4 896 m。3）新增温室蔬菜地向高海拔和大坡度区域转移，海拔3 675～3 800 m范围内温室蔬菜地面积比例由22.05%上升到30.41%，坡度6°～10°区域温室蔬菜地面积占比上升5.92%。4）温室蔬菜地新增源于耕地，减少多因为建设用地扩张。蔬菜需求量大和温室蔬菜收益高是温室蔬菜地面积增加的基本动力，区域土地利用调整是温室蔬菜地格局变化的重要推动力。

Spatial-temporal variation characteristics of greenhouse-vegetable land in Lhasa of Tibet from 2008 to 2018

Greenhouse-vegetable production serves as a sort of farming, in which vegetable crops grow in built structures, such as wood, plastic, metal and net. Recently, the greenhouse-vegetable farming has become an ideal way to meet the increasing demand of residents for vegetable consumption, particularly on Lhasa in the cold regions. However, a clear understanding for the changing process is still lacking in the greenhouse pattern. This study aims to clarify the change characteristics in the spatial and temporal pattern of the greenhouse-vegetable land in Lhasa from 2008 to 2018, particularly on land use, soil texture and vegetable yield. 11 high-resolution remote sensing images of greenhouse were captured from Lhasa in the northwestern China, from 2008 to 2018. Combined with field research, the barycenter shift and geostatistical techniques were used to determine the total area of greenhouse-vegetable land in various districts or counties. The movement of barycenter position was related to the direction of tracking position, including the altitude gradient and slope. Super-resolution images were obtained for the layout of greenhouses facility in alpine regions, as well the early built greenhouses-vegetable land. The results show that, 1) there was an upward trend in the area of greenhouse-vegetable land in Lhasa from 2008 to 2018, with an average annual growth rate of 6.93%. Three stages were observed for the change features of greenhouse-vegetable land in the study period, including developing, adjustment, and stability. The annual average areas of greenhouse-vegetable land in each stage were 1 050 hm2, 1 413 hm2 and 1 668 hm2, respectively, while the average annual change rates were 11.08%, -2.13%, 0.77%, respectively. 2) In the past ten years, the proportion of greenhouse-vegetable land in Chengguan and Doilungdêqên of Lhasa decreased by 56.2%, while the proportion in Dagze and Quxu increased by 51.58%. 3) The newly developed greenhouse-vegetable lands were transferring to high-altitude and high-slope regions, far away from urban or industrial areas. In the altitude range of 3 675-3 800 m, the areas of greenhouse-vegetable lands increased from 22.05% to 30.41%, while that in the 6°-10° slop regions increased by 5.92%. 4) The spatial change of greenhouse-vegetable lands in Lhasa revealed that the newly added greenhouse-vegetable land much more than farmland, indicating the expansion of construction land. A basic driving force for the growth of greenhouse vegetable lands can be attributed to the large demand for vegetables and the high yield of the greenhouse. Regional land use can also be another important driving force for the distribution of greenhouse-vegetable land. In greenhouse-vegetable land operation, there was no obvious effect on soil texture, indicating the particle size of soil texture changed a little at different elevation gradients. The overall output of vegetables in Lhasa was increasing, with an average annual growth rate of 9.57%. The increase in the greenhouse area has effectively promoted the production capacity of vegetables, thereby to meet the demand of residents for vegetable consumption in Lhasa in the cold regions.