压砂种植模式对地表热场景观格局的影响

基于Landsat ETM+数据,反演了宁夏环香山地区的地表温度,计算热场指数差异,运用景观指数对压砂地热场景观格局动态变化进行分析。研究表明:在宁夏环香山地区各土地利用类型中,压砂地的地表温度及热场变异指数最高,其次为未利用地,而草地、耕地、林地的地表温度较低。近十年间,宁夏环香山地区的热场呈现出高温斑块数量先增加后减少,景观由简单到复杂、再趋向简单的演变趋势。在2004—2009年间,热场景观斑块总数及密度明显增加,景观破碎化程度加深;高等级斑块类型的优势度明显提升,形状趋向复杂;由于大量低等级斑块转向高等级斑块,导致区域热岛效应明显增强。但在2009—2013年间,宁夏环香山地区的热场景观格局变化却表现出与2004—2009年间完全相反的变化态势。引起热场景观格局变化的主要原因是当地种植模式的变化,在2009年之前,宁夏环香山地区的压砂地面积的迅速扩张,由分散、局部、小面积转变为集中、连片、大面积的模式,大规模改变下垫面性质造成地表温度升高;然而2009—2013年,虽然压砂地面积继续扩大,但由于调整了种植结构,实行枣瓜间作,使得地表植被覆盖度增加,高温斑块面积比例开始下降。

Effects of cropping patterns on surface thermal landscape in gravel-sand mulching field

The method of gravel-mulched moisture conservation has been adopted to a large extent in the Xiangshan region of Ningxia for the past few years. Covered with gravel and coarse sand, land surface was affected obviously in soil temperature. It was of importance to quantify the characteristics of thermal landscape for evaluating regional ecologic security and thereby serving for agricultural production. Based on Landsat Enhanced Thematic Mapper Plus (ETM+) thermal images, land surface temperature was retrieved around Xiangshan region. Differences of thermal parameters were calculated, followed by landscape metrics to analyze dynamic changes of thermal field landscape pattern. The results showed that gravel-mulched land topped the list for land surface temperature and heat field variation index around Xiangshan region in Ningxia, followed by unutilized land. Moreover, land surface temperature of grassland, farmland and forestland was lower. In the past ten years, thermal field exhibited an evolving trend: high-grde thermal patches increased first and then decreased, and landscape changed from simplicity to complexity and finally to simplicity. From 2004 to 2009, the patch amount and density increased significantly, thermal landscape became more fragmented. The dominance of high-grade thermal landscape patch was upgraded obviously, and the patch shape trended to complex. Regional heat island effect was enhanced significantly because of the conversion of a great number of patches from low-grade to high-grad. From 2009 to 2013, however, thermal landscape pattern showed an opposite tendency in comparison with that between 2004 and 2009. The changes of planting structure were the main causes of thermal landscape pattern evolution. The area of gravel-mulched land expanded rapidly around Xiangshan region in Ningxia, the gravel-mulched land changed from fragmentation to concentration before 2009. Changing the properties of underlying surface on a large scale resulted in land surface temperature rising. From 2009 to 2003, although the area of gravel-mulched land kept on expanding, the vegetation coverage increased and the area proportion of high-grade thermal patches started to decline due to the adjustment of planting structure and the implementation of jujube-melon intercropping.