广西东北部喀斯特城市森林净初级生产力的时空变化规律研究

Ecological environment is fragile in karst area. Forest is difficult to recover once damaged. It results in soil erosion, large areas of exposed bedrock and formation of rocky desertification landscapes. Rocky desertification will affect the ecological environment and socio-economic development seriously. Human activities are the main factors leading to rocky desertification. Karst city is the place where human activity is most intense. Net primary productivity (NPP) is an important parameter characterizing plant activities. However the existing remote sensing model for estimating NPP does not apply to karst cities. Recently eco-environmental problems have resulted from swift urban expansion, rapid variations of land use and land cover in Guilin karst city of northeast Guangxi which is famous for South China Karst of World Heritage. Digital Elevation Model data were used to correct terrain effects on ground solar radiation. With the ground data such as forest leaf area index, soil water content and biomass were measured, the soil water equilibrium model for karst area (karst SWEM ) was constructed. And BEPS model for karst urban ecosystem (karst urban BEPS model) was got after BEPS model was integrated with karst SWEM. Then net primary productivity (NPP) of urban forest was estimated with karst urban BEPS model and different temporal remote sensing images and was validated with ground NPP measurements. Land use images were got from Landsat satellite data based on mixed pixel decomposing and SVM. With the analysis of spatio-temporal variation of NPP and its influencing factors, the maintenance and promotion mechanism of urban forest NPP in karst city was studied. The research will provide scientific data for sustainable development and ecological environmental protection in karst cities.

喀斯特地区生态环境脆弱，森林植被一旦破坏即难以恢复，水土流失，基岩大面积出露，形成石漠化景观，严重影响生态环境和社会经济发展。人为活动是导致石漠化的主要因素，而喀斯特城市是人类活动最剧烈的地方。净初级生产力NPP是表征植物活动的重要参数，现有估算其的遥感模型并不适用于喀斯特城市。针对“中国南方喀斯特”世界遗产广西东北部喀斯特地区桂林等城市快速扩展所引起的生态环境问题，利用数字地形高程数据修正地形对地表接收太阳辐射的影响，观测森林样地叶面积指数、土壤水分、生物量等数据，构造喀斯特土壤水分层均衡模型并与BEPS遥感模型耦合以改进模型，利用模型和不同时相Landsat遥感图像估算广西东北部喀斯特地区城市森林NPP并验证，利用混合像元分解结合支持向量机对遥感图像进行土地利用分类，定量研究NPP时空变化规律及影响因素、维持稳定性与提高机理，为喀斯特地区城市的生态环境保护和可持续发展提供科学数据。

喀斯特地区生态环境脆弱，森林植被一旦破坏即难以恢复，水土流失，基岩大面积出露，形成石漠化景观，严重影响生态环境和社会经济发展。人为活动是导致石漠化的主要因素，而喀斯特城市是人类活动最剧烈的地方。净初级生产力NPP是表征植物活动的重要参数，现有估算其的遥感模型并不适用于喀斯特城市。针对“中国南方喀斯特”世界遗产广西东北部喀斯特地区桂林等城市快速扩展所引起的生态环境问题，利用数字地形高程数据修正地形对地表接收太阳辐射的影响，观测森林样地叶面积指数、土壤水分、生物量等数据，构造喀斯特土壤水分层均衡模型并与BEPS遥感模型耦合以改进模型，利用模型和不同时相Landsat遥感图像估算研究区城市森林NPP并验证，定量研究NPP时空变化规律及影响因素。结果表明，2000～2019年研究区年NPP均值在150～300 g C/（m2a），地面园林绿化森林的年NPP均值高于喀斯特山峰森林10%～35%。归一化年NPP在0～0.4的低值区面积比例主要受城市扩展的影响，整体呈增加趋势，由2000年33.5%上升到2010年最高值57.4%，之后略下降保持稳定；低值区面积比例的增加主要导致0.4～0.7中值区面积比例的减少；0.7～1.0高值区面积比例由2000年11.1%波动上升到2006年15.3%，之后下降维持在约5%。喀斯特山峰森林和地面园林绿化森林年NPP均值与年日照时数呈显著正相关，太阳辐射是最重要影响因素之一。年降水量与喀斯特山峰森林年NPP均值呈显著正相关，影响较大；降水量对地面园林绿化森林NPP的影响不显著。年平均气温对两种林地的NPP影响不显著。由于高程变化不超过400 m，对NPP的影响较小。已在中文核心期刊发表、录用论文10篇，2篇审稿返修中，培养硕士毕业生10人。研究结果可监测喀斯特山峰植被生长状态，为中国西南喀斯特地区城市的生态环境保护和可持续发展提供科学数据。