2000年以来浐灞河流域不同地貌区植被变化特征及影响因素研究

Study on Vegetation Variation Characteristics and Influencing Factors in Different Geomorphic Zones in the Chanbahe River Basin since 2000

秦岭是中国南北气候分界线。2000年以来植被的快速恢复,对该区域生态水文过程产生了深远的影响。秦岭地区地貌多样,分析不同地貌区植被恢复特征、影响因素及其对生态水文过程的影响,对秦岭生态环境保护具有重要的借鉴意义。以位于秦岭北坡的浐灞河流域为研究对象,将整个研究区分为上游山地区、中游丘陵区和下游平原区3个分区,以归一化植被指数(NDVI)为基础数据,基于趋势分析和回归分析等方法,研究了浐灞河流域不同地貌区的植被恢复差异、影响因素及其对径流输沙的影响。结果表明,浐灞河流域上游山地区NDVI值呈极显著增加趋势,中游丘陵区NDVI值呈缓慢增加趋势,而下游平原区呈极显著减少趋势。上游山地区NDVI在6—9月处于较高水平,中游丘陵区和下游平原区NDVI的年内分布呈现双峰特征。整个浐灞河流域的植被恢复速度为0.0019/a,上游山地区、中游丘陵区以及下游平原区的植被恢复速度存在显著差异(P<0.05)。上游山地区海拔对植被恢复速度具有显著影响(P<0.05),中游地区不同坡度的植被恢复存在显著差异(P<0.05)。上游山地区植被恢复的主要驱动力是林地自身植被覆盖度的提升,中游丘陵区部分林地覆盖度的提升是这一区域植被覆盖度提升的主要原因,而下游平原区耕地转为建设用地是植被退化的主要原因。年降水量对上游山地区的植被覆盖度影响不显著,但对中游丘陵区的植被覆盖度具有极显著的正相关关系(P<0.001)。在浐灞河流域,植被恢复对径流量的影响较小,而对土壤侵蚀模数影响较大。综上,植被在秦岭北坡不同地貌区的恢复特征和影响因素不同,深入研究植被恢复的时空差异及其对气象因子的响应,对于秦岭地区植被保护具有重要意义。

The Qinling Mountains form a climatic boundary between northern and southern China.The rapid restoration of vegetation since 2000 has had a profound impact on the eco-hydrological processes of this region.The Qinling Mountains consist of diverse geomorphic landforms.Thus,analyses of vegetation restoration characteristics,influencing factors,and their influences on ecohydrological processes in different landforms are important for environmental protection in the region.We investigated the Chanbahe River Basin on the northern slope of the Qinling Mountains,and divided the study area into three zones(i.e.,the upstream mountainous zone,the midstream hilly zone,and the downstream plain zone).Based on the normalized difference vegetation index(NDVI),we conducted trend and regression analyses to explore the differences in vegetation restoration,the influencing factors,and their effects on runoff and sediment transport.The results showed that the NDVI values had a highly significant increasing trend in the upstream mountainous zone,a gradual increasing trend in the midstream hilly zone,and a highly significant decreasing trend in the downstream plain zone.In the upstream mountainous zone,the NDVI value was the highest from June to September,whereas in the midstream hilly and downstream plain zones,the annual NDVI distribution showed a double-peak.The vegetation restoration speed across the entire basin was 0.0019/a but showed significant differences among the three zones(P<0.05).Altitude had a significant influence on the vegetation restoration speed in the upstream mountainous zone(P<0.05).Furthermore,the vegetation restoration speed showed significant differences among different slope gradients in the midstream zone(P<0.05).The primary driver of vegetation restoration in the upstream mountainous midstream hilly zones was an increase in vegetation coverage in the forest land.The main cause of vegetation degradation in the downstream plain zone was the conversion of farmland into construction land.Annual precipitation had a non-significant influence on vegetation coverage in the upstream mountainous zone but was significantly positively correlated with vegetation coverage in the midstream hilly zone(P<0.001).Across the basin,vegetation restoration had little influence on the runoff volume but a considerable effect on the soil erosion modulus.In summary,vegetation restoration characteristics and influencing factors varied among the three geomorphic zones on the northern slope of the Qinling Mountains.Further in-depth study on the spatiotemporal differences in vegetation restoration and its response to meteorological factors should be conducted for the improvement of vegetation protection in the Qinling Mountains.