玛曲县植被覆被变化及其对环境要素的响应

Variation in vegetation and its response to environmental factors in Maqu County

植被覆被变化是气象要素和人类活动综合作用的结果,能够反映区域内生态系统的演替趋势。玛曲高寒生态区作为黄河上游重要的水源涵养和补给区,具有维持区域生物多样性和生态安全,保障经济社会健康发展的重要作用,因此厘清该区域植被变化与气候及人类活动等环境要素的相互关系有助于为玛曲县生态治理与恢复提供科学参考。鉴于此,以2000—2015年MODIS/NDVI数据为基础,结合同期气象与人类活动数据,应用趋势分析法、相关分析以及通径分析等方法,分析了玛曲县植被NDVI的时空变化规律,并详细探讨了气象要素和人类活动对植被覆被变化的影响。结果表明:(1) 2000—2015年玛曲县NDVI呈波动上升趋势,上升速率为0.01015/10a;各土地利用/覆被类型中,增加幅度由大到小依次为高山稀疏植被、湿地、沙化草甸、山地疏林地、高寒草甸、亚高山硬叶灌丛、亚高山阔叶灌丛和高寒草原;增加面积占相应地类总面积比例由大到小分别是高山稀疏植被(75.57%)、山地疏林地(71. 45%)、沙化草甸(71. 18%)、湿地(70. 66%)、高寒草甸(68. 15%)、亚高山硬叶灌丛(66.96%)、亚高山阔叶灌丛(66.24%)和高寒草原(66.05%);(2)气象要素中,气温与NDVI间具有显著正相关(P<0.05),是影响植被覆被的决定性因子,利于植被的生长与发育;降水与NDVI间相关不显著(P>0.05),对植被覆被的影响较小;(3)人类活动要素中,与放牧强度密切相关的大牲畜存栏数和羊存栏数是植被生长的主控因子,其中大牲畜存栏数呈显著的抑制作用(P<0.05),羊存栏数具有较强的促进作用(P<0.05);(4)通径分析发现,气温、大牲畜存栏数和羊存栏数的决定系数依次为0.3005,-0.0563和0.0128,说明气温对NDVI的综合作用强度最高、大牲畜存栏数次之,羊存栏数最低;此外,剩余通径系数为0.53。该数值较大,表明仍有部分对NDVI增加存在影响的环境要素未考虑到,需在今后的研究中给予关注。

Change in vegetation coverage,which can reflect the direction of regional succession in ecosystems,is the result of the combined action of meteorological factors and human activities.As an important water conservation and recharge area in the upper reaches of the Yellow River,the alpine ecological zone of Maqu County plays an important role in maintaining regional biodiversity and ecological security,and also in ensuring the healthy development of human economy and society.Clarification of the relationships among vegetation change and climatic conditions and human activities or other environmental factors in this region would thus make an important contribution to ecological management and restoration in Maqu County.Therefore,we used trend,correlation,and path analyses to analyze the temporal and spatial variation of vegetation normalized difference vegetation index(NDVI)in Maqu County based on MODIS/NDVI data obtained between2000 and 2015 and meteorological and human activity data for the same period.Furthermore,we present a detailed discussion on the effect of meteorological factors and human activities on vegetation cover change.The following results were obtained.(1)Fluctuation in the NDVI of Maqu County increased from 2000 to 2015,with a rate of increase of 0.01015/10 a.Among all land use and cover types,the range increased in the following order:alpine sparse vegetation>wetland>desertification meadow>open forest>alpine meadow>subalpine sclerophyllous shrubs>subalpine broadleaf shrubs>alpine grassland.The order of the increasing area accounting for the total area was alpine sparse vegetation(75.57%)>open forest(71.45%)>desertification meadow(71.18%)>wetland(70.66%)>alpine meadow(68.15%)>subalpine sclerophyllous shrubs(66.96%)>subalpine broadleaf shrubs(66.24%)>alpine grassland(66.05%).(2)Among the meteorological factors examined,there was a significant positive correlation between temperature and NDVI(P<0.05),which was a decisive factor affecting vegetation cover and beneficial to the growth and development of vegetation.Vegetation cover was less affected by precipitation and there was no significant correlation between precipitation and NDVI(P>0.05).(3)Among the human activities examined,large livestock and sheep population numbers were the main factors controlling vegetation growth,which was closely related to grazing intensity,with large livestock populations having significant inhibitory effects(P<0.05)and sheep populations having strong promoting effects(P<0.05).(4)Path analysis yielded decision coefficients of 0.3005,-0.0563,and 0.0128 for air temperature,large livestock population number,and sheep population number,respectively,indicating that the effect of temperature on NDVI was the strongest and the effect of sheep population number was the weakest.In addition,the residual path coefficient of 0.53 indicated that there are certain other environmental factors that have an effect on the increase of NDVI,but were not taken into consideration,which warrant further attention in future research.