秦巴山地NPP及对气候变化响应的多维地带性与暖温带-亚热带界线

秦巴山地位于我国的南北过渡带,对我国生态地理格局产生重要影响。为了探索秦巴山地植被净第一性生产力(NPP,Net Primary Productivity)的时空格局及其气候响应的多样性和复杂性,为我国暖温带-亚热带界线的具体分布提供新的佐证,基于2000—2015年的MOD17A3的地表植被NPP数据和秦巴山地93个气象站点数据,从经度、纬度、海拔、坡向多个维度研究了秦巴山地地表植被NPP的分布及与气候因子的关系。结果表明:从2000—2015年,(1)秦巴山地中低山地区,自北向南随纬度降低,地表植被多年平均NPP呈现增加的趋势,体现了纬度地带性;年均NPP与温度的关系由负相关变为正相关,转折点出现在汉江;与降水的相关性减弱。(2)自西向东多年平均NPP值先增加后减少,秦岭一线地表植被年均NPP与温度由正相关变为负相关,与降水主要呈正相关,相关性先增加后减少。(3)随高度的增加,秦巴山地多年NPP值及增长率均呈现先增加后减少的趋势。(4)秦岭和大巴山多年平均NPP均呈现增加趋势,但是秦岭增长较大巴山更明显;2000m以下,秦岭南坡增长率明显高于北坡,大巴山北坡增长率明显高于南坡;2000—3000m,秦岭南北坡差异较小,但是大巴山差异明显;中山地区(1000—2500m),秦岭年均NPP与气温呈负相关,而大巴山则呈现正相关或弱相关;秦岭地区年均NPP与降水的相关性整体强于大巴山地区。这就意味着全球变暖、气温升高对秦岭植被尤其是中低山地区的植被产生不利影响,但是对大巴山则有利,而前者植被生长主要与降水增加有关。这也说明了基于汉江为界的秦岭和大巴山无论是地表植被NPP的均值还是其南北坡差异以及对气候因子的响应呈现了明显的差异,而汉江作为中山地区植被NPP与气温相关性由正相关性到负相关的转折点,与降水的关系由弱相关到正相关的转折点,更合适作为南北分界线。

Assessing the dividing line between warm temperate and subtropical zones based on the zonality discussion on multi-dimensional response of Net Primary Productivity to climate change in the Qinling-Daba Mountains

Situated in the north-south transition zones and being part of the division between the Yangtze River and the Yellow River,the Qinling-Daba Mountains(QDM)play a key role in affecting the distribution of ecological and geographic patterns in China.The Net Primary Productivity(NPP)in forest ecosystem is being affected by changing climate from regional to global scale.To explore the spatial-temporal distribution patterns of NPP and assess the effect of temperature and precipitation on NPP in the QDM,as well as to provide new proof about the detailed locations of the dividing line between warm temperate and subtropical zones in China,historical NPP data of MOD17 A3 and the temperature and precipitation data at 93 weather stations surrounding the QDM from 2000 to 2015 were acquired,and then kriging method,pearson correlation and topographic factor analysis were applied for developing spatial map of stations based on temperature and precipitation and assessing the effects of temperature and precipitation on NPP at different dimensions,including the latitudinal,longitudinal altitudinal gradients and aspect,etc.The results indicate that:(1)as the latitudes decrease from north to south,an increasing trend of the multi-year(2000 to 2015)averaged NPP is observed within the homogeneous low-middle altitude zones in the QDM,which reflects the latitudinal zonality of NPP distribution.Correlation between annual vegetation NPP and precipitation tends to decrease and correlation between annual vegetation NPP and air temperature changes from negative to positive with the turning point at the Han Jiang river valley from north to south,which implies that Han Jiang could be the important dividing line between the Qinling and Daba Mountains.(2)From west to east as the longitudes increase,the multi-year(2000 to 2015)averaged NPP increases first and then decrease,correlation between annual vegetation NPP and air temperature is first positive and then nagative in the Qinling Mountains where the relationship between annual vegetation NPP and precipitation is positive.(3)With the increase of altitude,the multi-year(2000 to 2015)averaged NPP and its change rate increase first and then decrease in the QDM.(4)From different aspects,variation and response of annual vegetation NPP to temperature and precipitation differ greatly between the northern and southern slopes in the QMD.Below an elevation of 2000 m,the annual change rate of NPP is obviously higher in the southern slope than in the northern slope in the Qinling Mountains,whereas it is vice versa in case of the Daba Mountains.At the elevation of 2000—3000 m,the difference in the change rate of average annual vegetation NPP between the northern and southern slopes is smaller in the Qinling Mountains than that in the Daba Mountains.Correlation between annual vegetation NPP and temperature is negative in the mid-altitude zone from 1000 to 2500 m in the Qinling Mountains,while the positive or weak correlations are observed in the Daba Mountains,and correlation of annual vegetation NPP with precipitation is much stronger in the Qinling Mountains than that in the Daba Mountains.It implies that global warming has negative effect on vegetation growth in the Qinling Mountains,especially at the low-middle elevation whereas it is vice versa for the Daba Mountains.On the contrary,wetter climate contributes more to vegetation growth in the Qinling Mountains than in the Daba Mountains.Han Jiang river valley,as the dividing line between the Qinling Mountains and the Daba Mountains,is a turning point of the relationship between annual vegetation NPP and temperature from positive to negative,and a tipping point between annual vegetation NPP and precipitation from weak to significantly positive from south to north at middle altitudes in the QDM.Consequently,it is more suitable to be applied in determining north-south dividing line.Our finding will help to understand productivity in these complex QDM areas and thereby contribute to sustainable forest management and policy making in the QDM.