黄土丘陵区小流域不同海拔刺槐径向生长对气候的响应差异

Radial growth responses of black locust(Robinia pseudoacacia L.)to climate at different elevations in a Loess Plateau watershed

为明确黄土高原丘陵区第三副区典型流域⁃甘肃天水罗玉沟流域刺槐生长过程及其与气候关系随海拔变化的规律。利用树木年代学方法分别建立高、中、低3个海拔刺槐的标准年表,并分析不同海拔刺槐径向生长过程以及对气候变化的响应。研究结果表明:(1)中、低海拔刺槐径向生长与温度因素多为负相关,而高海拔刺槐径向生长与温度因素多呈正相关。高海拔刺槐生长与上一年生长季(6月)、休眠期(当年3—4月)和当年生长季(6月)均温、最低温和最高温呈显著正相关,其中受最低温影响最显著;中、低海拔刺槐与上一年生长季和当年生长季的均温、最高温和最低温呈显著负相关,低海拔受均温影响显著。(2)随海拔升高,刺槐径向生长与降水和相对湿度的正相关呈降低趋势。低海拔刺槐生长与上一年生长季(7—9月)和当年生长季(6—9月)降水、相对湿度呈显著正相关,中海拔刺槐与当年生长季(6—9月)降水、相对湿度呈显著正相关,而高海拔刺槐生长与上一年生长季(6—7月)相对湿度呈显著负相关。(3)低海拔刺槐与上一年6月—当年10月帕默尔干旱指数(PDSI)呈显著正相关;中海拔刺槐与上一年6月和当年2—10月PDSI呈显著正相关;高海拔刺槐与上一年6—7月PDSI呈显著负相关。中、低海拔刺槐遭受干旱胁迫,限制树木生长。在气候暖干化背景下,罗玉沟流域中、低海拔刺槐受水分胁迫更加严重。在黄土丘陵区开展水土流失治理生物措施经营管理过程中,须注意刺槐林生长对气候响应的海拔差异。

The purpose of this study is to determine the growth process of black locust(Robinia pseudoacacia L.)and its relationship with climate and elevation in the Luoyugou watershed of the Chinese Loess Plateau.Standard chronologies of black locust trees were measured at high,middle,and low elevation areas using dendrochronology method.The results indicated that the radial growth of black locust at middle and low elevation areas were negatively correlated with temperature factors;however,a positive correlation between temperature and radial growth of black locusts was observed at high elevation.In addition,black locust growth at high elevation was positively correlated with the mean temperature,minimum temperature,and maximum temperature during the previous year(June),dormant period(March—April),and current growing season(June).At middle and low elevation areas,the black locust growth were negatively correlated with the mean temperature,minimum temperature,and maximum temperature during the previous and current growing seasons.Black locust growth at low elevation was also significantly affected by the mean temperature.With elevation,a decreasing trend in the positive correlations between radial growth,precipitation,and relative humidity was observed.Black locust growth at low elevation was positively correlated with the precipitation and relative humidity during the previous year(July—September)and current growing season(June—September).At middle elevation,black locust growth was positively correlated with the precipitation and relative humidity during the current growing season(June—September),while the growth of black locust at high elevation was negatively correlated with the relative humidity during the previous growth season(June and July).At low elevation,black locust growth was positively correlated with the Palmer drought index(PDSI)from June of the previous year to October of the current year,whereas black locust growth at middle elevation was positively correlated with the PDSI in June of the previous year and in February—October of the current year.A significantly negative correlation was observed between high elevation black locust growth and PDSI in June⁃July of the previous year.Black locust growth at middle and low elevation areas were subjected to drought stress,which restricted tree growth.Under climatic warming and drying background conditions,black locusts experienced more severe water stress at middle and low elevation areas in the Luoyugou Watershed.Thus,while implementing biological management strategies aimed at soil and water loss prevention in the hilly areas of the Loess Plateau,elevation differences in the responses of black locust forest growth should be considered.