不同利用方式和载畜率对内蒙古典型草原群落初级生产力和植物补偿性生长的影响

Impacts of grazing intensity and management regimes on aboveground primary productivity and compensatory growth of grassland ecosystems in Inner Mongolia

基于2005年6月开始的放牧控制实验,研究了不同草地利用方式和放牧强度对内蒙古典型羊草(Leymus chi-nensis)草原群落初级生产力和补偿性生长的影响。草地利用方式包括:传统放牧、传统割草和放牧与割草轮换利用(混合利用)。结果表明:传统放牧和混合利用方式下,羊草群落地上生物量均随放牧强度增加逐渐降低。高载畜率下,羊草群落地上净初级生产力表现为:混合利用>传统割草>传统放牧,说明混合利用方式优于传统放牧和传统割草利用方式;而低载畜率则有利于草原的可持续利用和植物的补偿性生长。这一实验结果在一定程度上验证了放牧优化假说。在不同利用方式、地形因素的影响和采用不同的群落净生长量计算方法时,随着放牧强度的变化,等补偿、超补偿和欠补偿效应都可能出现。在低载畜率下,群落大多表现出等补偿生长,在高载畜率下,群落大多表现出欠补偿生长。植物群落的补偿性生长与载畜率的关系可以用开口向下的二次函数或者斜率为负的线性函数模拟。说明随着载畜率的增加,一些系统表现为欠补偿生长,而另一些系统则表现为超补偿生长,这可能与植物群落组成、地形部位(平地、坡地)和载畜率以及净生长量的计算方法有关。

Based on the ongoing Sino-German grazing experiment, which was designed to test how grazing intensity and management regimes （traditional system vs. mixed system） would affect the aboveground net primary productivity （ANPP） and compensatory growth of a typical steppe ecosystem in Inner Mongolia dominated by Leymus chinensis and Stipa grandis. Our experimental treatments included two management systems （e.g., a traditional versus a mixed system） and seven levels of stocking （i.e., 0, 1.5, 3.0, 4.5, 6.0, 7.5, and 9.0 sheep/ha）. The traditional system was managed with grazing and haymaking on two different areas. The mixed system was managed with a yearly shift between grazing and haymaking on the same area. The results showed that, with increasing stocking rate, aboveground net primary productivity （ANPP） declined in both traditional and mixed grazing plots. At high stocking rates, ANPP in mixed grazing plots was significantly higher than that in the traditional grazing plots. Our results were partially in agreement with the grazing optimization hypothesis. Under the two management regimes, and using different methods for estimating the annual ANPP, we observed overcompensation, equal-compensation, and under-compensation in plant growth along a gradient of stocking rates. Equal-compensation was generally observed in the low stocking rate plots, while under-compensation was found in the high stocking rate plots. For most systems, compensatory growth could be simulated with linear or quadratic models when the percent biomass eaten by sheep was used as an index for estimating the relative stocking rate. Our study suggests that stocking rate, grazing regime, topographic position, and methods for estimating the net aboveground productivity were all important factors determining the magnitude and directions of estimated ANPP responses to grazing.