Threshold changes in vegetation along a grazing gradient in Mongolian rangelands
Threshold changes in vegetation along a grazing gradient in Mongolian rangelands
复制标题
DOI：
10.1111/j.1365-2745.2007.01315.x
复制
发表时间：
2007-10
影响因子：
5.5
通讯作者：
Takehiro Sasaki;Tomoo Okayasu;U. Jamsran;K. Takeuchi
中科院分区：
文献类型：
--
作者：
Takehiro Sasaki;Tomoo Okayasu;U. Jamsran;K. Takeuchi
1阈值的概念在生态学中已经变得很重要，但对牧场生态系统中植被对放牧的潜在阈值反应的性质仍然知之甚少。我们的目标是确定沿放牧梯度的植被变化的生态阈值，并检查阈值变化是否在不同的生态地点表现出相似的表现。2为了实现这一目标，我们在蒙古中部和南部牧场的10个生态站点沿放牧坡度调查了植被，每个生态站点都位于不同的景观位置。通过将数据的线性模型与用指数曲线、逆曲线、分段回归和Sigmoid Logistic曲线拟合的非线性模型进行比较，检验了植物区系组成沿放牧梯度变化的阈值的证据。3三种非线性模型(分段模型、指数模型和Sigmoid模型)比线性模型对数据的拟合更好，突出了放牧梯度上植被变化的不连续性。不同地点的最佳拟合模型的形状及其与数据的拟合度基本相似，表明在放牧阈值水平以下，植物区系组成的变化相对恒定，之后曲线变化剧烈。4除两个站点外，最佳拟合模型的Bootstrap可信区间(95%CI)相对较窄，特别是在临界点或变化率加快的区域附近，强调我们的结果是稳健和决定性的。5综合。我们的研究为所有生态站点沿放牧梯度的植被变化存在生态阈值提供了强有力的证据。这表明，研究区的植被对放牧的反应基本上是非线性的。认识到实际放牧梯度中存在真正的阈值变化将有助于土地管理者防止不良状态的发生，并促进理想状态的发生，因此将使牧场生态系统的可持续管理向前迈进一大步。
1 The concept of threshold has become important in ecology, but the nature of potential threshold responses of vegetation to grazing in rangeland ecosystems remains poorly understood. We aimed to identify ecological thresholds in vegetation changes along a grazing gradient and to examine whether threshold changes were expressed similarly at a variety of ecological sites. 2 To accomplish this, we surveyed the vegetation along grazing gradients at 10 ecological sites, each located at different landscape positions in Mongolia's central and southern rangelands. Evidence for a threshold in changes in floristic composition along the grazing gradient was examined by comparing linear models of the data with nonlinear models fitted using an exponential curve, an inverse curve, a piecewise regression and a sigmoid logistic curve. 3 Three nonlinear models (piecewise, exponential and sigmoid) provided a much better fit to the data than the linear models, highlighting the presence of a discontinuity in vegetation changes along the grazing gradient. The shapes of the best‐fit models and their fit to the data were generally similar across sites, indicating that the changes in floristic composition were relatively constant below a threshold level of grazing, after which the curve changed sharply. 4 Except for two sites, the best‐fit models had relatively narrow bootstrap confidence intervals (95% CI), especially around threshold points or zones where the rate of change accelerated, emphasizing that our results were robust and conclusive. 5 Synthesis. Our study provided strong evidence for the existence of ecological thresholds in vegetation change along a grazing gradient across all ecological sites. This suggests that vegetation responses to grazing in the study areas are essentially nonlinear. The recognition that real threshold changes exist in real grazing gradients will help land managers to prevent the occurrence of undesirable states and promote the occurrence of desirable states, and will therefore permit a major step forward in the sustainable management of rangeland ecosystems.