Abstract

Aims

Grasslands are globally threatened by climate changes and unsustainable land-use, which often cause transitions among alternative stable states, and even catastrophic transition to desertification. Spatial vegetation patch configurations have been shown to signify such transitions at large spatial scale. Here, we demonstrate how small-scale patch configurations can also indicate state transitions.

Methods

The whole spatial series of degradation successions were chosen in alpine grasslands characterized as seven typical communities. Patch numbers, and perimeter and cover of each patch were recorded using adjacent quadrats along transects in each type of the communities. Species abundance within each patch was measured.

Important Findings

Across seven grazing-induced degradation stages in the world’s largest expanse of grassland, from dense ungrazed turf to bare black-soil crust, patch numbers and perimeters first increased as patch cover decreased. Numbers and perimeters then decreased rapidly beyond an intersection point at 68% of initial continuous vegetation cover. Around this point, the vegetation fluctuated back and forth between the sedge-dominated grassland breaking-up phase and the forb-dominated phase, suggesting impending shift of grassland state. This study thus demonstrates how ground-based small-scale vegetation surveys can provide a quantitative, easy-to-use signals for vegetation degradation, with promise for detecting the catastrophic transition to desertification.

中文翻译：

---

斑块的覆盖-周缘关系的小范围转换表明草原退化过程中优势种的转移

摘要

目的

全球草原受到气候变化和不可持续土地利用的威胁，这通常会导致其他稳定国家之间的过渡，甚至发生灾难性的向荒漠化的过渡。已经显示出空间植被斑块的配置在较大的空间尺度上表明了这种过渡。在这里，我们演示了小型补丁程序配置也可以指示状态转换。

方法

在具有七个典型群落特征的高寒草原中，选择了退化演替的整个空间序列。使用相邻社区沿样带在每种类型的样带中记录样片编号，每个样片的周长和覆盖率。测量每个斑块内的物种丰度。

重要发现

在世界上最大的草原上，从放牧草皮到裸露的黑土结皮，在七个放牧导致的退化阶段中，随着斑块覆盖率的降低，斑块数量和周长首先增加。然后，其数量和周长迅速下降，超过交汇点的初始连续植被覆盖的68％。在这一点附近，植被在以莎草为主的草丛分裂期和以草为主导的草丛期之间来回波动，表明草地状态即将发生变化。因此，这项研究表明，地面小规模植被调查如何能够为植被退化提供定量，易于使用的信号，有望检测出向荒漠化的灾难性转变。