Spatial vegetation patterns and imminent desertification in Mediterranean arid ecosystems
Spatial vegetation patterns and imminent desertification in Mediterranean arid ecosystems
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DOI：
10.1038/nature06111
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发表时间：
2007-09-13
期刊：
影响因子：
64.8
通讯作者：
de Ruiter, Peter C.
中科院分区：
文献类型：
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作者：
Kéfi, Sonia;Rietkerk, Max;de Ruiter, Peter C.
人类和气候影响生态系统及其服务(1)，这可能涉及从一种稳定状态到另一种稳定状态的连续和不连续的转变(2)。不连续的转变是突然的、不可逆转的，是已确定的最灾难性的生态系统变化之一(1)。对于陆地生态系统，人们假设植被斑块可以作为即将发生的过渡的标志(3，4)。在这里，我们利用野外数据和模拟方法分析了不同放牧压力下干旱生态系统中植被斑块的变化。在模型方法中，我们将我们的分析外推到更高的放牧压力，以调查荒漠化迫在眉睫时的植被斑块。在西班牙、希腊和摩洛哥的三个干旱的地中海生态系统中，我们发现植被的斑块大小分布遵循幂规律。利用随机元胞自动机模型，我们证明了植物之间的局部正相互作用可以解释这种幂规律分布。此外，随着放牧压力的增加，野外数据显示出一致的偏离幂定律的情况。放牧压力的增加导致了模型中类似的偏差。当放牧在模型中进一步增加时，我们发现这些偏差总是并且只发生在向沙漠过渡的附近，与过渡的类型无关，也与植被覆盖无关。因此，我们认为斑块大小分布可能是荒漠化开始的预警信号。
Humans and climate affect ecosystems and their services(1), which may involve continuous and discontinuous transitions from one stable state to another(2). Discontinuous transitions are abrupt, irreversible and among the most catastrophic changes of ecosystems identified(1). For terrestrial ecosystems, it has been hypothesized that vegetation patchiness could be used as a signature of imminent transitions(3,4). Here, we analyse how vegetation patchiness changes in arid ecosystems with different grazing pressures, using both field data and a modelling approach. In the modelling approach, we extrapolated our analysis to even higher grazing pressures to investigate the vegetation patchiness when desertification is imminent. In three arid Mediterranean ecosystems in Spain, Greece and Morocco, we found that the patch-size distribution of the vegetation follows a power law. Using a stochastic cellular automaton model, we show that local positive interactions among plants can explain such power-law distributions. Furthermore, with increasing grazing pressure, the field data revealed consistent deviations from power laws. Increased grazing pressure leads to similar deviations in the model. When grazing was further increased in the model, we found that these deviations always and only occurred close to transition to desert, independent of the type of transition, and regardless of the vegetation cover. Therefore, we propose that patch-size distributions may be a warning signal for the onset of desertification.