Combined effects of grazing and climate warming drive shrub dominance on the Tibetan Plateau
Combined effects of grazing and climate warming drive shrub dominance on the Tibetan Plateau
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DOI：
10.1071/rj19027
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发表时间：
2019-01-01
影响因子：
1.2
通讯作者：
Jeltsch, Florian
中科院分区：
文献类型：
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作者：
Geissler, Katja;Fiedler, Sebastian;Jeltsch, Florian
灌木入侵青藏高原独特的牧区草地生态系统，对生态系统服务功能，特别是牧草生产产生重大影响。我们开发了一个基于过程的生态水文模型，以确定在青海省内的高寒草甸灌木入侵的主要驱动程序的相对重要性。具体而言，我们探讨了夏季牲畜放牧（强度和牲畜类型）的影响以及气候变暖的影响，包括草本和木本植被之间的相互作用以及土壤，水和植被之间的反馈回路。在目前的气候条件和传统的畜群组成下，放牧强度增加到阈值0.32 +/- 0.10大牲畜单位（LSU）公顷（-1）天（-1）以上，植被组成将从草本植物变为木本和裸露土壤为主的系统。非常高的放牧强度（超过0.8 LSU ha（-1）天（-1））导致任何植被的完全丧失。在较温暖的条件下，植被对畜牧业表现出较高的适应力。当牛群有更高的浏览器：食草动物的比例时，这种弹性会增强。较冷的气候有灌木侵蚀的效果，而温暖的条件增加了草本植被的覆盖。这种影响主要是由于季节长度和随之而来的竞争性损失的生长较慢的灌木，而不是蒸发水分流失导致土壤水分更深层次的深层生根灌木。如果气候变暖正在推动当前的灌木入侵，我们得出结论，这只是间接的。这将是一个进步的灌木线，并可以被视为特定的灌木物种，如金露梅的气候逃避。在最近的高强度放牧下，只有更多的食草动物放牧才有可能防止灌木入侵和草本植被的完全丧失。
Encroachment of shrubs into the unique pastoral grassland ecosystems of the Tibetan Plateau has significant impact on ecosystem services, especially forage production. We developed a process-based ecohydrological model to identify the relative importance of the main drivers of shrub encroachment for the alpine meadows within the Qinghai province. Specifically, we explored the effects of summer livestock grazing (intensity and type of livestock) together with the effects of climate warming, including interactions between herbaceous and woody vegetation and feedback loops between soil, water and vegetation. Under current climatic conditions and a traditional herd composition, an increasing grazing intensity above a threshold value of 0.32 +/- 0.10 large stock units (LSU) ha(-1) day(-1) changes the vegetation composition from herbaceous towards a woody and bare soil dominated system. Very high grazing intensity (above 0.8 LSU ha(-1) day(-1)) leads to a complete loss of any vegetation. Under warmer conditions, the vegetation showed a higher resilience against livestock farming. This resilience is enhanced when the herd has a higher browser : grazer ratio. A cooler climate has a shrub encroaching effect, whereas warmer conditions increase the cover of the herbaceous vegetation. This effect was primarily due to season length and an accompanied competitive loss of slower growing shrubs, rather than evaporative water loss leading to less soil water in deeper soil layers for deeper rooting shrubs. If climate warming is driving current shrub encroachment, we conclude it is only indirectly so. It would be manifest by an advancing shrubline and could be regarded as a climatic escape of specific shrub species such as Potentilla fruticosa. Under the recent high intensity of grazing, only herding by more browsing animals can potentially prevent both shrub encroachment and the complete loss of herbaceous vegetation.