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首页> 外文期刊>Forest Ecology and Management >Lower forest-grassland ecotones and 20th Century livestock herbivory effects in northern Mongolia.
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Lower forest-grassland ecotones and 20th Century livestock herbivory effects in northern Mongolia.

机译：蒙古北部低森林草原交错带和20世纪牲畜的食草作用。

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We studied five lower forest-grassland ecotones in the Darhad Valley in northern Mongolia and investigated the effects of 20th century grazing regimes and changes in grazing management on ecotone dynamics at a local scale. A total of 2968 Siberian larch (Larix sibirica) trees were cored and tree-age distribution was constructed to determine 20th Century tree establishment. Tree age and location within the ecotones were correlated and seedling density and their distribution were explored to describe forest-grassland ecotone shift. To examine livestock herbivory effects on ecotone shift, the number of new trees was analysed with five different grazing regimes and changes in grazing practices during the last 80 years in the Darhad Valley. We documented some evidence of ecotone shift into the adjacent grassland. Rates and patterns of ecotone shift varied with different grazing regimes. Siberian larch tree establishment was greater at overall grazing intensities of low and high levels, which were dominated by sheep and cattle grazing. In contrast, larch establishment was lower at overall grazing intensities of low and medium levels, which were dominated by goat grazing. Twentieth Century changes in grazing practices also influenced Siberian larch regeneration. An abrupt decline in Darhad Valley larch establishment during the 20th Century coincided with locally increased grazing pressure. Furthermore, regional climate variability showed important interaction with local grazing regimes in affecting larch regeneration. A 20th Century pulse in larch establishment coincided with a time period of regionally known warmer temperatures and locally reduced grazing pressure. Our results suggest that overall grazing intensity, livestock species composition, and changes in grazing patterns are important in understanding grazing effects on Siberian larch tree encroachment..
机译：我们研究了蒙古北部达哈德河谷的五个较低的草地草原生态交错带，并研究了20世纪放牧制度的影响以及放牧管理方式在局部尺度上对生态交错带动态的影响。总共对2968棵西伯利亚落叶松（Larix sibirica）树进行了核心处理，并构建了树龄分布来确定20世纪树的建立。分析了生态交错带内树木的年龄和位置，并探讨了幼苗密度及其分布，以描述森林-草原生态交错带的转变。为了研究牲畜草食对过渡带转变的影响，在过去的80年中，通过五个不同的放牧制度和放牧方式的变化，分析了新树的数量。我们记录了过渡带转移到邻近草地的一些证据。过渡带的变化速率和模式随放牧方式的不同而不同。西伯利亚落叶松树的建立在低和高水平的总体放牧强度上更大，而绵羊和牛则以放牧为主。相反，在中低水平的总体放牧强度下，落叶松的建立较低，这主要是山羊放牧。 20世纪放牧方式的变化也影响了西伯利亚落叶松的再生。在20世纪，达哈德山谷落叶松的建立突然减少，与此同时，当地放牧的压力也在增加。此外，区域气候多变性显示出与当地放牧制度的重要相互作用，从而影响了落叶松的再生。落叶松建立的20世纪脉搏恰好是当地已知的温度升高和局部放牧压力降低的时期。我们的研究结果表明，总体放牧强度，牲畜物种组成以及放牧方式的变化对于了解放牧对西伯利亚落叶松入侵的影响非常重要。

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