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Forest stand dynamics and livestock grazing in historical context

机译：历史背景下的林分动态和牲畜放牧

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Livestock grazing has been implicated as a cause of the unhealthy condition of ponderosa pine forest stands in the western United States. An evaluation of livestock grazing impacts on natural resources requires an understanding of the context in which grazing occurred. Context should include timing of grazing, duration of grazing, intensity of grazing, and species of grazing animal Historical context, when and under what circumstances grazing occurred, is also an important consideration. Many of the dense ponderosa pine forests and less-than-desirable forest health conditions of today originated in the early 1900s. Contributing to that condition was a convergence of fire, climate, and grazing factors that were unique to that time. During that time period, substantially fewer low-intensity ground fires (those that thinned dense stands of younger trees) were the result of reduced fine fuels (grazing), a substantial reduction in fires initiated by Native Americans, and effective fire-suppression programs. Especially favorable climate years for tree reproduction occurred during the early 1900s. Exceptionally heavy, unregulated, unmanaged grazing by very large numbers of horses, cattle, and sheep during the late nineteenth and early twentieth centuries occurred in most of the US. West and beginning earlier in portions of the Southwest. Today, livestock numbers on public lands are substantially lower than they were during this time and grazing is generally managed. Grazing then and grazing now are not the same.
机译：牲畜放牧被认为是美国西部黄松松林林地不健康状况的原因。评估放牧对自然资源的影响需要了解放牧发生的环境。环境应包括放牧的时间，放牧的持续时间，放牧的强度和放牧的动物种类历史环境，在什么时候，什么情况下发生放牧，也是一个重要的考虑因素。如今，许多茂密的美国黄松林和健康状况不尽人意的起源于1900年代初。造成这种情况的原因是当时独特的火灾，气候和放牧因素的融合。在此期间，低强度地面火灾（使年轻的树木茂密的林分变薄了）的数量大大减少，这是由于减少了精细燃料（放牧），由美洲原住民引发的火灾大量减少以及有效的灭火计划的结果。在1900年代初，气候特别有利于树木繁殖。在美国大部分地区，在十九世纪末期和二十世纪初，发生了异常沉重，不受监管，不受管理的放牧，大量马，牛和羊被捕。西部，从西南部分开始。如今，公共土地上的牲畜数量大大低于这段时间，放牧通常得到管理。然后放牧和现在放牧是不一样的。

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