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Multidecadal directional shift in shortgrass stocking rates
Rangeland Ecology & Management ( IF 2.3 ) Pub Date : 2020-10-23 , DOI: 10.1016/j.rama.2020.09.005
Edward J. Raynor , Justin D. Derner , Tevyn Baldwin , John P. Ritten , David J. Augustine

Bement (1969) developed a stocking rate (SR) guide for yearling cattle grazing shortgrass steppe based on relationships among average daily weight gain (ADG, kg · d−1), beef production per hectare (BP, kg · ha−1), and stocking rate (animal unit days, AUD · ha−1) measured in long-term grazing experiments conducted from 1940 to 1963. These analyses identified an optimal biophysical SR of 13.5 AUD · ha−1. Here, we 1) examine modern era (2000−2018) SR results from these same long-term grazing experiments to determine if there has been a shift in the optimal biophysical SR and 2) assess the influence of drought (< 75% of normal precipitation) on the optimal biophysical SR. For all years in the modern era, the optimal SR occurred at 23.2 AUD · ha−1, 72% higher than the value reported by Bement (1969). For the 3 drought yr, the optimum SR was 14.2 AUD · ha−1, which still exceeded the optimal SR by Bement (1969). Our results show the capacity of this shortgrass steppe rangeland to produce livestock weight gains has increased substantially between the Bement and modern eras. This multidecadal directional shift to a higher optimum biophysical SR is likely driven by two nonmutually exclusive factors. First, the plant community changed from dominance by a C4 shortgrass (Bouteloua gracilis) in the Bement era to codominance with a more productive C3 midgrass (Pascopyrum smithii) in the modern era. This change has resulted in pasture-level forage production increasing notably between the two eras. Second, the entry weights and genetic growth potential of yearling steers increased over the 8 decades and may have influenced the efficiency of weight gain for a given amount of forage consumed. Our findings provide guidance for incorporating flexible optimum SR in nondrought and drought years for adaptive grazing management strategies.



中文翻译:

短草放养率的十年变化

Bement(1969)根据平均日增重(ADG,kg·d -1),每公顷牛肉产量(BP,kg·ha -1)之间的关系,为一岁牛放牧短草草原的一岁牛制定了放牧率(SR)指南,和从1940年至1963年进行的长期放牧实验中测得的放养率(动物单位天数,AUD·ha -1)。这些分析确定了最佳生物物理SR为13.5 AUD·ha -1。在这里,我们(1)研究了这些长期放牧实验的现代时代(2000-2018)SR结果,以确定最佳生物物理SR是否发生了变化; 2)评估干旱的影响(<正常值的75%最佳生物物理SR。在现代的所有年份中,最佳SR发生在23.2 AUD·ha -1,比Bement(1969)报告的值高72%。对于3年干旱,最佳SR为14.2 AUD·ha -1,仍然超过Bement(1969)的最佳SR。我们的结果表明,在贝门特时期和现代时期之间,这种矮草草原牧场生产牲畜体重增加的能力大大提高。这种向更高的最佳生物物理SR的十年方向转移可能是由两个互不排斥的因素驱动的。首先,植物群落从显性被C改变4矮草(格兰马草)在Bement时代共显性与更高效的Ç 3个midgrass (硬叶偃麦草史密斯)在现代时代。这种变化导致了两个时代之间草场级牧草产量的显着增加。第二,一岁公牛的进入体重和遗传增长潜力在过去的八十年中有所增加,并且可能影响了一定数量的饲草消耗后体重增加的效率。我们的研究结果为在非干旱和干旱年份采用灵活的最佳SR提供了指导,以适应性放牧管理策略。

更新日期:2020-10-29
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