Seefeldt Steven S, McCoy Scott D
United States Department of Agriculture-Agriculture Research Service, United States Sheep Experiment Station, HC 62 Box 2010, Dubois, Idaho 83423, USA.
Environ Manage. 2003 Aug;32(2):234-45. doi: 10.1007/s00267-003-0073-7.
In July 2000, a 490-ha wildfire burned a portion of a long-term grazing study that had been established in 1924 at the US Sheep Experiment Station north of Dubois, Idaho, USA. Earlier vegetation measurements in this tall threetip sagebrush (Artemisia tripartita spp. tripartita) bunchgrass plant community documented significant changes in vegetation due to grazing and the timing of grazing by sheep. A study was initiated in May 2001 using 12 multiscale modified Whittaker plots to determine the consequences of previous grazing practices on postfire vegetation composition. Because there was only one wildfire and it did not burn all of the original plots, the treatments are not replicated in time or space. We reduce the potential effects of psuedoreplication by confining our discussion to the sample area only. There were a total of 84 species in the sampled areas with 69 in the spring-grazed area and 70 each in the fall- and ungrazed areas. Vegetation within plots was equally rich and even with similar numbers of abundant species. The spring-grazed plots, however, had half as much plant cover as the fall- and ungrazed plots and the spring-grazed plots had the largest proportion of plant cover composed of introduced (27%) and annual (34%) plants. The fall-grazed plots had the highest proportion of native perennial grasses (43%) and the lowest proportion of native annual forbs (1%). The ungrazed plots had the lowest proportion of introduced plants (4%) and the highest proportion of native perennial forbs (66%). The vegetation of spring-grazed plots is in a degraded condition for the environment and further degradation may continue, with or without continued grazing or some other disturbance. If ecosystem condition was based solely on plant diversity and only a count of species numbers was used to determine plant diversity, this research would have falsely concluded that grazing and timing of grazing did not impact the condition of the ecosystem.
2000年7月，一场490公顷的野火烧毁了美国爱达荷州杜波依斯以北的美国绵羊实验站于1924年建立的一项长期放牧研究区域的一部分。在这个高丛三齿蒿（Artemisia tripartita spp. tripartita）丛生禾本科植物群落中，早期的植被测量记录了由于放牧以及绵羊放牧时间不同而导致的植被显著变化。2001年5月启动了一项研究，使用12个多尺度改良惠特克样地来确定先前放牧方式对火灾后植被组成的影响。由于只有一场野火且并未烧毁所有原始样地，所以这些处理在时间或空间上没有重复。我们仅将讨论局限于样本区域，以减少伪重复的潜在影响。在采样区域共有84个物种，春季放牧区域有69种，秋季放牧区域和未放牧区域各有70种。样地内的植被丰富度和均匀度相当，丰富物种数量相近。然而，春季放牧样地的植被覆盖度只有秋季放牧样地和未放牧样地的一半，且春季放牧样地中引入植物（27%）和一年生植物（34%）所占的植被覆盖比例最大。秋季放牧样地中本地多年生禾本科植物的比例最高（43%），本地一年生杂类草的比例最低（1%）。未放牧样地中引入植物的比例最低（4%），本地多年生杂类草的比例最高（66%）。春季放牧样地的植被处于环境退化状态，无论是否继续放牧或受到其他干扰，可能会继续进一步退化。如果生态系统状况仅基于植物多样性，且仅用物种数量计数来确定植物多样性，那么这项研究可能会错误地得出放牧和放牧时间对生态系统状况没有影响的结论。
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