SGS-LTER Bouteloua gracilis Removal Experiment Vegetation Density Data on the Central Plains Experimental Range, Nunn, Colorado, USA 1997-2008

Six sites approximately 6 km apart were selected at the Central Plains Experimental Range in 1997. Within each site, there was a pair of adjacent ungrazed and moderately summer grazed (40-60% removal of annual aboveground production by cattle) locations. Grazed locations had been grazed from 1939 to present and ungrazed locations had been protected from 1991 to present by the establishment of exclosures. Within grazed and ungrazed locations, all tillers and root crowns of B. gracilis were removed from two treatment plots (3 m x 3 m) with all other vegetation undisturbed. Two control plots were established adjacent to the treatment plots. Plant density was measured annually by species in a fixed 1m x 1m quadrat in the center of treatment and control plots. For clonal species, an individual plant was defined as a group of tillers connected by a crown (Coffin & Lauenroth 1988, Fair et al. 1999). Seedlings were counted as separate individuals. In the same quadrat, basal cover by species, bare soil, and litter were estimated annually using a point frame. A total of 40 points were read from four locations halfway between the center point and corners of the 1m x 1m quadrat. Density was measured from 1998 to 2005 and cover from 1997 to 2006. All measurements were taken in late June/early July.

1997年，研究人员在中部平原试验场（Central Plains Experimental Range）选取了6个间距约6公里的样地。每个样地内均设置一对相邻样点，分别为未放牧区与夏季适度放牧区（牛群啃食年度地上生物量的40%~60%）。其中，放牧样点自1939年起持续放牧至今，未放牧样点则自1991年起通过设置禁牧围栏（exclosures）得到保护至今。
在放牧与未放牧样点内，各选取两块3米×3米的处理样地，移除其中所有细茎冰草（B. gracilis）的分蘖与根颈，其余植被保持未受干扰状态；并在该处理样地的相邻位置设置两块对照样地。
每年针对物种分类，在处理与对照样地中心的固定1米×1米样方内测定植物密度。对于克隆植物，将由根颈连接的分蘖群定义为单株个体（Coffin & Lauenroth 1988, Fair et al. 1999），幼苗则被计为独立个体。
在同一样方内，采用点样针架（point frame）每年估算各物种的基部盖度、裸土覆盖率与枯落物盖度：在1米×1米样方的中心点与各角点的中点共4个位置读取数据，总计获取40个测点。
植物密度的测定周期为1998年至2005年，盖度的测定周期为1997年至2006年。所有测定工作均于6月下旬至7月上旬开展。