REP38083 - Laserfiche WebLink

Home Browse Search

• Although these data were collected from different areas during these years, and the numbers are thus not strictly comparable, the trend of decreasing, or of least not increasing, shrub density is probably real end may be related to competition from the heavy herbaceous growth that comprises the high production discussed above. It may also be related to effects of the ongoing drought. In the Wadge Pasture, shrub densities in 1988, 1989, 1990, and 1991 were 320, 476, 408, and 288 stems per acre, respectively. Thus, the apparent substantial increase in density in 1989 was partially lost by 1990, and, by 1991, a substantial decrease was encountered. In 1989, slightly over 50 percent of the shrubs encountered in the Wadge Pasture sampling were classified as seedlings. It is possible that a large portion of these seedlings died by 1990, accounting for most of the losses. There were virtually no seedlings found in 1990. In 1991, seedlings were encountered in the amounts of about 1 to 7 percent of total density in the reclaimed areas; while nowhere near 1989 levels, the presence oT seedlings may reflect a response to greater moisture in 1991. Judging from the shrub density data for individual reclaimed areas sampled in 1991, it is also apparent that there has been a substantial dropoff in shrub establishment in the reclaimed areas beginning in about 1987, the approximate beginning of the drought. Again this pattern suggests • that it is possible that conditions for shrub seedling establishment and survival during that period have been too dry. Species Diversity and Composition Species density reflects the total number of species present (richness) in 100 square meters adjacent to cover sample transacts. Species density data are graphically presented in Figure 4. As can be seen in Figure 4, as well as the data in Table 29, the total species density of the reference areas in 1991 is in the range of 29 to 32 species/ 100 sq.m. With the exception of the 1987 Wolf Creek reclaimed area, this level was not equaled in any of the reclaimed areas examined in 1991. This is primarily due to the increase in native species presence, especially native perennialforbs, in the two reference areas in 1991, perhaps in response to more favorable moisture conditions. In terms of native species density, the reclaimed area values varied from 9.9 to 18.3 species per 100 m2 in 1991, compared to 9.5 to 18.9 species per 100 m2 in 1990. This compared to Mountain Brush and Sagebrush reference areas values of 28.7 and 27.7 species per 100 m2 , respectively in 1991 and 22.9 and 25.9 species per 100 m2 ,respectively in 1990. Thus, while the reclaimed .1 17