Mountain big sagebrush (Artemisia tridentata Nutt. ssp. vaseyana) covers large areas in arid regions of western North America. Climate-change models predict a decrease in the range of sagebrush, but few studies have examined details of predicted changes on sagebrush growth and the potential impacts of these changes on the community. We analyzed effects of temperature, precipitation, and snow depth on sagebrush annual ring width for 1969 to 2007 in the Gunnison Basin of Colorado. Temperature at all times of year except winter had negative correlations with ring widths; summer temperature had the strongest negative relationship. Ring widths correlated positively with precipitation in various seasons except summer; winter precipitation had the strongest relationship with growth. Maximum snow depth also correlated positively and strongly with ring width. Multiple regressions showed that summer temperature and either winter precipitation or maximum snow depth, which recharges deeper soil horizons, are both important in controlling growth. Overall, water stress and perhaps especially maximum snow depth appear to limit growth of this species. With predicted increases in temperature and probable reduced snow depth, sagebrush growth rates are likely to decrease. If so, sagebrush populations and cover may decline, which may have substantial effects on community composition and carbon balance.
Small plots (0.25 to 1.0 m2) denuded 13 and 31 yr previously were studied to investigate vegetation recovery at the alpine site of the Long-Term Ecological Research network. Recovery was slow, probably due to poor seedling survival. Covers of vascular plants and lichens were much lower on denuded plots than on controls except in late-melting snowbanks where natural disturbance by pocket gophers may have selected for disturbance-adapted species. Moister communities generally regained cover faster than drier communities. Vegetative expansion from plot edges provided most cover, although some colonizers originated from seed. Kobresia myosuroides, previously unknown to reproduce sexually in the Southern Rocky Mountains, occasionally colonized by seed. Essentially all vascular species acted as both colonizers and components of mature vegetation, and the vast majority of species are present in similar relative frequencies in control and disturbed plots. Previously studied alpine sites show either a similar lack of differentiation of early- and late-successional species or higher relative abundance of grasses in disturbed sites. In contrast to vegetation recovery in most temperate ecosystems, in these small plots on Niwot Ridge sequential replacement of species after disturbance does not occur.
Evaluating techniques for restoring alpine environments is important due to increasing human impacts on Colorado mountains. We studied restoration success after 1 yr on an alpine area disturbed by trampling at 3700 m a.s.l., Humboldt Peak, Sangre de Cristo Mountains, Colorado. This area was revegetated in summer 1997 by transplanting pieces of turf cut from a new trail. For both transplants and controls, 100 points were sampled in seventeen 70 X 70 cm plots. Vascular plant species richness did not differ between transplant and control plots. Thirtyone species showed absolute covers not significantly different between transplant and control plots, and twelve species had higher covers in control plots or showed a strong trend in that direction. Sums of covers of all species declined by 35% in transplant plots. Transplant and control plots had differential relative success of some important species as measured by relative cover although almost all differences were small. Grasses increased moderately and forbs declined by 9%. Relative cover of the dominant, Geum rossii, as well as two common graminoids, Carex phaeocephala and Trisetum spicatum, decreased in transplant plots. The forbs Polygonum bistortoides and Potentilla subjuga increased in relative cover in transplant plots; one of the dominant species, Carex elynoides, and many secondary species, were not different between treatments. Success in total cover and of almost all species after 1 yr indicates turf-transplants work well in this community and should be employed to restore other damaged alpine areas when feasible.
Heavy, increasing recreation on Colorado’s high peaks has created numerous social trails requiring restoration. We studied success of turf transplants 3 yr after transplanting on Mount Belford in the Sawatch Range, and Humboldt Peak in the Sangre de Cristo Range. Based on point-intercept data, sum of all vascular species’ covers was 12% to 31% lower in transplanted plots than in control areas. We found no differences in canopy density and height between transplant and control plots on Mount Belford, while both were about 40% lower in transplants on Humboldt Peak. Species richness adjusted for plot size was slightly greater in transplant plots on Mount Belford and slightly lower on Humboldt Peak. On both peaks, we found greater absolute cover of grasses in transplant plots, while forb cover was lower. After 3 yr, turf transplants effectively established vegetation cover and maintained high species richness in these communities. Whenever turf is available, e.g., new trail construction, it should be used to restore closed social trails and campsites, and turf transplants can be considered in other ecosystems for small disturbances in high-value areas where restoration would otherwise be slow.