Treesearch

Aspen has been declining in the Yellowstone Ecosystem for more than 80 years. Some authors have suggested that aspen is a marginal plant community in Yellowstone and that recent climatic variation has adversely affected aspen, while others contend that excessive browsing by native ungulates is primarily responsible for aspen's widespread decline. To test these hypotheses, I measured all the long-term aspen exclosures (n = 14) in the Yellowstone Ecosystem. Aspen stands inside all exclosures successfully produced new stems greater than 2 m tall without fire or other disturbance, while few...

Aspen exhibits a variety of ecological roles. In southern Colorado, the 1880 landscape mosaic contained a range of stand ages, of which half were >70 years old and half were younger. Pure aspen stands in southern Colorado are widespread and may result from previous short fire intervals that eliminated local conifer seed sources. Aspen regeneration in northern Yellowstone Park is controlled by ungulate browsing pressure and fire, so it has been limited since 1920. However, an episode of aspen seedling establishment occurred after the 1988 fires. We urgently need additional detailed, local...

We investigated vascular plant and butterfly diversity in Rocky Mountain National Park. We identified 188 vascular plant species unique to the aspen vegetation type. The slope of the mean species-area curve for the aspen vegetation type was the steepest of the 10 types sampled, thus, an increase in aspen area could have much greater positive impacts on plant species richness than other vegetation types. Aspen plots contained the greatest number of butterfly species and ranked highest with all diversity indices tested. However, aspen plots were the most heavily invaded by nonnative plant...

Quaking aspen (Populus tremuloides) employs two major systems of defense against damage by environmental agents: chemical defense and tolerance. Aspen accumulates appreciable quantities of phenolic glycosides (salicylates) and condensed tannins in most tissues and accumulates coniferyl benzoate in flower buds. Phenolic glycosides are toxic and/or deterrent to pathogens, insects, and small mammals, and coniferyl benzoate is toxic to ruffed grouse, but the functional significance of tannins remains unclear. Levels of secondary compounds are influenced by both genetic and environmental (e.g.,...

Native mycorrhizal fungi associated with aspen were surveyed on three soil types in the north-central Rocky Mountains. Selected isolates were tested for the ability to enhance aspen seedling growth in vitro. Over 50 species of ectomycorrhizal fungi occur with Populus tremuloides in this region, primarily basidiomycete fungi in the Agaricales. Almost one-third (30%) were ubiquitous with aspen and were found on all three soil types. Over one-third (37%) were restricted to the acidic, sandy soil of the smelter-impacted Butte-Anaconda area, revealing a subset of fungi that tolerate these...

Aspen clearcuts in the 1960s and 1970s on the Peaks Ranger District of the Coconino National Forest in northern Arizona failed to regenerate successfully because of browsing primarily by elk. Since 1985, over 400 acres have been successfully regenerated using fencing of various designs to exclude elk. The expense and visual impact of establishing and maintaining over 20 miles of fence along with continued damage to aspen greater than 3.0 inches d.b.h. outside the fenced areas have resulted in the Arizona Game and Fish Department increasing the elk hunting permits by 400% in an effort to...

Eighty-five 0.02-ha plots in the Gros Ventre River drainage of northwestern Wyoming with high elk usage had 39% fewer aspen stems in 1985 than in 1970. Sixtyfive of these plots were remeasured in 1989 and 53 additional plots established in 1986 on the Hoback River drainage (lower winter elk usage) were remeasured in 1990. Overall mortality (average/year) of aspen stems >2.5 cm d.b.h. was 2.6% (1970-1985), 2.4% (1985-1989), and 2.3% (1989-1999) for the Gros Ventre plots, and 1.9% (1986-1990) for the Hoback plots. Larger stems (>15 cm) had lower mortality rates than smaller stems. Additional...

To determine the number of cavity-containing aspens in old-growth (>80 years), we counted the number of stems containing cavities in 132 0.02-ha plots in Wyoming. There were 8.7 cavities/ha of aspen type. At least 84% of the cavity stems were alive when the initial cavity was constructed; 60% were alive when examined. Fruiting bodies and Phellinus tremulae (a heartrot fungus) were present on 71% of all cavity-bearing stems but on only 9.6% of all stems >15 cm d.b.h. Cavities were present in 7.7% and 0.2% of living stems with and without fruiting bodies, respectively. Average d.b.h. of...

Aspen has been declining in Jackson Hole for many years, a condition generally attributed to the fact that lightning fires have been aggressively suppressed since the early 1900s. It is also believed that burning will successfully regenerate aspen stands despite high elk numbers. To test this hypothesis, I evaluated 467 burned and 495 adjacent, unburned aspen stands at eight different locations within Jackson Hole. Aspen suckering was stimulated by burning, but most aspen stands still failed to produce new stems greater than 2 m tall where ungulate use was moderate or high. Only when elk...

Humans assign four types of meanings to aspen landscapes: (1) instrumental meanings dealing with the attainment of a goal - such as production of pulp or provision of recreation opportunities; (2) aesthetic meanings; (3) cultural/symbolic meanings dealing with spiritual and social attachments to landscapes; and (4) individual/expressive meanings derived out of interactions with aspen landscapes at the personal level. The amount of knowledge available for each meaning varies, with most knowledge developed for instrumental meanings. Management of aspen occurs within a dynamic social and...