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Forests of the southern Rocky Mountains are punctuated by persistent meadows called parks that are dominated by grasses and forbs. In an attempt to elucidate the maintenance of subalpine parks in the Gunnison Basin, Colorado, soil texture and tree morphology differences along 60-m transects spanning the forest-park ecotone were studied in 6 representative parks. Seedling survivorship, percent seed germination, and soil moisture available to plants were also studied along one of the transects in Willow Park. Soil analyses revealed 40% more silt and significantly less sand and clay in all 6 parks (P < 0.001), which supports the traditional hypotheses that edaphic factors are involved in restricting establishment of...
Spruce beetle (Dendroctonus rufipennis Kirby) outbreaks are important disturbances affecting subalpine forests of Engelmann spruce (Picea engelmannii), subalpine fir (Abies lasiocarpa), and lodgepole pine (Pinus contorta) in the southern Rocky Mountains. However, little is known about the influences of these outbreaks on overall forest dynamics. We used age-structure analyses and dendrochronological techniques to investigate the effects of a major spruce beetle outbreak on stand composition, dominance, tree age and size structures, radial growth, and succession in subalpine forests in Colorado. This outbreak, which occurred in the 1940s, caused a shift in dominance from spruce to fir and a reduction in average and...
Pollen and plant macrofossils from the Keystone Ironbog are used to document changes in species composition and the dynamics of the subalpine forest in western Colorado over the past 8000 years. Modern pollen spectra (particularly pollen influx), plant macrofossils, observations on modern species composition, and quantified densities and mean basal areas of forest trees are used to interpret the paleoecology of the forest. From 8000 to 2600 years ago the fen was surrounded by a subalpine forest. However, unlike the modern subalpine forest where Abies lasiocarpa (Hooker) Nuttall is slightly more abundant than Picea engelmannii (Parry) Engelmann, these Holocene forests had a greater dominance of P. engelmannii, perhaps...
We used data from 142 stands in Colorado and Wyoming, USA, to test the expectations of a model of growth dominance and stand development. Growth dominance relates the distribution of growth rates of individual trees within a stand to tree sizes. Stands with large trees that account for a greater share of stand growth than of stand mass exhibit strong growth dominance. Stands with large trees that contribute less to stand growth than to stand mass show reverse growth dominance. The four-phase model predicts that forests move from a period of little dominance (Phase 1), with trees accounting for similar contributions to stand growth and stand mass. Phase 2 is a period of strong growth dominance, where larger trees...
A five-stand chronosequence spanning >500 yr is used to characterize changes in age structure, overstory mortality, recruitment, and understory growth in developing Colorado Engelmann spruce (Picea engelmannii)-subalpine fir (Abies lasiocarpa) forests. Stand development follows a postdisturbance sequence of colonization, spruce exclusion, spruce reinitiation, and second-generation forest. This model of spruce-fir forest development reflects a range of disturbance intensities from large conflagrations to small-scale tree deaths. Catastrophic disturbance initiates stand development, and canopy gap replacements occur at predictable times during stand development as the life-spans of the two species are expressed. Previous,...
    map background search result map search result map Persistence of subalpine forest--meadow ecotones in the Gunnison Basin, Colorado Persistence of subalpine forest--meadow ecotones in the Gunnison Basin, Colorado