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Great Basin Naturalist

Abstract

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 hypothesis that edaphic factors are involved in restricting establishment of trees in parks. In Willow Park moisture available to plants in soils at field capacity varied significantly across the ecotone (P = 0.011), with 54% more water in forest than in park soils. Measures of growth rate obtained from tree height, dbh, and age were significantly higher nearer the ecotone (P < 0.001). The coefficient of variation of annual-ring width was significantly higher in forest than in ecotone trees (P = 0.002). These results suggest that stress of mature Engelmann spruce (Picea engelmannii) and lodgepole pine (Pinus contorta) is an unlikely explanation of park maintenance. P. engelmanii percent seed germination and seedling survivorship were significantly higher in the forest than in the park (P < 0.001). This may be largely due to the more severe seedling microclimate observed in the park. Results indicate that limited seedling establishment is primarily responsible for maintenance of subalpine parks in the Gunnison Basin.

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