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active. In the context of high subalpine and alpine environments, where typical annual <br />precipitation may exceed 30 inches per year, soil leaching could actually be strong enough to <br />effect calcium depletion. Thus, high-altitude occurrences of Leadville Limestone in Colorado, <br />such as at Hoosier Ridge, may represent sites of biologically significantly greater calcium <br />availability <br />With regard to occurrences of limestone at low altitude such as that at Dowe Flats in northern <br />Boulder County, availability of calcium in the general environment is at present likely to be <br />limiting few if any plant species. 6camination of the site for rare species that might be relict <br />from previous periods of higher precipitation when 'Limestone Ridge` represented an island of <br />adequate calcium availability was certainly appropriate before any further disturbance. No <br />rare species were located during a detailed examination of the area in 1987, and during another <br />examination in 1993 specifically for, perhaps the most likely species, Physaria bellii. <br />It should be noted that 'calciphily' is not a phenomenon confined to, or exclusively associated <br />with, rare plants. It merely suggests an affinity for calcium. Common species may have their <br />distributions adjusted by the presence of varying amounts of calcium also. For example, the <br />position of the upper limit of growth of Engelmann spruce (Picea enaelmannii) and subalpine <br />fir (Abies Iasi Tocaroal in the Tenmile Range of central Colorado has been observed to be adjusted <br />by the local position of the boundary between calcareous and non-calcareous soil parent <br />material (Curry 1962). <br />As time goes on, there is little likelyhood that rare species will 'colonize' Limestone Ridge, or <br />any of the other outcrops of limestone or gypsum in Boulder County until (through climate <br />change to substantially wetter conditions, the onset of more intensive leaching of soils of the <br />region, and the eventually resulting loss of calcium from presently calcium-rich regional <br />soils) limestone/gypsum sites represent refuges from critical calcium scarcity. <br />It should be painted out that the reclamation plan for the Dowe Flats quarry includes the <br />creation of "rimrocks' along the upper slopes of created hills and ridges and that these features <br />would be composed of calcareous rocks that would provide not only the wildlife habitat structure <br />and varied plant microtopography sought in the short term, but also the long-term potential to <br />function as calcium refuges, should climate change increase regional leaching of soil calcium, as <br />discussed above. Thus, the 'geochemical diversity' of Dowe Flafs will preserved. <br />