The Vascular Flora of Limestone Hills, Northern Extension of the Ogilvie Mountains, Yukon Territory


  • A.E. Porsild



Biological clocks


Owing to its relative inaccessibility the flora of unglaciated central and northern Yukon, from 65°N to the Arctic Coast, and between the 136°W and 141°W, has until recently remained totally unexplored. The Dempster Highway, still under construction, will provide an easy access to what until now was the largest botanically unknown part of Canada. ... From 3 to 12 July 1970, my brother ... and I made a hurried trip along the southern part of the Dempster Highway to visit places between the North Klondike Pass and Mile 89 where he had made large collections of vascular plants ... during the summers of 1966 and 1968. ... Beyond Mile 89 a few days were spent examining the flora of light-gray limestone hills that form a northward extension of the Ogilvie Mountains, at approximately 65°20'N, 138°30'W, south of Mile 100 to 110 on the Dempster Highway and thus beyond the point accessible by road to R. T. Porsild, in 1968. In strong contrast to the more fertile and better vegetated southern Ogilvie Mountains between the North Klondike Pass and Mile 89, the much lower northward extension of the Ogilvie Mountains, at approximately 65°03'N presents a strange and weird landscape of dendritically eroded plateaus of a general elevation about 3,500 feet above sea-level .... screes and ridges [are] covered by a pale-grey mantle of huge, angular blocks of frost-shattered grey limestone, [and are] often totally or nearly devoid of vegetation .... Soil is either totally absent, or at best confined to small pockets that may harbour tufts of mosses among which may be seen individual plants such as Oxyria digyna, Saxifraga oppositifolia or Luzula confusa, that only there could have gained a precarious foothold. Growing from deep down amongst the rocks, we were surprised also to find occasional specimens of the otherwise exceedingly rare Smelowskia borealis, here mainly sterile and etiolated, because of the shady habitat. ... About 50 species of vascular plants, nearly all pronounced calciphiles, were noted on the lower third of a southwest-facing slope, most of them growing in the ravines. By far the most common were Kobresia myosuroides and Dryas sylvatica. ... Stony flood plain valley bottom is oriented southeast-northwest between low limestone hills [directly south of Mile 110 of the Dempster Highway]. Starting at the head of the valley, the following more or less distinct plant habitats were examined in some detail: 1) Well-drained gravelly or sandy stream banks, the down-stream parts subject to spring flooding; 2) Dry, stony ridges usually with some soil around or between the stones; 3) Moist flood-plain meadows; 4) Moist, peaty bogs well above present flooding; 5) Low willow thickets, mostly on boulder flats between former stream beds but no longer subject to flooding; the space between boulders now well filled by sediments topped by a humus layer; the older and mature willow thickets are now being invaded by white spruce .... [Plants found in each of the above 5 habitats are listed.]