| Alpine Larch (Larix lyallii Parl.) is a high elevation conifer that occurs over a limited area of the northern United States and southern Canada. This species is generally found near timberline, often forming the tree limit in these harsh environments. However, at the northern edge of the larch's distribution, the species forms extensive subalpine associations with Engelmann spruce (Picea engelmannii Parry.) and subalpine fir (Abies lasiocarpa (Hook) Nutt.). Because there was little known about the occurrence of the larch in these subalpine locations, my objective was to determine the importance of disturbance and the resultant forest structure in maintaining these peripheral populations over a range of forest ages present in the southern Canadian Rockies. I found alpine larch initially established following fire disturbance (<40 years old) over a broad elevation range. Most larch regeneration occurred on northern aspects, although some seedlings were also found on shaded southern slopes. Seedlings were generally dispersed within 300 m of surviving parent trees and appeared to require moderate shrub cover for successful recruitment. In maturing forests (c.150 years), larch seedlings were not found in the lower subalpine zone, even though canopy larch were present. This was linked to the combination of increased fir basal area and increased shrub and canopy cover. In older forests (>300 years) larch recruitment remained inhibited at lower elevations where canopy height, canopy cover, and shrub cover was high, even though tree fall gap disturbance had started. However, at higher elevations, where there was a reduction in these competitive influences, larch regeneration reinitiated. This was linked to the changed gap structure. In these forests larch seedlings were found only in gaps. Larch gap fillers were more frequent at the northern edge of the larger (>70m2), lighter gaps, and where the surrounding average canopy height was less than 17 m. I suggest that the ability of larch to disperse into recent burns and the maintenance of a viable population within some part of the subalpine forest over time may be important for (1) maintaining genetic diversity between otherwise isolated timberline populations and (2) enabling migration as the climate changes. |
