Pacific silver fir and subalpine fir, both typically inhabiting high-elevation forests in northwestern North America, were considered shade-tolerant species, the former more tolerant than the latter. To determine their relative shade tolerance, established advance regeneration was sampled along a light gradient ranging from open areas to inside a forest stand, and analysis of irradiance, growth, and leaf measures was obtained. Relationships between the percentage of above-canopy light (in the photosynthetically active wavelengths) associated with each study tree and its 1991 height increment, 1991 lateral increment, caliper at the base of the 1991 leader, and specific leaf area were examined for individual sites, and sites were grouped according to soil moisture. There were strong, consistent, and similar relationships between irradiance, growth performance, and specific leaf area for both species. As irradiance decreased, growth performance decreased and specific leaf area increased. In spite of ecological differences between the study sites for each species, it was concluded that on fresh sites, Pacific silver fir and subalpine fir are very tolerant of shade. Both are equally well adapted to survive under high shade and snowpack by allocating more resources to caliper and lateral growth than to height growth and by increasing specific leaf area. Key words: shade tolerance, advance regeneration, irradiance, growth performance, specific leaf area, Pacific silver fir, subalpine fir.
ont ete utilisees a h d'examiner les relations entre l'indice de stawere found to be strongly negatively correlated with site index tion et la croissance en hauteur et l'altitude, la latitude et la lonof both study species. Spruce site index (bh age 50) was predicted gitude. L'altitude et la latitude se sont averees &re correlees de to decrease 2.9 m and fir site index 2.5 m with every 100 m and fqon t&s negative par mpport a l'indice de station des deux espkes. l o increase in elevation and latitude, respectively; however, (i) L'indice de station de l'epinette (Lge hp 50) a ete estime en site index of both species appeared to decline faster with increasdecroissance de 2.9 m et l'indice de station du sapin de 2.5 m pour ing latitude than elevation, and (ii) decrease appeared to be chaque 100 met 1" d'altitude et de latitude, respectivement; touts faster for spruce than for fir. Comparison of height growth fois, (i) l'indice de station des espkes semblait diminuer plus rapicurves for stands on zonal and azonal sites with similar site dement en fonction de l'augrnentation de la latitude que de l'altiindex from different elevations and latitudes suggested that there tude, et (ii) la diminution semblait 6tre plus rapide pour l'epinette are probably inconsequential differences between the shape of curves que pour le sapin. La comparaison entre les courbes de croissance for either species. These findings imply that (i) subalpine fir is beten hauteur pour les peuplements des stations situees dans la ter adapted to subalpine boreal climates than Engelmann spruce zone et hors de la zone ayant des indices de stations semblables and (ii) development of polymorphic site index curves for estimais des altitudes et des latitudes differentes laissaient entendre mating site index of both species may be appropriate.qu'il existe probablement des differences sans consequence dans la forme des courbes de chacune des especes. Ces conclusions
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