Influence of ecological conditions on Engelmann spruce ( Picea engelmannii) and subalpine fir ( Abies lasiocarpa) germinant survival and initial seedling growth in south-central British Columbia

Abstract

The influence of seedbed (undisturbed forest floor, burned forest floor, and mineral soil), light (closed forest, open forest, and clearcut), and competing vegetation (present, not present) on germination and initial seedling survival and growth of subalpine fir ( Abies lasiocarpa) and Engelmann spruce ( Picea engelmannii) was investigated after applying seeds to small (1 m 2) plots established in each of the two major site types present in the wet cold Engelmann spruce–subalpine fir biogeoclimatic subzone (ESSFwc) of south-central British Columbia. Seedling survival and growth generally did not differ between site types and were little influenced by competing vegetation. After three growing seasons, the number of living seedlings of both species increased as the degree of forest floor disturbance increased. The number of living fir seedlings increased as the amount of light increased whereas partial shade benefitted spruce seedling survival. After two growing seasons, surviving fir seedlings had grown larger, (height, basal diameter, and crown volume) and were generally less influenced by seedbed, light, and competition, than spruce seedlings. Spruce seedling growth was greatest on undisturbed forest floor seedbeds in clearcut areas. If ESSFwc forests are to be naturally regenerated with Engelmann spruce and subalpine fir, clearcutting with exposure of mineral soil would be the optimum treatment for promoting fir seed germination and initial seedling growth as long as a seed source is present and sufficient seed survives predation. If spruce is to be promoted, provision of partial shade initially, for up to 2 yrs, and provision of small patches of mineral soil should assist seedling survival and minimize potential growth losses.