Growth of White Spruce, <em>Picea glauca</em>, Seedlings in Relation to Microenvironmental Conditions in a Forest-Prairie Ecotone of Southwestern Manitoba

Abstract

The influence of microenvironmental conditions on the growth performance (i.e., diameter and height growth) of White Spruce [Picea glauca (Moench) Voss] seedlings was examined within three contrasting habitats: White Spruce tree islands, open prairies and Trembling Aspen (Populus tremuloides Michx.) groves. These habitats exist within a disjunct occurrence of White Spruce at its southern limit of distribution in three mixed-grass prairie preserves in the Spruce Woods Provincial Park within the forest-prairie ecotone of southwestern Manitoba. Microenvironmental measurements (i.e., light, temperature, relative humidity, soil moisture) were obtained on 10 sites in each of the three habitats and growth characteristics of 60 White Spruce seedlings were measured in each of three habitats. Higher light and soil temperature conditions occurred within the open prairie. In contrast, lower light and soil temperature conditions occurred under the tree canopy of aspen groves and the northern aspect of spruce islands, which moderated the effect of the dry regional climate. Height growth did not vary significantly among the three habitats. The greater diameter growth and decreased slenderness of White Spruce seedlings in the open versus the shaded habitats appears to be a result of increased photosynthesis at higher light intensity and may also represent a morphological adaptation to withstand the effect of increased wind exposure. The increased slenderness of White Spruce in the shaded habitats appears to be a morphological adaptation of increasing carbon allocation towards height growth and thus maximizing effective competition for light.

Climatic Sensitivity of a Mixed Forest Association of White Spruce and Trembling Aspen at Their Southern Range Limit

“…Interspecific interactions between trees can be negative in the form of competition for resources such as light, moisture, and nutrients during forest stand development [4]. In hot and dry environments for tree growth, such as the southern limit of tree distributions gradating with grassland ecosystems, direct sunlight can raise temperatures and lead to increased rates of evapotranspiration [5]. In these harsh environments, trees can promote facilitative interactions whereby increased tree cover and shade can help reduce the rate of evapotranspiration.…”

Topographic Variation in Forest Expansion Processes across a Mosaic Landscape in Western Canada

“…Areas with lower precipitation were considered to be disturbance-driven, meaning fire, grazing, and browsing were required to maintain the presence of both trees and grasses. Moisture availability also influences tree establishment and development in semi-arid climates [11][12][13], and it has been hypothesized that moisture and temperature limitations help to maintain forest-grassland boundaries [14][15][16][17].…”