White spruce recruitment distances relative to lodgepole pine in southern Yukon, Canada

ABSTRACT

Eleven seral, postfire forest stands in southern Yukon (Canada) were sampled to determine where western white spruce (Picea albertiana ssp. albertiana) seedlings occurred with respect to distance to the nearest lodgepole pine (Pinus contorta var. latifolia) tree. Seedling-to-nearest tree distances were assessed at 10-cm increments up to 220 cm. On average, seedlings occurred 54 cm from the nearest pine (n = 490), but peak frequencies were 20–50 cm away, compared to a potential separation distance of 103 cm. Greatest average seedling density occurred 10–20 cm from pine (0.81 m⁻²), with values between 10 and 120 cm decreasing logarithmatically with increasing distance from pine (r = 0.994, p < .001, n = 11). Spruce seedling densities were <0.02 m⁻² beyond 120 cm. The differences in frequency, which represented moderately strong aggregation (Clark-Evans Index 0.34–0.52), and density suggest greater spruce recruitment near lodgepole pine was facilitated by more favorable ecological conditions than further away, for example, greater nutrient availability. The bias in seedling-to-nearest tree distances occurred regardless of stand age (57–165 years), pine density (1599–5935 stems ha⁻¹), or understory vegetation type, although the bias may be weakened by the abundant presence of feathermosses (Hylocomium splendens) on the forest floor.

KEYWORDS:

• Boreal forest
• establishment
• facilitation
• recruitment
• seedling
• spruce
• succession

Acknowledgements

Yukon Forest Management Branch provided access to forest cover maps. Yukon Energy, Mines and Resources Library acquired documents for review that were locally unavailable. Two anonymous reviewers provided constructive comments that improve the clarity of the manuscript.

Disclosure statement

No potential conflict of interest was reported by the author.