Abstract
BackgroundAspen naturally grows in large, single-species, even-aged stands that regenerate clonally after fire disturbance. This offers an opportunity for an intensive clonal forestry system that closely emulates the natural life history of the species. In this paper, we assess the potential of genetic tree improvement and clonal deployment to enhance the productivity of aspen forests in Alberta. We further investigate geographic patterns of genetic variation in aspen and infer forest management strategies under uncertain future climates.Methodology/Principal FindingsGenetic variation among 242 clones from Alberta was evaluated in 13 common garden trials after 5–8 growing seasons in the field. Broad-sense heritabilities for height and diameter at breast height (DBH) ranged from 0.36 to 0.64, allowing 5–15% genetic gains in height and 9–34% genetic gains in DBH. Geographic partitioning of genetic variance revealed predominant latitudinal genetic differentiation. We further observed that northward movement of clones almost always resulted in increased growth relative to local planting material, while southward movement had a strong opposite effect.Conclusion/SignificanceAspen forests are an important natural resource in western Canada that is used for pulp and oriented strandboard production, accounting for ∼40% of the total forest harvest. Moderate to high broad-sense heritabilities in growth traits suggest good potential for a genetic tree improvement program with aspen. Significant productivity gains appear possible through clonal selection from existing trials. We propose two breeding regions for Alberta, and suggest that well-tested southern clones may be used in the northern breeding region, accounting for a general warming trend observed over the last several decades in Alberta.
Highlights
The western boreal hardwood forests cover approximately 60 million hectares, mainly in northern Alberta [1]
This paper presents a synthesis of results from the first decade of Western Boreal Aspen Cooperative (WBAC)’s tree improvement program efforts, evaluating a series of 13 clonal trials to determine (1) geographic patterns of genetic variation of aspen in western Canada in order to delineate seed zones and breeding regions, and (2) to assess the potential of a clonal forestry system to enhance aspen forest productivity
Two breeding regions for aspen in Alberta, north and south of 56uN latitude are supported by our results
Summary
The western boreal hardwood forests cover approximately 60 million hectares, mainly in northern Alberta [1]. These resources have historically been underutilized [2]. Until the mid 80 s, conifer forest products were preferred for their superior fiber strength in both pulp and dimensional lumber products. This changed with advances in wood products technology, namely oriented strand board (OSB) that introduced oriented wafers of wood from poplars in combination with epoxy resins. Aspen naturally grows in large, single-species, even-aged stands that regenerate clonally after fire disturbance. We further investigate geographic patterns of genetic variation in aspen and infer forest management strategies under uncertain future climates
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