Survival and growth patterns of white spruce (Picea glauca [Moench] Voss) rangewide provenances and their implications for climate change adaptation

Abstract

Intraspecific assisted migration (ISAM) through seed transfer during artificial forest regeneration has been suggested as an adaptation strategy to enhance forest resilience and productivity under future climate. In this study, we assessed the risks and benefits of ISAM in white spruce based on long-term and multilocation, rangewide provenance test data. Our results indicate that the adaptive capacity and growth potential of white spruce varied considerably among 245 range-wide provenances sampled across North America; however, the results revealed that local populations could be outperformed by nonlocal ones. Provenances originating from south-central Ontario and southwestern Québec, Canada, close to the southern edge of the species' natural distribution, demonstrated superior growth in more northerly environments compared with local populations and performed much better than populations from western Canada and Alaska, United States. During the 19-28 years between planting and measurement, the southern provenances have not been more susceptible to freezing damage compared with local populations, indicating they have the potential to be used now for the reforestation of more northerly planting sites; based on changing temperature, these seed sources potentially could maintain or increase white spruce productivity at or above historical levels at northern sites. A universal response function (URF), which uses climatic variables to predict provenance performance across field trials, indicated a relatively weak relationship between provenance performance and the climate at provenance origin. Consequently, the URF from this study did not provide information useful to ISAM. The ecological and economic importance of conserving white spruce genetic resources in south-central Ontario and southwestern Québec for use in ISAM is discussed.

Keywords: Assisted migration; genetic conservation; genetic gain; geographic genetic variation; local adaptation; universal response function.

Figure 1

Locations of (A) white spruce provenance origin and (B) field trial sites in Ontario used in the white spruce 410-series rangewide test. Green shading in map (A) indicates the natural range of white spruce distribution and gray shading in map (B) indicates the managed forest area in Ontario.

Figure 2

The relationship of provenance survival with growing season length. The linear regression equation and coefficient of determination (R²) are presented.

Figure 3

Relationship of provenance survival with latitude, longitude, and elevation of provenance origin for trial locations with survival of (A) (<70%; n = 5) and (B) (>72%; n = 11). Quadratic polynomial models and coefficients of determination (R²) are presented.

Figure 4

Relationship of (A) tree height, (B) stem diameter, and (C) stem volume growth of provenances with latitude and longitude of provenance origin. The area between the two vertical lines represents the geographic region of provenances from south-central Ontario and southwestern Québec associated with superior tree growth. Polynomial models and coefficients of determination (R²) are presented.

Figure 5

Relative (A) height, (B) diameter, and (C) stem volume growth of three regional provenance groups to trial means as related to the mean annual temperature (MAT) of the field trial locations. The three regional provenance groups are southern (lat. < 47°N, n = 84), central (47°N ≥ lat. <50°N, n = 94) and northern (lat. ≥ 50°N, n = 63), where n is the number of provenances included. Coefficients of determination (R²) for linear regression equations are presented.