Morpho-Physiological Variation of White Spruce Seedlings from Various Seed Sources and Implications for Deployment under Climate Change

Abstract

Because of changes in climatic conditions, tree seeds originating from breeding programs may no longer be suited to sites where they are currently sent. As a consequence, new seed zones may have to be delineated. Assisted migration consists of transferring seed sources that match the future climatic conditions to which they are currently adapted. It represents a strategy that could be used to mitigate the potential negative consequences of climate change on forest productivity. Decisions with regard to the choice of the most appropriate seed sources have to rely on appropriate knowledge of morpho-physiological responses of trees. To meet this goal, white spruce (Picea glauca [Moench] Voss) seedlings from eight seed orchards were evaluated during two years in a forest nursery, and at the end of the first growing season on three plantation sites located in different bioclimatic domains in Quebec. The morpho-physiological responses obtained at the end of the second growing season (2+0) in the nursery made it possible to cluster the orchards into three distinct groups. Modeling growth curves of these different groups showed that the height growth of seedlings from the second-generation and southern first-generation seed orchards was significantly higher than that of those from other orchards, by at least 6%. A multiple regression model with three climatic variables (average growing season temperature, average July temperature, length of the growing season) showed that the final height of seedlings (2+0) from the first-generation seed orchards was significantly related to the local climatic conditions at the orchard sites of origin where parental trees from surrounding natural populations were sampled to provide grafts for orchard establishment. Seedling height growth was significantly affected by both seed source origins and planting sites, but the relative ranking of the different seed sources was maintained regardless of reforestation site. This knowledge could be used, in conjunction with transfer models, to refine operational seed transfer rules and select the most suitable sites in an assisted migration strategy.

Ecophysiology and Growth of White Spruce Seedlings from Various Seed Sources along a Climatic Gradient Support the Need for Assisted Migration

“…Nitrogen concentrations observed in the above-ground seedling parts at the nursery stage (1.50–1.68%) (Villeneuve et al, 2016 ) decreased to values between 1.08 and 1.27% at the southerly Watford site, between 1.10 and 1.17% at the intermediate Asselin site and, between 1.02 and 1.32% at Deville, the northerly site. Vector analysis showed that this reduction in concentration was accompanied by an increase in dry mass and nitrogen content, which translated into a general dilution of nitrogen content in the above-ground parts (Figure 6 ).…”

“…Before outplanting, seedlings were characterized in May 2013 (Villeneuve et al, 2016 ). Data was collected on 15 seedlings/seed orchard for height and diameter growth.…”

“…For example, more than 98% of the seedlings produced for reforestation in Québec are grown from improved seed (Lamhamedi and Carles, 2012 ). It is already known that certain morpho-physiological traits (e.g., traits related to growth or photosynthesis) of white spruce seedlings vary between seed orchards and regions (Carles et al, 2011 ; Benomar et al, 2015 ; Villeneuve et al, 2016 ), families (Carles et al, 2012 ), and somatic clones (Lamhamedi et al, 2000 ; Wahid et al, 2012 ), attesting to local genetic adaptation. Some of these traits may also be highly influenced by site and environmental characteristics (soil properties and fertility, temperature, precipitation, etc.…”

“…This article is the fourth of a series of papers addressing the anticipated impacts of climate change on the adaptation of the most frequently used white spruce seed sources in Québec's reforestation program. Recent work has focused on morpho-physiological characterization under controlled conditions (greenhouse), in a nursery and during the first 2 years of establishment on reforestation sites (Benomar et al, 2015 , 2016 ; Villeneuve et al, 2016 ). This characterization has revealed differences between seed sources (seed orchards) and established links between seedling performance and the climatic conditions of the original location of the parental trees that were sampled to provide grafts for orchard establishment (Villeneuve et al, 2016 ).…”

“…Recent work has focused on morpho-physiological characterization under controlled conditions (greenhouse), in a nursery and during the first 2 years of establishment on reforestation sites (Benomar et al, 2015 , 2016 ; Villeneuve et al, 2016 ). This characterization has revealed differences between seed sources (seed orchards) and established links between seedling performance and the climatic conditions of the original location of the parental trees that were sampled to provide grafts for orchard establishment (Villeneuve et al, 2016 ). The present study continues this investigation by examining these traits in experimental plantations established on a number of forest sites along a climate gradient.…”