CLIMATE AND PICEA MARIANA SEED MATURATION RELATIONSHIPS: A MULTI‐SCALE PERSPECTIVE

Abstract

One of the most important ways by which northern forests will respond to anticipated climate change is through variations in seed maturation. In this study, the relationship between growing degree‐days (DD) >5°C and seed maturity was evaluated at three spatial scales. At the continental scale, the development of female gametophytes and embryos was evaluated as a function of the heat sums obtained from 11 sites distributed across the Canadian range of black spruce. At the regional scale, cone size and the percentage of germinated seeds formed in 1998, 1999, and 2000 were analyzed from seven sites situated along a latitudinal gradient in northern Quebec. At the local scale, cones were collected along perilacustral and insular transects according to their exposure to large water bodies, and from 10 islands located within a 2835‐km2 hydroelectric reservoir. Our results confirm the 800–940 DD thermal sum threshold necessary for the complete maturation of black spruce embryos at several populations distributed across the total range of the species. Along the regional south‐to‐north climatic gradient, the percentage of germination can be predicted by a sigmoid function of a thermal sum (y = 2.8 + 25.1/[1 + e(x−896.6)/84.6]; r2 = 0.85, P < 0.0001) that attains a plateau at around 800–940 DD. Once the 800–940 DD threshold is attained, variations in the percentage of seed germination are mainly associated with inter‐tree differences and local site factors (thickness of organic matter, tree density, tree height, tree age, and fetch). In the springtime, cold enclaves are created by the presence of the hydroelectric reservoir. The seed germination percentages in these enclaves varied from 0.6% ± 0.7% to 14.9% ± 19.1% (mean ± SD) according to the site (compared to 22.7% ± 15.1% for a site not exposed to the reservoir), which was equivalent to the germination percentages for sites at latitudes 1–3° farther north. These data suggest that the potential for black spruce regeneration increases strongly beyond the 800 DD isotherm, which evokes the possibility that subarctic open forests may become more dense under the current anticipated climate changes.

Climatology of the Forest-Tundra Ecotone at a Maritime Subarctic-Alpine Site, Mealy Mountains, Labrador

“…Altitude results in a local bioclimatic gradient that encompasses a range of vegetation zones, from isolated patches of closed forest to alpine tundra. At latitude 53.6˚ N, the Mealy Mountains are more than 100 km south of the present latitudinal tree limit, but 200 km north of the 800 GDD isoline mapped by Meunier et al (2007) as the northern limit of black spruce seedling viability.…”

“…Meunier et al (2007) analyzed the thermal requirements for black spruce (Picea mariana), the dominant tree line species in the eastern Canadian boreal region, in relation to GDD. They found a threshold for seed viability of approximately 800 GDD and mapped this bioclimatic threshold for the Canadian boreal region in terms of recent and projected future climates.…”

“…The forest-tundra ecotone is defined here as "the transition zone between forest and tundra at high elevation or latitude" (Harper et al, 2011:480). We examine relevant abiotic factors, including air and soil temperature and moisture, precipitation, and soil nutrients (Timoney, 1995;Grace et al, 2002), and compare the results with biogeographic generalizations regarding tree line climate (e.g., Körner and Paulsen, 2004;Meunier et al, 2007). The overall objectives are 1) to provide a quantitative description of the local climate in the context of the long-term regional climate and climate change, 2) to assess the spatial variability of specific climatic and edaphic variables along an altitudinal gradient from the closed forest edge to the alpine tundra as factors determining tree line character, and 3) to relate observed changes in climate to reported and potential changes in the forest-tundra ecotone.…”

Temperate and boreal forest tree phenology: from organ-scale processes to terrestrial ecosystem models

“…The seasonality of fruit (cone) maturation (in terms of size and mass) is relatively well documented (see, e.g., Sharp andSpargue 1967, Fujii 1993 in temperate deciduous oaks; Troeng 1981, Koppel et al 1987 in boreal conifers), but there is scarce information regarding the environmental dependence of these processes. Temperature has been identified as a cue for both cone maturation (Mutke et al 2003) and seed maturation (Meunier et al 2007) in conifers.…”

Environment, climate and tree growth relationships at the western Canadian Arctic treeline.

“…The prevailing theory of advancing treelines suggests that increasing temperatures will lead to more favourable growing conditions for pioneer seedlings (Hobbie & Chapin, 1998). However, many other factors also contribute to the success rate of new recruits, such as fire severity (Sirois, 1993) and thinner post-fire soil organic layers (Greene et al, 2007) in existing forest stands, and below-ground competition (Hobbie & Chapin, 1998) and growing degree-days thermal sum in both forested and unforested sites (Sirois, 2000;Meunier et al, 2007). Current findings indicate that treeline movement has not occurred uniformly across the northern hemisphere in recent decades, though evidence of a recession of the treeline has not been prevalent Harsch et al, 2009).…”