title: Distinct genecological patterns in seedlings of Norway spruce and silver fir from a mountainous landscape.
abstract: Understanding the genecology of forest trees is critical for gene conservation, for predicting the effects of climate change and climate change adaptation, and for successful reforestation. Although common genecological patterns have emerged, species-specific details are also important. Which species are most vulnerable to climate change? Which are the most important adaptive traits and environmental drivers of natural selection? Even though species have been classified as adaptive specialists vs. adaptive generalists, large-scale studies comparing different species in the same experiment are rare. We studied the genecology of Norway spruce (Picea abies) and silver fir (Abies alba), two co-occurring but ecologically distinct European conifers in Central Europe. For each species, we collected seed from more than 90 populations across Switzerland, established a seedling common-garden test, and developed genecological models that associate population variation in seedling growth and phenology to climate, soil properties, and site water balance. Population differentiation and associations between seedling traits and environmental variables were much stronger for Norway spruce than for silver fir, and stronger for seedling height growth than for bud phenology. In Norway spruce, height growth and second flushing were strongly associated with temperature and elevation, with seedlings from the lowlands being taller and more prone to second flush than seedlings from the Alps. In silver fir, height growth was more weakly associated with temperature and elevation, but also associated with water availability. Soil characteristics explained little population variation in both species. We conclude that Norway spruce has become an adaptive specialist because trade-offs between rapid juvenile growth and frost avoidance have subjected it to strong diversifying natural selection based on temperature. In contrast, because silver fir has a more conservative growth habit, it has evolved to become an adaptive generalist. This study demonstrates that co-occurring tree species can develop very different adaptive strategies under identical environmental conditions, and suggests that Norway spruce might be more vulnerable to future maladaptation due to rapid climate change than silver fir.
authors.affiliation: Swiss Federal Institute for Forest, Snow and Landscape Research, WSL, CH-8903, Birmensdorf, Switzerland.
authors.forename: Aline
authors.initials: A
authors.lastname: Frank
authors.affiliation: Swiss Federal Institute for Forest, Snow and Landscape Research, WSL, CH-8903, Birmensdorf, Switzerland.
authors.forename: Christoph
authors.initials: C
authors.lastname: Sperisen
authors.affiliation: Department of Forest Ecosystems and Society, Oregon State University, 321 Richardson Hall, Corvallis, Oregon, 97331-5752, USA.
authors.forename: Glenn Thomas
authors.initials: GT
authors.lastname: Howe
authors.affiliation: Swiss Federal Institute for Forest, Snow and Landscape Research, WSL, CH-8903, Birmensdorf, Switzerland.
authors.forename: Peter
authors.initials: P
authors.lastname: Brang
authors.affiliation: Swiss Federal Institute for Forest, Snow and Landscape Research, WSL, CH-8903, Birmensdorf, Switzerland.
authors.forename: Lorenz
authors.initials: L
authors.lastname: Walthert
authors.affiliation: Pacific Northwest Research Station, USDA Forest Service, 3200 SW Jefferson Way, Corvallis, Oregon, 97331-4401, USA.
authors.forename: John Bradley
authors.initials: JB
authors.lastname: St Clair
authors.affiliation: Swiss Federal Institute for Forest, Snow and Landscape Research, WSL, CH-8903, Birmensdorf, Switzerland.
authors.forename: Caroline
authors.initials: C
authors.lastname: Heiri
mesh_terms: D028202:Abies / Q000235:genetics*; D028222:Picea / Q000235:genetics*; D036226:Seedlings / Q000235:genetics*; D013557:Switzerland; D014197:Trees
keywords: 
  Abies alba
  ; 
  Picea abies
  ; Central Europe; adaptive genetic variation; climate change; common garden; conifers; evolutionary adaptation; genecology; phenotype-environment associations; quantitative genetics; soils