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, 1 (1), 95-111

Adaptation, Migration or Extirpation: Climate Change Outcomes for Tree Populations


Adaptation, Migration or Extirpation: Climate Change Outcomes for Tree Populations

Sally N Aitken et al. Evol Appl.


Species distribution models predict a wholesale redistribution of trees in the next century, yet migratory responses necessary to spatially track climates far exceed maximum post-glacial rates. The extent to which populations will adapt will depend upon phenotypic variation, strength of selection, fecundity, interspecific competition, and biotic interactions. Populations of temperate and boreal trees show moderate to strong clines in phenology and growth along temperature gradients, indicating substantial local adaptation. Traits involved in local adaptation appear to be the product of small effects of many genes, and the resulting genotypic redundancy combined with high fecundity may facilitate rapid local adaptation despite high gene flow. Gene flow with preadapted alleles from warmer climates may promote adaptation and migration at the leading edge, while populations at the rear will likely face extirpation. Widespread species with large populations and high fecundity are likely to persist and adapt, but will likely suffer adaptational lag for a few generations. As all tree species will be suffering lags, interspecific competition may weaken, facilitating persistence under suboptimal conditions. Species with small populations, fragmented ranges, low fecundity, or suffering declines due to introduced insects or diseases should be candidates for facilitated migration.

Keywords: conifer; ecological genetics; forest; gene flow; genomics; population; selection; species distribution models.


Figure 1
Figure 1
Change in the number of tree species predicted to be adequately conserved (cumulative cover of 10 ha, Hamann and Wang 2006) into the future, under the assumption that species are capable to adapt to changed climate, (•), migrate to suitable habitat within a reserve, (○), both, migrate and adapt, or neither (•). The analysis is based on bioclimatic envelope models for 49 tree species and 906 protected areas in British Columbia (Hamann and Wang 2006; A. Hamann and S.N. Aitken, unpublished manuscript.).
Figure 2
Figure 2
Genetic clines along gradient in mean annual temperature for mean Julian date of bud set (r2 = 0.94) and for total height (r2 = 0.72) for 17 populations of Picea sitchensis from across the species range (data from Mimura and Aitken 2007a). The horizontal arrow illustrates the range of magnitude of warming predicted from global circulation models from 1961 to 1990 climate normals to the 2080s for the central population at Prince Rupert, BC population (indicated with triangle; current mean annual temperature 7.1°C, predicted for 2080s CGCM A2X 10.8°C; CGCM B2X 9.8°C; Hadley GCM A2X 10.5°C, estimated using Climate BC (Wang et al. 2006a)).
Figure 3
Figure 3
(A) Example of general transfer functions for Pinus contorta spp. latifolia and spp. contorta (figure from Rehfeldt et al. 1999). (B) Growth response functions for four populations of Pinus contorta (from Wang et al. 2006b). Populations comprise seed collections from the Bulkley Valley (BV), Nelson high elevation (NE high: 1400–2000 m), Nelson low elevation (NE low: 700–1400 m) seed planning zones in British Columbia, and from the Yukon Territory (Yukon). Mean annual temperatures (MAT) (°C) for each population are shown in brackets in the legend following the population codes.

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