GENETIC-VARIATION, CLIMATE MODELS AND THE ECOLOGICAL GENETICS OF LARIX OCCIDENTALIS

Provenance tests of 143 populations of Larix accidentalis revealed gen etic differentiation for eight variables describing growth, phenology, tolerance to spring frosts, effects of Meria laricis needle cast, and survival. Geographic variables accounted for as much as 34% of the va riance among Rocky Mountain populations. Patterns of genetic variation were dominated by the effects of latitude and elevation, with populat ions from the north and from high elevations having the lowest growth potential, the least tolerance to the needle cast, and the lowest surv ival. However, the slope of the geographic dines was relatively flat. Populations in the same geographic area, for instance, need to be sepa rated by about 500 m in elevation before genetic differentiation can b e expected. Regression models using geographic predictors were develop ed to describe variation in ten climatic variables from 192 weather st ations that best represented the Rocky Mountain distribution of L. occ identalis. Values of R(2) ranged from 0.43 to 0.92 and were higher for temperature than for precipitation variables. Using climatic effects predicted for each provenance to describe genetic variation produced v alues of R(2) between 0.15 and 0.27 which accounted for nearly as much (68-100%) of the genetic variance as had geographic variables. The an alyses suggested that genetic differentiation was controlled primarily by the relative mildness of the climate. Secondary effects of precipi tation were implicated for variables measuring the impact of Meria nee dle cast and survival.