alkanes to be dominant. Quantitatively, the chromatograms varied significantly among populations. Multivariate analyses showed that arid zone populations from mediterranean Chile and the Patagonian steppe were different from one another and were distinct from mesic populations close to the Valdivian rainforest vegetation zone. Mediterranean Chilean populations were characterized by higher concentrations of the longer carbon-chain alkanes, but retained equal amounts of shorter-chain homologues as the mesic populations. A greater variation in chain lengths and higher concentrations of longer carbon chains in the mediterranean populations is consistent with a model for the adaptation to reduced cuticular permeability. Partial Mantel matrix tests revealed significant climatic and inter-population distance effects with taxonomic distances based on multivariate and univariate hydrocarbon data. Annual rainfall was overall the most significant factor, particularly in regressions with the shorter-chain hydrocarbons. Annual mean temperature was most significant for the longer-chain hydrocarbons. This suggests, on the one hand, ecogenic adaptation to both temperature and precipitation of cuticular hydrocarbon composition, and, on the other hand, a weaker, but important effect of gene flow in determining hydrocarbon composition in this species. The northernmost populations at San Felipe and San Gabriel were the most distinctive. This could result from the effects of random changes in allele frequencies and\or to founder effects in isolated and small populations. These populations show some East-Andean affinities presumably due to historic migration patterns.
Several wood structural characteristics were measured in 15-year-old Abiesconcolor (white fir) from four populations along an elevational transect in the central Sierra Nevada region. The trees had been growing in a plantation near Placerville, California. Growth rings were narrower at breast height, latewood percentage tended to be greater, and tracheids were shorter in trees from higher elevation populations. Proportion of family variance components was greater than population for specific gravity and spiral grain angle. The characteristics that showed greatest population components of variation would be largely determined by durations and rates of shoot and radial growth. Presumably, length of the growing season would exert stronger selection pressure on these variables than on other characteristics of wood structure.
Wood X-ray densitometry (inter- and intra-ring wood density, ring width) and measurements of tracheid length were used to evaluate wood structural variability in 93 trees from 33 populations of white fir (Abiesconcolor (Gord. et Glend.) Lindl.). Individuals from populations representing the geographic range of the species had been growing for 24 years in a plantation near Placerville, California. Growth ring widths showed a clinal increase from northern Oregon to southern Californian populations, due mostly to variations in width of the earlywood. Rates of change from pith to bark in tracheid lengths and earlywood density decreased from northern Oregon to southern California, with the highest rates of change being among Utah populations. Slower rates of change in tracheid length and wood density would contribute to more uniform wood structure in these southern populations. Multivariate analyses confirmed the separation of regional groups within white fir. Results indicated that there is a differentiation between northern and southern Californian white fir, consistent with the former being ascribed to A. concolor var. lowiana and the latter to A. concolor var. concolor. Arizonan populations were grouped with southern Californian white fir.
Les feuilles, les cônes et les graines de 51 individus de Cupressus bakeri Jeps. ont été récoltés dans 6 populations naturelles du versant NE et NW du Mont de Goosenest dans la chaîne montagneuse de Cascades en Californie. L’analyse multivariante effectuée sur les caractères biométriques a montré un degré élevé de différenciation entre les diverses populations, même géographiquement très proches. La population GN2 du versant NW est bien distincte des autres. La variation entre les populations GN1 et GN2, très voisines, dans des conditions écologiques similaires, est surprenante et nous suggérons qu’il s’agit d’une différenciation plutôt d’origine génétique. La différence morphologique observée entre les populations du versant NE (GN4, GN5, GN6) est due aux conditions écologiques : c’est une différenciation phénotypique. Ces dernières populations possèdent les caractéristiques de celles du Mont Siskiyou et cela nous a incités à penser que le Mont de Goosenest pourrait être en effet une zone de transition et de différenciation pour cette espèce.
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