POPULATION VARIATION IN WOOD STRUCTURE OF WHITE FIR

Wood X-ray densitometry (inter- and intra-ring wood density, ring widt h) and measurements of tracheid length were used to evaluate wood stru ctural variability in 93 trees from 33 populations of white fir (Abies concolor (Gord. et Glend.) Lindl.). Individuals from populations repr esenting the geographic range of the species had been growing for 24 y ears 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 highe st rates of change being among Utah populations. Slower rates of chang e in tracheid length and wood density would contribute to more uniform wood structure in these southern populations. Multivariate analyses c onfirmed the separation of regional groups within white fir. Results i ndicated 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. A rizonan populations were grouped with southern Californian white fir.