Local Variation in Intergrading Abies grandis-Abies concolor Populations in the Central Oregon Cascades. III. Timing of Growth and Stomatal Characteristics in Relation to Environment

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Temperature, humidity, and timing of growth were observed for a population of Abies grandis saplings and three populations intermediate between A. grandis and A. concolor. The typical A. grandis population, which experienced the greatest moisture stress, had a more favorable temperature regime and less evaporative stress than populations on the other sites and began growth earlier. Two intermediate populations east of the Cascades, which never experienced severe plant moisture stress, grew in a cooler environment with drier air and started growth later. A third intermediate population experienced both high moisture stress and cool temperatures. For the typical A. grandis population, daily and seasonal stomatal closure in summer appears to be necessary to prevent fatal desiccation, but assimilation lost due to stomatal closure can probably be made up during the mild weather of other seasons. East-slope intermediate populations, without severe moisture stress, maintain open stomata, which would maximize ass...