Conifers and broadleaf species: stomatal sensitivity differs in western Oregon

Increasing stomatal closure was exhibited by two conifer and six broadleaf species as vapor pressure deficit increased.Conifers were more sensitive to high vapor pressure deficit than were the broadleaved species. One shrub, snowbrush(Ceanothus velutinus Dougl. ex Hook.), exhibited no stomatal closure as vapor pressure deficit increased. These traits, wheninterpreted in terms of known soil moisture depletion patterns, help explain why broadleaved species initially colonize disturbedareas in western Oregon, but are later replaced by long-lived conifers.