Spring and summer hydraulic conductivity of 14 woody species of the sub-boreal forest in British Columbia

Abstract

Four hydraulic properties of the xylem, the Huber value (HV), hydraulic conductivity (Kh), and specific (Ks) and leaf-specific hydraulic conductivity (K1) were studied during the spring before leaf-out and during the summer after full leaf-out for 14 co-occurring tree and shrub species in the sub-boreal mixedwood forests of central British Columbia. The 14 studied species were divided into deciduous and evergreen angiosperm and gymnosperm groups, including one deciduous gymnosperm species, the tamarack, Larix laricina (Du Roi) K. Koch. I tested whether species with different life forms and classification divisions have different hydraulic properties. HVs were statistically similar for all angiosperms but significantly different among gymnosperms. Long-lived, late-successional species had higher HVs than pioneer and early-successional species. Ks and K1 values for all species except one, subalpine fir, Abies lasiocarpa var. lasiocarpa (Hook.) Nutt., were significantly higher in the spring than in the summer. Conductivity was higher in angiosperms than in gymnosperms in both the spring and the summer, and was highest in deciduous species in both seasons. The results indicate that requirements for mechanical strength may account for the high HVs in conifers, and that the high HVs compensate for low Ks and K1 values. The high hydraulic conductivities observed in the spring coincide with high water availability and high water demand by trees with emerging leaves. The subsequent reduction in Ks and K1 values could be caused by drought-induced embolism and cavitation in early summer.