DIFFERENCES IN DROUGHT RESISTANCE BETWEEN COASTAL AND INLAND SOURCES OF DOUGLAS FIR

Abstract

By two drought-hardiness tests, "time to death" and "soil-moisture content at the death point", Douglas-fir seedlings from three coastal sources were shown to be less drought resistant than those from five inland sources. Lethal needle-moisture contents, although not a proved test of drought hardiness, tend to confirm this conclusion. In addition, these lethal needle-moisture values, useful as an index of whole plant viability, were established for the various sources. Two of the coastal sources differed from five inland sources in the level of this value, but the lethal points for two other sources from the Oregon Cascade Range were similar to the five inland sources. Needle moisture appears to be a workable index for determining the whole plant viability except when the plant is very close to its time of death. Plants could also be classified into coastal and inland groups on the basis of their needle moisture under well-watered conditions, with the exception of seedlings from the Arizona source which are like the coastal group.