The Environment of Chamaecyparis lawsoniana

Publisher Website
Google Scholar
Abstract
The environment of C. lawsoniana (A. Murr.) Parl. was measured at 10 or more sites in Oregon and California, USA, which represent 6 different plant communities. Water is probably the factor most limiting the species'' distribution. Most populations have late summer predawn xylem pressure potentials above -11 bars. The eastern range boundary coincides with a rapid decrease in the ratio of precipitation to evaporation. The species is usually confined to wet ultramafic parent materials except at high elevations and in the north. Its southern limit may coincide with absence of consistently wet ultramafics. Success of Chamaecyparis on ultramafics may result from failure of Pseudotsuga and other competitors to cope with the chemical composition and saturation of these substrates. Foliar nutrient concentrations of C. lawsoniana are lower on ultramafics than on other soils, but have a high Ca:Mg ratio. Mycorrhizae show no differences associated with soil type. Despite a large temperature range in the habitat of C. lawsoniana, temperature does not seem to limit the species directly. Mean annual air temperatures range from 4.4-10.9.degree. C. Especially at the northern end of the range, temperatures decrease more slowly in late summer than outside the range. Soils are cool, with little annual variation in areas with seepage. C. lawsoniana seems to be restricted by different aspects of the environment than are most dominant species with which it grows. Variations in temperature and parent material within its range are responsible for large changes in vegetation type without excluding the Chamaecyparis. Yet the changes in water availability which limit C. lawsoniana often do not produce discontinuities in the other vegetation present.