Crown architecture development in Salix 'Prairie Cascade', a pendulous willow

摘要

This paper presents a longitudinal quantitative architectural study of Salix 'Prairie Cascade', a hardy pendulous willow cultivar developed for the Canadian Prairies. Trees were propagated from cuttings in 1993 and detailed measurements were obtainedon amount of extension growth, orientation of shoots with respect to gravity, and the fate of buds and shoots until 2000. Instead of the mixed axis model of Champagnat typically ascribed to weeping willows, upright main-stem axes were constructed by vigorous, mostly distal shoots that remained more or less upright. The pendulous habit was largely the result of lateral shoots that were initially upright or semi-pendulous, drooping under their own weight to become pendulous. The pendulous habit was exacerbated by the weight of foliage. Sylleptic shoots were frequently incorporated into the main-stem axes. From original 1993 shoots, 40% of the buds developed into sylleptic shoots compared with 29% that developed into proleptic shoots. Two orders of sylleptic branching were often produced in one year. Willow is known for branch shedding but only 7% of 'Prairie Cascade' shoots were shed in the first year; however, more than half were gone by the third year and most of those remaining were located on the upper half of parent shoots.