The morphology and growth of Arctostaphylos uva-ursi (bearberry): an architectural analysis

Abstract

A study was made of the morphology and architecture of the prostrate ericaceous shrub, Arctostaphylos uva-ursi (L.) Spreng. (bearberry) from a sand-dune area and to a lesser extent a boreal forest area. In the open where more compact patches were recognized, a largely subterranean woody frame was found to support an aerial photosynthetic mat. The mat was made up of shoot complexes defined as consisting of not more than the four youngest annual growth increments or shoots. Two kinds of shoot complexes were recognized: (i) colonizing complexes consisting of a succession of long, low dominant shoots common in the periphal or colonizing zone of a patch and (ii) maintaining complexes consisting of short, essentially upright nondominant shoots and (or) intermediate shoots designated as subdominant, chiefly in the maintaining zone of a patch. Downward reorientation of older shoot increments which were not originally horizontal was recorded. The architecture of colonizing complexes was analysed quantitatively, including such parameters as shoot length, patterns of bud release, and divergence angles of daughter shoots. Several interesting patterns were revealed. The woody frame was analysed architecturally according to such principles as orders of branching, previously applied to trees. It was found to consist essentially of an ordered system of horizontal woody frame units, recognizable segments of the structural framework organized in a much branched hierarchical sequence. Two basic types of frame units were recognized: (i) major units constructed by colonizing complexes and (ii) minor units constructed by maintaining complexes. The initiation of the architectural pattern, including the establishment of original colonizing complexes, was investigated in seedlings. The reestablishment of bearberry following disturbance was also examined.