Rules of crown development in the clonal shrub Vaccinium hirtum in a low-light understory: a quantitative analysis of architecture

The rules of crown development in the clonal shrub Vaccinium hirtum Thunb. in a low-light understory were identified by architectural analysis, and the structure and dynamics of current-year shoots were quantified. Development started from an initial orthotropic axis, which forked into plagiotropic axes; consequently, arched stems were formed. Subsequently, a new orthotropic shoot arose from the dormant meristem on the stem. The process from orthotrophy to plagiotrophy was then repeated. Ramets developed vertically as a result of the repeated formation of such orthotropic shoots and reached a maximum height of about 2 m. These processes were mainly characterized by the sequential change from orthotrophy to plagiotrophy in stem orientation and by a sequential reduction in shoot growth, in which a long shoot forked into shorter shoots with increasing allocation to leaves relative to stems. These rules may be adaptive for efficient light capture under conditions of low light availability, in terms of a low degree of self-shading and low cost of supporting tissue. Simultaneously, these rules worked to restrict the developmental potential of crowns, including the lateral expansion of crowns and the longevity of branch systems. This may be associated with a shrub-specific, throwaway design for stems that are expendable in high-stress environments.