Light environment and crown architecture of two temperate Vaccinium species: inherent growth rules versus degree of plasticity in light response

Abstract

Light environment and crown architecture were investigated in two closely related species (deciduous Vaccinium hirtum and evergreen Vaccinium bracteatum) in a young and an old secondary forest. Light environment was determined by photographic estimation of light above ramets (30–500 cm tall). Crown architecture was examined to determine the effects of ramet age and light level on several architectural traits. In the young secondary forest, both species were mainly found in large gaps. In the old secondary forest, V. bracteatum persisted in deep shade, whereas V. hirtum was concentrated in small gaps. Vaccinium hirtum had narrower crowns and thinner stems than V. bracteatum, indicating lower structural costs in V. hirtum. Older ramets had greater total shoot extension (only V. bracteatum) and shorter length of the current-year shoots (markedly so in V. hirtum) than younger ramets. In higher light levels, V. bracteatum had greater aboveground growth and higher leaf area indices, whereas V. hirtum had only greater flowering intensity. Architectural traits were highly correlated with ramet age in V. hirtum, whereas these were mainly affected by light in V. bracteatum, indicating higher architectural plasticity in the latter species. The differences in architecture and its plasticity can be relevant for the segregation of light habitats between the species.Key words: light environment, crown architecture, leaf display, morphological plasticity, current-year shoot.