Apparent Commensalism among Three Vaccinium Species on a Climatic Gradient

Abstract

(1) Three Vaccinium species each in turn dominate a section of a gradient of light and temperature, with some overlap: V. uliginosum (ULI) dominates tundra sites, V. angustifolium (ANG) open but sheltered krummholz sites, and V. myrtilloides (MYR) shaded forest sites. This study examines congeneric interactions along that gradient. (2) Plant biomass, soil temperature and light intensity were used to characterize the gradient. The vertical distribution of biomass inside and outside congeneric interfaces (areas of direct interspecific contact) was determined to examine the nature of congeneric interactions. (3) Only 24-44% of the variation in biomass of ULI, ANG and MYR could be explained by light and temperature conditions alone, but adding the biomass of other vascular species to the analyses increased that range to 44-67%. (4) The biomass of each Vaccinium species was significantly reduced outside its own area of dominance, except in direct contact with the locally dominant congener. On the other hand, the biomass of the locally dominant Vaccinium species was either unchanged or somewhat larger in direct contact with a congener, compared to non-contact zones. (5) Several hypotheses are discussed to account for this apparent commensalism, including recent climatic changes, microsite effects, interspecific shelters against climate or pathogens, and innate or competition-induced growth patterns.