THE COMPOSITION OF BRYOPHYTE COMMUNITIES ON LIMESTONE VERSUS BASALT SUBSTRATES IN COASTAL AND MID-ELEVATION FORESTS OF MO'OREA, FRENCH POLYNESIA
Communities of non- vascular plants called bryophytes grow on limestone and basalt on Mo'orea, French Polynesia. The abiotic properties associated with living on each substrate is not well known, however. This study looks at the soil pH, buffering capacity, phosphate levels and substrate water holding ability associated with each substrate. In general, limestone has greater water holding capacity than basalt and its soils are more basic, have higher phosphate levels and have a greater pH buffering capacity than soils on basalt. This study also looks at the biological impact of these substrate abiotic differences by using multivariate discriminate analysis to compare bryophyte communities on each substrate. Five species are tightly correlated with a particular substrate. Ectropothecium sandwichense and Floribundaria aerunginosa prefer limestone whereas Calymperes aongstroemii, Taxithelium vernieri, and Ectropothecium sodale, prefer basalt. Because the distribution of these species is highly correlated with substrate in nature, a reciprocal transplant experiment was designed to see if substrate directly affected a specie's growth. Ectropothecium sodale and Ectropothecium sandwichense can, physiologically, grow on either substrate. This suggests that other factors like elevation, predation and community effects might be contributing to the segregated bryophyte communities observed in nature. Understanding the abiotic and potential biotic factors that influence the distributions of bryophytes enables locals, scientists and developers to use these plants as bioindicators of habitat change.