Bryophyte and macrolichen diversity of the Purdiaea nutans forest in southern Ecuador and its relationship to soil, climate and vegetation structure

Abstract

This study confirms that the unique Purdiaea nutans forest in the upper montane belt of the Reserva Biologíca San Francisco in southern Ecuador is an azonal ridge vegetation type. Our assumption that the mass occurrence of Purdiaea may be caused by extremely poor soils was not confirmed. From our point of view the development of this monodominant forest was more likely triggered by historical fire events and a combination of site specific abiotic factors, related to topography, geology, pedology, and macroclimate. Neither the terrestrial nor the epiphytic bryophyte and macrolichen species richness or composition were affected by the unusual tree species composition, but instead represent typical upper montane ridge communities of the region. Distribution of bryophytes and Macrolichens is primarily determined by differences in microclimatic conditions. Habitat differences between slope forest and ridge forest, and small scale habitat heterogeneity within ridges, define microclimatic conditions and are therefore responsible for the variability of terrestrial bryophyte and Macrolichen assemblages in upper montane forests in southern Ecuador. In the epiphytic habitat, microclimatic conditions follow a vertical gradient rather than a horizontal one. Accordingly, different species assemblages, indicator species and life forms are observed in different positions within the tree. Tree crowns are inhabited by rather small, desiccation-tolerant and wind-approved bryophytes and Macrolichens, whereas on trunks taller, shade tolerant bryophytes predominate. The higher species richness recorded from other Neotropical upper montane forests is mostly due to high species numbers of mosses and Macrolichens; liverworts are relatively more pronounced in our study sites. The extremely high precipitation of the area favours liverworts and strong winds constrain the growth of projecting or hanging species such as Meteoriaceae and macrolichens typical for outer canopies elsewhere. A taxonomic comparison of alpha and beta diversities reveals no universally valid pattern for lichens, liverworts, mosses, and ferns. The results indicate that diversity patterns for epiphytic and terrestrial species are distinct and should be treated separately. Among the studied taxonomic groups, ferns and liverworts show most similar patterns of alpha and beta diversity and therefore are most likely to work as surrogates for one another.