Lichen communities in neotropical lowland rain forests

During the actual project P-11562 Bio, lichenized fungi proved to be the most diverse group of non animal organisms at the rain forest plot Surumoni (Southern Venezuela). The species area curve suggests an even considerably higher total number of species than the actually 250 found on not more than 1.5 ha. Spatial distribution of lichen species and families was shown to depend on both the vertical, multi-factorial environmental gradient and the horizontal, equally complex substratum induced gradient. The project now proposed is planned to aim primarily on various aspects of lichen communities and their underlying deterministic rules. That includes the formal description of lichen communities by focusing on the ecologically relevant mechanisms which are known to be responsible for species co-occurrence, e.g. the rule of chance in species colonization, species relationships within certain habitats, and species dependencies on bark characteristics (texture, pH, water capacity) and microclimate as criteria of their ecological amplitude. Connected to that is the question to which extend the lichen communities change in the different successional stages of one phorophyte species. Within one single tree species the climatic and some bark conditions are assumed to remain more or less constant during its live span, at least in the understorey region, while others are quite variable. Thus, changes in lichen communities should give answers on their particular discriminating substrate conditions. Furthermore, the lichen communities establishing on growing twigs of trees both in the outermost canopy and in the understorey are subject to a detailed study that aims on principles of colonization and succession of lichens in a lowland rain forest. Rain forests are thought to harvest a specialized and unique epiphyte flora, but is this true? Isn`t there a floristic element that equally can be found in more open habitats as savannas or cultivated areas, and if so, what is the unique floristic element of a rain forest? Although in the literature some scattered hints are found which corroborate this so called `canopy effect`, jet no accurate comparison of these vegetation units exists. Answers on these questions are not only of scientific interest, they also provide information which is quite important for conservation properties in connection with forest management. To test the significance and general validity of the results already achieved at the rain forest plot Surumoni, investigations are expanded to the very similar crane plot in Panama. As the vegetation and climate of both sites is well documented, changes in species richness, composition and its spatial distribution can be related to these factors.

The bark surface of trunks, branches and twigs of trees is often inhabited by a large number of slowly growing cryptogamic plants (mainly lichens and bryophytes), which use this relatively stable surfaces as an ecological niche. Whereas in the extratropics these communities dominated by cryptogams are quite well studied, very little is known about those occurring in tropical forests. Such communities have been studied in this project at selected sites in South and Central America. Study sites were the Surumoni rainforest plot in the upper Orinoco basin (Venezuela) were access to the tree crowns was possible by use of a tower crane, as well as the savanna at La Esmeralda several km upstreams. Results achieved at that site have been compared and checked at a second forest plot in eastern Panama. The main goal of the project was to get first insights in corticolous lichen dominated synusia in neotropical rain forests. For the community analysis a plotless method based on the concept of the `nearest neighbour`-method was developed. The analyses of our field data by this method grouped the species in 5 entities with a positive association which means that two species occur more frequently together than randomly expected. Three of them represent canopy associations, two describe `savanna`-inhabiting communities. Another focal point of the project has been the elaboration of similarities and dissimilarities between cryptogamic synusiae in two different habitats - rain forest canopy and open shrubland. Since these two habitats are obviously very similar in their general appearance, at least regarding corticolous epiphytes, several investigations concentrated on the hypothesis of the so called `canopy effect`, that is the appearance of similar epiphytic species associations in the rain forest canopy and the open savanna. Middle canopy of Qualea trees was shown to be the most similar counterpart to the branches and stems of Clusia shrubs with respect to lichen species composition. However, individual species abundances differed clearly between the rain forest canopy and shrubland relevés. Among the fourteen most frequent taxa in each habitat, only one species occurred in both. The strikingly congruent colourful general aspect of the compared synusiae therefore chiefly could be explained by the presence of a high percentage of orange coloured Trypetheliaceae in both habitats, although most of them belonging to different taxa.