Diversity and vertical distribution of lichens in a Venezuelan tropical lowland rain forest.

Abstract

As part of Project Surumoni, an investigation was conducted in 1997-1998 on species diversity and vertical distribution of lichenized fungi within a tropical lowland rain forest in southern Venezuela. A tower crane at Surumoni, which gives easy access to all forest strata, facilitated the investigation. In the plot, nine trees were selected as phorophytes on which 250 species of lichenized fungi were observed. Study results showed crustose lichens as the dominant life form. Of these, Thelotremataceae, Graphidaceae, and Trypetheliaceae contributed to nearly three quarters of total species richness. The species spectrum showed a well-defined vertical stratification from forest floor to top of canopy. At ground level, shade- tolerant species (chiefly Thelotremataceae) occurred. Moving upward, the proportion of Graphidaceae and Trypetheliaceae increased continuously, but Thelotremataceae appeared to remain constant up to the inner canopy. Higher yet, Thelotremataceae were less frequent, with Graphidaceae and Trypetheliaceae domi- nating. The degree of species turnover along the vertical gradient is shown in several diagrams for trees of stratum A and B separately. Species replacement is highest between height zones 1 and 2 for investigated trees of stratum A, but the more uniformly barked trees of stratum B do not show this marked difference. Calculation of additive beta turnover reveals, depending on substratum, three to nearly four complete species turnovers along the vertical gradient in the forest.