Liana mortality and host-plant specificity in a Neotropical semideciduous forest

Background/Question/Methods

Lianas are woody plants that in some stage of their life need to climb a host-plant (phorophyte) to ascend to the forest canopy in order to increase light interception. Hence, the availability of the right host-plants may be limiting for liana survival. Some characters of the tree, such as bark roughness, may facilitate liana climbing and, therefore, positively influence liana-phorophyte relationship, increasing liana survivorship. Our aim was to investigate whether liana mortality is higher than expected by chance in some phorophyte species. We collected data in 100 plots (10 x 10 m each) in a Neotropical seasonal semideciduous forest in SE Brazil. We tagged and measured the diameter at 1 m from the rooting point (DRP) of every liana of the species Mansoa difficilis Bureau & K.Schum (Bignoniaceae) with DRP > 1 cm and identified its phorophyte. We resampled the individuals four years later. We constructed a matrix with pairs of dead lianas and its phorophytes. We used a Monte Carlo procedure to evaluate whether the observed number of pairs of dead M. difficilis and phorophyte species was different than expected by chance.

Results/Conclusions

Out of the 485 liana-phorophyte pairs we sampled in the first year, 25.77% of the lianas had died four years later. Mortality was higher for small lianas, most of dead lianas had DRP < 2 cm (67.2%) and only 1.6% of dead individuals had DRP > 5 cm. In the first year, M. difficilis climbed 50 different phorophyte species. We found 35 pairs of dead liana-phorophyte species, of which 8.57% had observed frequency higher than expected by chance. The tree species Astronium graveolens Jacq. (Anacardiaceae), Esenbeckia leiocarpa Engl. (Rutaceae) and Rollinia sylvatica (A.St.-Hil.) Mart. (Annonaceae) were the host species with observed frequency (8, 46 and 10 pairs, respectively) higher than expected by chance (3.9, 22.9 and 4.9 pairs, respectively). In the local studied A. graveolens and E. leiocarpa (with more than 5 cm at breast height) are abundant (66 and 179 individuals per hectare, respectively). However there are few individuals of R. sylvatica (10 individuals per hectare), showing that density of phorophyte individuals did not have weight in the analysis. These three tree species have smooth bark; since M. difficilis climbs with the aid of tendrils, smooth barked trees hamper liana climbing and supporting, reducing its survival.