Rain forest fragmentation and the structure of Amazonian liana communities

In tropical forests, lianas (woody vines) are important structural parasite s of trees. We assessed the effects of forest fragmentation, treefall distu rbance, soils, and stand attributes on liana communities in central Amazoni an rain forests. Over 27 500 liana stems (greater than or equal to2 cm diam eter at breast height [dbh]) were recorded in 27 1-ha plots in continuous f orest and 42 plots in 10 forest fragments ranging from 1 to 100 ha in area. For each plot, an index of forest disturbance was determined from a 20-yr study of tree-community dynamics, and 19 soil-texture and chemistry paramet ers were derived from soil surface samples (top 20 cm). Liana abundance was 187-701 stems/ha, and liana aboveground dry biomass var ied from 3.7 to 12.3 Mg/ha. Liana abundance increased significantly near fo rest edges and was significantly positively associated with forest disturba nce and significantly negatively associated with tree biomass. Liana biomas s was similarly associated with disturbance and tree biomass but also incre ased significantly along soil-fertility gradients. Plots near forest edges had a significantly higher proportion of small (2-3 c-m dbh) lianas and rel atively fewer large (greater than or equal to4 cm dbh) lianas than did site s in forest interiors. Liana communities were further assessed by comparing their species richness , composition, climbing guilds, and frequency of tree infestation in three 10-ha fragments. Within each fragment, data were collected in 24 small (400 -m(2)) plots, with half of the plots near edges and half in interiors. Sign ificantly more trees were infested on fragment edges than in interiors. All three major guilds (branch-twiners, mainstem-twiners, tendril-twiners) wer e significantly more abundant on edges. Species diversity of lianas (as mea sured by Fisher's diversity index) also was significantly higher on edges, and this was not simply an artifact of increased liana abundance on edges. We conclude that many aspects of liana community structure are affected by habitat fragmentation, and we suggest that lianas can have important impact s on forest dynamics and functioning in fragmented rain forests. By creatin g physical stresses on trees and competing for light and nutrients, heavy l iana infestations appear partly responsible for the dramatically elevated r ates of tree mortality and damage observed near fragment edges.