Factors limiting climber distribution and abundance in a southern African forest

Climber abundance was positively correlated with the altitudinal gradient in the Knysna Forest as well as with the level of base nutrients in the soil but not with the nitrogen concentration. However, these factors together with rainfall may covary and thus confound any power to explain the distribution of climbers. The hypothesis that climber abundance is limited by trellis availability (presence of small-diameter branches, and thus host-tree architecture and crown characteristics) was tested. Where the forest canopy is high, and small-diameter branches (trellises) are scarce, significantly more climbers enter their host trees horizontally from neighbouring trees than vertically; when the forest is low more climbers enter their host trees vertically via the available trellises. Density of climbers per host tree is correlated with the height of the lowest branches of the tree canopy. The trunk of trees is seldom used as an access route for climbers to the canopy of their host trees. -from Authors