Liana cover in rainforest canopies is not predicted from local ground-based measures

Lianas (woody climbers) are structural parasites of trees that compete with them for light and below ground resources. Most studies of liana–tree interactions are based on ground-level observations of liana stem density and size, with these assessments generally assumed to reflect the amount of liana canopy cover and overall burden to the tree. We tested this assumption in a 1-ha plot of lowland rainforest in tropical Australia. We recorded 1072 liana stems (≥1 cm diameter at breast height {dbh}) ha -1 across all trees (≥10 cm dbh) on the plot and selected 58 trees for detailed study. We estimated liana canopy cover on selected trees that hosted 0–15 liana individuals, using a 47-m-tall canopy crane. Notably, we found no significant correlations between liana canopy cover and three commonly used ground-based measurements of liana abundance as follows: liana stem counts per tree, liana above-ground biomass per tree and liana basal area per tree. We also explored the role of tree size and liana infestation and found that larger trees (≥20 cm dbh) were more likely to support lianas and to host more liana stems than smaller trees (≤20 cm dbh). This pattern of liana stem density, however, did not correlate with greater liana coverage in the canopy. Tree family was also found to have a significant effect on likelihood of hosting lianas, with trees in some families 3–4 times more likely to host a liana than other families. We suggest that local ground-based measures of liana–tree infestation may not accurately reflect liana canopy cover for individual trees because they were frequently observed spreading through neighbouring trees at our site. We believe that future liana research will benefit from new technologies such as high-quality aerial photography taken from drones when the aim is to detect the relative burden of lianas on individual trees