Environmental and forest structure variables
We used forest structure, climate and soil variables as predictors of
liana abundance (Figure S1). Canopy height, as derived from spaceborne
LiDAR, has been used as a proxy for forest height (Lefsky, 2010; Simard
et al., 2011) and has also been used in macroecological analyses to
approximate the amount of vertical habitat and niche space, for example,
of climbing palms (Couvreur et al., 2015), lianas (Meyer et al., 2020)
and primates (Gouveia et al., 2014). We used the 1-km resolution canopy
height map from Simard et al. (2011) and extracted the mean canopy
height for each point location correspondent to the plots with
information for the abundance of the lianas (Gentry’s transects). We
calculated the gap phase index (GP) based on the relative size
distribution of stems per each 0.1 ha plot following Feeley et al.
(2007). GP was calculated as follows: GP = ln([BA30 +
1] / [BA10 + 1]), where BA30 is
the total basal area of all stems with dbh ≥ 30 cm (dbh – diameter at
1.30 m above ground) and BA10 is the total basal area of
all stems with dbh ≥ 2.5 cm and ≤ 10 cm (Feeley et al., 2007). For these
calculations we considered only the stems of trees and shrubs that could
provide more suitable support for the lianas to climb on and which would
not include other growth forms such as hemiepiphytes or herbs, which
were also sampled in the methodology used by Gentry.
As bioclimatic variables may be highly colinear with each other and as
we were primarily interested in the influence of specific climatic
variables, per se, we quantified the influence of climate on the
abundance and richness of the liana climbing mechanisms by extracting
the mean annual precipitation (in millimeters per year) and mean annual
temperature (in degrees Celsius) for each plot location from the 30
arcsec resolution CHELSA dataset (Krager et al., 2007). We also included
the climatic water deficit, a proxy for the monthly water deficit
experienced by plants (Aragão et al., 2007). For edaphic conditions, we
extracted the cation exchange capacity (CEC) (a general proxy for soil
fertility; cmol (+) kg−1) at 250 m resolution from the
SoilGrids website (https://soilg rids.org/).