Contrasting patterns in leaf traits of Mediterranean shrub communities along an elevation gradient: measurements matter!

We assessed the changes in communityweighted
mean (CWM) and variability of specific leaf
area (SLA) and leaf area (LA) of different Mediterranean
shrub communities along an elevation gradient
in the island of Sardinia (Italy). Furthermore, we
explored the relative contribution of species turnover
and intraspecific variation to shifts in CWM values
along the gradient. Forty sampling units (5 9 5 m)
were selected in a probabilistic way along a 1300 m
elevation gradient which crossed four thermotypes (thermometric belts). Leaf traits were measured in
each sampling unit. ANOVA and a trend test for
monotonic changes in variance were used to assess,
respectively, CWM differences and variability in both
the leaf traits across thermotypes. Variance decomposition
of CWM values was used to identify the role of
inter- and intraspecific variation. SLA and LA
responded differently along the studied gradient in
terms of abundance-weighted mean values and variability:
CWM of SLA showed the lowest values in the
driest thermotype, while LA in the more humid one;
SLA variability showed a significant increasing trend
with increased water availability, while LA variability
did not show any pattern. The contribution of
intraspecific trait variation was significant for both
the leaf traits, but higher for SLA, where negative covariation between inter- and intraspecific variation
was detected. We highlight the importance of simultaneously
considering measurements of both leaf traits
to understand the functional response of communities
in Mediterranean environments. Moreover, neglecting
intraspecific variation in leaf traits, even along steep
gradients with relevant species compositional
changes, can result in the underestimation of the
amount of trait variation in response to environmental
changes.