Abstract

Questions: What is the role of microclimate relative to easily-obtainable
measures of forest structure in explaining epiphyte abundance? Do these roles
differ between epiphytic plant groups?

Location: Tropical premontane cloud forests of the Alto Mayo
watershed, Northern Peru (S 5°40’-6°10’; W 77°00’-77°40’), 1020-1450 m a.s.l.

Methods: We recorded vascular
epiphytic abundance, epiphytic bryophyte cover and forest structural features
in 36 plots (20 m x 20 m), and measured air temperature and humidity in a
subset of 17 plots. We modelled bryophyte cover, total vascular epiphytic
abundance, and the abundances of the main vascular epiphytic groups separately
(bromeliads, aroids, ferns), as a function of forest structure and microclimate
in spatial autoregressive models. Three forest structural variables (basal area,
tree height and canopy openness) and two microclimatic variables (minimum
humidity and maximum temperature) were considered. We constructed all possible
combinations of maximum two-variable models from the five explanatory variables
and carried out Akaike’s
Information Criterion-based model selection and variable importance tests with these as
input models.

Results: Canopy openness was the most important variable
explaining the abundance of the main epiphytic plant groups. It was also
strongly correlated with stand microclimate. Therefore, predictions of epiphyte
abundance did not improve with the inclusion of microclimatic data in the
models. There were some differences among the epiphytic plant groups in their
response to microclimate and forest structural features.

Conclusions: Forest stand microclimate, reflected through canopy
openness in particular, was a main determinant of the distributions of all
epiphyte plant groups. This implies that easily-measurable forest structural
variables alone can be used as good predictors of epiphyte abundance. Taxon-specific
differences in responses to microclimate imply that these taxa may also differ
in their sensitivity to predicted future changes in temperature and rainfall.