Abstract
While rainfall interception controls how much water will be ultimately
available for many ecological functions, it is not well understood how
canopy structure controls the spatial and temporal distribution of
throughfall inside forests. Specially in subtropical and highly
heterogenous forests, such as the Atlantic Forest in Brazil, rainfall
interception has been only timidly studied. In this paper we
investigated how the spatial and temporal variations of throughfall are
controlled by the canopy structure. Throughfall spatial variability was
measured for a period of over a year using 28 throughfall gauges
uniformly distributed in a 28 m² Atlantic Forest plot in Southern
Brazil. We proposed the use of the number of overlapping crowns (NOC) as
a measure of canopy structure and compared it to the commonly adopted
Canopy Cover Fraction (CCF) and the Leaf Area Index (LAI). Locations
with a higher CCF, LAI and NOC have a large throughfall variability
among rainfall events, even though throughfall amounts could not be
directly related to those canopy cover indices. This result implies that
the throughfall variability is due to preferential pathways created by
the overlapping canopy layers. Additionally, throughfall spatial
distribution for periods with lower amounts of gross rainfall is similar
to NOC, suggesting that for smaller events the canopy storage capacity
is the major control of the amount of rainfall reaching the soil.