Revista Chilena de Historia Natural 81 (3): 387-393, 2008
RESEARCH ARTICLE
The role of stand composition on pre-dispersal seed predation in Austrocedrus chilensis
(Cupressaceae) in north west Patagonia
We studied the variability of pre-dispersal seed predation by insects on
Austrocedrus chilensis (Cupressaceae). This is a dioecious conifer endemic to southern South America (central Chile
and the Chilean Argentinean Patagonia) that grows naturally in pure and mixed stands, typically in association with
broadleaved Nothofagus species. Seeds are attacked while still inside the cones, mainly by larvae
of Nanodacna austrocedrella (Lepidoptera: Elachistidae). Our working hypothesis was that observed variations
in pre dispersal seed damage levels were related to forest stand composition, specifically to the relative abundance
of A. chilensis versus accompanying Nothofagus species. We compared seed predation levels in six
pairs of sites using a block design which included a mixed and a pure stand for each paired site. At each site, we
manually collected 50 closed seed cones from each of five neighbouring adult trees of A. chilensis. Pre-dispersal
seed damage was highly variable among trees and sites, with values ranging between 16.7 to 73.0 % of seeds damaged. We
found significant differences in predation rates among stands differing in canopy composition. In mixed stands, with
Nothofagus, the proportion of seeds attacked was always greater than that observed in the paired pure A. chilensis
stand. We showed that canopy composition influenced the level of pre-dispersal seed predation by insects, supporting the
hypothesis that damage increases in mixed stands. Our study is the first to present data on variations of pre-dispersal seed predation
in A. chilensis at a large spatial scale, examining the effects of forest type. This information may be useful in planning for
commercial A. chilensis seed harvesting, as well as for the conservation this endemic
conifer.
Key words:
Cupressaceae, insect
herbivory, associational susceptibility, associational damage, Nanodacna Austrocedrella
