EVects of herbivory and patch size on tree seedling survivorship in a fog-dependent coastal rainforest in semiarid Chile

The landscape (matrix) surrounding habitat fragments critically aVects the biodiversity of those fragments due to biotic interchange and physical eVects. However, to date, there have been only a limited number of studies on plant– animal interactions in fragmented landscapes, particularly on how tree seedling herbivory is aVected by fragmentation. We have examined this question in a fog-dependent mosaic of rainforest fragments located on coastal mountaintops of semiarid Chile (30°S), where the eVects of the surrounding semiarid matrix and forest patch size (0.1–22 ha) on tree seedling survival were simultaneously addressed. The rainforest is strongly dominated by the endemic evergreen tree species Aextoxicon punctatum (Olivillo, approx. 80% of basal area). To assess the magnitudes and causes of Olivillo seedling mortality, we set up a Weld experiment where 512 tree seedlings of known age were transplanted into four forest fragments of diVerent sizes in four 1.5 £ 3-m plots per patch; one-half of each plot was fenced oV with chicken wire to exclude small mammals. The plots were monitored for 22 months. Overall, 50% of the plants died during the experiment. The exclusion of small mammals from the plots increased seedling survival by 25%, with the eVect being greater in smaller patches where matrix-dwelling herbivores are more abundant. This experiment highlights the important role of the surrounding matrix in aVecting the persistence of trees in forest fragments. Because herbivores from the matrix cause greater tree seedling mortality in small patches, their eVects must be taken into account in forest conservation–restoration plans.