Fragment size and local flower density influence seed set of the understorey tree Paypayrola blanchetiana (Violaceae) in Brazilian Atlantic rain forest

Abstract

Reproductive success of many plant species declines in fragmented habitat, but this effect is little studied in trees of tropical rain forest understorey. Paypayrola blanchetiana (Violaceae) is a continuous-flowering treelet endemic to the Atlantic rain forest of north-east Brazil. Plants are distributed in localized patches. Flower, fruit and seed production of a total of 86 trees was quantified in six forest fragments, each belonging to one of two categories of size (> 300 ha vs. < 50 ha) and fragmentation history (isolated for c. 25–30 y vs. at least c. 50 y). Relative fruit set (fruits/flower) and seed set (seeds/ovule) were calculated for a spatial (total fruit set of tree individuals) and a temporal analysis (combined month-by-month fruit set in patches in response to different flowering intensities). Fruit set (1%) and seed set (0.6%) were very low, but variable among trees. Plants in large fragments had significantly higher fruit set and seed set than plants in small fragments. Trees in older fragments, however, displayed similar fruit and seed set to those in recently created ones. We found no interaction effect on seed set of fragment size and isolation time. Seed set was a negative function of patch flower density. Possible drivers of the observed patterns are discussed.