Amur honeysuckle (Lonicera maackii) is a particularly effective invader of agricultural and suburban landscapes. It readily colonizes forest edge and the understories of both damaged and intact forests. Field observations suggest that honeysuckles in brightly lit habitats not only grow faster, but seem to produce more and larger fruit. In other species, better growing conditions tend to coincide with higher fruit production, larger seeds, and greater reproductive success. In this study we asked whether honeysuckle in forest edge environments exhibited reproductive advantages in terms of fruit and seed production, and seedling performance in sun and shade habitats. Flower and fruit production were assessed on ca. 100 individuals distributed among closed canopy and forest edge habitats. Fruit and seed size and mass were assessed for 10 randomly chosen maternal plants in each habitat. Seeds of each mother were germinated in the greenhouse and seedlings were subjected to sun and shade treatments to assess maternal and environmental components of phenotypic variation. We hypothesized significantly higher reproductive output, fruit and seed quality, and seedling success from the offspring of forest edge plants.
Results/Conclusions
Shrubs under closed canopies produced as many flowers as shrubs in the forest edge, but considerably fewer fruits. Fruit dry mass and diameter were greater for forest edge plants. Moreover, the number, size, and mass of individual seeds were appreciably higher for forest edge plants. Seed differences, maternal differences, or maternal habitat differences did not translate into higher germination rates in the greenhouse. Seedling heights and leaf counts at 40d after planting showed strong maternal differences, but no differences based on seed size or maternal habitat. These differences continued 21d into the subsequent factorial experiment evaluating phenotypic variation in response to light availability. Given that the higher vegetative growth rates of honeysuckle in brightly lit habitats is amplified by higher fruit and seed production rates, managers should be advised to eliminate forest edge shrubs as a first priority. Although there is presently no evidence for better performance of larger seeds or seeds from edge plants, large maternal effects on performance are present. This suggests that some genotypes may be more invasive that others.
