Effects of leaf litter on establishment, growth and survival of invasive plant seedlings in a deciduous forest

Disturbance often promotes plant invasion. Small disturbances to the forest floor expose bare soil to light which may promote seed germination and establishment. We tested the hypothesis that small disturbances to the litter layer allow invasive species to become established in forest interiors. We found that seedlings of the invasive shrub Lonicera maackii were found in sites with significantly lower leaf litter mass than regularly spaced points along a transect. We then investigated establishment and survival of L. maackii and the invasive biennial Alliaria petiolata in plots randomly assigned to three treatments: litter removed, litter added and control. Significantly more L. maackii seedlings established in the litter removed and control plots than the litter added treatments, but there was no effect on survival. Significantly more A. petiolata seedlings established in the litter removed plots than in the control or litter added treatments. Survival of established A. petiolata seedlings was significantly greater in control than in litter removed plots, but the final number of A. petiolata seedlings was greatest in the litter removed treatment. Our results confirm that bare patches of soil in the forest interior are colonization sites for invasive plant species.
INTRODUCTION Habitat disturbance is often invoked as a causal reason for the invasion of an exotic plant species (Hobbs and Huenneke, 1992). Generally the focus is on large disturbances that [...]