The Effect of Disturbance Scale on Sand Dune Colonization by Lithospermum Caroliniense

Abstract

Listen

Translate article

The effect of varying levels of natural sand deposition on emergence and survival of seedlings of Lithospermum caroliniense (Boraginaceae) was investigated experimentally at four different distances from Lake Michigan. Nutlet mass was varied in the experiments to test for potential interactions between nutlet mass and the degree of sand deposition. On the two rapidly accreting sand dunes closest to Lake Michigan, substantial sand deposition prevented emergence of all but a few seedlings. In two other sites located in stable areas farther from the lake, emergence averaged from 55 to 72.5%. The main effect of nutlet size on emergence was significant, although no interaction with distance from the lake was noted because of the lack of sand deposition at sites distant from the lake. Survival through the first season of seedlings located in one of the stable areas was only 9%, due to desiccation and the burrowing activity of mammals. Survival of seedlings in the other stable area, located on the first dune where naturally established L. caroliniense is found, averaged 36%. Most of these individuals survived to 1985, and fared far better than naturally established individuals located at greater distances from the lake, where lake climatic effects diminish. In a separate experiment, located at the periphery of a localized disturbance known as a blowout, 2—4 cm of sand deposition favored the emergence of seedlings in the two areas closest to the edge of the disturbance. There, seedlings produced by larger nutlets had a disproportionate advantage because of their ability to emerge from greater depths. In the third site, located further from the center of the blowout in a stable area, larger nutlets had no advantage during emergence. These experiments indicate that sand deposition has favored the evolution of increased nutlet mass in L. caroliniense. It appears that a combination of lake climatic effect and moderate sand deposition is most favorable for growth and establishment of this species.