The experimental ecology of plant reintroductions

Abstract

To deal with the accelerating, worldwide loss of plant species, conservation biology investigates species loss and effective methods for preserving species diversity. This thesis reports on three experiments in plant conservation biology, conducted in eastern Massachusetts. 1. Starting in 1993, 8 perennial species were introduced by 4 methods into experimental quadrats. The m ethods were: transplanting seedlings; transplanting mature plants; and sowing seeds on sites dug up with a shovel and on undisturbed sites. There was a low rate of success per seed sown (0.47%) and few of the resulting plants have reproduced. Transplanting of mature plants shows more success: 23% of the transplants survived, and plants on 25% of the quadrats reproduced. Thus, the most reliable method of establishing new populations of woodland perennials is by transplanting m ature plants. 2. Garlic mustard, introduced by seeds, was used to examine the relative importance of genotype and site characteristics in colonization success. These experiments also provide an indication of the maximum rates of success to be expected from species introduction by seed. Only 6.5% of the seeds produced seedlings. Genotypes did not differ significantly in rates of germination or reproduction; site characteristics were the determining factors in establishment success. The experiments provided useful demographic information such as rates of survival to flowering, average seed production, and rates of extinction of new populations. 3. Finally, the thesis reports on an experimental attempt to cause local extinctions of wild populations of garlic mustard. Understanding the process of population extinction is crucial to preventing species extinction and is a poorly understood aspect of population biology. Control populations were compared to experimental populations in which all reproducing individuals were removed for 3 years. Twenty-one percent of the experimental populations went extinct, in contrast to only 5% of the controls; the populations that went extinct were all initially small. Fifty-two percent of experimental populations were in decline at the end of the study, as compared with only 3% of the controls. The thesis results are of interest for conservation biology, in the design of species reintroductions, and in the control of aggressive weeds. Finally, the thesis suggests several lines of new research in plant ecology.