Herbivory on soap plant (Chlorogalum pomeridianum)Herbivory on soap plant (Chlorogalum pomeridianum)
Soap Plant, Chlorogalum pomeridianum, is an abundant, large bulb plant in many areas of Jasper Ridge. It is subject to substantial herbivory of both its leaves and inflorescence. In February 2009 Rodolfo Dirzo began a study of herbivory on this species at 4 sites across Jasper Ridge. Each site was near a camera trap location used during an earlier 3-year population study of large mammals. Two of the sites were chosen because the camera trap data indicated a relatively high population of deer and rabbits. The other 2 sites were chosen because camera trap data indicated a relatively low population of deer and rabbits. At each site the study involves plants with and without exclosure protection, plants with and without previous herbivory, and a transect of additional plants.
At each site 3 soap plants in close proximity, usually 1 to 2 meters apart, were identified as a triplet, and each triplet was replicated 10 times. One of the plants in the triplet was chosen because it showed no signs of herbivory. The second plant of the triplet was chosen because it showed signs of herbivory. Both of these plants were caged with wire exclosures approximately 1 meter high. A third plant in each triplet was left uncaged as a control. In addition to the 10 triplets at each site, 10 transects 5 meters long were identified with bamboo stakes. Soap plants within one meter on either side of a transect are being assessed for herbivory, growth, and reproduction.
Rodolfo plans to carry out annual assessments of herbivory, plant vigor, and reproductive success over five years. He also plans to conduct genetic studies at each site to determine whether the impact of herbivory on sexual reproduction reduces the recruitment of new genotypes, thereby reducing genetic variation in the population.