Current Research Projects in the Jules Lab
Wolves, elk, and aspen
Recently, well-known studies have claimed that the reintroduction of wolves (Canis lupus) into Yellowstone National Park (YNP) is leading to a recovery of aspen, presumably as aspen suffer less browsing in areas where elk are at higher risk of wolf predation (i.e., a behaviorally-mediated trophic cascade). This effect of wolves on aspen has become one of the most celebrated trophic cascades in contemporary ecology and a conservation success popularized in the news media. My colleagues (Matt Kauffman, Univ. of Wyoming & USGS, and Jed Brodie, Pennsylvania State Univ.) and I believed that the hypothesis concerning wolves, elk and aspen had not been adequately tested, and that the conclusions of a trophic cascade were premature. We've conducted tree demography studies and experimental exclosure studies in Yellowstone to address the hypothesis. I am also working on a related project using the tree cores we collected -- in this project, I am assessing the impact of climate variation on aspen growth.
Darlingtonia Fens and Fire:
The carnivorous Darlingtonia californica (California pitcher plant) is the dominant plant in uncommon wetlands of northern California and southwestern Oregon. Found on serpentine geology, these wetlands (fens) support a unique plant community that includes several rare taxa. Fire is the most common disturbance in these wetlands, though virtually nothing is known about how plants respond to fire in the fens. I have an ongoing collaborative project assessing the role of fire in these communities.
Invasion Ecology/Port Orford cedar:
This research concerns the factors that govern the rate and extent of 'biological invasions'. To date, our ability to ascribe general rules to the invasion process has been limited by a lack of detailed data on spread history coupled (simultaneously) with measures of important ecological features across the invasion landscape. To approach this issue, I study Port Orford cedar, a conifer endemic to northwest California and southwest Oregon. In 1952, a fatal, non-native root rot disease was accidentally introduced into the range of the cedar and has since been spreading rapidly. In my study, I have reconstructed the spread of the disease across a focal area in southwestern Oregon where I have measures of host and landscape characteristics at every potential infection site. This research is being conducted with Matt Kauffman of University of California, Santa Cruz.
Diversity in Logging Areas/Chronosequence Study:
The ability of understory plants (e.g., herbs) to recover after a logging event is poorly understood. The importance of this kind of information, however, is great, especially if managers are to develop strategies to maintain a diversity of species across forested landscapes. I have developed a chronosequence of forests in the Siskiyou Mountains of southwestern Oregon to assess the response of understory plants to clearcut harvesting. This chronosequence is a series of forest stands that range in age from 2 years (a clearcut) to 430 years (an old forest).
Plant Demography:
Demographic studies of rare and invasive species are vital for understanding how to best manage for reduced or increased population growth rates. Frequently, demographic studies can reveal aspects of populations that are not intuitive, and which point to management strategies that otherwise might not have been considered. I am currently initiating long-term demographic studies on several plants. In one study, I am assessing the viability of trillium populations in logged and old-growth forests of southwestern Oregon. I am interested in both the effects of population isolation in old-growth fragments and the factors limiting recovery in recent clearcuts. I am also involved in using long-term demographic data on the endangered Humboldt Bay wallflower to understand the influence of disease on population dynamics.