Tom Rooney - Academia.edu (original) (raw)

Papers by Tom Rooney

Invasive Plant Science and Management, 2011

Preinvasion baseline data on entire communities are absent for most taxa in most places, and this... more Preinvasion baseline data on entire communities are absent for most taxa in most places, and this limits our ability to connect long-term ecological changes to particular invasive species or invasion events. We obtained data on forest understory composition from 94 stands in the 1950s and again the 2000s. We recorded within-stand frequency of occurrence for garlic mustard, European buckthorn, and Bell's honeysuckle and identified changes in native plant species density in 20, 1-m2 quadrats in invaded and noninvaded stands. All three invasive species were absent from all study sites 50 yr ago, yet at least one was present in 77.7% of the stands by the 2000s. All three species were present in 14.9% of the stands. Garlic mustard and European buckthorn were found at 47.9% of resurveyed sites, and Bell's honeysuckle was found in 40.4% of resurveyed sites. Native understory plant species density declined an average of 23.1% during the past 50 yr. Declines were not significantly di...

Recovery of Gray Wolves in the Great Lakes Region of the United States, 2009

Annual Review of Ecology, Evolution, and Systematics, 2004

Key Words browsing, Cervidae, forest regeneration, herbivory, plant-herbivore interactions ■ Abst... more Key Words browsing, Cervidae, forest regeneration, herbivory, plant-herbivore interactions ■ Abstract Deer have expanded their range and increased dramatically in abundance worldwide in recent decades. They inflict major economic losses in forestry, agriculture, and transportation and contribute to the transmission of several animal and human diseases. Their impact on natural ecosystems is also dramatic but less quantified. By foraging selectively, deer affect the growth and survival of many herb, shrub, and tree species, modifying patterns of relative abundance and vegetation dynamics. Cascading effects on other species extend to insects, birds, and other mammals. In forests, sustained overbrowsing reduces plant cover and diversity, alters nutrient and carbon cycling, and redirects succession to shift future overstory composition. Many of these simplified alternative states appear to be stable and difficult to reverse. Given the influence of deer on other organisms and natural processes, ecologists should actively participate in efforts to understand, monitor, and reduce the impact of deer on ecosystems.

Journal of the Torrey Botanical Society, 1997

... The combined effects of deer browsing and the loss of primary forest have altered native plan... more ... The combined effects of deer browsing and the loss of primary forest have altered native plant populations over the past century. ... In this study, we test the hypothesis that pri-mary forest stands exhibit higher species diver-sity than mature secondary stands in northwest-ern ...

Global Ecology and Biogeography, 2006

Ongoing species invasions and extinctions are changing biological diversity in different ways at ... more Ongoing species invasions and extinctions are changing biological diversity in different ways at different spatial scales. Biotic homogenization (or BH) refers to the process by which the genetic, taxonomic or functional similarities of regional biotas increase over time. It is a multifaceted process that encompasses species invasions, extinctions and environmental alterations, focusing on how the identities of species (or their genetic or functional attributes) change over space and time. Despite the increasing use of the term BH in conservation biology, it is often used erroneously as a synonym for patterns of species invasions, loss of native species or changes in species richness through time. This reflects the absence of an agreed-upon, cogent definition of BH. Here, we offer an operational definition for BH and review the various methodologies used to study this process. We identify the strengths and weaknesses of these approaches, and make explicit recommendations for future studies. We conclude by citing the need for researchers to: (1) consider carefully the definition of BH by recognizing the genetic, taxonomic and functional realms of this process;

Forest Ecology and Management, 2003

Ungulates can profoundly alter the structure and composition of forest communities via both direc... more Ungulates can profoundly alter the structure and composition of forest communities via both direct and indirect mechanisms. Individual plant species often respond in a unique way to the direct effect of herbivory as a function of their sensitivity to browse damage, ungulate food preferences, and the density of ungulates present. Sustained browsing pressure can limit the regeneration of favored and susceptible woody plants and eliminate populations of favored or susceptible herbaceous plants. These losses, in turn, give rise to indirect effects via trophic cascades or physical habitat modification. These indirect effects affect many other plant and animal populations. In the mixed conifer-hardwood forests around the Great Lakes in North America, widespread habitat modification and the extirpation of native predators and other ungulates have acted to boost populations of white-tailed deer (Odocoileus virginianus) to historically high densities. Such densities have curtailed regeneration of several important conifers (e.g. Tsuga canadensis and Thuja occidentalis) as evidenced by demographic analysis. Deer also appear to limit regeneration of Quercus and Betula in many areas. Impacts on understory herbs are harder to assess, but baseline data from 50 years ago indicate that these communities are changing in a pattern that implicates deer: grasses, sedges, and some ferns are increasing while overall herb diversity is declining. Thus, deer are playing a keystone role in these communities. We are currently assessing an additional set of questions, including: How best can we measure and represent ungulate impacts? At which densities do deer threaten forest diversity? How do impacts depend on initial plant and ungulate densities? Which species emerge as 'winners' or 'losers' in heavily-browsed landscapes? What characteristics or traits make a species susceptible to ungulate herbivory? How do ungulates affect patterns of diversity and relative abundance in ecological communities? What are the pathways by which ungulates exert indirect effects on species? and How significant are indirect effects? #

Ecological Applications, 2000

Mature eastern hemlock-northern hardwood forest cover decreased drastically in the upper Midwest ... more Mature eastern hemlock-northern hardwood forest cover decreased drastically in the upper Midwest following European settlement and has yet to rebound substantially. Previous studies show that stands retaining substantial hemlock canopy coverage have low hemlock seedling and sapling densities. Results from various geographically restricted studies suggest several possible mechanisms that could cause low seedling or sapling density. We examined the relative importance of these proposed mechanisms in the Southern Superior Uplands Section of the Laurentian Forest Province. We surveyed 294m 2 plots in 100 hemlock stands in northern Wisconsin and western upper Michigan to assess how these proposed mechanisms affect the number of hemlock seedlings and saplings in four sequential size classes. Seedling and sapling abundance increases with greater light availability and differs significantly among geographically distinct ecological units (ecological subsections). In contrast, the abundance of medium and large saplings (30-99 and 100-300 cm tall) appears unrelated to light and geographic factors but declines as deer browsing increases, diminishing recruitment of larger saplings. The abundance of seedlings and saplings in each size class also depends strongly on the number of seedlings or saplings in the next smaller size class at the same site, reflecting demographic inertia. Path analysis integrates and separates these effects, explaining 24% of the regional variation in seedling abundance, 63% of small sapling abundance, and ϳ80% of medium and large sapling abundance. Light and ecological subsection directly affect the number of seedlings and small saplings, whereas deer browsing directly affects the number of medium saplings. Demographic inertia remains important for all larger size classes. These results imply that restoring hemlock populations requires both appropriate microsites for seedling establishment and sanctuary from excessive browse for successful recruitment.

Species loss over sixty-six years in the ground-layer vegetation of Heart's Content, an ... more Species loss over sixty-six years in the ground-layer vegetation of Heart's Content, an old-growth forest in Pennsylvania, USA. TP Rooney, WJ Dress Natural Areas Journal 17:44, 297-305, 10/1997. In 1929, baseline vegetation ...

Environmental …, 1995

Characteristics of a well-established population of the mantid, Tellodera sil/ell-sis (Saussure),... more Characteristics of a well-established population of the mantid, Tellodera sil/ell-sis (Saussure), were examined during the adult pOliion of its life cycle, for three COIlSl'cutivl' years (1990-1992). During the hill of 1992, changes in body mass of females in well-fed and ...

Journal of Ecology, 2013

We tested the hypothesis that wolves are reducing local browse intensity by white-tailed deer, th... more We tested the hypothesis that wolves are reducing local browse intensity by white-tailed deer, thus indirectly mitigating the biotic impoverishment of understorey plant communities in northern Wisconsin. 2. To assess the potential for such a top-down trophic cascade response, we developed a spatially and temporally explicit model of wolf territory occupancy based on three decades of wolf monitoring data. Using a nested multiscale vegetation survey protocol, we compared the understorey plant communities of northern white cedar wetlands found in high wolf areas with control sites found in low wolf areas. 3. We fit species-area curves for plant species grouped by vegetation growth form (based on their predicted response to release from herbivory, i.e. tree, seedling, shrub, forb, grass, sedge or fern) and duration of wolf territory occupancy. 4. As predicted for a trophic cascade response, forb species richness at local scales (10 m 2 ) was significantly higher in high wolf areas (high wolf areas: 10.7 AE 0.9, N = 16, low wolf areas: 7.5 AE 0.9, N = 16, P < 0.001), as was shrub species richness (high wolf areas: 4.4 AE 0.4, N = 16, low wolf areas: 3.2 AE 0.5, N = 16, P < 0.001). Also as predicted, percentage cover of ferns was lower in high wolf areas (high wolf areas: 6.2 AE 2.1, N = 16, low wolf areas: 11.6 AE 5.3, N = 16, P < 0.05). 5. Beta richness was similar between high and low wolf areas, supporting earlier assumptions that deer herbivory impacts plant species richness primarily at local scales. Sampling at multiple spatial scales revealed that changes in species richness were not consistent across scales nor among vegetation growth forms: forbs showed a stronger response at finer scales (1-100 m 2 ), while shrubs showed a response across relatively broader scales (10-1000 m 2 ). 6. Synthesis. Our results are consistent with hypothesized trophic effects on understorey plant communities triggered by a keystone predator recovering from regional extinction. In addition, we identified the response variables and spatial scales appropriate for detecting such differences in plant species composition. This study represents the first published evidence of a trophic cascade triggered by wolf recovery in the Great Lakes region.