Treesearch

Two adelgid predators, Laricobius nigrinus Fender and Laricobius rubidus LeConte, were recently discovered to produce hybrid progeny in the eastern United States. L. rubidus is native to eastern North America where it feeds on pine bark adelgid (Pineus strobi Hartig) and L. nigrinus is native to western North America and was introduced to the eastern United States in 2003 for biological control of hemlock woolly adelgid (Adelges tsugae Annand). Currently, L. nigrinus and L. rubidus form a mosaic of hybrid zones throughout the eastern United States. It is not known whether these zones will...

Bohemian knotweed spreads aggressively along rivers. This invasive weed chokes waterways, displaces native plants, erodes riverbanks, and keeps tree seedlings from growing. Communities in the Pacific Northwest spend millions of dollars to eradicate it on the assumption that it harms fish habitats. But knotweed is difficult to kill. It takes years of herbicide applications to destroy the weed, and a single fragment can sprout and start new infestations. Also, control programs typically don’t evaluate whether native plants reestablish themselves after knotweed is cleared. Forest Service...

The emerald ash borer (EAB; Agrilus planipennis) is an introduced Asian beetle species that was first detected in trees in the Fraxinus (ash) genus in the United States in 2002. Female EAB beetles lay between 40 to 70 eggs in cracks, crevices, and beneath bark flakes. The eggs hatch within about 2 weeks, larvae bore through the outer bark, and begin eating the inner cambium of the wood. As larvae carve galleries through the cambium, they effectively disrupt the ability of the tree to transport water and nutrients. The larvae eventually girdle the tree, resulting in canopy decline and death...

Development of efficient forest wildfire policies requires an understanding of the underlying reasons behind forest fire occurrences. Globally, there is a close relationship between forest wildfires and human activities; most wildfires are human events due to negligence (e.g., agricultural burning escapes) and deliberate actions (e.g., vandalism, pyromania, revenge, land use change attempts). We model the risk of wildfire as a function of the spatial pattern of urban development and the abandonment/intensity of agricultural and forestry activities, while controlling for biophysical and...

Climate change is expected to alter the frequency and severity of atmospheric conditions conducive for wildfires. In this study, we assess potential changes in fire weather conditions for the contiguous United States using the Haines Index (HI), a fire weather index that has been employed operationally to detect atmospheric conditions favorable for large and erratic fire behavior. The index summarizes lower atmosphere stability and dryness into an integer value with higher values indicting more fire-prone conditions. We use simulations produced by the North American Regional Climate Change...

Northern white-cedar (Thuja occidentalis) and balsam fir (Abies balsamea.) are co-occurring species in riparian forests of the western Great Lakes region. Throughout much of the region, northern white-cedar has been experiencing population declines due to herbivory by white-tailed deer (Odocoileus virginianus). Preferential browse on northern white-cedar removes seedlings and saplings, allowing balsam fir, as less-preferred browse species, to recruit into larger size classes and potentially out-compete northern white-cedar. There is great interest in restoring and sustaining northern...

Simulating the magnitude and variability of terrestrial methane sources and sinks poses a challenge to ecosystem models because the biophysical and biogeochemical processes that lead to methane emissions from terrestrial and freshwater ecosystems are, by their nature, episodic and spatially disjunct. As a consequence, model predictions of regional methane emissions based on field campaigns from short eddy covariance towers or static chambers have large uncertainties, because measurements focused on a particular known source of methane emission will be biased compared to regional estimates...

Assessment of potential climate change impacts on stream water temperature (Ts) across large scales remains challenging for resource managers because energy exchange processes between the atmosphere and the stream environment are complex and uncertain, and few long-term datasets are available to evaluate changes over time. In this study, we demonstrate how simple monthly linear regression models based on short-term historical Ts observations and readily available interpolated air temperature (Ta) estimates can be used for rapid assessment of historical and future changes in Ts. Models were...

The Lacey Act of 1900 was amended on May 22, 2008, to prohibit the import of illegally sourced plant materials and products manufactured from them into the United States and its territories, and to similarly ban their interstate transport. Trade theory suggests that the effect of the new law would be to reduce the flow of illegally sourced fiber into the United States, increasing prices. Monthly U.S. import data on tropical lumber (January 1989-June 2013) and hardwood plywood (January 1996-June 2013) quantity and unit value were used to estimate alternative statistical models that quantify...

Coarse woody debris (CWD) is an important nursery environment for many tree species. Understanding the communities of ectomycorrhizal fungi (ECMF) and the effect of ECMF species on tree seedling condition in CWD will elucidate the potential for ECMF-mediated effects on seedling dynamics. In hemlock-dominated stands, we characterized ECMF communities associated with eastern hemlock (Tsuga canadensis (L.) Carr) and yellow birch (Betula alleghaniensis Britt) seedling pairs growing on CWD. Seedling foliage and CWD were analyzed chemically, and seedling growth, canopy cover, and canopy species...