Treesearch

Shrubland birds have experienced widespread declines in the eastern United States. Habitat for shrubland birds is typically dynamic, in which available habitat changes temporally and spatially in response to disturbance and succession. Despite widespread concerns among conservationists about shrubland birds, much is still poorly understood regarding fundamental demographic processes associated with the persistence of species in dynamic landscapes, such as the age of colonists, their success upon establishment, the fate of birds displaced by disturbance, and the effect of displaced birds on...

Continental-scale monitoring programs with standardized survey protocols play an important role in conservation science by identifying species in decline and prioritizing conservation action. However, rare, inaccessible, or spatially fragmented communities may be underrepresented in continental-scale surveys. Data on these communities often come from decentralized, local monitoring efforts that differ in their goals and survey protocols. We combine 16 point count datasets, controlling for differences in protocol and detection probabilities to estimate regional trends for 14 spruce-fir...

The terrestrial biosphere is currently a strong carbon (C) sink but may switch to a source in the 21st century as climate-driven losses exceed CO2-driven C gains, thereby accelerating global warming. Although it has long been recognized that tropical climate plays a critical role in regulating interannual climate variability, the causal link between changes in temperature and precipitation and terrestrial processes remains uncertain. Here, we combine atmospheric mass balance, remote sensing-modeled datasets of vegetation C uptake, and climate datasets to characterize the temporal variabilit...

In seasonal plant communities where water availability changes dramatically both between and within seasons, understanding the mechanisms that enable plants to exploit water pulses and to survive drought periods is crucial. By measuring rates of physiological processes, we examined the trade-off between water exploitation and drought tolerance among seedlings of trees of a tropical dry forest, and identified biophysical traits most closely associated with plant water-use strategies. We also explored whether early and late secondary successional species occupy different portions of trade-off...

We investigated depth of water uptake of trees on shale-derived soils in order to assess the importance of roots over a meter deep as a driver of water use in a central Pennsylvania catchment. This information is not only needed to improve basic understanding of water use in these forests but also to improve descriptions of root function at depth in hydrologic process models. The study took place at the Susquehanna Shale Hills Critical Zone Observatory in central Pennsylvania. We asked two main questions: (i) Do trees in a mixed-hardwood, humid temperate forest in a central Pennsylvania...

Additives that alter the rheology of lignocellulosic biomass suspensions were tested under conditions of variable pH, temperature, and solid concentration. The effects of certain ions, biomass type, after the addition of rheological modifier were also examined. Torque and vane rheometry were used to measure the yield stress of samples. It was found that the effectiveness of rheological modifiers depends on pH over a range of 1.5 to 6, biomass type, concentration of certain ions, and time after addition. The time-dependent properties of rheologically modified biomass are sensitive to the...

Cellulose nanofibrils (CNFs) are a class of cellulosic nanomaterials with high aspect ratios that can be extracted from various natural sources. Their highly crystalline structures provide the nanofibrils with excellent mechanical and thermal properties. The main challenges of CNFs in nanocomposite applications are associated with their high hydrophilicity, which makes CNFs incompatible with hydrophobic polymers. In this study, highly transparent and toughened poly(methyl methacrylate) (PMMA) nanocomposite films were prepared using various percentages of CNFs covered with surface carboxylic...

The most popular use of wood–plastic composite (WPC) members in the United States has been as outdoor decking material in residential construction. If the use of these products expands into more structural applications, such as beams and joists, it is imperative that the material’s mechanical behavior be understood. Since most of the potential structural uses of this material are as flexural members, it is particularly important that the response to this mode of loading is well characterized. Like many filled polymers, WPCs are anisotropic and bimodal, and thus their shear and two axial...

The USDA Forest Service Forest Inventory and Analysi (FIA) program collects data on a wealth of variables related to trees in forests. Some of these trees produce nontimber forest products (NTFPs) (e.g., fruit, bark and sap) that are harvested for culinary, decorative, building, and medicinal purposes. At least 11 tree species inventoried by FIA are valued for their bark. For example, slippery elm (Ulmus rubra Muhl.) is included in FIA forest inventories, and the bark is used for its medicinal value. Despite widespread use of NTFPs, little quantitative information about abundance, distribut...

The Virginia landscape supports a remarkable diversity of forests, from maritime dunes, swamp forests, and pine savannas of the Atlantic coastal plain, to post-agricultural pine-hardwood forests of the piedmont, to mixed oak, mixed-mesophytic, northern hardwood, and high elevation conifer forests in Appalachian mountain provinces. Virginia’s forests also have been profoundly shaped by disturbance. Chestnut blight, hemlock woolly adelgid, emerald ash borer, and other pests have caused declines or functional extirpation of foundation species. Invasive plants like multiflora rose, Oriental...