Treesearch

Recent widespread and severe bark beetle outbreaks in western North America have resulted in larger carbon (C) pools in beetle-killed trees than in fire-killed trees (Hicke and others 2013). Mortality from these outbreaks modifies forest structure, changes the course of forest development, and affects nutrient and carbon cycling at multiple scales of time and space (Edburg and others 2012, Hansen 2014, Hicke and others 2012). Knowledge of post-outbreak C productivity (the rate of stand-level C accumulation from live plants) and storage (the amount of C biomass held in stands at a point in...

Whitebark pine (Pinus albicaulis) occurs on over 2 million acres in the Greater Yellowstone Ecosystem (GYE). As a keystone and foundation species, whitebark pine influences ecosystem functions such as biodiversity, vegetation structure, and hydrology. It has declined throughout its range in the Northern Rockies due to the combined effects of mountain pine beetle (Dendroctonus ponderosae), white pine blister rust (Cronartium ribicola), altered fire regimes, and climate change.

Black stain root disease, caused by the vascular wilt pathogen Leptographium wageneri, is widely distributed in Douglas-fir (Pseudotsuga menziesii) on substantial acreages throughout the forests of northern California and western Oregon. As a vascular wilt pathogen, Leptographium wageneri kills its hosts by growing within and plugging up the water-conductive tissues of the xylem (Hessburg and others 1995). Symptoms of the disease include the presence of individual or small groups of dead and declining trees with sparse chlorotic crowns, reduced growth, and heavy stress cone crops (fig....

Between 2011 and 2014, foresters and landowners in Missouri reported abnormally high levels of white oak (Quercus alba) mortality, with large numbers of white oak trees dying abruptly after leaf-out or during late summer. Entire tree crowns rapidly wilted and dead leaves remained attached to branches. Foresters reported that mortality occurred mostly on lower slopes and in the bottoms of upland drainages. This new syndrome was named rapid white oak mortality (RWOM). Reports of RWOM peaked in 2012, but reports of new mortality are still being received. A number of regional events, including...

Free-burning wildland fire has been a frequent ecological phenomenon on the American landscape, and its expression has changed as new peoples and land uses have become predominant (Pyne 2010). As a pervasive disturbance agent operating at many spatial and temporal scales, wildland fire is a key abiotic factor affecting forest health both positively and negatively. In some ecosystems, wildland fires have been essential for regulating processes that maintain forest health (Lundquist and others 2011). Wildland fire, for example, is an important ecological mechanism that shapes the distribution...

Droughts occur in most forest ecosystems of the United States, but their frequency and intensity vary widely (Hanson and Weltzin 2000). Annual seasonal droughts are typical in Western U.S. forests. In contrast, Eastern U.S. forests usually exhibit one of two predominant drought patterns: random (i.e., occurring at any time of year) occasional droughts, as typically seen in the Appalachian Mountains and the Northeast, or frequent late-summer droughts, as observed in the Southeastern Coastal Plain and the eastern side of the Great Plains (Hanson and Weltzin 2000).

Tsuga canadensis (Eastern Hemlock) and T. caroliniana (Carolina Hemlock) are important components of western North Carolina forests. The invasive Adelges tsugae (Hemlock Woolly Adelgid [HWA]) was first reported in NC in 1995, and by 2007 the entire range of hemlock in the state was infested. An examination of the Forest Inventory and Analysis (FIA) program data for FIA Unit 4 (21 mountainous counties in western North Carolina), looking at remeasured trees for the time period 1999–2013, demonstrated that diameter net growth of hemlock decreased and mortality increased with increasing...

Globally, peatland ecosystems store tremendous amounts of C relative to their extent on the landscape, largely owing to saturated soils which limit decomposition. While there is still considerable uncertainty regarding CO2 production potential below the water table in peatland ecosystems, extracellular Fe reduction has been suggested as a dominant pathway for anaerobic metabolism. However, colorimetric methods commonly used to quantitate Fe and partition between redox species are known to be unreliable in the presence of complex humic substances, which are common in peatland pore water. We...