Treesearch

Quercus garryana habitats are increasingly being managed with prescribed fire, but acorn dependent wildlife might be adversely affected if fires damage acorn crops. We examined one way that fire might affect subsequent acorn crops: through direct heating and damage of buds containing the following year's floral organs. We measured internal bud temperatures during controlled time and temperature treatments, described damage to heated buds at the tissue and cellular levels and quantified spring flowering to assess the consequences of the treatments. We found that internal bud temperature was...

What roles do ruderals and residuals play in early forest succession and how does repeated disturbance affect them? We examined this question by monitoring plant cover and composition on a productive site for 6 years after clearcutting and planting Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco). The replicated experiment included three treatments: vegetation control with five annual herbicide applications superimposed over two levels of slash removal (bole only or total tree plus most other wood) and an untreated control. Three species groups were analyzed: native forest, native...

Sap flow sensors are uniquely able to continuously monitor whole tree physiology. Recently, Burgess and Dawson (Burgess SSO, Dawson TE, Plant Soil 305:5-13, 2008) urged caution in using sap flow probes to estimate water storage use in trees. Here we respond to three criticisms raised there: (1) sampling: that tree water storage, estimated from branch-bole sap flow lags, was compromised by unaccounted variation in branch position and orientation; (2) instrumentation: that sap flow sensor response times may be sensor artifacts rather than manifestations of tree water storage; and (3) theory:...

Persistent changes in tree mortality rates can alter forest structure, composition, and ecosystem services such as carbon sequestration. Our analyses of longitudinal data from unmanaged old forests in the Western United States showed that background (noncatastrophic) mortality rates have increased rapidly in recent decades, with doubling periods ranging from 17 to 29 years among regions. Increases were also pervasive across elevations, tree sizes, dominant genera, and past fire histories. Forest density and basal area declined slightly, which suggests that increasing mortality was not...

The species self-thinning boundary line has been widely analyzed with a variety of statistical techniques. There is growing evidence that the use of stochastic frontier analysis is an effective statistical means for objectively fitting the species self-thinning boundary line, offering the opportunity to test the influence of additional covariates. Using extensive even-aged coastal Douglas-fir (Pseudotsuga menziesii var. menziesii [Mirb.] Franco), western hemlock (Tsuga heterophylla), and red alder (Alnus rubra Bong.) data sets in the Pacific Northwest, we examined the assumption that the...

Forest soil measurements were made at over 180 sites distributed throughout the H.J. Andrews Experimental Forest (HJA) in the Oregon Cascade Mountains. The influences of both elevation and aspect on soil variables were measured in the early (1998) and late summer (1994). Increased elevation significantly increased soil moisture, mean annual precipitation, soil organic matter, labile C and mineralizable N, microbial activities, extractable ammonium, and denitrification potentials. In contrast, bulk density, pH, and soil temperature (1998 only) were significantly lower at the higher elevation...

Dissolved organic matter (DOM) transport during storms is studied because it is important in the annual watershed export budget for dissolved organic carbon (DOC). We sampled stream water from two watersheds (upland and wetland-dominated) and three subcatchments (bog, forested wetland, and mineral forest) located within the wetland-dominated watershed during a fall and summer storm to investigate changes in the magnitude and chemical quality of DOM during stormflows. The percentage of biodegradable DOC (BDOC) decreased during both storms in the upland watershed, whereas percentage BDOC...

In 1- to 2-year-old Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. menziesii) plantations near Cave Junction and Glendale, Oregon, sprout clumps of tanoak (Lahocarpus densiflorus (Hook. & Arn.) Rehd.) and other hardwoods were removed with herbicides in April 1983 to leave relative covers of 0, 25, 50, or 100 percent of the nontreated cover, which averaged 15 percent. In 1996 (Cave Junction) and 1998 (Glendale), precommercial thinning (PCT) of Douglas-fir and cutting of nonconifer woody species were operationally applied across the four densities of tanoak. In 2005, Douglas-fir in 0...

In spite of numerous habitat restoration programs in fresh waters with an aggregate annual funding of millions of dollars, many populations of Pacific salmon remain significantly imperiled. Habitat restoration strategies that address limited environmental attributes and partial salmon life-history requirements or approaches that attempt to force aquatic habitat to conform to idealized but ecologically unsustainable conditions may partly explain this lack of response. Natural watershed processes generate highly variable environmental conditions and population responses, i.e., multiple life...

Exposure of soil to severe heating during a wildfire volatilizes soil nutrients and causes mortality of microbial communities, potentially facilitating invasion by nonnative plant species. In this study, we investigated the chemical and biotic factors associated with severely burned "red" soil and less severely burned "black" soil from a recently burned forest on the eastern slope of the Cascade Range in Oregon. Specifically, we examined the effects of burn severity on plant growth, arbuscular mycorrhizal (AM) fungal colonization and soil microbial communities as indicated by PLFA (phosphol...