Treesearch

In recent decades, an increasing number of plant species have been negatively affected by anthropogenic habitat fragmentation and disturbance. In many cases, the habitat matrix between populations has been converted from a natural to an urban environment. One such species, Lilium philadelphicum (Liliaceae) a showy perennial with a naturally patchy distribution, currently has populations in parts of its range in North America that persist on highly urbanized and fragmented landscapes. In this study, we used six nuclear microsatellite loci to characterize the amount and apportionment of...

The branching pattern of A. amabilis was regular (normal shoot-length distribution, less variable branching angle and bifurcation ratio), whereas that of T. heterophylla was more plastic (positively skewed shoot-length distribution, more variable branching angle and bifurcation ratio). The two species had similar shoot morphologies: number of leaves per unit shoot length and leaf to axis dry mass ratio. Leaf morphology, in contrast, was significantly different. Leaves of A. amabilis were larger and heavier than those of T. heterophylla, which resulted in lower mass-based photosynthetic...

The objectives of this study were to measure Kleaf, using a rehydration kinetics method, (1) in the laboratory (under controlled conditions) across a range of water potentials to construct vulnerability curves (VC) and (2) over the course of the day in the field along with leaf water potential and stomatal conductance. The results presented here, from the previous work of the authors and from other published studies, were consistent with two different strategies regarding daily maintenance of Kleaf: (1) substantial loss and subsequent recovery or (2) a more conservative strategy of loss...

Of all the ecological services of forests, a sustainable water supply may be the most important. Streamflow from forests provides two-thirds of fresh water supply in the United States. Removing forest cover temporarily increases the proportion of precipitation that becomes streamflow, and this effect has spurred political pressure to cut trees for the purpose of augmenting water supply, especially in western states where population and water demand are rising. However, this strategy is not sustainable: increases in flow are typically short-lived, and the combination of roads and repeated...

Forest thinning and prescribed fires are practices used by managers to address concerns over ecosystem degradation and severe wildland fire potential in dry forests. There is some debate, however, about treatment effectiveness in meeting management objectives as well as their ecological consequences. The purpose of this study was to assess changes to forest stand structure following thinning and prescribed fire treatments, alone and combined, in the eastern Cascade Mountains of Washington State. Treatments were applied to 12 management units, with each treatment combination replicated...

The survival and growth of yellow-cedar (Chamaecyparis nootkatensis) seedlings and rooted cuttings (stecklings) were monitored for 6 years after planting at three sites near Ketchikan in southeast Alaska to determine whether stecklings could serve as a suitable planting stock. Survival for both seedlings and stecklings was >85% at the three sites. Survival, final diameter, and final height differed by site but not by the use or absence of Vexar as protection from browsing by Sitka black-tailed deer (Odocoileus hemionus sitkensis). Vexar produced a lower rate of browsing but contributed to...

Hybridization and polyploidization are exceedingly important processes because both influence the ecological envelope and evolutionary trajectory of land plants. These processes are frequently invoked for Castilleja (Indian paintbrushes) as contributors to morphological and genetic novelty and as complicating factors in species delimitations. Here, we provide a detailed analysis of morphological and genetic evidence for hybridization in a well-characterized hybrid swarm involving three broadly sympatric species (c. miniata, C. rhexiifolia, C. sulphurea) in western Colorado. This study...

In 2005 the USDA and DOE jointly published a report concluding that it would be technically feasible to supply a billion dry tons of biomass annually from farms and forests throughout the United States in support of an emerging bioenergy and bioproducts industry. The report was criticized because it defined "supply" largely in terms of physical availability without a formal evaluation of economic feasibility. As a result, during 2008 and early 2009 the two agencies conducted a follow-up study in an effort to assess the potential biomass supply economically by deriving county-level supply...

The discovery that shade trees can reduce home cooling costs is hardly surprising. Anybody who has sat under a tree on a warm summer day understands the shade benefit of trees. However, quantifying the effect a shade tree has on home energy use and carbon footprint, and identifying the optimal location for a shade tree, is less straightforward. Past studies that have looked at the effect of trees on energy use have either taken a modeling approach or have been small-scale field experiments [see Akbari et al. (1997); Simpson and McPherson (1996)]. In this article, we summarize the results...

We used multiple regression and hierarchical mixed-effects models to examine spatial patterns of overwinter survival and size at smolting in juvenile coho salmon Oncorhynchus kisutch in relation to habitat attributes across an extensive stream network in southwestern Oregon over 3 years. Contributing basin area explained the majority of spatial variation (R2 = 0.57-0.63) in coho salmon overwinter survival (range = 0.02-0.63), with highest survival rates observed in smaller headwater and intermittent streams. Other habitat attributes, including proportional pool area, percent exposed...