Composition, structure, and biomass of cottonwood-dominated gallery forests along a successional gradient, Willamette River, Oregon

Recognizing the importance of native black cottonwood-dominated riparian forests is especially important to preserve, protect, and manage for biodiversity in the Willamette River Valley. Species composition, structure, and biomass along a successional gradient from stand initiation to late succession of black cottonwood (Populus balsamfera L. subsp. trichocarpa (T. & G.) Brayshaw) dominated gallery forests was investigated along 145 km of the Willamette River, Oregon. These forests were found to generally follow disturbance-initiated successional stages; stand initiation, stem exclusion, early succession/understory re-initiation, mid succession, and late succession. Young stands were dominated by black cottonwood and opportunistic herbaceous species. Understory shrub and late-successional tree species established 12 - 15 years after stand initiation. Oregon ash (Fraxinus latfolia Benth.) was the dominant late-successional tree species. Biotic habitat variables, in contrast to abiotic environmental variables, appeared to be the most important determinants of herbaceous and understory species presence and abundance. Relative stand age, as represented by average black cottonwood diameter at breast height (dbh), was the most important measured environmental variable based on non-metric multidimensional scaling (NMS) ordination using understory plant species composition and abundance in sites of all ages. Abundance of reed canarygrass (Phalaris arundinacea L.) was also an important variable across stand ages. Based on NMS ordination of stands >20 cm average dbh, this variable was the most highly correlated environmental variable with plant species composition and abundance. High abundance of reed canarygrass resulted in lower values of understory species diversity and total species richness by inhibiting establishment of understory tree, shrub, and herbaceous species as well as late-successional tree species. Total above ground tree biomass was calculated for all stands and ranged from <1 to 549 Mg/ha in stand initiation and late succession stages respectively. Black cottonwood biomass was 36 - 100% of total above ground tree biomass (<1- 427 Mg/ha). Biomass in these forests exceeded all other published above-ground biomass estimates for deciduous riparian forests. As cottonwood trees senesced and pioneer tree species dominance decreased, biomass also decreased. Annual biomass accumulation was lowest during stand initiation (0.01 Mg/halyr), peaked when stands were between 7 and 12 years old (23.7 Mg/halyr), and decreased thereafter as stands aged (2.9 to 7.3 Mg/ha/yr in stands >65 years old, n = 6). Structural diversity increased during early succession as understory trees, shrubs, and herbs established along with late-successional tree species, and created multiple vegetative layers. This understory re-initiation occurred around 12 to 15 years after stand initiation, when the cottonwood canopy opened up. Total tree densities were highest in early successional stands, 20,800 to 96,200 trees/ha, and decreased in older forest stands 443 to 3710 trees/ha. Large tree (>10 cm diameter at 1.3 meters in height) densities ranged from 180 to 1350 trees/ha. Standing dead tree density decreased with stand age from a peak in a 4 year old stand of 9,600 snags/ha. Standing dead tree biomass and downed wood biomass increased through time as stands aged from 0 to 12.7 Mglha and 0 to 2.1 Mg, respectively. Abundance of invasive plant species appeared to negatively impact structural diversity by inhibiting establishment of understory and late-successional tree species. This study indicated that Willaniette River cottonwood-dominated gallery forests are structurally diverse with high carbon storage potential, but as late successional species come to dominate, diversity and biomass decreased. Relative stand age was important across stands relative to species composition and abundance. However, considering only older stands, reed canarygrass was the most strongly correlated variable with species composition and abundance. Without intervention to control establishment and survival of reed canarygrass, and perhaps some other invasive species, such as Himalaya blackberry (Rubus arm eniacus L.) and English ivy (Hedera helix L.), it is likely that these species will become more influential and that plant diversity in Willamette River riparian forests will be negatively impacted. In addition, stands are small in area, few remain, and pioneer forest regeneration appears to be limited to areas where they are subject to scour and excessive inundation during high winter flow events. As cottonwood dominance continues to decline, late successional tree species and non-native understory vegetation are expected to increase in dominance at the riverscape level, decreasing overall biodiversity in the Willamette River Valley

The role of feeding strategy in the tolerance of a terrestrial salamander (Plethodon cinereus) to biogeochemical changes in northern hardwood forests

We investigated whether the trophic ecology of an apex predator is influenced by ecosystem-level nutrient depletion. The feeding behavior and nutrient assimilation of a terrestrial salamander (Plethodon cinereus (Green,1818)) was surveyed along a gradient of forest biogeochemistry. Recent studies have documented populations of these salamanders in forests with low-pH soils that were long thought to be fatal. One mechanism that may enable P. cinereus to tolerate acid-impaired habitats is its generalist life history. We sampled diet, invertebrate prey abundance, and tissue composition of P. cinereus from sites that range in calcium availability and soil pH in northern forests of North America. We found P. cinereus consistently exhibited a generalist feeding strategy, having diverse diets closely represented resource availability. Prey abundances were unrelated to the biogeochemical gradient (excluding gastropods), indicating relatively intact food webs. Although P. cinereus at the two most acid-impaired sites consumed more prey, overall trophic strategies were consistent across the gradient. Salamander tissue composition was unrelated to variation in forest biogeochemistry, although manganese levels were elevated in the most acid-impaired forests. We suggest that a generalist feeding strategy, combined with diverse and compositionally stable food webs, facilitates tolerance by this abundant predator of the challenges imposed by acid-impaired habitats.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Two Novel Prey Families for the Buprestid-Hunting WaspCerceris fumipennisSay (Hymenoptera: Crabronidae)

Rutledge, Claire E., Hellman, Warren, Teerling, Colleen, Fierke, Melissa K. (2011): Two Novel Prey Families for the Buprestid-Hunting WaspCerceris fumipennisSay (Hymenoptera: Crabronidae). The Coleopterists Bulletin 65 (2): 194-196, DOI: 10.1649/072.065.0223, URL: http://dx.doi.org/10.1649/072.065.022

Protein Design: Toward Functional Metalloenzymes

The scope of this Review is to discuss the construction of metal sites in designed protein scaffolds. We categorize the effort of designing proteins into redesign, which is to rationally engineer desired functionality into an existing protein scaffold,(1-9) and de novo design, which is to build a peptidic or protein system that is not directly related to any sequence found in nature yet folds into a predicted structure and/or carries out desired reactions.(10-12) We will analyze and interpret the significance of designed protein systems from a coordination chemistry and biochemistry perspective, with an emphasis on those containing constructed metal sites as mimics for metalloenzymes