Fine Structure of Acid Mist Treated Sitka Spruce Needles: Open-top Chamber and Field Experiments

Sitka spruce grafts (clones DF and 141) grown in open-top chambers(OTC) and ‘mature ’, 6 –8m tall Sitka spruce(clone DF) grown in the field were exposed to acid mist containingan equimolar ion mixture of H₂SO₄and NH₄NO₃at pH2.5. Mist wasapplied 4 times a week (4 x1mm) in the OTC experiment and twicea week (2 x2mm) on average in the field experiment, betweenMay and Oct. 1991. Samples for light and electron microscopywere collected in Nov. and Jan. following acid mist treatment.Acid mist significantly decreased the amount of calcium depositedin the outer epidermal cell walls, the reduction being mostpronounced in the OTCs. Ultrastructurally, acid mist causeda significant increase in chloroplast and grana width. Othersymptoms associated with acid mist included swelling of chloroplastthylakoids, chloroplast protrusions, cytoplasm vacuolization,increase in large lipid accumulations and sickle-shaped chloroplastthylakoids. In the OTCs, acid mist hastened the acquisitionof frost hardening in both clones. In the field, the controltrees exhibited more frost injury than the acid mist treatedtrees suggesting, again, that acid mist had either hastenedor enhanced the stage of frost hardiness of treated trees. Ingeneral, acid mist induced changes were more pronounced in theOTCs than in the field. Picea sitchensis; Sitka spruce; acid mist; fine structure; calcium oxalate; frost hardening     

Habitat Selection of Rocky Mountain Elk in a Nonforested Environment

Abstract: Recent expansions by Rocky Mountain elk (Cervus elaphus) into nonforested habitats across the Intermountain West have required managers to reconsider the traditional paradigms of forage and cover as they relate to managing elk and their habitats. We examined seasonal habitat selection patterns of a hunted elk population in a nonforested high-desert region of southwestern Wyoming, USA. We used 35,246 global positioning system locations collected from 33 adult female elk to model probability of use as a function of 6 habitat variables: slope, aspect, elevation, habitat diversity, distance to shrub cover, and distance to road. We developed resource selection probability functions for individual elk, and then we averaged the coefficients to estimate population-level models for summer and winter periods. We used the population-level models to generate predictive maps by assigning pixels across the study area to 1 of 4 use categories (i.e., high, medium-high, medium-low, or low), based on quartiles of the predictions. Model coefficients and predictive maps indicated that elk selected for summer habitats characterized by higher elevations in areas of high vegetative diversity, close to shrub cover, northerly aspects, moderate slopes, and away from roads. Winter habitat selection patterns were similar, except elk shifted to areas with lower elevations and southerly aspects. We validated predictive maps by using 528 locations collected from an independent sample of radiomarked elk (n = 55) and calculating the proportion of locations that occurred in each of the 4 use categories. Together, the high- and medium-high use categories of the summer and winter predictive maps contained 92% and 74% of summer and winter elk locations, respectively. Our population-level models and associated predictive maps were successful in predicting winter and summer habitat use by elk in a nonforested environment. In the absence of forest cover, elk seemed to rely on a combination of shrubs, topography, and low human disturbance to meet their thermal and hiding cover requirements.