Size, age, and density relationships to curlleaf mahogany ( Cercocarpus ledifolus ) populations in western and central Nevada: competitive implications

Size-density-age relationships in curlleaf mountain mahogany communities were studied in 25 study plots, each 30 x 30 m, in western and central Nevada. The influence of total vegetation cover (site potential) and relative mahogany cover (mahogany dominance) on the observed size-density-age relationships was investigated. A positive linear relationship was found between mean mahogany height and mean mahogany age. A positive nonlinear relationship was found between mean mahogany crown volume and mean mahogany age. Negative nonlinear relationships were found between mean mahogany density and mean mahogany age, and mean mahogany density and mean mahogany crown volume. Strong negative relationships were found between the mean combined density of established seedlings, juvenile, and immature mahogany and mean mahogany age and mean mahogany crown volume. Including total cover in the regression relationships between size, age, and density never increased the r 2 value by more than .05. The addition of relative mahogany cover improved the r 2 value for the relationship between mean mahogany density and mean mahogany crown volume by .28. The strong size-density and age-density relationships found indicate that intraspecific competition is probably occurring in the communities sampled, and that established seedlings, juvenile, and immature plants are the first individuals affected. Direct tests are needed to confirm these relationships.     

Seasonal microhabitat relationships of blue grouse in southeastern Idaho

Microhabitat characteristics of blue grouse ( Dendragapus obscurus ) were analyzed in breeding and wintering habitats in southeastern Idaho. Breeding habitats typically were open sagebrush ( Artemisia spp.), mixed shrub, mountain mahogany ( Cercocarpus ledifolius ) , and maple ( Acer grandidentatum ) stands on east to south facing aspects of slopes below 2100 m elevation. Breeding blue grouse selected areas with approximately a 50:50 or greater open to cover ratio. Blue grouse selected areas with higher tree coverage than available on average within the mixed shrub vegetation type. Hens with broods preferred sites with relatively tall (>50 cm) herbaceous vegetation. During autumn and winter, blue grouse preferred high elevation (>2285 m) stands of open (50% tree cover) conifer. Douglas-fir ( Pseudotsuga menziesii ) were preferred as winter roost trees. Sites selected in winter had significantly more Douglas-fir than those selected in autumn.      

Winter habitats and foods of Blue Grouse in the Sheeprock Mountains, Utah

Winter habitat use and food habits of Blue Grouse ( Dendragapus obscurus ) were studied in an isolated Utah desert mountain range that contained little typical Douglas-fir ( Pseudotsuga menziesii ) winter habitat. Habitat use was concentrated in the Douglas-fir and pinyon ( Pinus edulis )-juniper ( Juniperus spp. ) habitat. Douglas-fir and pinyon pine were the most consumed foods. Other foods that represented >15% of the composition of an individual fecal sample were limber pine ( Pinus flexilis ), mahogany ( Cercocarpus ledifoliu ), juniper, and an Anteunaria-Cirsium type. The breadth in winter diet indicates that Blue Grouse may successfully occupy other habitats when typical winter habitat is scarce.     

Seed dispersal, seed entrapment, and seedling recruitment in a temporally variable desert playa

Natural establishment of seedlings in desert playas with temporally variable precipitation hinges on many factors, including seed production, seed dispersal, seed entrapment, seed germination, and seedling survival. We investigated natural seed dispersal patterns and the effects of surface texture, wind barriers, resource availability (water and nutrients), and protection from herbivory on seedling establishment in a desert playa. We hypothesized that the seed rain would be consistent throughout the year and that seedling establishment would improve in resource-amended plots with barriers to wind dispersal. Contrary to our hypotheses, seed flux peaked seasonally during the winter, and fertilization had no consistent effect on seedling establishment. Seed availability for dispersal correlated with precipitation in the previous water year, whereas seedling recruitment was greatest when current-year precipitation during the spring germination and summer seedling growth periods was high. Gravel and barrier surface treatments contained more surviving seedlings than other surface treatments. Comparison with plots located outside of herbivore exclosures, however, showed that greater seedling presence in gravel plots may be due somewhat to protection from herbivory provided by the gravel, rather than simply to the greater seed-trapping quality of the gravel. With abundant seed availability, application of surface treatments, like coarse gravel, combined with increased seasonal water availability could lead to improved shrub establishment from seed in desert playas.     

Does the presence of Wyethia mollis affect growth of Pinus jeffreyi seedlings?

Regeneration of Pinus jeffreyi in the Sierra Nevada is often limited on sites dominated by Wyethia mollis . Allelopathic chemicals and competition for soil moisture have been suggested as possible mechanisms for limiting regeneration. We tested the hypothesis that soil chemical and microbial properties from sites in different stages of succession influence seedling growth of Pinus jeffreyi . Soil was collected from an early-seral site dominated by Wyethia mollis , a mid-seral site dominated by the shrubs Arctostaphylos patula, Ceanothus prostratus, C. velutinus , and Purshia tridentata , and a late-seral site dominated by mature Pinus . These sites were compared for nutrient content, Pinus seedling growth capacity, and microbial population size. Soil (0-33 cm) from the early-seral site had the lowest C, microbial biomass, and fungal and bacterial populations. There were no consistent trends in soil nutrient content among sites. The early-seral site had the lowest soil Ca and Mg contents but also had a lower C/N ratio and more than twofold greater P content than either the mid- or late-seral site. Pinus seedling growth and foliar nutrient concentrations were compared at 3 harvest dates (220, 314, and 417 days after germination) in a greenhouse bioassay. The treatment design was a 3 × 2 factorial with soil from each of the 3 sites either with or without Pinus seedlings. Pots without seedlings were used as controls to assess the effects of seedlings on microbial biomass. Seedling growth in the early-seral soil was initially suppressed in comparison to growth in the mid-seral soil, but by the final harvest total seedling weight was similar between these 2 treatments. The most obvious treatment effect was a reduction in growth for seedlings planted in lateseral soil, probably due to a nutrient imbalance in the soil. Seedlings grown in late-seral soil had Fe and Al levels that were nearly twice those of seedlings grown in early- and mid-seral soils. Microbial biomass followed a temporal pattern similar to that found for seedling growth. Differences in microbial biomass between the early- and mid-seral soils, although initially large, were not detected by the final harvest. We interpret these results to indicate that allelopathy or soil nutrient deficiencies resulting from the presence of Wyethia are unlikely to be responsible for limited growth of Pinus seedlings in Wyethia -dominated stands.     

Historic expansion of Juniperus occidentalis (western juniper) in southeastern Oregon

The chronology of Juniperus occidentalis (western juniper) expansion in eastern Oregon, the effect of plant canopy and interspace on J. occidentalis seedling establishment and growth rates, and the age of J. occidentalis maximum reproductive potential were determined. Measurements were recorded in twenty-two 0.4-ha plots established in sagebrush-grassland communities and six 0.1-ha plots in Populus tremuloides (quaking aspen) communities. J. occidentalis began increasing during the 1880s in stands containing > 130 yr old. Relatively steady establishment ensued into the 1950s and then began to progress at a geometric rate in the 19602. J. occidentalis encroachment into aspen stands began between 1910 and 1920. The largest proportion of juvenile trees established beneath Artemisia species in sagebrush-grassland communities. J. occidentalis trees appeared to reach full reproductive potential at > 50 yr of age. The ratio of male:female trees increased from 1.7 in scattered J. occidentalis stands to 3.8 in closed stands. The initiation of J. occidentalis encroachment during the late 1800s coincides with optimal climatic conditions for Juniperus berry production and establishment, reduced fire-return intervals, and heavy livestock grazing. The accelerated increase in J. occidentalis expansion since 1960 may be due to the continued absence of fire, abundant woody plant cover, and the large increase in J. occidentalis seed production.     

Winter nutrient content and deer use of gambel oak twigs in north central Utah

We examined winter nutritional quality of current-year bud and stem tissues from burned and unburned stands of Gambel oak ( Quercus gambelii Nutt.). Nutritional analyses were based on the amount of forage consumed by wintering mule deer. Deer use along the Utah Valley foothills averaged 6.25-10.7 cm of current-year growth. Of the tissues examined, post-fire bud tissue had the highest nutrient content, with a mean of 9.51% crude protein, 0.19% phosphorus, and 34.0% in vitro digestibility. Composite values (bud + stem) for unburned stands were slightly higher in crude protein and phosphorus and lower in digestibility than those reported in previous studies. Nutrient values from burned stands were significantly higher than those of unburned stands for all three measures. Tannin content of the burned-area regrowth was also higher. Overall forage value of Gambel oak to wintering mule deer is relatively low.     

Infection of young Douglas-firs and spruces by dwarf mistletoes in the Southwest

Mistletoe infection of Douglas-fir and spruce seedlings increased as the mean dwarf mistletoe rating of the overstory, seedling density, and total age of seedlings increased. Percent of spruce seedlings infected increased more rapidly than for Douglas-fir as overstory dwarf mistletoe ratings increased. However, the intensity of infection as measured by the mean dwarf mistletoe rating of seedlings, increased at about the same rate for spruce and Douglas-fir. Percent infection of seedlings less than 20 years total age was higher for spruce than for Douglas-fir. Douglas-fir and spruce seedling mortality was from two to three times greater in heavily infested stands than in healthy stands.     

A mountain cercocarpus population-revisited

A mountain cercocarpus ( Cercocarpus montanus Raf.) population was analyzed first in 1965 and again in 1975 to gain insight into the growth and reproduction of this species. The basis for comparison was plant height and number of basal stems. Growth (measured by height) was slow during the 10 - year period, with plants on the northeast - facing slope having an average increase of 37 cm and those on the southwest - facing slope maintaining relatively the same average height. There was an overall decrease in average number of base stems for plants positioned on both slopes.        

Ecological relationships of curlleaf mountain-mahogany ( Cercocarpus ledifolius Nutt.) communities in Utah and implications for management

Curlleaf mountain-mahogany is a widely distributed shrubby tree of western North America. Well-developed stands are most often found on warm, dry, rocky ridges and slopes at high elevations on mostly southern exposures. It can, however, be found onall exposures. The species appears to be indifferent to substrate with soils which are invariably shallow and of low fertility. However, the nitrogen-fixing root nodules help overcome soil deficiencies. This highly palatable species is preferred by mountain sheep, mountain goats, deer, and elk. Its nutritive value (about 12% protein) and digestibility ratings (around 50%) in the winter are high when compared with most other associated winter browse species. Early research with curlleaf mountain-mahogany basically dealt with two major management problems: (1) how to increase available forage production on old, even-aged stands too tall for big game to browse, and (2) how to increase reproduction in these same communities. Selective dozer thinning, sometimes in conjunction with the seeding of fast-growing plants, appears to be a promising management technique providing browse until the younger curlleaf becomes established.     

Plant age/size distributions in black sagebrush ( Artemisia nova ): effects on community structure

The demography of black sagebrush ( Artemisia nova Nelson) was investigated in the Buckskin Mountains of western Nevada to determine patterns of stand renewal in sagebrush communities currently free from wildfires. Biomass sampling was conducted to develop growth classes that reflected apparent age of the shrubs. The density of black sagebrush plants was twice that of basin big sagebrush ( A. tridentata ssp. tridentata Nutt.) in adjacent communities on contrasting soils (2.2 versus 1.1 plants per m 2 ). Black sagebrush accumulated only 75% as much woody biomass as big sagebrush. Regression equations were developed and tested for predicting total woody biomass, current annual growth (CAG), and leaf weight of black sagebrush plants. Apparent age classes were developed both for the black sagebrush plants and the sub-canopy mounds on which they grew. Discriminant analysis was used to test this classification system. Plant succession, apparently controlled by nitrate content of the surface soil, appeared to eliminate the successful establishment of black sagebrush seedlings on the mounds. After the shrubs die, the mounds eventually deflate. We propose that mounds reform around shrub seedlings, but because seedling establishment is so rare in these communities, this could not be verified.     

Dynamics of a dwarf bear-poppy ( Arctomecon humilis ) population over a sixteen-year period

A population of the dwarf bear-poppy ( Arctomecon humilis Coville, Papaveraceae) at Red Bluff, Washington County, Utah, was monitored twice annually between 1987 and 2002. This is a narrowly endemic, gypsophilous species that has been formally listed as endangered since 1979. During the 16 years of observation, density of this species has fluctuated between 3 and 1336 individuals on the 0.07-ha monitoring plot. Moderate to large recruitments of seedlings occurred in 1992, 1995, and 2001. Seedling recruitments from a large, long-lived seed bank are triggered by abundant precipitation during the February-April period. At least 5.0 cm of rainfall is required during that interval to produce any seedlings. Seedlings experienced considerable mortality in the 1st few months of life in all observed cases. The average seedling initiated in the very large recruitment event of 1992 survived for only 2.6 years. Seedlings in that cohort that were alive 1 year after germination had an average longevity of 4.6 years. None of the seedlings that emerged in 1992 were still alive in October 2002. Mortality in this species was poorly correlated with fluctuations in precipitation or temperature. No epidemics of parasites or herbivores were observed. Mortality in the species appears to be caused by a variety of factors acting over a cohort's lifetime.     

Natural history and invasion of Russian olive along eastern Montana rivers

Russian olive and tamarisk are introduced woody plants invading western North American riparian communities. Beavers can play an important role in structuring these communities by removing the dominant cottonwood trees. Our study explored the way in which beavers interact with cottonwood, Russian olive, and tamarisk along 4 rivers on the Great Plains of eastern Montana. We sampled cottonwood stands that supported populations of 1 or both exotic species, recording beaver damage and density in addition to size and age of cottonwood, Russian olive, and tamarisk. In stands where beaver had been present, they felled an average of 80% of cottonwood trees while rarely using Russian olive or tamarisk. Beaver foraging was apparent in nearly 90% of stands within 50 m of the river channel but only 21% of stands farther away, creating a sunny corridor along the river channel that may increase the invasive potential of Russian olive and tamarisk. Growth rates of both Russian olive and tamarisk were substantially higher where beavers had reduced the cottonwood canopy cover. Managers wishing to reintroduce beavers should consider the potential effect on invasive exotic plants.     

Beavers indirectly enhance the growth of Russian olive and tamarisk along eastern Montana rivers

Russian olive and tamarisk are introduced woody plants invading western North American riparian communities. Beavers can play an important role in structuring these communities by removing the dominant cottonwood trees. Our study explored the way in which beavers interact with cottonwood, Russian olive, and tamarisk along 4 rivers on the Great Plains of eastern Montana. We sampled cottonwood stands that supported populations of 1 or both exotic species, recording beaver damage and density in addition to size and age of cottonwood, Russian olive, and tamarisk. In stands where beaver had been present, they felled an average of 80% of cottonwood trees while rarely using Russian olive or tamarisk. Beaver foraging was apparent in nearly 90% of stands within 50 m of the river channel but only 21% of stands farther away, creating a sunny corridor along the river channel that may increase the invasive potential of Russian olive and tamarisk. Growth rates of both Russian olive and tamarisk were substantially higher where beavers had reduced the cottonwood canopy cover. Managers wishing to reintroduce beavers should consider the potential effect on invasive exotic plants.     

Late Quaternary vegetation and climate in the Escalante River Basin on the central Colorado Plateau

Five alcoves (rock shelters) in the Forty-Mile Canyon—Willow Gulch area of the Escalante River Basin in southeastern Utah yielded rich deposits of late Quaternary macrobotanical remains. The deposits were sampled and the contents identified in order to construct a chronology of vegetational change. Fourteen radiocarbon dates indicate that the fossils were deposited between 12,690 and 7510 yr B.P. (years before present). Ninety-one plant taxa were identified, 62 to species. Six species were common to all alcoves: Gambel oak ( Quercus gambelii ), box-elder ( Acer negundo ), prickly pear ( Opuntia subgenus Platyopuntia), skunkbush ( Rhus aromatica var. trilobata ), serviceberry ( Amelanchier utahensis ), and Indian ricegrass ( Oryzopsis hymenoides ). Late Pleistocene samples (>11,000 yr B.P.) contain extralocal, elevationally depressed species such as Douglas fir ( Pseudotsuga menziesii ), spruce ( Picea sp.), and mountain mahogany ( Cercocarpus ledifolius ), and mesophytic species such as rose ( Rosa woodsii ) and water birch ( Betula occidentalis ). Early Holocene samples (11,000-8000 yr B.P.) contain no elevationally depressed conifers, and the remaining mesophytic species decrease in relative abundance. Reticulated hackberry ( Celtis reticulata ) becomes common. The terminal Early Holocene sample (8000-7000 yr B.P.) contains abundant Gambel oak and prickly pear, but little else. Paleoclimatic interpretations for the Late Pleistocene correspond well to those of most other workers on the Colorado Plateau. Climates that were wetter and at least seasonally cooler than they are today are inferred from the macrobotanical assemblage. However, the increased moisture is attributed to higher stream base levels and increased groundwater rather than directly to increased precipitation. Early Holocene climates are interpreted as warmer and drier than those of the Late Pleistocene but still wetter than the present climate. Groundwater levels appear to be decreasing due to stream entrenchment. Terminal Early Holocene climates were much warmer and at least seasonally drier. By the end of the period, groundwater levels had decreased so much that the alcoves were unable to sustain plant communities; stream base level was probably near the present level.     

Seedling size and survival for Chrysothamnus nauseosus

Seedling size and survival in relation to summer drought were examined for Chrysothamnus nauseosus growing under field and greenhouse conditions. In the field, summer survival rates were less than 2% annually for the three years monitored. The effect of initial seedling height on subsequent survival was examined in both the field and greenhouse by grouping seedlings into live and dead categories on each census date and comparing initial heights for seedlings in these categories. For a majority of the census dates, the initial height of surviving seedlings was greater than the initial height of those that subsequently died (significant differences ranged from 1 to 8 mm), indicating that seedlings that were taller at the initiation of the drought period had a higher probability of survival. In the greenhouse, taller seedlings had greater shoot and root biomass and rooting depth. Seedlings that are larger (i.e., taller and have greater aboveground biomass) in late spring appear to have a higher probability of surviving summer drought due to greater rooting depth and hence increased access to moisture in deeper soil layers. Seed availability and safe sites for germination were probably not limiting since large numbers of seedlings successfully germinated in a patchy pattern during the study period. Seedling size and probability of survival were not related to either seedling density or the distance to nearest seedling neighbor. Survival through summer drought appears to be the main limitation to seedling recruitment in this population.     

Selection of big sagebrush by sage grouse

Feeding sites of wintering sage grouse ( Centrocercus urophasianus ) were located, one each in stands of three subspecies of big sagebrush ( Artemisia tridentata : ssp. tridentata , basin; ssp. vaseyana , mountain; and ssp. Wyomingensis , Wyoming). Evidences of differential use of plants within subspecies were observed. Whole leaves from fed-on and nonfed-on big sagebrush plants were examined for intrasubspecies chemical comparisons of crude protein, phosphorus, in vitro digestibility, and monoterpenoids. No significant differences were detected except for in vitro digestibility of Wyoming fed-on and nonfed-on big sagebrush and monoterpenoid content of basin big sagebrush. Nutritive content of all three subspecies was high, which may in part help to explain wintering sage grouse weight gains.     

Response of winterfat ( Ceratoides lanata ) communities to release from grazing pressure

Sixteen study sites were established in grazed and ungrazed stands of winterfat in Kane County, Utah. The area is located within the winter range of cattle and along U.S. Highway 89 between Kanab, Utah, and Page, Arizona. Road construction in 1957 dissected several winterfat communities, and following fencing part of the communities were released from grazing. Differences in species composition, vegetation, and soil characteristics between grazed and ungrazed sites were assessed. Major differences in site characteristics appeared due to the influence of winter grazing by cattle. Winterfat and Indian ricegrass showed increased cover on the nongrazed sites following release from grazing pressure. Winterfat also showed significant negative interspecific association patterns with all major species.     

Spatial pattern and interference in pi?on-juniper woodlands of northwest Colorado

The local spatial arrangement of the coniferous trees Pinus edulis and Juniperus osteosperma was mapped in two woodland stands and measured in two shrub-dominated stands in the semiarid Piceance Basin of northwest Colorado. In the woodlands, small trees were often clumped, while medium and large trees were either randomly or uniformly dispersed. Significant regressions were obtained between a tree?s basal area or canopy area and the area of its Dirichlet domain (the region closer to it than to any other tree). Both findings from the woodland stands accord with results obtained by other workers in other vegetation. Like earlier workers, we interpret these patterns to indicate density-dependent mortality and density-dependent depression of growth rates among the trees in the woodlands. In contrast, the trees in the shrub-dominated stands are located at random with respect to each other. However, they are strongly associated with shrub cover. Apparently tree seeds arrive in these stands primarily by long-distance dispersal, and the establishment of seedlings is more likely in the shade of shrubs.