Effects of browsing by native ungulates on the shrubs in big sagebrush communities in Yellowstone National Park

The effects of elk ( Cervus elaphus ), pronghorn ( Antilocapra americana ), and mule deer ( Odocoileus hemionus ) browsing on shrubs in big sagebrush ( Artemisia tridentata ) communities were monitored over a 31-year period in Yellowstone National Park. Ungulates were restricting Wyoming big sagebrush (spp. wyomingensis ) heights, size, and recruitment on the lower-elevation stratum only, while no such suppression was observed on the high-elevation stratum. Parallel increases in mountain big sagebrush (spp. vaseyana ) densities and cover occurred over the study period on both browsed and unbrowsed sites at the higher-elevation stratum, although big sagebrush, green rabbitbrush ( Chrysothamnus viscidiflorus ), and horsebrush ( Tetradymia canescens ) were slightly taller and crown sizes were slightly larger on unbrowsed than browsed sites. Wyoming big sagebrush utilization (percent leader use) was eight times higher (￣ x = 87 ± 7.2% by pronghorns, mule deer, and elk) on the low-elevation winter ranges stratum (the Boundary Line Area [BLA] portion of the winter range), while mostly mountain big sagebrush with leader use averaged only 11 ± 4.1% (nearly all by elk) on the high-elevation range stratum. In addition, annual aboveground biomass production of big sagebrush did not differ between browsed and unbrowsed study sites on the high-elevation stratum of the winter range. Population turnover was higher on browsed plots versus unbrowsed plots. No difference was observed in percent dieback of big sagebrush adult plants between browsed and unbrowsed plots at the higher stratum. Browsing did not influence the number of leaves or seedstalks per plant ( P > .05), but leaves averaged 45% longer and seedstalks 42% longer on browsed big sagebrush. Ungulate browsing, however, apparently suppressed production, germination, and survival of Wyoming big sagebrush on the low-elevation stratum. Numbers of Wyoming big sagebrush declined 43% and cover declined 29%, 1957-1990, on browsed sites on the BLA. Annual biomass production on browsed sites at the low-elevation stratum was only 6-35% that of unbrowsed sites, and big sagebrush recruitment was less on browsed sites. Percent leader use of big sagebrush did not differ between the period of ungulate reductions, 1962-1969, and the 1980s on the lower stratum (￣ x = 87% leader use), but utilization was less on higher portions of the winter range during the period of elk reductions (￣ x = 2%) than during the 1980s following cessation of elk controls (￣ x = 11%).     

Role of livestock and black-tailed jackrabbits in changing abundance of Kochia americana

Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4 st1\:*{behavior:url(#ieooui) } /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"Times New Roman"; mso-fareast-theme-font:minor-fareast; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;} Historical accounts and matched photographs indicate sharp decline of once-abundant Kochia americana in eastern Great Basin vegetation since the early 1900s, most of the decline by the late 1950s. Exclosure data show further decline from 1957 to 1973, then some increase between 1970 and 1973 and 1976 and 1981. Utah sheep numbers, at maximum from 1925 to 1940 and declining steadily to the 1970s, may have induced the long-term changes. Black-tailed jackrabbits ( Lepus californicus ), could not have induced vegetation decline, but could have added to livestock pressure and abetted the trend. In 1972, rabbits near a cyclic high were indirectly estimated to completely utilize K. americana in Curlew Valley, northwestern Utah. In 1976–1977 at rabbit low, direct measurements show 4%–18% of plants browsed by late summer, about 30%–50% of herbage removed from browsed plants. The latter rose to 45%–82% by end of winter. Late-summer percent browsed may have risen slightly (11%–21%) in 1980–1981 at next rabbit high. Increase in K. americana density from 1973 to 1976, then a slight decrease from 1976 to 1980, suggests fluctuating K. americana abundance induced by rabbit browsing, superimposed on long-term K. americana decline and recovery.     

Effects of browsing by mule deer on tree growth and fruit productions in juvenile orchards

The effects of big game depredation on juvenile fruit trees were studied in northern Utah. Utilization of trees was determined by counts of nipped and intact buds in spring. Height, width, basal diameter, number of buds, and initial fruit production of peach and apple trees were determined from trees protected from or browsed by mule deer in winter: Results from the 10 orchards studied indicated that removal of buds at the observed browsing levels had no effect on tree growth or initial fruit production.     

Ungulate herbivory on alpine willow in the Sangre de Cristo Mountains of Colorado

In many areas of the Rocky Mountains, elk ( Cervus elaphus ) migrate from low-elevation mountain valleys during spring to high-elevation subalpine and alpine areas for the summer. Research has focused on the impacts of elk herbivory on winter-range plant communities, particularly on woody species such as willow and aspen; however, little information is available on the effects of elk herbivory on alpine willows. In the Sangre de Cristo Mountains of south central Colorado, select alpine areas appear to receive high levels of summer elk herbivory, while other areas are nearly unbrowsed. In 2005 and 2008, we measured willow height, cover, and utilization on sites that appeared to be used heavily by elk, as well as on sites that appeared to be used lightly, to determine differences between these communities over time. We found less willow cover and shorter willows at sites that received higher levels of browsing compared to those that had lower levels of browsing. Human recreational use was greater at lightly browsed sites than at highly browsed sites. From 2005 to 2008, willow utilization declined, and willow cover and height increased at sites with heavy browsing, likely owing to ownership change of adjacent valley land which led to (1) removal of grazing competition from cattle at valley locations and (2) increased human use in alpine areas, which displaced elk. We discuss the implications of increased human use and climate change on elk use of these alpine habitats. En muchas áreas de las Montañas Rocosas, el ciervo rojo ( Cervus elaphus ) migra durante la primavera de valles montañosos de baja elevación a áreas altas subalpinas y alpinas para el verano. Hasta ahora la investigación se ha enfocado en el impacto de la herbivoría del ciervo rojo sobre las comunidades de plantas en el invierno, particularmente en las especies leñosas como el sauce y el álamo; sin embargo, existe poca información disponible sobre el efecto de la herbivoría del ciervo rojo en los sauces alpinos. En la cordillera Sangre de Cristo al centro-sur de Colorado, ciertas áreas alpinas parecen tener altos niveles de herbivoría de verano por el ciervo rojo, en tanto que otras áreas quedan casi sin ramoneo. En 2005 y 2008 medimos la altura, cobertura y uso de los sauces en sitios en los que parecía haber sido abundante el ramoneo y los comparamos con sitios donde parecía haber sido más ligero, a fin de determinar las diferencias entre estas comunidades en el tiempo. Encontramos menos cobertura y altura de sauces en los sitios que recibían niveles más altos de ramoneo en comparación a los que tenían menos evidencia de ello. El uso humano recreativo era mayor en los sitios de ramoneo ligero que en donde era abundante. De 2005 a 2008, disminuyó el uso y aumentó la cobertura y la altura en sitios de ramoneo abundante, probablemente debido a que un valle adyacente cambió de propietario, lo cual provocó (1) la eliminación de la competencia por el pastoreo en ganado en el valle; y (2) un aumento del uso humano en áreas alpinas, desplazando al ciervo rojo. Discutimos las implicaciones del aumento del uso humano y el cambio climático en el uso por el ciervo rojo de estos hábitats alpinos.     

Bottom-up factors influencing riparian willow recovery in Yellowstone National Park

After the elimination of wolves ( Canis lupis L.) in the 1920s, woody riparian plant communities on the northern range of Yellowstone National Park (YNP) declined an estimated 50%. After the reintroduction of wolves in 1995–1996, riparian willows ( Salix spp.) on YNP’s northern range showed significant growth for the first time since the 1920s. However, the pace of willow recovery has not been uniform. Some communities have exceeded 400 cm, while others are still at pre-1995 levels of <80 cm mean height. We took intensive, repeated measurements of abiotic factors, including soil and water-table characteristics, to determine whether these factors might be contributing to the varying pace of willow recovery. Willows at all of our study sites were “short” (<250 cm max. height) prior to 1995 and have recovered to varying degrees since. We contrasted “tall” (>250 cm max. height) willow sites where willows had escaped elk ( Cervus elaphus L.) browsing with “short” willow sites that could still be browsed. Unlike studies that manipulated willow height with fences and artificial dams, we examined sites that had natural growth differences in height since the reintroduction of wolves. Tall willow sites had greater water availability, more-rapid net soil nitrogen mineralization, greater snow depth, lower soil respiration rates, and cooler summer soil temperatures than nearby short willow sites. Most of these differences were measured both in herbaceous areas adjacent to the willow patches and in the willow patches themselves, suggesting that they were not effects of varying willow height recovery but were instead preexisting site differences that may have contributed to increased plant productivity. Our results agree with earlier studies in experimental plots which suggest that the varying pace of willow recovery has been influenced by abiotic limiting factors that interact with top-down reductions in willow browsing by elk.     

Effects of dwarf mistletoe on growth and mortality of Douglas-fir in the Southwest

The effects of dwarf mistletoe ( Arceuthobium douglasii ) on growth and mortality of Douglas-fir ( Pseudotsuga menziesii ) were studied on 387 plots in mixed-conifer stands in three national forests in New Mexico and two in Arizona. Analyses of 8,570 trees showed that low infection ratings (dwarf mistletoe classes 1 or 2) had no significant effect on tree growth, but that losses increased markedly as infection severity increased. Average volume growth losses for trees over 10 inches in diameter were: dwarf mistletoe class 3, 10%; class 4, 25%; class 5, 45%; and class 6, 65%. Mortality of Douglas-fir in stands severely infested with dwarf mistletoe was three to four times that of healthy stands. These high losses confirm the need for silvicultural control of Douglas-fir dwarf mistletoe in the Southwest.     

Increased willow heights along northern Yellowstone's Blacktail Deer Creek following wolf reintroduction

Gray wolves ( Canis lupus ) were reintroduced into Yellowstone National Park in 1995–1996. In August 2004 we measured plant architecture of Geyer willow ( Salix geyeriana ) stems along three 100-m reaches of Blacktail Deer Creek in Yellowstone's northern elk ( Cervus elaphus ) winter range to evaluate changes in patterns of browsing and height growth following wolf reintroduction. Average browsing intensities ( n = 3 stream reaches) of 100% in 1997 decreased to 0%–55% by 2003, whereas average stem heights of 25–74 cm in 1997 increased to 149–268 cm by 2003, indicating that willow height growth was inversely related to browsing intensity. In addition, average willow canopy cover over the streams increased from < 5% in 1997 to 14%–73% in 2004. These findings were consistent with a hypothesis that increased willow heights following the 1995–1996 wolf reintroduction represent a trophic cascade involving wolves, elk, and deciduous woody vegetation.     

Ecology of Celtis reticulata in Idaho

The small deciduous tree Celtis reticulata (neatleaf hackberry) reaches its northern limit in Idaho, where, contrary to most of its western range, it often occurs as an overstory dominantly. Two hundred fifty stands of this tree were sampled throughout Idaho. Celtis is slow-growing, averaging 4 m tall at 50 yr, and long-lived (to 300-400yr). It occurs in a variety of habitats, from riparian to rocky uplands. Trees grow best where topographically sheltered, such as in draws and narrow canyons, and were soils are loamy. Although plants grow more slowly as surface rock cover increases, stands are often associated with rock, with a mean surface cover of 39% rock. Differences in growth rates were unrelated to parent material and aspect. Most stands are reproducing, in spite of habitat degradation caused by overgrazing, alien plant invasion, and increasing fire frequencies. Stands are typically represented by one dominant cohort; however, young, even-aged stands are rare and are generally found along waterways on stream terraces or at the high-water line. Although slow growing, C. reticulata shows promise for land mangers interested in site enhancement. This native species is long-lived, produces fruit used by wildlife, and provides structural diversity in a semiarid landscape (with a maximum height o 12 m) in areas that are becoming increasingly dominated by exotic plant species.     

Aspen and conifer heterogeneity effects on bird diversity in the northern Yellowstone ecosystem

We addressed the following question: Do conifers within aspen stands (conifer invasion) increase bird species diversity in western landscapes? We tested the hypotheses that bird species diversity, measured as species richness or with the Shannon-Weiner diversity index, responds to aspen-conifer ratios (from 0% to 100% conifer) in a quadratic manner with a maximum occurring at an intermediate ratio of aspen and conifer. Extra sum-of-squares F tests comparing quadratic with linear models suggested that migratory bird diversity was inversely linearly related to the extent of conifer invasion. These linear responses were moderate (species richness: R 2 ≥ 0.34, P 2 ≥ 0.34, P 2 ≤ 0.13, P ≥ 0.09) and was marginal for the Shannon- Weiner diversity index (R 2 ≤ 0.27, P ≤ 0.01). We concluded that mixed aspen-conifer stands do not have higher bird species diversity than pure aspen stands and that management activities should focus on heavily conifer-invaded stands to increase bird diversity in western landscapes and help reverse the decline of aspen habitat due to conifer invasion.     

Spatial relationships among young Cercogarpus ledifolius (curlleaf mountain mahogany)

This study analyzed spatial location patterns Cercocarpus ledifolius Nutt. (cutleaf mountain mahogany) plants, classified as current-year seedling, established seedling, juvenile, and immature individuals, at a central Nevada study site. Most current-year seedlings were located in mahogany stands in which large, mature individuals had the greatest abundance. These stands had greater litter cover and a thicker layer of litter than areas with few current-year seedlings. Most established young Cercocarpus were located in adjacent Artemisia tridentata spp. vaseyana (mountain big sagebrush) communities, or in frequent canopy gaps between relatively few large, mature Cercocarpus . We discuss potential roles of plant litter, root growth characteristics, nurse plants, and herbivory in the establishment and renewal of Cercocarpus communities.     

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.     

Long-term effects of tebuthiuron on Bromus tectorum

Use of herbicides to thin dense stands of Artemisia spp. (sagebrush) can free up resources for herbaceous plants and increase forage production, but may also facilitate weed invasion. We revisited a sagebrush thinning experiment in a north central Wyoming big sagebrush–grassland 11 years after application of tebuthiuron (N-[5-(1,1- dimethylethyl)-1,3,4-thiadiazol-2-yl]-N-N′-dimethylurea) to determine the long-term responses of shrubs, available soil resources, perennial grasses, and Bromus tectorum L. (downy brome). Tebuthiuron reduced shrub cover by more than half, from 31% in untreated plots to 15% in treated plots ( P = 0.002), and increased downy brome cover approximately 4-fold, from 0.9% in untreated plots to 3.5% in treated plots ( P = 0.02). Treatment with tebuthiuron also resulted in marginally significant increases in cover of perennial grasses (from 9% to 12.3%; P = 0.07) and bare ground (from 39.1% to 43.9%; P = 0.08). In comparisons of resource availability among microsites, available NO 3 was higher under dead sagebrush than under live sagebrush ( P = 0.03). No significant differences in soil water content were detected. The relatively recent expansion of downy brome populations at this site and the high NO 3 –N levels observed under dead sagebrush suggest that conditions facilitating downy brome invasion may persist for many years following sagebrush thinning. We demonstrate that sagebrush thinning can cause increases in downy brome populations years after initial treatment and suggest that managers should use caution when considering thinning sagebrush if downy brome is present, even if initial populations are small.     

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.     

Identification of Purshia subintegra (Rosaceae)

Populations of Purshia in central Arizona are intermediate in some characters between Purshia subintegra , an endangered species, and Purshia stansburiana , the common cliffrose. These intermediates may represent forms derived from a history of hybridization and introgression between putative parent species. Morphological data were obtained from 216 pressed speciments of P. subintegra , P. stansburiana , and introgressed forms. Over 50 separate discriminant function analyses (DFA) and principal components analyses (PCA) were run on numerous combinations of raw and log-transformed data. The best variable suite, providing the clearest discrimination between groups, used log-transformed data on 15 morphological characters, but DFA post-hoc identifications were 90-100% correct with only 7 characters using raw data. DFA distinguished four separate nodes of variation. Two groups consisting of 122 P. subintegra and 29 P. stansburiana were easily discriminated in DFA and were distinguished in PCA as well. Introgressed forms were consistently identified in two much less well-defined groups of 46 and 19 specimens. Introgressed forms are not intermediate between the two supposed parents in some characters, appearing most similar to P. stansburiana in most measured characteristics. Principal distinguishing characteristics of the four groups are as follows: P. subintegra -usually eglandular, has 0-2 leaf lobes and short hypanthia-pedicels; P. stansburiana -always abundantly glandular, has 4 leaf lobes and short hypanthia-pedicels; the introgressed from ""Tonto"" is usually eglanduluar, has 4 leaf lobes and long hypanthia-pedicels; the introgressed form ""Verde"" is usually glandular, has 4 leaf lobes and slightly shorter hypanthia-pedicels.     

Effects of dwarf mistletoe on spruce in the White Mountains, Arizona

Mortality of spruce in mixed conifer stands moderately to heavily infested with western spruce dwarf mistletoe was two to five times greater than in healthy stands in the White Mountains, Arizona. Ten-year volume growth loss for heavily infected spruce trees ranged from 25&#37; to 40&#37;. Estimates of growth loss for spruce on a stand basis ranged from 10&#37; to 20&#37; in heavily infested stands. Because western spruce dwarf mistletoe is prevalent in the White Mountains and causes increased mortality and reduced growth, its control should be included in management of mixed conifer stands there.     

Bole volume growth in stems of Quercus gambelii

Shrub-form and tree-form Gambel oak ( Quercus gambelii ) stands contain a potentially significant fuelwood resource. Information on their growth characteristics can form a basis for future stand management. Stem analyses showed that height growth of shrub-form stems essentially ceased after age 50, while tree-form stems continued to increase in height until approximately age 100. Both stem forms continued to increase in basal area and volume at a relatively constant rate as the stems increased in age and size. Increases in all size measures were substantially greater in tree-form stems than in shrub-form stems. Mean bole volume for tree-form stems at age 100 was over 16 times that of shrub-form stems. Sprouts from tree-form stands would reach minimum size for fuelwood marketing in approximately 45 years.     

Taxonomy and phylogeny of the Old World jumping plant-louse genus Paurocephala (Insecta,Hemiptera, Psylloidea)

Fifty-one species are recognized in the genus Paurocephala, with an additional 14 species which remain unnamed. Thirty-five species are described as new, and five species are synonymized: P. pumilae and P. zhejiangensis with P. chonchaiensis, P. debregeasiae with P. sauteri, and P. guangxiensis and P. tremae with P. trematos. Two varieties, P. psylloptera maculipennis and P. psylloptera setifera, are raised to species level. P. bifasciata is reinstated from former synonymy with P. chonchaiensis, and Anomoterga kleinhofiae is transferred back to Paurocephala. Lectotypes are designated for P. brevicephala, P. chonchaiensis, P. psylloptera, P. sauteri, P. setifera and P. wilderi. The four New World species of Paurocephala are not considered to be congeneric with the Old World species and will be transferred to Diclidophlebia. Two South African species, P. bicarinata and P. hottentotti, are removed from Paurocephala and have to be accommodated in a new genus in the Diaphorininae. Thus Paurocephala is an Old World genus with nine Afrotropical and 42 Indo-Australian described species. Keys for the identification of adults and fifth instar larvae are provided. All 51 named species are diagnosed and illustrated, and information is given on distribution and host plants. Based on two cladistic analyses, one using adult characters only, and one using both adult and larval characters, four monophyletic species groups are recognized. In both analyses a basal group of 10 species, the brevicephala -group, forms the sister group to all other Paurocephala spp. The Afrotropical species are monophyletic and, together with one Oriental species constitute the gossypii group. In the analysis with adult characters only, the gossypii -group is the sister taxon of the kleinhofiae -group and, both together, are the sister group of the psylloptera -group, the largest species group with 27 species. In the analysis of adult and larval characters, the relationships between the last three species groups are not resolved. The result of the phylogenetic analysis confirms the synonymy of the subgenus Thoracocorna with Paurocephala. Known host plants of Paurocephala spp. belong to the Malviflorae with the exception of the Afrotropical P. insolita which develops on Theiflorae (Theales, Clusiaceae). The brevicephala -, kleinhofiae - and gossypii -groups are associated with hosts of the order Malvales (Malvaceae and Sterculiaceae), whereas the psylloptera -group is with Urticales (Urticaceae, Moraceae and Ulmaceae).     

Three naturally occurring Penstemon hybrids

Three wild Penstemon hybrids are documented herein: Penstemon clevelandii × spectabilis, P. centranthifolius × spectabilis , and P. centranthifolius × eatonii . Each putative hybrid was compared to its respective parental species using manifold floral and vegetative characters for which the parents differed. For each hybrid hypothesis, characters were counted as being intermediate or not intermediate. There were significantly more intermediate characters in all 3 cases (one-sided sign tests, P Penstemon species evidently do hybridize naturally, and for nearly all characters the hybrids are consistent with the view that the parents differ largely by additive genetic effects.