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1.
We evaluated elk (Cervus elaphus), mule deer (Odocoileus hemionus), cattle (Bos taurus), and domestic sheep (Ovis aries) diet composition, diet overlap, and forage selection on aspen (Populus tremuloides Michaux)–sagebrush (Artemisia spp. L.) summer range in northeastern Nevada to understand potential for forage competition to provide better information for managing these communities. Diets were determined through microhistological fecal analysis from 1998 to 2000, and forage selection was evaluated at feeding sites in aspen and sagebrush communities in 1999 and 2000. Elk spring diets were the most diverse in composition; summer elk diets were dominated by forbs (59%–78%); deer consumed mostly woody browse (64%–72%); and cattle and sheep ate mostly graminoids. Lupines (Lupinus spp. L.) constituted ≥ 11% of elk, deer, and sheep diets in summer. Spurred lupine (Lupinus caudatus Kellogg) was the lupine typically selected in feeding sites and greatest consumption occurred in summer when total alkaloid levels were lowest. Highest diet overlap was between cattle and sheep in 1999 (68%) and lowest between deer and cattle in 2000 (3%). Summer elk and deer diets overlapped moderately (45%–59%). Diets did not differ between elk in spring with sheep, elk in summer with deer and sheep, or cattle with sheep. Cattle foraged selectively on forbs in aspen communities (68%) and on graminoids in sagebrush communities (88%), reflecting relative forage availabilities. We detected no differences among elk, cattle, and sheep for forage selection in aspen communities. Electivity indices indicated elk preferred forbs in aspen and sagebrush communities; cattle preferred graminoids in sagebrush; and foraging sheep preferred forbs in aspen. Our results suggest potential for forage competition among ungulates on aspen–sagebrush summer range is highest for forbs in aspen communities. Monitoring productivity and use of key forage species, particularly forbs in aspen communities, should complement management objectives on shared aspen–sagebrush summer range.  相似文献   

2.
As pinyon–juniper (specifically, Pinus monophylla and Juniperus osteosperma) woodlands in the western United States increase in distribution and density, understory growth declines and the occurrence of crown fires increases, leaving mountainsides open to both soil erosion and invasion by exotic species. We examined if the loss in understory cover that occurred with increasing tree cover was reflected in the density and diversity of the seed bank. Seed banks in stands with low, medium, and high tree cover were measured in late October for 2 yr. Multivariate analyses indicated that cover and diversity of standing vegetation changed as tree cover increased. However, the seed bank did not differ in overall seed density or species diversity because seeds of the 13 species that comprised 86% of the seed bank occurred in similar density across the tree-cover groups. Sixty-three percent of the species that were in the seed bank were absent from the vegetation (mostly annual forbs). In addition, 49% of the species that occurred in the standing vegetation were not in the seed bank (mostly perennial forbs and shrubs). Only Artemisia tridentata, Bromus tectorum, and Collinsia parviflora displayed positive Spearman rank correlations between percent cover in the vegetation and density in the seed bank. Thus, much of the standing vegetation was not represented in the seed bank, and the few species that dominated the seed bank occurred across varying covers of pinyon–juniper.  相似文献   

3.
The impacts of wild herbivores on cattle diet selection were investigated in an East African rangeland during August 2001 and February 2002. The study compared cattle diets in plots exclusively accessible to cattle (C) and those accessible to megaherbivores (elephants and giraffes), non-megaherbivore wild herbivores > 15 kg (zebras, hartebeests, Grant's gazelles, oryx, elands, and buffaloes) and cattle (MWC); or non-megaherbivore wild herbivores and cattle (WC). There were no treatment differences in selection of most grass species in either sampling period (P > 0.05). However, selection of forbs differed among treatments during February when conditions were relatively dry and percent of bites taken by cattle on this forage class increased (P < 0.005) from 1.8% ± 0.3 to 7.7% ± 1.6 (mean ± SE). During this period, cattle took a lower percent of bites on forbs in MWC (4.3% ± 1.7; P = 0.01) and WC (5.9% ± 2.2; P = 0.03) than in C (12.9% ± 0.9). These patterns were generally driven by Commelina spp., which comprised 65% ± 9.4 of total bites on forbs. Notably, these differences were associated with differences in cover of forbs, which was positively correlated with percent of bites on forbs (r2 = 0.86, P < 0.01). Because forbs may be critical components of cattle diets in such rangelands during relatively dry periods, these dietary changes may indicate potential seasonal costs of wildlife to cattle production. Looking for ways to offset such costs may be worthwhile for livestock properties that accommodate wildlife.  相似文献   

4.
Agricultural land use is known to alter ecological processes, and native plant communities can require decades to centuries to recover from the disturbance of cultivation. “Recovery” is typically measured by comparison to undisturbed adjacent sites as a control. Recovery following cultivation in sagebrush ecosystems of the Great Basin remains largely unexamined even though nearly a half million hectares of land were dry-farmed and abandoned in the early 1900s. We tested the hypothesis that the native vegetation has not recovered from this exotic disturbance by evaluating differences in canopy cover of shrubs, grasses, and forbs between paired sets of historically dry-farmed land and adjacent never-cultivated areas. Paired sites were located in three ecological sites in northwestern Utah. We found that vegetation recovery from cultivation is variable by growth form, species, and ecological site. Shrub recovery was different among sagebrush (Artemisia) species. Yellow rabbitbrush (Chrysothamnus viscidiflorus [Hook.] Nutt.) and black greasewood (Sarcobatus vermiculatus [Hook.] Torr.), which often increase following disturbance, maintained higher cover inside old fields. At one of the paired sets, shrub composition was altered from a mix of four species to dominance of mainly Wyoming big sagebrush (Artemisia tridentata Nutt. subsp. wyomingensis Beetle & Young). Total forb cover was generally lower in cultivated areas and some species, such as spiny phlox (Phlox hoodii Richardson), had not recovered. The most common grass species encountered across all ecological sites, bottlebrush squirreltail (Elymus elymoides [Raf.] Swezey), had higher cover in cultivated areas. Surprisingly, exotic annual species, such as cheatgrass (Bromus tectorum L.), did not dominate these sites as they have for decades after cultivation in other areas of the Great Basin. This study demonstrates that the land-use legacy of dry farming on vegetation remains nearly a century after cultivation has ceased, and has direct implications for describing ecological site conditions.  相似文献   

5.
Vegetation features radiating from residential areas in response to livestock grazing were quantified for an arid steppe rangeland in the Keshiketeng Banner, Chifeng Prefecture, in northeastern Inner Mongolia in 2004 and 2006. The aim of this study was to estimate grazing impacts on the vegetation dynamics of these historical grazed ecosystems. Grazing intensities were classified as reference area (RA), light (LG), moderate (MG), and heavy (HG) according to the vegetation utilization across the study area. Rangelands were studied along a grazing gradient, where characteristics of plant communities, heights of dominant species, aboveground vertical structures, and belowground biomass were investigated. Along this grazing gradient, vegetation changed from the original dominant plant species Leymus chinensis (Trin.) Tzvel. to a semi-subshrub species Artemisia frigida Willd. when moving from the reference area (RA) to the region around the settlement. Canopy coverage, aboveground productivity, and the number of perennial species declined as one moved toward the residential area. Heights of five dominant species, except for Stipa grandis P. Smirn., declined with increased grazing intensity. Aboveground vertical structure in the RA treatment showed more resilience than the other treatments. There was no difference in root biomass in the top 1 m of soil (P > 0.05) between the RA treatment and the area immediately around settlement (HG treatment). Generally, we found that the intensity of grazing disturbance did not exceed the tolerance of the rangeland ecosystem within LG treatment. However, vegetative conditions in HG treatment became worse with increased grazing pressure. Rangelands in this arid steppe are under tremendous threat due to excessive forage utilization, which cannot be considered a sustainable practice.  相似文献   

6.
Knowledge of herbivory tolerance of dominant plant species and their responses to varying grazing intensity is required for sustainable grazing management in semiarid rangeland ecosystems. In a field experiment, we studied the effects of simulated grazing 0%, 30%, 50%, and 80% leaf removal (control, partial, intermediate, and heavy leaf removal) of three dominant perennial legumes: Astragalus cyclophyllon, Astragalus effuses, and Hedysarum criniferum in semiarid rangelands of southwestern Iran for 2 yr and tested 1) differential herbivory tolerance in terms of regrowth ability of belowground and aboveground biomass (AGB), fecundity, and nonstructural carbohydrate reserves; and 2) trade-off between forage quantity and quality—less defoliated plants produce larger amount of biomass with less forage quality and vice versa. The results showed a reduction in AGB and reproduction in each of the three plants. However, three forbs exhibited some sort of variations in shoot and root growth, reproduction and forage quality under intermediate and heavy leaf removal. Leaf removal in individuals of A. effusus and H. criniferum are more likely to compensate for tissue loss by allocating the available resources to the expansion of root biomass, at the cost of AGB and reproductive effort. Leaf removal also led to an increase in forage quality in each of the three forb species, depending on the level of height removal. The control plant had a higher amount of biomass production and lower amount of crude protein compared with heavy leaf removal treatments (i.e., 80%), by contrasting responses of acid detergent fiber and neutral detergent fiber, indicating a trade-off between forage quality and forage quantity. The results indicate that there is a balance among forage quantity, quality, and regrowth ability of belowground and aboveground tissues in intermediate leaf removal treatments of these forb species. This balance is used to develop principles for grazing management of steppe rangelands because such a regime meets different criteria including forage quantity, quality, and nonstructural carbohydrate reserves.  相似文献   

7.
Sagebrush (Artemisia spp.) communities constitute the largest temperate semidesert in North America and provide important rangelands for livestock and habitat for wildlife. Remote sensing methods might provide an efficient method to monitor sagebrush communities. This study used airborne LiDAR and field data to measure vegetation heights in five different community types at the Reynolds Creek Experimental Watershed, southwestern Idaho: herbaceous-dominated, low sagebrush (Artemisia arbuscula) –dominated, big sagebrush (Artemisia tridentata spp.) –dominated, bitterbrush (Purshia tridentata) -dominated, and other vegetation community types. The objectives were 1) to quantify the correlation between field-measured and airborne LiDAR-derived shrub heights, and 2) to determine if airborne LiDAR-derived mean vegetation heights can be used to classify the five community types. The dominant vegetation type and vegetation heights were measured in 3 × 3 m field plots. The LiDAR point cloud data were converted into a raster format to generate a maximum vegetation height map in 3-m raster cells. The regression relationship between field-based and airborne LiDAR-derived shrub heights was significant (R2=0.77; P value < 0.001). An analysis of variance test with all pairwise post hoc comparisons indicated that LiDAR-derived vegetation heights were significantly different among all vegetation community types (all P values < 0.01), except for herbaceous-dominated communities compared to low sagebrush-dominated communities. Although LiDAR measurements consistently underestimated vegetation heights in all community types, shrub heights at some locations were overestimated due to adjacent taller vegetation. We recommend for future studies a smaller rasterized pixel size that is consistent with the target vegetation canopy diameter.  相似文献   

8.
Anthropogenic disturbances, wildfires, and weedy-plant invasions have destroyed and fragmented many sagebrush (Artemisia L. spp.) habitats. Sagebrush-dependent species like greater sage-grouse (Centrocercus urophasianus) are vulnerable to these changes, making habitat monitoring essential to effective management. Conventional ground inventory methods are time consuming (expensive) and have lower data collection potentials than remote sensing. Our study evaluated the feasibility of ground (0.3-mm ground surface distance [GSD]) and aerial imagery (primarily, 1-mm GSD) to assess ground cover for big sagebrush (Artemisia tridentata Nutt.) and other vegetation functional groups important in sage-grouse breeding habitat (lekking, nesting, and brood rearing). We surveyed ∼ 526 km2 of the upper Powder River watershed in Natrona County, Wyoming, USA, a region dominated by Wyoming big sagebrush (Artemisia tridentata Nutt. ssp. wyomingensis Beetle & Young) communities interspersed with narrow riparian corridors. Our study area was used year-round by sage-grouse and included 16 leks. In June 2010, we acquired aerial images (1-mm resolution) for 3 228 systematic sampling locations; additional images were acquired as rapid-succession bursts where aerial transects crossed riparian areas and for 39 riparian and 39 upland ground locations (0.3-mm resolution) within 3.2-km of leks. We used SamplePoint software to quantify cover for plant taxa and functional groups using all ground images and a systematic sampling of aerial images. Canopy cover of sage-grouse food forbs—as averaged across aerial and ground imagery around all leks—was 1.8% and 7.8% in riparian and 0.5% and 4.0% in upland areas, respectively. Big sagebrush cover was 8.7% from upland aerial images and 9.4% from upland ground images. Aerial and ground imagery provided similar values for bare ground and shrubs in riparian and upland areas, whereas ground imagery provided finer-scale herbaceous-cover data that complemented the aerial imagery. These and other image-derived archival data provide a practical basis for landscape-scale management and are a cost-effective means for monitoring extensive sagebrush habitats.  相似文献   

9.
Forage selection patterns of cattle in sagebrush (Artemisia L.) communities are influenced by a variety of environmental and plant-associated factors. The relative preference of cattle for interspace versus under-sagebrush canopy bunchgrasses has not been documented. Potential preferences may indirectly affect habitat for sage-grouse and other ground-nesting birds. Our objectives were to investigate grazing patterns of cattle with respect to undercanopy (shrub) and interspace tussocks, determine the influence of cattle grazing on screening cover, and relate shrub morphology to undercanopy grazing occurrence. Eighteen-day replicated trials were conducted in the summers of 2003 and 2004. Findings suggest cattle initially concentrate grazing on tussocks between shrubs, and begin foraging on tussocks beneath shrubs as interspace plants are depleted. Grazing of undercanopy grass tussocks was negligible at light-to-moderate utilization levels (< 40% by weight). Grass tussocks under spreading, umbrella-shaped shrub canopies were less likely (P < 0.001) to be grazed than those beneath erect, narrow canopies. Horizontal screening cover decreased (P < 0.001) with pasture utilization. At the trial’s end, removal of 75% of the herbaceous standing crop induced about a 5% decrease in screening cover in all strata from ground level to 1 m with no differences among strata (P = 0.531). This implied that shrubs constituted the majority of screening vegetation. Our data suggest that conservative forage use, approaching 40% by weight, will affect a majority (about 70%) of interspace tussocks and a lesser proportion (about 15%) of potential nest-screening tussocks beneath sagebrush. Probability of grazing of tussocks beneath shrubs, however, is also affected by shrub morphology. These findings will help managers design grazing programs in locales where habitat for ground nesting birds is a concern.  相似文献   

10.
Leafy spurge (Euphorbia esula L.) is an aggressive exotic species that has been successfully suppressed in a variety of situations using classical biological control (flea beetles; Aphthona spp.). This 9-yr study investigated patterns of vegetation responses following significant reductions in leafy spurge cover and density by flea beetles in southeastern Montana. We hypothesized that the vegetation following leafy spurge suppression would be dominated by species and plant functional groups able to persist through heavy infestations. Flea beetles were first released in 1998, and by 2006 leafy spurge foliar cover was reduced 80% to 90% compared to 1998 values on both release and nonrelease plots. Although total cover of the resident vegetation, excluding leafy spurge, increased 72% to 88%, relative cover of the functional groups (native forbs, native sedges, native grasses, and non-native species) was similar among years and between release and nonrelease plots. Mean diversity and mean species richness values did not differ among years or between release and nonrelease plots (P < 0.05), but mean diversity on both release and nonrelease plots was significantly less than noninfested plots, although richness was similar (P < 0.05). Indicator species analysis revealed that non-native Poa spp. replaced leafy spurge as the dominant species on release and nonrelease plots. Conversely, noninfested plots contained a variety of native species with high indicator values. Although total abundance of the resident vegetation in 2006 was significantly greater than 1998, plant species composition and relative cover showed little change for the duration of the study. Failure of the native vegetation to recover to a community that approached nearby noninfested conditions may be attributed to a variety of interacting scenarios, some of which may be ameliorated by treating infestations as soon as possible to avoid long-term residual effects.  相似文献   

11.
Greater sage-grouse (Centrocercus urophasianus) habitat management involves vegetation manipulations to increase or decrease specific habitat components. For sage-grouse habitat management to be most effective, an understanding of the functional response of sage-grouse to changes in resource availability is critical. We investigated temporal variation in diet composition and nutrient content (crude protein, calcium, and phosphorus) of foods consumed by preincubating female sage-grouse relative to food supply and age of hen. We collected 86 preincubating female greater sage-grouse at foraging areas during early (18–31 March) and late (1–12 April) preincubation periods during 2002–2003. Females consumed 22 food types including low sagebrush (Artemisia arbuscula Nutt.), big sagebrush (Artemisia tridentata Nutt.), 15 forb species, 2 insect taxa, sagebrush galls, moss, and a trace amount of unidentified grasses. Low sagebrush was the most common food item, but forbs were found in 89% of the crops and composed 30.1% aggregate dry mass (ADM) of the diet. ADM and species composition of female diets were highly variable between collection periods and years, and coincided with temporal variation in forb availability. Adult females consumed more forbs and less low sagebrush compared to yearling females. Because of higher levels of crude protein, calcium, and phosphorus, forbs were important diet components in comparison with low sagebrush, which had the lowest nutrient content of all foods consumed. Our results indicate that increased forb abundance in areas used by female sage-grouse prior to nesting would increase their forb consumption and nutritional status for reproduction. We recommend that managers should emphasize delineation of habitats used by preincubating sage-grouse and evaluate the need for enhancing forb abundance and diversity.  相似文献   

12.
Traditional management of sand sagebrush (Artemisia filifolia) rangelands has emphasized sagebrush control to increase forage for livestock. Since the 1950s shrub removal has been primarily achieved with herbicides. Concerns over declining lesser prairie-chicken (Tympanuchus pallidicinctus; LPC) populations have led to increased scrutiny over the use of herbicides to control shrubs. The objective of our research was to describe changes to LPC habitat qualities following chemical control of sand sagebrush in northwest Oklahoma. Study pastures ranged in size from 10 to 21 ha. Five pastures were sprayed with 2,4-dichlorophenoxyacetic acid (2,4-D) in 2003 (RECENT), five were sprayed with 2,4-D in 1984 (OLD), and four received no treatment (SAGE). We measured habitat structure (sagebrush cover, sagebrush density, visual obstruction &lsqb;VO], and basal grass cover), and dietary resources (forb density, forb richness, and grasshopper density) in all pastures from 2003 to 2006. OLD and RECENT pastures had less sagebrush (cover and density) and VO than SAGE pastures. OLD pastures produced more annual forbs than either SAGE or RECENT pastures. SAGE pastures had more perennial forbs than RECENT pastures. Herbicide application reduced protective cover while providing no increase in forb abundance in RECENT pastures. Our results indicated that it may take several years to realize increases in annual forbs following application of 2,4-D. However, loss of protective cover may persist for multiple years (20+ yr), and removal of sagebrush did not increase forb richness or grasshopper abundance. Thus, 2,4-D may have limited use as a habitat management tool because it takes numerous years to reap the benefit of increased forb abundance while reducing habitat structure in the long term.  相似文献   

13.
This paper gives a preliminary report on the factors affecting the distribution of wild ungulates on a ranch in Kenya. The study covers only one phase of an overall project on the compatabfiity of wild and domestic ungulates. The major factors considered are vegetation, water, fire, cattle grazing, hunting and animal behaviour. These factors are related to five major wild ungulate species which occur on Akira - Coke's hartebeest (kongoni), Grant's gazelle, Thomson's gazelle, eland and giraffe.

The major influence on wild ungulate densities and distribution was vegetation. The condition of vegetation was determined by rainfall, fire and grazing intensities. Generally game populations increased with cattle populations which indicated that vegetation conditions were improving during the period of this study. Overgrazing was generally detrimental to all species except to the Thomson's gazelle which was attracted to short grass areas around water, bomas and overgrazed sites. Kongoni were found usually in tall grass areas while Grant's gazelle were not as selective as Thomson's gazelle or eland. Giraffe were confined mostly to Acacia communities and eland, though found in grassland, were most frequently in high bush country where the variety of shrubs was greater.

The effects of other factors on each of the ungulates are also presented. The interrelationships of all factors are being considered as the study continues.  相似文献   

14.
A decrease in fire frequency and past grazing practices has led to dense mountain big sagebrush (Artemisia tridentata Nutt. subsp. vaseyana [Rydb.] Beetle) stands with reduced herbaceous understories. To reverse this trend, sagebrush-reducing treatments often are applied with the goal of increasing herbaceous vegetation. Mechanical mowing is a sagebrush-reducing treatment that commonly is applied; however, information detailing vegetation responses to mowing treatments generally are lacking. Specifically, information is needed to determine whether projected increases in perennial grasses and forbs are realized and how exotic annual grasses respond to mowing treatments. To answer these questions, we evaluated vegetation responses to mowing treatments in mountain big sagebrush plant communities at eight sites. Mowing was implemented in the fall of 2007 and vegetation characteristics were measured for 3 yr post-treatment. In the first growing season post-treatment, there were few vegetation differences between the mowed treatment and untreated control (P > 0.05), other than sagebrush cover being reduced from 28% to 3% with mowing (P < 0.001). By the second growing season post-treatment, perennial grass, annual forb, and total herbaceous vegetation were generally greater in the mowed than control treatment (P < 0.05). Total herbaceous vegetation production was increased 1.7-fold and 1.5-fold with mowing in the second and third growing seasons, respectively (P < 0.001). However, not all plant functional groups increased with mowing. Perennial forbs and exotic annual grasses did not respond to the mowing treatment (P > 0.05). These results suggest that the abundance of sagebrush might not be the factor limiting some herbaceous plant functional groups, or they respond slowly to sagebrush-removing disturbances. However, this study suggests that mowing can be used to increase herbaceous vegetation and decrease sagebrush in some mountain big sagebrush plant communities without promoting exotic annual grass invasion.  相似文献   

15.
The Przewalski’s gazelles in the Hudong area of the Qinghai Lake area in China were affected by an ailment characterized by pica, emaciation, dyskinesia, loss of appetite, and anemia. Concentrations of copper (Cu) in soil and forage from affected and unaffected areas were similar and within the normal range, but concentrations of sulfur (S) in soil and forage were significantly higher (P < 0.01) in affected than in unaffected areas. Concentrations of Cu in blood, hair, and liver from the affected Przewalski’s gazelles were significantly lower (P < 0.01) than those in healthy animals. Affected Przewalski’s gazelles showed a hypochromic microcytic anemia and a low level of ceruloplasmin. Oral administration of copper sulphate (CuSO4) prevented and cured the disease. We conclude that the disorder of Przewalski’s gazelles was caused by secondary Cu deficiency, mainly due to high S content in forage.  相似文献   

16.
Increased cover of perennial grasses and forbs would increase the wildlife and forage value of many Wyoming big sagebrush (Artemisia tridentata ssp. wyomingensis Beetle & Young) communities, as well as increase their resistance to weeds. We compared six mechanical treatments in conjunction with seeding a Wyoming big sagebrush community in northern Utah over a 10-yr period. The treatments included disk plow followed by land imprinter, one-way Ely chain, one- and two-way pipe harrow, all applied in fall, and meadow aerator applied in fall and spring. A mixture of native and introduced grasses and forbs was broadcast seeded at 18.3 kg PLS ha? 1 after the disk and before the imprinter and all other treatments. The experiment was installed in three randomized blocks, and density and cover data were collected before treatment in 2001 and 1, 2, 5, and 10 yr after treatment. All treatments initially reduced sagebrush and residual herbaceous cover and increased seeded species cover compared with the untreated control. By 10 yr after treatment, sagebrush cover was 24.5% ± 0.35% on the control, 1.6% ± 0.28% on the disk imprinter treatment, and 11.7% ± 0.79% on all other treatments. At that time, seeded grass cover was 16.5% ± 1.22% on the disk imprinter treatment and an average of 2% ± 0.1% on all other mechanical treatments. Sagebrush seedlings were recruited in all of the mechanical treatments, but least in the disk imprinter treatment. After 10 yr, the untreated control was dominated by decadent sagebrush and rabbitbrush, the disk imprinter treatment was dominated by seeded perennial grasses, and the other mechanical treatments shared dominance of sagebrush and native perennial grasses. Mechanical treatments changed the composition of this community while retaining sagebrush, but greatest understory increases were associated with greatest control of sagebrush and establishment of seeded species by disk imprinting.  相似文献   

17.
Russian knapweed (Acroptilon repens [L.] DC.), an exotic perennial forb, has invaded many native ecosystems in western North America. Russian knapweed's success is attributed to allelopathy, extensive tap rooting, zinc accumulation in soils, and a lack of North American predators. Revegetation following chemical control slows exotic reestablishment, but the impacts of Russian knapweed-invaded soils on the establishment of native forbs and shrubs have not been determined. In a greenhouse experiment, we monitored the establishment of two native forbs, Indian blanketflower (Gaillardia aristata Pursh) and purple prairie clover (Dalea purpurea Vent.) and two native shrubs, winterfat (Krascheninnikovia lanata [Pursh] A.D.J. Meeuse & Smit syn. Ceratoides lanata) and Wyoming big sagebrush (Artemisia tridentata Nutt. subsp. wyomingensis [Hook.] Nutt.) in soils obtained from three Russian knapweed invasions and adjacent noninvaded areas. We analyzed soils collected near Greybull and Riverton, Wyoming, and Greeley, Colorado, for cation exchange capacity, organic matter, electroconductivity, pH, and total nitrogen, carbon, and plant-available potassium, zinc, manganese, copper, and phosphate. We documented seedling emergence of the four natives and Russian knapweed every two days for 14–17 weeks, harvested seedlings biweekly to assess their growth, and determined their zinc accumulation. All species established in invaded soil and seedlings were larger in invaded than in noninvaded soils. Invaded rangeland soils had greater organic matter (8.6% and 1.1% in invaded vs. 2.5% and 0.4% in noninvaded soils) and lower pH (7.4 in invaded versus 8.0 noninvaded soils). Zinc concentrations in invaded soils (from 0.15 to 6.56 mg · kg-1) were not high enough to limit plant growth. Reports that Russian knapweed is a hyper-accumulator of zinc are not supported by our seedling data, which suggests that previously invaded soils may not limit native seedlings.  相似文献   

18.
Productivity of mule deer (Odocoileus hemionus Raf.) populations is closely linked to individual nutritional condition. We modeled body fat of individual does as a function of vegetation cover, composition, and water characteristics of their annual, summer, and winter home ranges in north-central New Mexico. We also modeled home range size as a function of the same characteristics. Levels of body fat were most closely and negatively related to the amount of pinyon-juniper in an individual deer's annual home range (F1,21 = 7.6; P = 0.012; r2 = 0.26). Pinyon-juniper types provided little (combined ground cover of preferred forbs and shrubs = 5.7%) mule deer forage but were included in home ranges in excess of their availability on the landscape, likely because of security cover attributes. Proportion of grasslands in home ranges was most strongly related to both annual (F1,23 = 4.9; P = 0.037; r2 = 0.18) and summer (F2,25 = 5.7; P = 0.009; r2 = 0.31) home range sizes, and home ranges increased as the grassland component increased, indicating that this habitat type was providing little value to mule deer. Grassland (0.2% combined cover of preferred forb and shrub) and montane conifer (3.2% ground cover of preferred forb and shrub) habitat types similarly lacked preferred mule deer food, and grasslands also lacked cover. Most immediate gains in mule deer habitat in north-central New Mexico may be attained by management of pinyon-juniper communities to increase forage quantity and quality while maintaining cover attributes. Gains can also be realized in grasslands, but here management must establish both cover and forage.  相似文献   

19.
Knowledge of how tallgrass prairie vegetation responds to fire in the late growing season is relatively sparse and is based upon studies that are either spatially or temporally limited. To gain a more robust perspective of vegetation response to summer burning and to determine if repeated summer fire can drive vegetational changes in native tallgrass prairie, we evaluated species cover and richness over a 14-yr period on different topographic positions from ungrazed watersheds that were burned biennially in the growing season. We found that annual forbs were the primary beneficiaries of summer burning, but their fluctuations varied inconsistently among years. Concomitantly, species richness and diversity increased significantly with summer burning but remained stable through time with annual spring burning. After 14 yr, species richness was 28% higher in prairie that was burned in the summer than in prairie burned in the spring. Canopy cover of big bluestem (Andropogon gerardii Vitman) and Indiangrass (Sorghastrum nutans [L.] Nash) increased significantly over time with both summer and spring burning, whereas heath aster (Symphyotrichum ericoides [L.] Nesom), aromatic aster (Symphyotrichum oblongifolium [Nutt.] Nesom), and sedges (Carex spp.) increased in response to only summer burning. Kentucky bluegrass (Poa pratensis L.) cover declined in both spring-burned and summer-burned watersheds. Repeated burning in either spring or summer did not reduce the cover or frequency of any woody species. Most perennial species were neutral in their reaction to summer fire, but a few species responded with large and inconsistent temporal fluctuations that overwhelmed any clear patterns of change. Although summer burning did not preferentially encourage spring-flowering forbs or suppress dominance of the warm-season grasses, it is a potentially useful tool to increase community heterogeneity in ungrazed prairie.  相似文献   

20.
Smoke or heat from fire can act as a cue that affects seed germination. We examined germination responses of 10 plant species (six forbs, two shrubs, two grasses) native to the southern High Plains in the United States, to smoke, heat, and their interaction in a laboratory experiment. Smoke treatments were applied by soaking seeds in 1∶5, 1∶10, or 1∶100 (v/v) Regen 2000® smoke solution for 20 h. Heat treatments were applied by placing seeds in an oven at 50°C or 80°C for 5 min. Nine species responded to smoke, heat, or both. Results showed that smoke can enhance, inhibit, or not affect seed germination. Germination capacities of Gutierrezia sarothrae (Pursh) Britton & Rusby and Astragalus crassicarpus Nutt. were promoted by 1∶5 and 1∶100 dilutions of smoke water, respectively; Coreopsis tinctoria Nutt., G. sarothrae, Salvia reflexa Hornem., Digitaria ciliaris (Retz.) Koeler, and Panicum virgatum L. were inhibited by high and/or moderate concentrations of smoke water either in germination percentage or in mean germination time. Germination percentage of Solanum elaeagnifolium Cav. increased following an 80°C heat treatment. Interaction effects between smoke and heat on germination also were detected. Smoke and heat treatments might be useful as management tools for promoting or suppressing specific target species of shortgrass prairie communities in future habitat management.  相似文献   

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