首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 15 毫秒
1.
Re-establishing native communities that resist exotic weed invasion and provide diverse habitat for wildlife are high priorities for restoration in sagebrush ecosystems. Native forbs are an important component of healthy rangelands in this system, but they are rarely included in seedings. Understanding competitive interactions between forb and grass seedlings is required to devise seeding strategies that can enhance establishment of diverse native species assemblages in degraded sagebrush communities. We conducted a greenhouse experiment to examine seedling biomass and relative growth rate of common native forb species when grown alone or in the presence of a native bunchgrass or an exotic annual grass. Forb species included bigseed biscuitroot (Lomatium macrocarpum [Nutt. ex Torr. & A. Gray] J.M. Coult. & Rose), sulphur-flower buckwheat (Eriogonum umbellatum Torr.), hoary aster (Machaeranthera canescens [Pursh] Gray), royal penstemon (Penstemon speciosus Douglas ex Lindl.), and Munro's globemallow (Sphaeralcea munroana [Douglas ex Lindl.] Spach ex Gray); and neighboring grass species included bottlebrush squirreltail (Elymus elymoides [Raf.] Swezey), Sandberg bluegrass (Poa secunda J. Presl); and cheatgrass (Bromus tectorum L.). Forbs and grasses were harvested after 6, 9, or 12 wk of growth for biomass determination and calculation of relative growth rates (RGR) of forbs. Neither bunchgrass reduced biomass of any forb. RGR was reduced for royal penstemon when grown with either native grass and for Munro's globemallow when grown with bottlebrush squirreltail. Although only assessed qualitatively, forbs with vertically oriented root morphologies exhibited no reduction in RGR when grown with native grasses, compared to forbs with dense lateral branching, similar to the root morphology of native grasses. Biomass of forbs was reduced by 50% to 91% and RGR by 37% to 80% when grown with cheatgrass. Understanding native forb interactions with native grasses and cheatgrass will aid land managers in selecting effective seed mixes and making better use of costly seed.  相似文献   

2.
Treatments to reduce shrub cover are commonly implemented with the objective of shifting community structure away from shrub dominance and toward shrub and perennial grass codominance. In sagebrush (Artemisia L.) ecosystems, shrub reduction treatments have had variable effects on target shrubs, herbaceous perennials, and non-native annual plants. The factors mediating this variability are not well understood. We used long-term data from Utah’s Watershed Restoration Initiative project to assess short-term (1 − 4 yr post-treatment) and long-term (5 − 12 yr post-treatment) responses of sagebrush plant communities to five shrub reduction treatments at 94 sites that span a range of abiotic conditions and sagebrush community types. Treatments were pipe harrow with one or two passes, aerator, and fire with and without postfire seeding. We analyzed effect sizes (log of response ratio) to assess responses of sagebrush, perennial and annual grasses and forbs, and ground cover to treatments. Most treatments successfully reduced sagebrush cover over the short and long term. All treatments increased long-term perennial grass cover in Wyoming big sagebrush (A. tridentata Nutt. ssp. wyomingensis Beetle & Young) communities, but in mountain big sagebrush (ssp. vaseyana [Rydb.] Beetle) communities, perennial grasses increased only when seeded after fire. In both sagebrush communities, treatments generally resulted in short-term, but not long-term, increases in perennial forb cover. Annual grasses (largely invasive cheatgrass, Bromus tectorum L.) increased in all treatments on sites dominated by mountain big sagebrush but stayed constant or decreased on sites dominated by Wyoming big sagebrush. This result was unexpected because sites dominated by Wyoming big sagebrush are typically thought to be less resilient to disturbance and less resistant to invasion than sites dominated by mountain big sagebrush. Together, these results indicate some of the benefits, risks, and contingent outcomes of sagebrush reduction treatments that should be considered carefully in any future decisions about applying such treatments.  相似文献   

3.
Broadleaf herbicides are commonly used in rangelands to suppress exotic weeds and release native communities from negative impacts of invasion. However, few studies have comprehensively evaluated treatment effects on differing community components across a gradient of initial invasion levels. We conducted a 6-yr experiment within grasslands of western Montana to measure local-scale effects of a broadcast application of picloram on 1) cover of the target invader, spotted knapweed (Centaurea stoebe L.), 2) prevalence of native functional groups, and 3) the secondary invader cheatgrass (Bromus tectorum L.) at differing initial levels of knapweed invasion. Treatment effectively suppressed knapweed, with cover in treated vs. control plots reduced by >60% in the sixth posttreatment year. Treatment also appeared to alleviate knapweed’s impacts on native perennial grasses, but only at the highest initial level of invasion, where cover of this group increased by >30% in treated vs. control plots to equal levels associated with noninvaded plots. In some cases, treatment appeared to exacerbate knapweed’s impacts on native forbs. At the no-invasion level, perennial forb cover declined by >20% in treated vs. control plots to match values associated with moderate or high levels of invasion, but these treatment effects were minimal at the latter invasion levels. Across initial invasion levels, species richness of perennial and/or annual forbs declined by >20% in treated vs. control plots. Treatment also promoted increases in cheatgrass cover, although differences between treated and control plots were relatively small by the sixth posttreatment year. Overall, effects of picloram application depended on initial levels of knapweed invasion, largely due to the varying strength of release effects. Selective treatment of invaded patches vs. broadcast applications would reduce side effects of broadleaf herbicide application and increase compatibility with other management measures designed to improve rangeland conditions and restore grassland communities.  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.
Western juniper (Juniperus occidentalis Hook.) encroachment and exotic annual grass (medusahead [Taeniatherum caput-medusae L. Nevski] and cheatgrass [Bromus tectorum L.]) invasion of sagebrush (Artemisia L.) communities decrease ecosystem services and degrade ecosystem function. Traditionally, these compositional changes were largely confined to separate areas, but more sagebrush communities are now simultaneously being altered by juniper and exotic annual grasses. Few efforts have evaluated attempts to restore these sagebrush communities. The Crooked River National Grassland initiated a project to restore juniper-encroached and annual grass-invaded sagebrush steppe using summer (mid-July) applied prescribed fires and postfire seeding. Treatments were unburned, burned, burned and seeded with a native seed mix, and burned and seeded with an introduced seed mix. Prescribed burning removed all juniper and initially reduced medusahead cover but did not influence cheatgrass cover. Neither the native nor introduced seed mix were successful at increasing large bunchgrass cover, and 6 yr post fire, medusahead cover was greater in burned treatments compared with the unburned treatment. Large bunchgrass cover and biological soil crusts were less in treatments that included burning. Exotic forbs and bulbous bluegrass (Poa bulbosa L.), an exotic grass, were greater in burned treatments compared with the unburned treatment. Sagebrush communities that are both juniper encroached and exotic annual grass invaded will need specific management of both juniper and annual grasses. We suggest that additional treatments, such as pre-emergent herbicide control of annuals and possibly multiple seeding events, are necessary to restore these communities. We recommend an adaptive management approach in which additional treatments are applied on the basis of monitoring data.  相似文献   

6.
Long-term control of the invasive annual grass cheatgrass is predicated on its biological suppression. Perennial grasses vary in their suppressive ability. We compared the ability of a non-native grass (“Hycrest” crested wheatgrass) and two native grasses (Snake River wheatgrass and bluebunch wheatgrass) to suppress cheatgrass. In a greenhouse in separate tubs, 5 replicates of each perennial grass were established for 96 d, on which two seeds of cheatgrass, 15 cm apart, were then sown in a semicircular pattern at distances of 10 cm, 30 cm, and 80 cm from the established perennial bunchgrasses. Water was not limiting. After 60 d growth, cheatgrass plants were harvested, dried, weight recorded, and tissue C and N quantified. Soil N availability was quantified at each location where cheatgrass was sown, both before sowing and after harvest. Relative to cheatgrass grown at 80 cm, all perennial grasses significantly reduced aboveground biomass at 30 cm (68% average reduction) and at 10 cm (98% average reduction). Sown at 10 cm from established perennial grasses, cheatgrass aboveground biomass was inversely related with perennial grass root mass per unit volume of soil. All cheatgrass sown at 10 cm from “Hycrest” crested wheatgrass died within 38 d. Before sowing of cheatgrass, soil 10 cm from established perennial grasses had significantly less mineral N than soil taken at 30 cm and 80 cm. Relative to cheatgrass tissue N for plants grown at 80 cm, cheatgrass nearest to the established perennial grasses contained significantly less tissue N. All perennial grasses inhibited the NO2− to NO3− nitrification step; for “Hycrest” crested wheatgrass, soil taken at 10 cm from the plant had a molar proportion of NO2− in the NO2− + NO3− pool of > 90%. In summary, a combination of reduced nitrogen availability, occupation of soil space by perennial roots, and attenuation of the nitrogen cycle all contributed to suppression of cheatgrass.  相似文献   

7.
  相似文献   

8.
Crested wheatgrass, an introduced perennial bunchgrass, has been seeded extensively on the rangelands of western North America. There is a perception that this species is very competitive and that it forms monoculture or low diversity stands where successfully seeded. However, there is limited information on species composition in sites previously seeded to crested wheatgrass. We measured native vegetation and environmental characteristics in areas seeded with crested wheatgrass across the northwestern Great Basin. Plant community composition within these crested wheatgrass stands was variable, from seedings that were near monocultures of crested wheatgrass to those that contained more diverse assemblages of native vegetation, especially shrubs. Environmental factors explained a range of functional group variability from 0% of annual grass density to 56% of large native bunchgrass density. Soil texture appeared to be an important environmental characteristic in explaining vegetation cover and density. Native vegetation was, for all functional groups, positively correlated with soils lower in sand content. Our results suggest environmental differences explain some of the variability of native vegetation in crested wheatgrass stands, and this information will be useful in assessing the potential for native vegetation to co-occupy sites seeded with crested wheatgrass. This research also suggests that crested wheatgrass seedings do not always remain in near monoculture vegetation states as seedings substantially varied in native vegetation composition and abundance with some seeded areas having a more diverse assemblage of native vegetation. In half the sites, there were five or more perennial herbaceous species and 63% of sites contained Wyoming big sagebrush. Although not exclusively true, species most commonly encountered in crested wheatgrass seedings are those that are able to minimize competition with crested wheatgrass via temporal (i.e., Sandberg bluegrass, annual forbs, annual grasses) or spatial (i.e., shrubs) differentiation in resource use.  相似文献   

9.
Invasion of exotic grasses into grasslands dominated by native plants changes fire cycles and reduces biodiversity. Brush management practices that create soil disturbance, such as aeration, may potentially result in invasion of exotic grasses and replacement of native vegetation. We tested the hypothesis that a long-term effect of aeration and prescribed burning is an increase in exotic grasses. The study was conducted at the Chaparral Wildlife Management Area in the western south Texas plains where four treatments were evaluated: aeration, warm-season burn, aeration followed by a warm-season burn, and no treatment (control). The experimental design was a randomized complete block with four replicates. We estimated percentage canopy cover of exotic grasses, native grasses, forbs, litter, bare ground, and woody and succulent plants in 2007. There was a multivariate main effect among treatments for the dependent variables absolute canopy cover of exotic grasses, native grasses, forbs, litter, and bare ground (Wilks's Lambda F15,179.84 = 2.78, P = 0.001). Variables that contributed to the significant overall effect included litter (F3,69 = 4.32, P = 0.008) and native grasses (F3,69 = 6.11, P = 0.001). The multivariate main effect of treatment was significant (Wilks's Lambda F9,180.25 = 2.04, P = 0.038) for the relative canopy cover of herbaceous species. Relative cover of exotic grasses was 31% higher (P = 0.024) in control than in the prescribed burn treatment. Native grasses relative cover was 30% higher (P = 0.003) in prescribed burn than in the control treatment. We did not detect differences among treatments in the percentage of total woody and succulent plants canopy cover (P = 0.083). Under the environmental conditions at the time of the study, aeration and/or prescribed burning do not increase exotic grasses.  相似文献   

10.
The interaction of resource availability and disturbance can strongly affect plant species richness and the spread of exotic plants. Several ecological theories posit that disturbance mediates the richness-reducing effects of increased competition as resource levels rise. In the low-nutrient serpentine grasslands of the San Francisco Bay Area, the fertilizing effects of atmospheric nitrogen (N) deposition may threaten native species by promoting nitrophilic exotic grasses. Attempts to mitigate these N deposition effects have focused on cattle grazing as a strategy to reduce exotic grass cover. We simulated realistic N deposition increases with low-level fertilization, manipulated grazing with fencing, and monitored grazing intensity using camera traps in a 4 yr factorial experiment to assess the effects of grazing and N deposition on several measures of native and exotic species dynamics in California's largest serpentine grassland. Our results suggest that native species diversity may increase slightly under low-level N deposition with moderate grazing in this system. However, grazing may not be effective at limiting exotic cover as N accumulates in the future. Examination of treatment trajectories using principal response curves indicated that responses to grazing might be determined more by functional group (forb or grass) than origin (native or exotic). Grazing intensity varied dramatically within the single stocking rate used to manage this ecosystem. Given this variation and the contrasting effects of grazing on different functional groups, more targeted management may be required to improve conservation outcomes.  相似文献   

11.
三峡地区灌丛草地放牧山羊日粮组成及其喜食性   总被引：2，自引：1，他引：1  
在三峡地区灌丛草地研究放牧山羊的日粮组成及其喜食性。结果表明,在山羊日粮中50%以上由灌木植物组成。山羊对灌木的喜食性指数极显著地高于禾草和杂类草(P<0.01),而对禾草和杂类草喜食性的差异不明显。在灌木中,山羊对马桑和杉木等的喜食程度较高,其中马桑的喜食性指数为63%,而麻栎、水锦树和柳杉仅为15%、13%和12%。对于禾草,山羊明显喜食芒和黄背草(P<0.05),喜食性指数分别为16%和12%。对杂类草中的竹节草喜食性指数为13%。  相似文献   

12.
以内蒙古锡林郭勒盟白音锡勒牧场境内的中国科学院内蒙古草原生态系统定位站羊草样地为研究对象,选取2004年,1999年和1979年围封羊草样地,分种记录生物量、盖度、密度、株高等相关指标,研究不同围封年限条件下草原群落的物种组成、生物多样性及群落的功能群特征。结果表明,随着围封年限的增加,植物功能群结构及其多样性发生了变化,且最终趋于稳定。1999和1979年围封与2004年围封相比,多年生禾草和灌木、半灌木累积优势度显著降低(P＜0.05),多年生杂类草累积优势度出现不同程度升高;1999年和1979年围封条件下香农-韦弗指数显著高于2004年,1999年和1979年之间没有显著差异(P＞0.05);丰富度指数和均匀度指数2004年围封条件下显著高于1999年和1979年围封条件,1999年和1979年之间没有显著差异(P＞0.05);1999年和1979年围封条件下总生物量、多年生杂类草生物量、多年生禾草生物量及灌木和半灌木生物量均比2004年增加,其中总生物量及灌木和半灌木生物量显著高于2004年围封,1979年围封条件下灌木和半灌木生物量显著高于1999年围封,1999年和1979年围封条件下总生物量之间没有显著差异(P＞0.05),杂类草生物量1999年,1979年和2004年围封之间均表现出显著差异(P＜0.05),顺序为1979年＞1999年＞2004年。综上所述,长期围封促使草场灌丛化,降低草地利用价值,导致草地出现退化。  相似文献   

13.
In 1998, fires burned more than 11 330 ha of rangeland on Dugway Proving Ground in Utah's west desert. Postfire revegetation was implemented in 2 affected salt desert shrub communities (greasewood; Sarcobatus vermiculatus Hook. and black sagebrush/shadscale; Artemisia nova A. Nels; Atriplex confertifolia Torr. & Frem.) to deter cheatgrass (Bromus tectorum L.) encroachment. We monitored cheatgrass densities for 3 years after the fire in burned drill seeded, burned not-seeded, and unburned plots to assess the rate of invasion and determine the impact on cheatgrass of drill seeding perennial species. Cheatgrass invaded quickly in both shrub sites following the fires. In the greasewood site, drill seeded species germinated but did not establish. This was likely due to a combination of soil salinity and extremely dry weather conditions during the second year of the study. Drill seeded species in the black sagebrush site germinated and established well, resulting in the establishment of 16.5 perennial grasses · m-2 and 1 356 shrubs · ha-1. Cheatgrass densities were consistently lower in drill seeded versus not-seeded plots, although these were not always statistically different when Bonferroni comparisons were considered. The initial decrease in cheatgrass densities in drill seeded plots may have resulted from soil disturbance coupled with extremely low precipitation rather than competitive effects. Nevertheless, as seeded species mature and increase their competitive ability, we predict long-term suppression of cheatgrass in the absence of further disturbance.  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.
Ventenata (Ventenata dubia [Leers] Coss.) is an exotic annual grass that can invade intermountain rangeland plant communities, where it can form monotypic stands, degrade wildlife habitat, and reduce livestock forage. There is limited information on ventenata control in rangelands as it has only recently been identified as a substantial problem. Imazapic is a pre-emergent herbicide commonly used to control other exotic annual grasses and, therefore, is likely to control ventenata in rangelands. We evaluated five application rates of imazapic (0 − 175 g ae ∙ ha− 1) on ventenata and other exotic annual grass control and plant community response at two rangeland sites in 2 yr (2014 and 2015). Imazapic reduced exotic annual grass (largely ventenata) cover and density, with greater control with increasing imazapic rates. Exotic annual grass density at the highest levels of control (82%−94%) was 184 − 299 plants ∙ m− 2 the first yr after imazapic application. Exotic annual grasses fully recovered in the second or third yr after imazapic application. Bare ground generally increased with imazapic application. However, density of perennial vegetation (grasses and forbs) did not vary among treatments. Perennial vegetation cover generally did not increase with imazapic control of ventenata and other exotic annual grasses. Imazapic can control ventenata; however, even at the highest rates, control was not enough to shift the dominance from exotic annual species to perennial species. Integrating other treatments with imazapic application may be a strategy to improve ventenata control and increase perennial vegetation and will require further investigation. The difficulty and likely expense of achieving substantial and lasting control of ventenata suggest, similar to other exotic annual grasses, that preventing ventenata invasion and dominance should be a high management priority.  相似文献   

16.
In and around the Great Basin, United States, restoration of shrub steppe vegetation is needed where rangelands are transitioning to annual grasslands. Mechanical seedbed preparation can aid native species recovery by reducing annual grass competition. This study was designed to investigate the nature and persistence of hydrologic and erosion impacts caused by different mechanical rangeland seeding treatments and to identify interactions between such impacts and related soil and vegetation properties. A cheatgrass (Bromus tectorum L.)–dominated site was burned and seeded with native grasses and shrubs in the fall of the year. An Amazon-drill and a disk-chain seeder were used to provide varying levels of surface soil disturbance. An undisturbed broadcast seeding was used as a control. Simulated rainfall was applied to 6 large (32.5-m2) plots per treatment over 3 growing seasons at a rate of 63.5 mm · h-1. Rainfall was applied for 60 minutes under dry antecedent moisture conditions and for 30 minutes, 24 hours later under wet antecedent moisture conditions. The disk-chain created the largest reduction in infiltration and increase in sediment yield, which lasted for 3 growing seasons posttreatment. The Amazon-drill had a lesser impact, which was insignificant after the second growing season posttreatment. Surface soil properties showed little correlation with treatment-induced hydrologic and erosion impacts. Hydrologic recovery was strongly correlated with litter dynamics. The seeding treatments were unsuccessful at establishing seeded plant species, and the site once again became dominated by cheatgrass. A continuous upward trend in biomass production and surface litter cover was observed for all treatments between the beginning and end of the study because of cheatgrass invasion. Although the initial goal of using mechanical seeding treatments to enhance recovery of native grass species failed, cheatgrass production provided sufficient biomass to rapidly replenish surface litter cover necessary for rapid hydrologic stability of the site.  相似文献   

17.
Fire suppression has led to large fuel accumulations in many regions of the United States. In response to concerns about associated wildfire hazards, land managers in the western United States are carrying out extensive fuel-reduction thinning programs. Although reductions in cover by woody vegetation seem likely to cause changes in herbaceous communities, few published studies have reported on consequences of such treatments for native or exotic plant species. We compared vegetation and abiotic characteristics between paired thinned and unthinned chaparral and oak woodland communities of southwestern Oregon 4–7 yr posttreatment and contrasted impacts of manual vs. mechanical treatments. Herbaceous cover increased on thinned sites, but species richness did not change. Herbaceous communities at thinned sites had an early postdisturbance type of composition dominated by native annual forbs and exotic annual grasses; cover by annuals was nearly twice as high on treated as on untreated sites. Absolute and proportional cover of native annual forbs increased more than any other trait group, whereas exotic annual forbs and native perennial forbs declined. Exotic annual grass cover (absolute and proportional) increased, whereas cover by native perennial grasses did not. Shrub reestablishment was sparse after thinning, probably because of a lack of fire-stimulated germination. Manual and mechanical treatment impacts on abiotic site conditions differed, but differences in vegetation impacts were not statistically significant. Fuel-reduction thinning may have some unintended negative impacts, including expansion of exotic grasses, reductions in native perennial species cover, persistent domination by annuals, and increased surface fuels. Coupled with sparse tree or shrub regeneration, these alterations suggest that ecological-state changes may occur in treated communities. Such changes might be mitigated by retaining more woody cover than is currently retained, seeding with native perennials after treatment, or other practices; further research is needed to inform management in these ecosystems.  相似文献   

18.
Fire plays a central role in influencing ecosystem patterns and processes. However, documentation of fire seasonality and plant community response is limited in semiarid grasslands. We evaluated aboveground biomass, cover, and frequency response to summer, fall, and spring fires and no fire on silty and clayey sites in semiarid, C3-dominated grassland. The magnitude of change in biomass between years was greater than any differences among fire treatments. Still, differences existed among seasons of fire. Summer fire reduced non-native annual forb frequency (3% vs. 10% ± 2%) and Hesperostipa comata, reduced native annual forbs the first year, increased Poa secunda and bare ground, and increased Vulpia octoflora the second year. Fall fire increased grass biomass (1224 vs. 1058 ± 56 kg ? ha? 1), but fall fire effects were generally similar to those of summer fire. Spring fire effects tended to be intermediate between no fire and summer and fall fire with the exception that spring fire was most detrimental to H. comata the first growing season and did not increase bare ground. All seasons of fire reduced litter, forb biomass, and frequency of Bromus japonicus and Artemisia spp., and they reduced H. comata, V. octoflora, and native annual forbs the first year, but increased basal cover of C3 perennial grasses (2.2% vs. 0.6% ± 0.4%). Fire during any season increased dominance of native species compared with no fire (6.6% vs. 2.0% ± 1.0% basal cover) and maintained productivity. Seasonal timing of fire manipulated species composition, but increased C3 perennial grass cover and native species dominance with fire during any season indicated that using fire was more important than the season in which it occurred. In addition, fire effects on the vegetation components tended to be counter to previously observed effects of grazing, suggesting fire and grazing may be complementary.  相似文献   

19.
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   

20.
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   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号