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1.
Native perennial grasses were once common in California prairies that are now dominated by annual grasses introduced from Europe. Competition from exotics may be a principal impediment to reestablishment of native perennial grasses. Introduced annual grasses, such as Vulpia myuros (zorro fescue), are often included with native perennial species in revegetation seed mixtures used in California. To examine the potential suppressive effect of this graminoid, we evaluated the growth and performance of a mixture of California native perennial grasses and resident weeds when grown with varying densities of V. myuros. The annual fescue exhibited a strongly plastic growth response to plant density, producing similar amounts of above‐ground biomass at all seeding densities. Perennial grass seedling survival and above‐ ground biomass decreased and individuals became thinner (i.e., reduced weight‐to‐height ratio) with increasing V. myuros seeding density. V. myuros also significantly suppressed above‐ground biomass and densities of weeds and had a more negative effect on weed densities than on native perennial grass densities. Biomass of native grasses and weeds was not differentially affected by increasing densities of V. myuros. Overall, because V. myuros significantly reduced the survival and performance of the mixture of native perennial grasses and this effect increased with increasing V. myuros density, we conclude that including this exotic annual in native seed mixtures is counterproductive to restoration efforts.  相似文献   

2.
Annual growth rings of roots in perennial forbs have been used in studies of climate change and the ecology of grasslands. However, little has been done in this aspect of research in China. In this study, we report the characteristics of growth rings in the main roots of 13 herb species sampled in Duolun of the Inner Mongolia grassland in northern China. The results show that around two thirds of the species possess clearly demarcated annual rings in the root xylem. Some species of the same genera show different patterns in anatomical structure of the root xylem. Standardized annual ring widths of three species, Potentilla anserine L., Cymbaria dahurica L. and Lespedeza daurica (Laxm.) Schindh, show a common linear trend, indicating a continued favorable growth condition in the sampling sites. Our results provide evidence that growth rings in roots of some perennial forbs in the Inner Mongolia grassland can serve as a new and useful indicator of past changes in the grassland environment.  相似文献   

3.
Plant invasions have the potential to significantly alter soil microbial communities, given their often considerable aboveground effects. We examined how plant invasions altered the arbuscular mycorrhizal fungi of native plant roots in a grassland site in California and one in Utah. In the California site, we used experimentally created plant communities composed of exotic (Avena barbata, Bromus hordeaceus) and native (Nassella pulchra, Lupinus bicolor) monocultures and mixtures. In the Utah semi-arid grassland, we took advantage of invasion by Bromus tectorum into long-term plots dominated by either of two native grasses, Hilaria jamesii or Stipa hymenoides. Arbuscular mycorrhizal fungi colonizing roots were characterized with PCR amplification of the ITS region, cloning, and sequencing. We saw a significant effect of the presence of exotic grasses on the diversity of mycorrhizal fungi colonizing native plant roots. In the three native grasses, richness of mycorrhizal fungi decreased; in the native forb at the California site, the number of fungal RFLP patterns increased in the presence of exotics. The exotic grasses also caused the composition of the mycorrhizal community in native roots to shift dramatically both in California, with turnover of Glomus spp., and Utah, with replacement of Glomus spp. by apparently non-mycorrhizal fungi. Invading plants may be able to influence the network of mycorrhizal fungi in soil that is available to natives through either earlier root activity or differential carbon provision compared to natives. Alteration of the soil microbial community by plant invasion can provide a mechanism for both successful invasion and the resulting effects of invaders on the ecosystem.  相似文献   

4.
To assess the potential for enhancing an existing stand of native perennial grasses on a California Coast Range Grassland site, we experimentally manipulated the seasonal timing and presence of grazing for 3 years (1994 through 1996) and of autumn burning for 2 years (1994 and 1995) and measured species cover for 6 years (1993 through 1998). We subjected the species matrix to classification (TWINSPAN) and ordination (CCA) and tested the ordination site scores as well as diversity indices with linear mixed effects models. Four distinct plant community groups emerged from the classification. Two of these were dominated by annual grasses and two by perennial grasses. No treatment effects were observed on diversity. For composition, temporal and spatial random effects were important mixed effects model parameters, as was the fixed effect covariate, pre‐treatment CCA site score, indicating the importance of random environmental variation and initial starting conditions. Incorporation of these random effects and initial condition terms made for more powerful tests of the fixed effects, grazing season, and burning. We found no significant burning effects. Grazing removal imparted a shift in plant community from more annual‐dominated toward more perennial‐dominated vegetation. Individual perennial grass species responded differently according to genus and species. Nassella spp. increased gradually over time regardless of grazing treatment. Nassella pulchra (purple needlegrass) increase was greatest under spring grazing and N. lepida (foothill needlegrass) was greatest with grazing removal. Danthonia californica (California oatgrass) had little response over time under seasonal grazing treatments, but increased with grazing removal. Under relatively mesic weather conditions it appears that grazing removal from Coast Range Grasslands with existing native perennial grass populations can increase their cover. However if N. pulchra is the sole existing population, spring season‐restricted grazing should be equally effective at enhancing cover of the native grass species.  相似文献   

5.
Grassy woodlands dominated by Eucalyptus species such as E. albens Benth., E. melliodora A. Cunn. ex Schauer, and E. microcarpa Maiden are poorly conserved in Australia, owing to widespread agricultural development. Understorey restoration is vitally important to enhance degraded remnants but no reliable techniques are available to restore herbaceous understorey species over large areas. Reestablishment of dominant native grasses such as Kangaroo grass (Themeda triandra Forssk.) is particularly important. This study compared Themeda establishment using a variety of sowing techniques across a range of landscape positions in degraded woodlands in central New South Wales. Four localities were sampled at three landscape positions (upper, mid‐, and lower slopes). Existing vegetative cover was sprayed with herbicide and removed by mowing. A randomized block experiment was established at each site with five replicates of five seedbed treatments: all four factorial combinations of soil disturbance (disturbed, nondisturbed) and weed control (atrazine, nonatrazine), plus topsoil scalping followed by soil disturbance. After 117 days, all plots were subject to a common herbicide (atrazine) treatment to control weeds. Themeda establishment was not significantly affected by landscape position, despite significant differences in the cover of exotic species among landscape positions. The scalped/disturbed treatment resulted in significantly better establishment at 400 days (18% or 3.9 plants/m2) than the control (8% or 1.8 plants/m2). All other treatments did not differ significantly from the control suggesting that seedbed treatments are not critical to successful Themeda establishment. These results suggest that Themeda swards can be reestablished in degraded woodlands relatively simply. The similarity in outcomes across all landscape positions suggests that general recommendations for “best‐bet” establishment methods may prove robust under a wide range of environmental and seasonal conditions.  相似文献   

6.
Buffelgrass ( Pennisetum ciliare ) is an exotic grass that threatens arid and semiarid ecosystems. The objective of this study was to determine effectiveness of several herbicides at reducing competition from buffelgrass to enhance establishment of planted native grasses. In Duval County, Texas, plots were delineated in two experiments in a buffelgrass-dominated pasture and mowed on 2 September 2002. On 18 September 2002 and 7 October 2002, a 41% glyphosate (N-(phosphonomethyl) glycine) herbicide was applied to all plots. A mixture of three native grasses—green sprangletop ( Leptochloa dubia ), plains bristlegrass ( Setaria leucopila ), and four-flower trichloris ( Chloris pluriflora )—was planted on 8 October 2002. On 9 October 2002, 1.12 and 2.24 kg/ha of a 80% tebuthiuron ( N -[5-(1,1-dimethyethyl)-1,3,4-thiadiazol-2-yl]- N , N '-dimethylurea) herbicide was applied preemergence to the first experiment, and all other herbicides were applied postemergence on 27 July 2003 to the second experiment. Percent canopy cover of vegetation was estimated with a 20 × 50–cm sampling frame during April, June, and October 2003 and August 2004. Postemergent herbicides had no significant effect on canopy cover of buffelgrass or planted species ( p ≥ 0.05). Canopy cover of native grasses did not exceed 8% on any treatment or sampling date, and buffelgrass cover returned to pre-treatment conditions in less than 1 year; however, the 2.24 kg/ha rate of tebuthiuron suppressed ( p < 0.05) canopy cover of buffelgrass compared with controls and increased ( p < 0.05) native grasses almost 2 years past application. Tebuthiuron may have potential value in reducing buffelgrass canopy cover and increasing cover of native grasses, particularly Chloris spp.  相似文献   

7.
One of the major challenges confronting grassland restoration of highly invaded communities is increasing the diversity of native species. There is surprisingly little research investigating how reconstructed native grasslands respond to common management techniques and how these techniques influence the relative establishment of both native grasses and forbs. Despite the diversity and wide distribution of native clovers in California, few practitioners incorporate them into grassland restoration plans. Conversely, non‐native clovers have been seeded extensively onto California rangelands. This study addresses the following questions: (1) Using readily available management tools, is there a strategy that can benefit the growth of both planted native bunchgrasses and seeded clovers? (2) Do native bunchgrasses compete with establishing clovers and non‐native grasses? (3) Do native and non‐native clovers differ in their response to management treatments or in their productivity? Plots were established to test three factors in different combinations over 3 years: (1) early spring clipping, (2) initial broadleaf herbicide, and (3) native bunchgrass planting density. Native and non‐native clovers were seeded in years 2 and 3. Early spring clipping did not have a significant effect on native bunchgrass cover, yet it did result in greater growth of native and non‐native clovers. The direction of the response to broadleaf herbicide changed between years for native bunchgrasses and was consistently negative for native clovers. Plots with higher native grass densities did not adversely affect the seeded clovers, yet non‐native grass cover was reduced. Native and non‐native clovers exhibited similar responses to clipping and established at similar densities.  相似文献   

8.
The Central Valley of California is noted for its dearth of remnant native grass populations and for low native grass seedling establishment within grasslands now dominated by non‐native annual species. In contrast, remnant populations are common along the coast, and studies have shown an ability for seedlings and adults to compete with non‐native annual grasses. The invasibility of well‐established populations of native grasses in the Central Valley remains unclear. The objectives of this study were to compare the invasibility of native grasses differing in density and species composition and, given the species in this study, to assess the ability of mixes with greater species richness to resist invasion relative to their abilities in monoculture. In the Sacramento Valley of California, six species of native grasses were planted at three densities in monospecific and mixed‐species plots. Percent cover of native perennial and non‐native annual grasses was measured in years 2 and 3, and biomass was sampled in year 5. Native grass biomass and, to a lesser extent, species composition were important in explaining variation in non‐native grass invasibility in the fifth year. Species‐rich treatments did not experience less invasion than would be expected by the proportional invasibility of each species in monoculture. However, invasibility of plots consisting of slower growing, shorter statured species decreased over time, suggesting a successional benefit to diverse communities. This study demonstrates that established stands of native grasses in the Sacramento Valley can resist invasion by non‐native annual grasses and that stand biomass is a particularly important factor in determining invasibility.  相似文献   

9.
Populations of the rare annual forb Amsinckia grandiflora may be declining because of competitive suppression by exotic annual grasses, and may perform better in a matrix of native perennial bunchgrasses. We conducted a field competition experiment in which Amsinckia seedlings were transplanted into forty 0.64‐m2 experimental plots of exotic annual grassland or restored perennial grassland. The perennial grassland plots were restored using mature 3 cm‐diameter plants of the native perennial bunchgrass Poa secunda planted in three densities. The exotic annual grassland plots were established in four densities through manual removal of existing plants. Both grass types reduced soil water potential with increasing biomass, but this reduction was not significantly different between grass types. Both grass types significantly reduced the production of Amsinckia inflorescences. At low and intermediate densities (dry biomass per unit area of 20–80 g/m2), the exotic annual grasses reduced Amsinckia inflorescence number to a greater extent than did Poa, although at high densities (>90 g/m2) both grass types reduced the number of Amsinckia inflorescences to the same extent. The response of Amsinckia inflorescence number to Poa biomass was linear, whereas the same response to the annual grass biomass is logarithmic, and appeared to be related to graminoid cover. This may be because of the different growth forms exhibited by the two grass types. Results of this research suggest that restored native perennial grasslands at intermediate densities have a high habitat value for the potential establishment of the native annual A. grandiflora.  相似文献   

10.
Dominance of warm‐season grasses modulates tallgrass prairie ecosystem structure and function. Reintroduction of these grasses is a widespread practice to conserve soil and restore prairie ecosystems degraded from human land use changes. Seed sources for reintroduction of dominant prairie grass species include local (non‐cultivar) and selected (cultivar) populations. The primary objective of this study was to quantify whether intraspecific variation in developing root systems exists between population sources (non‐cultivar and cultivar) of two dominant grasses (Sorghastrum nutans and Schizachyrium scoparium) widely used in restoration. Non‐cultivar and cultivar grass seedlings of both species were isolated in an experimental prairie restoration at the Konza Prairie Biological Station. We measured above‐ and belowground net primary production (ANPP and BNPP, respectively), root architecture, and root tissue quality, as well as soil moisture and plant available inorganic nitrogen (N) in soil associated with each species and source at the end of the first growing season. Cultivars had greater root length, surface area, and volume than non‐cultivars. Available inorganic N and soil moisture were present in lower amounts in soil proximal to roots of cultivars than non‐cultivars. Additionally, soil NO3–N was negatively correlated with root volume in S. nutans cultivars. While cultivars had greater BNPP than non‐cultivars, this was not reflected aboveground root structure, as ANPP was similar between cultivars and non‐cultivars. Intraspecific variation in belowground root structure and function exists between cultivar and non‐cultivar sources of the dominant prairie grasses during initial reestablishment of tallgrass prairie. Population source selection should be considered in setting restoration goals and objectives.  相似文献   

11.
Many early attempts at tallgrass prairie reconstruction failed to achieve the high species diversity of remnant prairies, and instead consist primarily of C4 grasses. We hypothesized that frequent mowing of established prairie grasses could create sufficient gaps in the aboveground and belowground environment to allow for the establishment of native forbs from seed. We studied forb seedling establishment in a 25‐year‐old prairie planting in northern Iowa that was dominated by native warm‐season grasses. In winter 1999, 23 species of native forbs were broadcast into the recently burned sod at a rate of 350 viable seeds/m2. Treatment plots were mowed weekly for either one or two growing seasons, and control plots were unmowed. Mowed plots had greater light availability than controls, especially when warm‐season grasses began to flower. Overwinter seedling mortality was 3% in mowed treatments compared to 29% in the controls. Forbs in mowed plots had significantly greater root and shoot mass than those in control plots in the first and second growing seasons but were not significantly more abundant. By the fourth growing season, however, forbs were twice as abundant in the mowed treatments. No lasting negative impacts of frequent mowing on the grass population were observed. Mowing a second year influenced species composition but did not change total seedling establishment. Experimental evidence is consistent with the idea that mowing reduced competition for light from large established grasses, allowing forb seedlings the opportunity to reach sufficient size to establish, survive, and flower in the second and subsequent years.  相似文献   

12.
Little is known about restoring the perennial herbaceous understory of Midwestern deciduous woodlands, despite the significant and widespread degradation of remnants due to human activities. Because many woodland understory species have reproductive characters that make reestablishment from seed slow or difficult, we investigated transplanting as a strategy for introducing 24 species to a degraded early-successional woodland in central Iowa, U.S.A. Plants were planted in single-species groups of generally four individuals, and then monitored for survival five times over a 7-year period, and for flowering during the first year. After 7 years, persistence of these groups was 57% averaged across species. Survival in years 5–7 does not reflect individuals that spread beyond the original planting units by self-sowing or vegetative spread and is therefore a minimum estimate of the abundance of many species at the site. Mean percent flowering was 72% across single-species groups for 15 species monitored. We consider these survival and flowering rates acceptable indicators of establishment success, especially given drought conditions at our site in the first few years and lack of weed control beyond the first year, and evidence that transplanted species were establishing outside the original planting locations. Additional work is needed to investigate regional differences in transplant success, and methods for sustainable production of species are not suitable for introduction by seed. We caution that our results do not necessarily apply to the restoration of rare species.  相似文献   

13.
Exotic annual grasses are a major challenge to successful restoration in temperate and Mediterranean climates. Experiments to restore abandoned agricultural fields from exotic grassland to coastal sage scrub habitat were conducted over two years in southern California, U.S.A. Grass control methods were tested in 5 m2 plots using soil and vegetation treatments seeded with a mix of natives. The treatments compared grass‐specific herbicide, mowing, and black plastic winter solarization with disking and a control. In year two, herbicide and mowing treatments were repeated on the first‐year plots, plus new control and solarization plots were added. Treatments were evaluated using percent cover, richness and biomass of native and exotic plants. Disking alone reduced exotic grasses, but solarization was the most effective control in both years even without soil sterilization, and produced the highest cover of natives. Native richness was greatest in solarization and herbicide plots. Herbicide application reduced exotics and increased natives more than disking or mowing, but produced higher exotic forb biomass than solarization in the second year. Mowing reduced grass biomass and cover in both years, but did not improve native establishment more than disking. Solarization was the most effective restoration method, but grass‐specific herbicide may be a valuable addition or alternative. Solarization using black plastic could improve restoration in regions with cool, wet summers or winter growing seasons by managing exotic seedbanks prior to seeding. While solarization may be impractical at very large scales, it will be useful for rapid establishment of annual assemblages on small scales.  相似文献   

14.
Along rural roadsides of the Sacramento Valley of California, we seeded native and non-native perennial grasses to gauge their potential value in roadside vegetation management programs. In trial I (polycultures), three seeded complexes and a control (resident vegetation only) were tested. Each seeded plant complex included a different mix of perennial grasses seeded into each of several roadside topographic zones. The seeded levels of plant complex were: native perennial grasses 1 (8 species); native perennial grasses 2 (13 species); and non-native perennial grasses (3 species). In trial II, plots were seeded to monocultural plots of 15 accessions of native Californian and three cultivars of non-native perennial grasses. Plots in both trials were seeded during January 1992 and evaluated for three successive years.  相似文献   

15.
Many semiarid rangelands in the Great Basin, U.S.A., are shifting dominance to woody species as a consequence of land degradation including intense livestock grazing and fire suppression. Whereas past rehabilitation efforts in Big sagebrush (Artemisia tridentata) steppes removed the shrub and added introduced forage grasses to successfully shift communities from shrublands to grasslands, current consensus is that native species should be included in restoration projects and that retention of some woody plants is desirable. We examined the potential for interseeding grasses into dense shrub communities as a precursor to thinning shrubs and releasing grasses from shrub interference. We compared seedling establishment of the native grass, Bluebunch wheatgrass (Pseudoroegneria spicata), with that of the Eurasia grass, Crested wheatgrass (Agropyron desertorum), in dense Ar. tridentata stands. Shrubs may play an important role as nurse plants for seedling establishment (reduced solar radiation, “island of fertility” effect) but result in highly contrasting light environments and root interference for seedlings. In experimental plots, we examined effects of Ar. tridentata shade levels (0, 40, 70, and 90% reduction of solar radiation) and initial root exclusion (present/absent) on the establishment and growth of P. spicata and Ag. desertorum seedlings. With this design we evaluated the interference effects of Ar. tridentata on the two grasses and identified the most beneficial microsites for grass restoration in Ar. tridentata–dominated communities. We predicted seedling survival and growth to be greater under moderate shade (40% reduction) and limited root competition than under no or strong shade conditions (0 and 90%) and unrestricted root interactions. Fifty to 85% of the P. spicata and Ag. desertorum seedlings survived the dry summer months of 1995 and 1996 and the intervening winter. Neither shading nor root exclusion from Ar. tridentata affected final seedling survival of either species. Seedling biomass of both grass species was negatively affected by initial root interactions with Ar. tridentata. However, the analysis of seedling biomass variability (coefficient of variation) indicated that in all shade and root‐exclusion treatments, some seedlings of both species developed to large individuals to survive in Ar. tridentata–dominated rangelands. Thus, the use of interseeding techniques shows promise for restoring herbaceous species in dense Ar. tridentata stands and should be given further consideration when shrub retention is an important consideration.  相似文献   

16.
黎华寿  骆世明 《生态科学》2001,20(1):121-126
从生态学角度综述了草类在生态环境保护中的地位和作用。草类作为r型生态对策的先锋物种,在生态恢复和重建中作用显著,干旱瘦薄地种草明显优于种树。我国草资源丰富,其合理开发利用在生态农业建设中有重要意义,发展果-草原合生态果园已被证明是退化坡地恢复和利用的优化模式。草类还具有美化环境、净化空气、处理废水、降低噪声和辐射污染等功能。  相似文献   

17.
Insect herbivory of ovules and seeds is known to have a negative impact on individual plant reproductive success by reducing overall seed set. Although this seed set reduction has been well documented in plant populations found in native habitats, little work has been done on populations found in restored habitats. In a 4-year study (2001–2004), I investigated the herbivory of the Gelechiid moth ( Coleotechnites eryngiella ) of Eryngium yuccifolium populations in native and restored prairies. Data were collected from 20 E. yuccifolium populations (10 native prairies/10 restored prairies) in Illinois. Percent herbivory and percent seed set were determined for each population. From 2001 to 2004, percent herbivory in prairie restorations ranged from 0 to 93 and percent seed set ranged from 2 to 82. In native prairies, percent herbivory ranged from 0 to 98 and percent seed set ranged from 0 to 71. No differences were found between native and restored prairies for percent herbivory or percent seed set. However, significant differences were found among years for percent seed set. This study shows that the antagonistic effects of insect herbivory can reach similar levels in restored and native prairies.  相似文献   

18.
Alleviation of Salinity-Induced Dormancy in Perennial Grasses   总被引:2,自引:0,他引:2  
All seeds of Aeluropus lagopoides and Urochondra setulosa germinated under non-saline conditions except for Sporobolus ioclados which showed only 40 % germination. Increase in salinity substantially inhibited germination and few seeds germinated at 400 mM NaCl. Germination at 200 mM NaCl was alleviated in U. setulosa by the application of gibberellic acid and fusicoccin, in A. lagopoides by thiourea, betaine, kinetin, fusicoccin and ethephon, and in S. ioclados by gibberellin and ethephon. High salinity (400 mM NaCl) induced germination inhibition was alleviated by proline, kinetin, fusicoccin and ethephon only in A. lagopoides.  相似文献   

19.
The quantitative role of the canopy size of nurse shrubs on microenvironment and native tree establishment in degraded tropical lands has been seldom studied. In a 21‐month field experiment, we aimed to test the effect of a native shrub with different canopy sizes on the early establishment of native trees as part of the effort of forest restoration in tropical China. We examined the microenvironment, and the seedling establishment and growth of two native trees: Castanopsis fissa and Syzygium hancei in both open space (OS) microsite and microsite under the canopy of the native pioneer shrub Rhodomyrtus tomentosa. Shrub microsite was further divided into large canopy (LC), and medium canopy (MC) microsite, based on the shrub leaf area indices. Results showed that relative to OS, LC had higher soil nutrient concentration and water content, and lower photosynthetic active radiation (PAR), while MC had lower PAR and higher soil exchangeable Mg, K, and Ca. Survival and growth were mostly enhanced, while water stress and photoinhibition reduced for C. fissa seedlings in MC and S. hancei seedlings in LC. It is found that the beneficial effects of the native shrub on seedling establishment and growth result mostly from the improvement in nutrient and water availabilities, the reduction in plant stress caused by harsh summer light, and the specific ecological requirements of different tree species. We suggest that different canopy sizes of native shrub R. tomentosa may be explored to target different native trees and hence promote forest restoration in degraded tropical ecosystems.  相似文献   

20.
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