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1.
Arundo donax L. (Poaceae) is an aggressive invader in California’s riparian habitats. Field experiments were conducted to examine invader
and site attributes important in early invasion. One hundred A. donax rhizomes were planted along five transects into each of three southern California riparian habitats. Pre-planting rhizome
weight was recorded, along with site variables including percent bare ground, litter depth, PAR, soil moisture, soil temperature,
incidence of herbivory, native canopy cover, and plant community richness and diversity. A. donax shoot emergence, survival time, and shoot height were recorded for approximately 10 months. The experiment was repeated over
three years in different locations within each site. When years and sites were pooled to reveal large-scale patterns, A. donax performance was explained by rhizome weight, soil moisture, bare ground, soil temperature, and herbivory. When each site
was considered singly, A. donax was positively correlated with different variables in each location. Species richness was correlated with A. donax performance in only one site. Our results indicate that A. donax establishment in riparian habitats is promoted by both vegetative reproduction and favorable abiotic environmental factors
and relatively unaffected by the composition of the native community. The positive response of A. donax to disturbance (bare ground) and high resource availability (soil moisture), combined with a competitive perennial habit
suggest that this species takes advantage of a competitive-ruderal life history. The ability of A. donax to respond to different conditions in each site combined with low genetic and phenotypic variation seen in other studies
also suggests that a high degree of environmental tolerance contributes to invasion success. 相似文献
2.
Biological invasions by exotic species are occurring at exceptional rates and spatial scales worldwide and are increasingly
recognized as key forms of global environmental change. Despite this growing prominence, surprisingly few ecological studies
have quantified the impacts of exotic taxa on the plant communities they invade, and this is especially evident in riparian
ecosystems. Along the Russian River in northern California, we used both comparative and experimental studies to investigate
the influence of two exotic clonal plant species—giant reed (Arundo donax) and blue periwinkle (Vinca major)—on the composition of riparian plant communities. Our results indicate that Arundo invasion was associated with significantly lower richness of native perennial plant species on stream banks and floodplains,
whereas there was no relationship on gravel bars. Additional research showed that plots invaded by Arundo and Vinca, both individually and collectively, exhibited significantly lower native and exotic species richness and abundance of both
established plants and seedlings than uninvaded plots. Finally, after 2 years, experimental reductions of Arundo biomass via cutting and herbicide resulted in significantly increased native plant species richness and abundances of both
established plants and seedlings, while having no effects on other exotics. In summary, our results indicate that Arundo and Vinca have strongly negative effects on diverse components of a riparian plant community, which must be addressed via effective
control and restoration efforts. 相似文献
3.
Mitigating impacts of weeds and kangaroo grazing following prescribed fire in a Banksia woodland 下载免费PDF全文
Banksia woodlands are renowned for their flammability and prescribed fire is increasingly employed to reduce the risk of wildfire and to protect life and property, particularly where these woodlands occur on the urban interface. Prescribed fire is also employed as a tool for protecting biodiversity assets but can have adverse impacts on native plant communities. We investigated changes in species richness and cover in native and introduced flora following autumn prescribed fire in a 700‐hectare Banksia/Tuart (Eucalyptus gomphocephala) woodland that had not burnt for more than 30 years. Effectiveness of management techniques at reducing weed cover and the impacts of grazing by Western Grey Kangaroo (Macropus fuliginosus) postfire were also investigated. Thirty plots were established across a designated burn boundary immediately before a prescribed fire in May 2011, and species richness and cover were measured 3 years after the fire, in spring of 2013. Fencing treatments were established immediately following the fire, and weed management treatments were applied annually in winter over the subsequent 3 years. Our results indicate that autumn prescribed fire can facilitate increases in weed cover, but management techniques can limit the establishment of targeted weeds postfire. Postfire grazing was found to have significant adverse impacts on native species cover and vegetation structure, but it also limited establishment of some serious weeds including Pigface (Carpobrotus edulis). Manipulating herbivores in time and space following prescribed fire could be an important and cost‐effective way of maintaining biodiversity values. 相似文献
4.
5.
该研究采用盆栽试验法,选取石菖蒲、水生鸢尾、美人蕉、花叶芦竹为试验材料,将石菖蒲、水生鸢尾、美人蕉与花叶芦竹混种,用花叶芦竹单种作为对照,研究了混种对花叶芦竹生物量、根冠比以及铅积累量的影响。结果表明:(1)在不同浓度铅污染处理下,与花叶芦竹单种相比,混种模式增加了花叶芦竹的根冠比,且随着铅污染浓度的增加,表现出先上升后下降的趋势。(2)在单种和混种模式下花叶芦竹体内和土壤内的铅含量均表现出明显的浓度积聚效应;在混种模式下植物体内和土壤内的铅含量明显低于单种模式,且与单种模式之间的差异性显著(P<0.05)。(3)在高浓度铅污染处理下,单种和混种模式的花叶芦竹铅转运系数均大于1,而富集系数则表现为在低浓度和高浓度铅污染处理下均大于1;在美人蕉+花叶芦竹的混种模式中,花叶芦竹的地上部分和地下部分的铅富集系数达到最大。因此,我们认为美人蕉+花叶芦竹混种模式,显著提高了花叶芦竹的生物量和根冠比,并对铅污染土壤的净化效果最佳。 相似文献
6.
J. A. Goolsby A. T. Vacek C. Salinas A. Racelis P. J. Moran A. A. Kirk 《Biocontrol Science and Technology》2017,27(6):781-795
The fundamental host range of the arundo leafminer, Lasioptera donacis a candidate agent for the invasive weed, Arundo donax was evaluated. L. donacis collects and inserts spores of a saprophytic fungus, Arthrinium arundinis, during oviposition. Larvae feed and develop in the decomposing leaf sheath channel tissue. Thirty-six closely related and economic grass species along with several key habitat associates were evaluated in no-choice tests. L. donacis and its associated saprophyte completed development only on A. donax, in concurrence with published reports from its native range in Mediterranean Europe. The arundo leafminer feeding leads to premature defoliation, constituting a different mode of attack on the host plant as compared to two previously released insects, the arundo wasp and arundo scale, which feed on shoot tips and rhizomes, respectively. Defoliation of A. donax is expected to increase light penetration into stands of A. donax which increases visibility for law enforcement, reduces the survival of cattle fever ticks, and enhance recovery of the native riparian vegetation along the Rio Grande and other habitats where this weed is invasive. 相似文献
7.
Alberto Maceda-Veiga Helena Basas Gerard Lanzaco Miquel Sala Adolfo de Sostoa Antoni Serra 《Biological invasions》2016,18(3):731-749
Riparian areas have experienced long-term anthropogenic impacts including the effects of plant introductions. In this study, 27 plots were surveyed across three Mediterranean rivers in north-eastern Spain to explore the effects of the invader giant reed (Arundo donax) on riparian habitat features and the diversity, trophic structure, body size, and abundances of epigeal and hypogeal arthropods in riparian areas. Using pitfall traps and Berlese funnels, this study detected a significant increase in collembola abundance and a decrease in the abundance, body size and diversity of macro-arthropods at order and family levels in invaded plots compared to native stands. Invaded and un-invaded areas also differed in the taxonomical structure of arthropod assemblies but not in trophic guild proportions. However, the fact that arthropods were smaller in A. donax soils, together with the absence of particular taxa within each trophic guild or even an entire trophic group (parasitoids), suggests that food-web alterations in invaded areas cannot be discarded. Habitat features also differed between invaded and un-invaded areas with the poorest herbaceous understory and the largest leaf litter deposition and soil carbon stock observed in A. donax plots. The type of vegetation in riparian areas followed by the total native plant species richness were identified as major causal factors to changes in the abundance, diversity and composition of macro-arthropods. However, our analyses also showed that some alterations related to A. donax invasion were inconsistent across rivers, suggesting that A. donax effects may be context dependent. In conclusion, this study highlights an impoverishment of native flora and arthropod fauna in A. donax soils, and suggests major changes in riparian food webs if A. donax displaces native riparian vegetation. 相似文献
8.
Woody plant encroachment of savanna ecosystems has been related to altered disturbance regimes, mainly fire suppression and
herbivore exclusion. In contrast, neighbourhood interactions among resident and colonising woody species have received little
attention, despite their likely influence on the pattern and rate of tree establishment. We examined how resident palm trees
(Butia yatay) and established adults of two riparian forest tree species (Allophylus edulis and Sebastiania commersoniana) influenced seed arrival and seedling performance of the latter two species in a humid savanna of east-central Argentina.
Seed traps and seedlings of both riparian species were placed in herbaceous openings, and beneath palm, conspecific and heterospecific
adult trees in two unburned savanna patches, and were monitored for 2 years. Only seeds of the bird-dispersed Allophylus arrived in palm microsites, yet survival of Allophylus seedlings near adult palms was limited by animal damage through trampling and burrowing, a non-trophic mechanism of apparent
competition. Seeds of both riparian species dispersed into conspecific microsites, although adult trees selectively reduced
growth of conspecific seedlings, a pattern consistent with the “escape hypothesis”. Further, survival of Sebastiania increased in the moister Allophylus microsites, suggesting a one-way facilitative interaction between woody colonisers. Our results indicate that dispersal facilitation
by resident savanna trees may be critical to riparian species invasion after fire suppression. Distance-dependent effects
of conspecific and heterospecific adult trees could contribute to shape the subsequent dynamics of woody seedling establishment.
Overall, we show that indirect interactions can play a prominent role in savanna encroachment by non-resident woody species. 相似文献
9.
Short-term soil inorganic N pulse after experimental fire alters invasive and native annual plant production in a Mojave Desert shrubland 总被引:1,自引:0,他引:1
Todd C. Esque Jason P. Kaye Sara E. Eckert Lesley A. DeFalco C. Richard Tracy 《Oecologia》2010,164(1):253-263
Post-fire changes in desert vegetation patterns are known, but the mechanisms are poorly understood. Theory suggests that
pulse dynamics of resource availability confer advantages to invasive annual species, and that pulse timing can influence
survival and competition among species. Precipitation patterns in the American Southwest are predicted to shift toward a drier
climate, potentially altering post-fire resource availability and consequent vegetation dynamics. We quantified post-fire
inorganic N dynamics and determined how annual plants respond to soil inorganic nitrogen variability following experimental
fires in a Mojave Desert shrub community. Soil inorganic N, soil net N mineralization, and production of annual plants were
measured beneath shrubs and in interspaces during 6 months following fire. Soil inorganic N pools in burned plots were up
to 1 g m−2 greater than unburned plots for several weeks and increased under shrubs (0.5–1.0 g m−2) more than interspaces (0.1–0.2 g m−2). Soil NO3
−−N (nitrate−N) increased more and persisted longer than soil NH4
+−N (ammonium−N). Laboratory incubations simulating low soil moisture conditions, and consistent with field moisture during
the study, suggest that soil net ammonification and net nitrification were low and mostly unaffected by shrub canopy or burning.
After late season rains, and where soil inorganic N pools were elevated after fire, productivity of the predominant invasive
Schismus spp. increased and native annuals declined. Results suggest that increased N availability following wildfire can favor invasive
annuals over natives. Whether the short-term success of invasive species following fire will direct long-term species composition
changes remains to be seen, yet predicted changes in precipitation variability will likely interact with N cycling to affect
invasive annual plant dominance following wildfire. 相似文献
10.
The non-indigenous perennial grass, Arundo donax, is an aggressive invader of riparian areas throughout California and many sub-tropical regions of the world, and is hypothesized to provide poorer quality habitat for native wildlife in riparian systems. We sampled aerial and ground-dwelling insects and other terrestrial arthropods associated with Arundo, native willow vegetation (Salix spp.), and mixtures of the two vegetation types during two seasons to determine how Arundo influences invertebrate composition in a low gradient stream in central California. The total number of organisms, total biomass and taxonomic richness of aerial invertebrates associated with native vegetation was approximately twice that associated with Arundo vegetation, while mixed vegetation supported intermediate arthropod levels. Shannon-Weaver (Weiner) diversity associated with native vegetation stands was also higher than that of Arundo vegetation. Ground-dwelling assemblages did not show differences as great as aerial assemblages which are more critical to foraging avian species. These results indicate that vegetation type is a significant factor reducing the abundance and diversity of invertebrates in this, and presumably in many other riparian ecosystems where this invasive species has become a dominant component. Arundo invasion changes the vegetation structure of riparian zones and in turn, may increasingly jeopardize its habitat value for birds and other wildlife whose diets are largely composed of insects found in native riparian vegetation. 相似文献
11.
Francesco Fabbrini Riccardo Ludovisi Omar Alasia Jaume Flexas Cyril Douthe Miquel Ribas Carb Paul Robson Gail Taylor Giuseppe Scarascia‐Mugnozza Joost J. B. Keurentjes Antoine Harfouche 《Global Change Biology Bioenergy》2019,11(1):152-170
Giant reed (Arundo donax L.) is a perennial rhizomatous grass, which has attracted great attention as a potential lignocellulosic feedstock for bioethanol production due to high biomass yield in marginal land areas, high polysaccharide content and low inhibitor levels in microbial fermentations. However, little is known about the trait variation that is available across a broad ecotypic panel of A. donax nor the traits that contribute most significantly to yield and growth in drought prone environments. A collection of 82 ecotypes of A. donax sampled across the Mediterranean basin was planted in a common garden experimental field in Savigliano, Italy. We analysed the collection using 367 clumps representing replicate plantings of 82 ecotypes for variation in 21 traits important for biomass accumulation and to identify the particular set of ecotypes with the most promising potential for biomass production. We measured morpho‐physiological, phenological and biomass traits and analysed causal relationships between traits and productivity characteristics assessed at leaf and canopy levels. The results identified differences among the 82 ecotypes for all studied traits: those showing the highest level of variability included stomatal resistance, stem density (StN), stem dry mass (StDM) and total biomass production (TotDM). Multiple regression analysis revealed that leaf area index, StDM, StN, number of nodes per stem, stem height and diameter were the most significant predictors of TotDM and the most important early selection criteria for bioenergy production from A. donax. These traits were used in a hierarchical cluster analysis to identify groups of similar ecotypes, and a selection was made of promising ecotypes for multiyear and multisite testing for biomass production. Heritability estimates were significant for all traits. The potential of this ecotype collection as a resource for studies of germplasm diversity and for the analysis of traits underpinning high productivity of A. donax is highlighted. 相似文献
12.
E. Cortés J.A. Goolsby P.J. Moran M.A. Marcos-García 《Biocontrol Science and Technology》2011,21(5):535-545
The effect of feeding by the armored scale, Rhizaspidiotus donacis (Leonardi, 1920) (Hemiptera: Diaspididae) on the growth of the plant Arundo donax L. (Poaceae) was evaluated under field conditions in its native range. The study was designed to evaluate the impact of R. donacis, a candidate agent for biological control of A. donax which is invasive in arid riparian ecosystems of the Southwestern USA and Mexico. The study was carried out at five A. donax sites in the Province of Alicante, Spain, differing in altitude and climate. At each site, 30 infested lateral shoots were selected and 15 were randomly treated monthly with imidacloprid insecticide. Shoot lengths were measured monthly over a 1-year period in a comparative growth analysis. Shoots infested with R. donacis had an over 2-fold reduced growth rate as compared to treated shoots. Growth of shoots varied by site, and the effect of R. donacis on growth was most pronounced in the late spring, when mature females produced first instar scale crawlers. The impact of R. donacis on A. donax growth under field conditions in the native range, combined with its narrow host specificity, indicate that R. donacis is a promising candidate for biological control of A. donax in North America and other areas invaded by this weed. 相似文献
13.
John Goolsby Elena Cortés Mendoza Patrick Moran John Adamczyk M. Ángeles Marcos García Alan Kirk 《Biocontrol Science and Technology》2013,23(5):499-506
A pre-release evaluation of survival and fecundity of the arundo scale, Rhizaspidiotus donacis, was conducted on three invasive genotypes of the riparian weed, Arundo donax. The three A. donax genotypes were collected from Laredo, Austin and Balmorhea, TX, which represented the majority of the genotypic diversity found in Texas watersheds. Although R. donacis developed on all three genotypes of the plant, the Austin A. donax genotype, followed by the Laredo genotype, were the most suitable in terms of the size of first-generation immature and adult scale populations that developed after crawler release. Both the Laredo and Austin genotypes of A. donax are likely to be of Spanish origin and are close genetic matches with scale's original host plant genotype in Alicante, Spain. In comparison, survival was lowest on the phylogenetically distant genotype of A. donax from Balmorhea, TX. Although the population size of settled, immature second-generation scales varied in a manner similar to that of the first generation, the fecundity of isolated first-generation females was not significantly different across the three plant genotypes, suggesting that R. donacis is not a genotype specialist in terms of nutrient assimilation for reproduction. Rather, differences in genotype suitability affect rates of success of crawler settling. These results indicate that selection of scale genotype from the native range may have a moderate influence on the success of R. donacis and ultimately the biological control programme. 相似文献
14.
Michael L. Scott Pamela L. Nagler Edward P. Glenn Carlos Valdes-Casillas Joseph A. Erker Elizabeth W. Reynolds Patrick B. Shafroth Euduardo Gomez-Limon Cory L. Jones 《Biodiversity and Conservation》2009,18(2):247-269
Conservation of forested riparian ecosystems is of international concern. Relatively little is known of the structure, composition,
diversity, and extent of riparian ecosystems in Mexico. We used high- and low-resolution satellite imagery from 2000 to 2006,
and ground-based sampling in 2006, to assess the spatial pattern, extent, and woody plant composition of riparian forests
across a range of spatial scales for the state of Sonora, Mexico. For all 3rd and higher order streams, river bottomlands
with riparian forests occupied a total area of 2,301 km2. Where forested bottomlands remained, on average, 34% of the area had been converted to agriculture while 39% remained forested.
We estimated that the total area of riparian forest along the principal streams was 897 km2. Including fencerow trees, the total forested riparian area was 944 km2, or 0.5% of the total land area of Sonora. Ground-based sampling of woody riparian vegetation consisted of 92, 50 m radius
circular plots. About 79 woody plant species were noted. The most important tree species, based on cover and frequency, were
willow species Salix spp. (primarily S. goodingii and S. bonplandiana), mesquite species Prosopis spp. (primarily P. velutina), and Fremont cottonwood Populus fremontii. Woody riparian taxa at the reach scale showed a trend of increasing diversity from north to south within Sonora. Species
richness was greatest in the willow-bald cypress Taxodium distichum var. mexicanum—Mexican cottonwood P. mexicana subsp. dimorphia ecosystem. The non-native tamarisk Tamarix spp. was rare, occurring at just three study reaches. Relatively natural stream flow patterns and fluvial disturbance regimes
likely limit its establishment and spread. 相似文献
15.
In southern California, wildfire is a ubiquitous agent shaping plant communities. Although fire impacts have been widely studied
in chaparral-covered uplands, few data are available regarding fire and riparian vegetation. This study provides an example
of the impact of a severe fire on riparian habitat. Plant species found in southern California gallery forests are typically
adapted to maintaining populations following flood disturbances; we seek to determine whether structural and compositional
changes following fire here demonstrate a similar quasi-equilibrium response. We sampled 65 quadrats on 11 transects along
two streams in the Los Padres National Forest to characterize tree species size–class distributions before and after the 2002
Wolf Fire. We tested whether species exhibited differential patterns of survivorship and regeneration following the fire,
and also tested for spatial variability in mortality within the floodplain. Alnus rhombifolia dominated the pre-fire forest, but experienced severe mortality in the fire and showed very limited resprouting after 3 years.
Other prominent taxa (Populus, Salix, Quercus spp.) also lost considerable standing basal area, but had substantially greater rates of resprouting, resulting in a dramatically
altered post-fire vegetation composition and structure. Fire impacts did not vary with landform position, leading to a distinctive
homogenizing disturbance that contrasts with the spatially zoned and relatively stabilizing compositional influence that flood
events have in this same riparian setting. 相似文献
16.
Abstract: We studied breeding populations of 2 coexisting ground-nesting birds, the red-faced warbler (Cardellina rubrifrons) and yellow-eyed junco (Junco phaeonotus), in high-elevation (>2,000 m) forested drainages of the Santa Catalina Mountains, Arizona, USA. From 2004 to 2005, we 1) estimated density and nesting success of breeding populations of red-faced warblers and yellow-eyed juncos, 2) identified nest-site characteristics for each species (i.e., used sites vs. random plots), 3) compared nest-site characteristics between the 2 species, and 4) examined effects of a recent (2003) wildfire on distribution of nests of both species. In addition, we estimated the areal extent of montane riparian forest (the preferred breeding habitat of both species) within high-elevation forests of the Santa Catalina Mountains. We found that red-faced warblers and yellow-eyed juncos were the 2 most common ground-nesting birds within our study area with an average density of 2.4 and 1.4 singing males/ha, respectively, along drainage bottoms. Compared to random plots, most red-faced warbler and yellow-eyed junco nests were located close (≤30 m) to drainage bottoms within a strip of montane riparian forest characterized by abundant brush, small woody debris, ferns, and forbs (both species), high number and diversity of saplings and small trees (red-faced warblers), and abundant shrubs and downed logs and less canopy cover (yellow-eyed juncos). Although both species nested in close proximity within montane riparian forest, nest-site characteristics differed between the 2 species, especially at finer spatial scales. For example, most yellow-eyed juncos nested adjacent to grass (principally Muhlenbergia spp.), whereas red-faced warblers nested adjacent to a variety of plant species, including grass, bigtooth maple (Acer grandidentatum), white fir (Abies concolor), and Douglas-fir (Pseudotsuga menziesii). Both red-faced warblers and yellow-eyed juncos avoided nesting in areas burned during a recent wildfire. In addition, nesting success was low for red-faced warblers (13%) and yellow-eyed juncos (19%) following the wildfire, suggesting an indirect negative effect of fire on breeding populations in the short-term. Montane riparian forest appears to provide important breeding habitat for red-faced warblers and yellow-eyed juncos. However, little research or conservation planning has been directed toward montane riparian forest in the region, even though this forest type is limited in its areal extent (<11% of high-elevation forest in the Santa Catalina Mountains) and increasingly threatened by disturbance. Results from our study can be used to facilitate the management and conservation of breeding populations of red-faced warblers and yellow-eyed juncos in high-elevation forests of the southwestern United States. 相似文献
17.
Abstract. Grass and herb cover, and woody plant densities were measured on 25 native and 25 exotic grassland plots in southeastern Arizona between 1984 and 1990. At least 40 yr previously, the exotic plots had been seeded with two species of lovegrasses (Eragrostis spp.) native to southern Africa. A 1987 wildfire burned 11 native and 11 exotic plots. The fire reduced cover of both native and African grasses for two post-fire growing seasons. Herb cover as a whole increased after the fire for 2 yr, although there were important differences among species. One of two dominant shrubs (Haplopappus tenuisectus) was killed by the fire, while the other (Baccharis pteronioides) was little affected. Mesquite trees (Prosopis juliflora) were killed to the ground by the fire, but 62 of 66 trees had re-sprouted to an average 48% of pre-burn height by 1990. Native and exotic grasses appeared equally tolerant of fire, probably because both evolved in fire-type ecosystems. There was no evidence that fire can be used to permanently restore the diverse native flora to species-poor plantations of the South African exotics. 相似文献
18.
Madhusudan P. Srinivasan 《Biological invasions》2012,14(5):1009-1028
In recent years, invasion of native grasslands by exotic woody plants has been recognized as a global problem with multiple
adverse ecological and socio-economic consequences. Reasons for such expansions are numerous, including fire suppression.
An important example of this problem is the native montane grassland in the Nilgiris of the Western Ghats in India, a biodiversity
hotspot threatened by invasion of multiple woody species. In this study, the impacts of the highly invasive, nitrogen fixing
exotic shrub Cytisus scoparius (Scotch broom) on the grassland community and ecosystem function have been quantified and the role of fire as a potential
management tool evaluated. I established paired plots in uninvaded and broom-invaded grasslands that were either unburned
or burned by an unplanned wildfire event. Invasion negatively impacted the grassland community structure and composition,
favoring shade tolerant and weedy native plants, but did not greatly alter ecosystem function. Burning broom patches to eliminate
the stands resulted in lower soil moisture and nitrogen levels 18 months after the fire. Yet, there were no notable fire effects
on the grassland communities or ecosystem properties. Taken together, the results suggest that fire might be an effective
tool for broom control. At the end of the study period burned-broom communities did not become more similar to uninvaded-grasslands;
presumably the recovery process may be slow without additional management intervention. 相似文献
19.
M. Marshall A. T. Vacek P. J. Moran A. A. Kirk E. Cortes Mendoza 《Biocontrol Science and Technology》2018,28(8):772-785
Tetramesa romana is a biological control agent of the giant reed, Arundo donax (Poaceae: Arundinoideae), which is an invasive weed in the riparian habitats of the Rio Grande Basin of Texas, the southwestern U.S.A. and northern Mexico. Field evaluations were conducted in the native range of T. romana in Mediterranean Europe and in the introduced ranges of Texas, California, and South Africa to compare densities of the wasp. Population densities and percentage parasitism levels for the 2017 year are compared to meteorological variables (average temperature, precipitation, and heat units). In the introduced ranges of Texas (intentional) and South Africa (adventive) T. romana population densities were 39 and 10-fold higher than in the native range, respectively. Percentage parasitism of T. romana in Texas and in the native range of Thessaloniki, Greece were 2.0% and 34.3%, respectively. Annual heat unit accumulation was 1.3–2.7-fold higher at Texas sites than at other introduced or native sites, and heat units were positively associated with exit hole counts at introduced sites. Annual precipitation was 2-fold higher at Texas and South African sites than in California and the native range sites. Favourable weather conditions and reduced parasitism in Texas along the Rio Grande, as compared to the native range, allows T. romana to reach higher population levels and cause considerable damage to A. donax. 相似文献
20.
Arundo donax L. is a rhizomatous perennial, asexually reproducing species that has invaded riparian habitats throughout Mediterranean
climate zones. This research evaluated ramet demography of A. donax in two California riparian communities that differed in nitrogen availability. Quadrats were established along 100 m transects
at each site and oriented across the advancing fronts of established populations. Morphology and phenology were assessed monthly
over 1 year for calculation of demographic parameters and rhizomes were excavated and mapped at the end of the experiment.
A. donax exhibited seasonal patterns of recruitment but no dormancy at the high nitrogen site, while at the low nitrogen site no recruitment
occurred in the winter and maximum recruitment was delayed by a month relative to the high nitrogen site. Spread of A. donax was delayed until spring and lower overall in the low nitrogen site compared to the high nitrogen site, where lower initial
density, greater production of shoots, and higher linear and areal addition indicated that this population was spreading more
rapidly. Temperature and precipitation influenced seasonality and amount of recruitment of A. donax in this study. Several recently established, immature clumps were found in gaps at the low nitrogen site, likely due to flood-mediated
dispersal of propagules. Recruitment in these clumps occurred from shoot buds, in contrast to the mature populations that
reproduced from rhizome buds. Ecologically based management strategies for A. donax and other exotic species should account for differences such as those described here and be tailored to local conditions
where the species occurs. 相似文献