Rangeland Monitoring and Invasive Weeds

One of the serious biological obstacles that must be addressed in any comprehensive revision of rangeland ecological condition assessment is what to do with sites dominated by exotic self-invasive species. In certain cases such species have truncated succession so that with a bare minimum of disturbance, the sites will never return to dominance by native perennial species. Are such sites destined to remain always in what is defined as "poor" ecological condition. Many communities dominated by exotic annuals are closed to the recruitment of seedlings of native perennial species. At the same time the communities are open to invasion by other introduced species. Should susceptibility to future invasions be a criteria in assessing the ecological condition of rangeland communities. The sustainability of communities dominated by exotic invasive species is assessing the ecological condition of such communities. Deviation from the plant community concepts of range condition and trend judgement involves setting new benchmark standards. This is an endeavor fraught with many perils.     

What criteria are relevant for predicting the invasive capacity of a new agricultural weed? The case of invasive American species in France

In Europe, exotic species are assessed for their potential threat only after they have already become weeds. To test hypotheses underlying risk assessment procedures, 274 North and South American exotic species naturalized in France were compared to differentiate environmental from agricultural weeds and to characterize weeds of several crops. Most agricultural exotic weeds belonged to the Asteraceae and the Poaceae, but proportionally to the total number of invasive species from a family the most successful families were the Amaranthaceae, Euphorbiaceae and Poaceae. Weed status in North and South America was the best predictor of agricultural weed status in France, and a pre-1900 date of introduction was associated with a greater likelihood of having become a major weed. The characteristics of 78 species present in field crops were examined in relation to management practices. In annual crops, the life-cycle compatibility of weeds appeared to be the main factor of selection. Exotic species differed in their C4 photosynthesis pathway in maize and rice. In vineyards, many ecological strategies are possible because the habitat is heterogeneous. Intrageneric comparison of exotic and native species showed a superior relative growth rate and higher biomass production under nutrient-rich conditions for exotics. However, it is still difficult to find a predictive function that fits well with all observed cases of weed invasion.     

Fluctuating resources, disturbance and plant strategies:diverse mechanisms underlying plant invasions

This paper examines the hypothesis that non-native plant invasions are related to fluctuating resource availability as proposed by Davis et al.(2000).I measured relative functional responses of both invasive and native plants to changed resource availability due to nutrient enrichment and rainfall,and to increased disturbance.Data are presented from studies in two contrasting ecosystems.First is a series of glasshouse and field experiments on the invader Hieracium lepidulum and associated invasive and native species in subalpine temperate New Zealand.Second is a field study of invasive and native plant responses to altered disturbance regimes and rainfall from tropical savannas of north eastern Australia.Invaders responded differently from native species to changes in resource availability in both subalpine and tropical studies.However,invaders differed among themselves showing that different species exploit different functional niches to invade their respective habitats.These findings contribute to the contention that the fluctuating resource hypothesis does not provide a universal explanation for plant invasions.The diverse functional responses to increased resource availability among invaders in this and previous studies suggest that the cause of invasion depends on unique combinations of habitat and functional attributes of invaders and native assemblages.Such findings imply that universal predictions of what will happen under climate change scenarios across the globe will be difficult to make.     

Adaptation of native syrphid flies to new exotic plant (Impatiens spp.)-aphidant associations in Central Europe (Dipt., Syrphidae; Hom., Aphididae; Hym., Formicidae)

Impatiens parviflora andI. glandulifera, two invasive touchme-not species of exotic origin were found to be associated with two aphid groups in Central Europe: a) Exotic species subsequently following their invasive plant hosts (Impatientinum asiaticum Nevsky), b) native species secondarily adapted to the new exotic hosts (Aphis fabae cirsiiacanthoidis Scop.). The species number (listed) of associated syrphid flies in the newly developed guilds was rather high, consisting of broadly oligophagous species. The plant phenology and adaptation of the aphids have resulted in associations which apparently represent seasonally significant sources of prey, their importance apparently increasing with the decreasing season. Antattendance was determined in both aphid species, and no adverse interference with the preying syrphid larvae was observed. In spite of an overall classification of the target plants as expansive weeds, they are classified positively as contributing to the enhancement of syrphid fly populations in the biocorridors in the cultivated landscape.     

北京市湿地入侵植物群落与本地植物群落的生物多样性比较

为明确外来入侵植物对本地湿地植物多样性的影响，在北京市湿地选择23个样地共245个样方进行物种多样性调查，并从不同植物性状数据库获取样方中所有植物的株高、叶长、叶宽、叶面积和比叶面积等10个功能性状数据，对比分析入侵群落与本地群落的物种多样性、系统发育多样性和功能多样性特征。结果显示，在北京市湿地共记录到26种外来入侵草本植物，隶属10科19属，其中，菊科外来入侵植物种类最多，有10种。除比叶面积、叶片碳含量和株高的系统发育信号显著外，其余7种植物功能性状的系统发育信号均不显著，表明大多数功能性状未表现出系统发育保守性。入侵群落所有物种的物种多样性指标Shannon-Wiener多样性指数、物种丰富度指数和Simpson优势度指数以及系统发育多样性指标谱系多样性和平均最近谱系发育距离均显著高于本地群落和入侵群落本地物种，而入侵群落本地物种的功能分散指数和Rao''Q二次熵指数均显著高于本地群落，表明外来物种入侵改变了湿地植物的生物多样性，且外来物种入侵后群落谱系多样性趋于发散，说明与本地植物亲缘关系越远的入侵物种越容易在湿地群落中建立种群，符合达尔文归化假说。     

内蒙古荒漠地区丛枝菌根植物的初步研究

本文对内蒙古荒漠建群及优势植物的丛枝菌根共生状况进行了调查。在观察的16科76种植物中,被丛枝菌根真菌侵染的植物有61(占79. 8% )种;其中多年生草本植物被丛枝菌根真菌侵染的比例较高,占94. 46%;而一年生和二年生的草本植物的比例仅65%。须根系植物中菌根植物约占91. 3%,高于直根系(75. 5% )。古地中海孑遗种四合木(Tetraenamongolica)、棉刺(Potaniniamongolica)、沙冬青(Ammopiptanthusmongolicus)和强旱生植物半日花(Helianthemumsoongoricum)有一定的菌根侵染。本地区野生植物的丛枝菌根形态结构类型多数为Arum类型,占83. 6%;而Paris类型少,只占3. 3%。丛枝菌根结构类型与植物的生活型、根系类型和侵染率无关。     

Patterns of loss of biodiversity associated with invasion by Chrysanthemoides monilifera subsp. monilifera (boneseed) across a large geographic region

To investigate the impact of invasion by Chrysanthemoides monilifera ssp. monilifera (boneseed) on plant communities, sites that were invaded and uninvaded were surveyed across Tasmania, South Australia and Victoria, Australia. Above‐ground cover abundance was estimated and samples of the seed bank from invaded and uninvaded sites in each state were collected and germinated in the glasshouse. We compared species richness and composition between invaded and uninvaded sites for both above‐ground and below‐ground samples. Across this broad geographic area, C. monilifera invaded sites had 25% fewer species than uninvaded sites and twice as many exotic species. Most growth forms showed reduced richness in invaded sites. There were no differences in the composition of native species communities between invaded and uninvaded sites in most regions, except South Australia. The composition of the seed bank differed from the above‐ground vegetation, but was similar within each state. Herbs and grasses were most abundant. The species composition of the seed bank was different in invaded sites only in Victoria, suggesting that invasion may negatively influence the capacity of the seed bank to restore vegetation in some areas. However, the underlying mechanisms for the observed patterns were not tested in this study. The capacity of all sites to regenerate effectively from the seed bank was limited and, in order to ensure the conservation of biodiversity into the future, monitoring of species richness at smaller scales, particularly those where management of C. monilifera has occurred, will be needed to ensure management can facilitate the establishment of missing species. This study suggests that C. monilifera impacts a range of functional groups and different species across its distribution and is therefore non‐selective in how it influences changes in communities.     

The role of community composition in grassland response to two methods of exotic forb removal

Invasive plants can seriously threaten biodiversity and ecosystem function. Thus, controlling the abundance and mitigating the deleterious effects of invasive plants is imperative. The effectiveness of removal methods could vary based on potential damage to non‐target species and on the ecological context of invasion. For example, species‐poor communities might benefit disproportionately from invasive removal because they tend to be more heavily invaded than species‐rich communities. In this study, we tested the efficacy of two common methods of invasive plant control, hand removal and 2,4‐D herbicide application, against the invasive forb, Galium verum. We further tested whether the community response to G. verum removal varied across communities that differed in native grass richness (one, three or six species) and composition. Grass diversity did not interact with G. verum removal to influence any response. Instead, hand removal and herbicide application each reduced G. verum stem density by >50% relative to controls. Furthermore, hand removal of G. verum increased species richness by 25% relative to controls and herbicide‐sprayed plots. Despite this benefit, hand removal is labour‐intensive and impractical for large areas. These results also suggest that applying herbicide may control G. verum spread without substantially reducing forb diversity in invaded tallgrass prairie. Thus, herbicide application may be most suitable for grasslands with low native forb diversity, especially in managed grasslands and pastures where maintaining native forb diversity is a lower priority than maintaining high grass productivity.     

Introductions of non-native plant pathogens into Great Britain, 1970–2004

An analysis of records of plant pathogens first identified in Great Britain from 1970 to 2004 (inclusive) was undertaken to determine the numbers of new species that have become established over time. Results show that the numbers of newly recorded pathogens have not varied significantly. Of the 234 pathogens recorded for the first time between 1970 and 2004, 157 were fungi, 27 were oomycetes, 26 were viruses, 23 were bacteria, and one was a phytoplasma. Approximately 53% of pathogens were found on ornamental crops, 16% on horticultural crops, 15% on wild native species, 12% on agricultural crops, 2% on pasture plants and 2% on exotic forestry tree species. Where the origin of introductions was known or strongly suspected, 47% came from the Netherlands. About 38% of newly recorded pathogens with information on the location of first record were discovered in the South East region of England. Plant Pathologists regarded 19% of all new pathogens as important because of actual or potential economic/environmental losses. The results indicate that the numbers of new or important pathogens establishing in recent years are not increasing and that most new findings are associated with ornamental plants.     

Vegetation of semi-stable rangeland dunes of the Navajo Nation,Southwestern USA

Dune destabilization and increased mobility is a worldwide issue causing ecological, economic, and health problems for the inhabitants of areas with extensive dune fields. Dunes cover nearly a third of the Navajo Nation within the Colorado Plateau of southwestern USA. There, higher temperatures and prolonged drought beginning in 1996 have produced significant increases in dune mobility. Vegetation plays an important role in dune stabilization, but there are few studies of the plants of the aeolian surfaces of this region. We examined plant species and their attributes within a moderately vegetated dune field of the Navajo Nation to understand the types and characteristics of plants that stabilize rangeland dunes. These dunes supported a low cover of mixed grass-scrubland with fifty-two perennial and annual species including extensive occurrence of non-native annual Salsola spp. Perennial grass richness and shrub cover were positively associated with increased soil sand composition. Taprooted shrubs were more common on sandier substrates. Most dominant grasses had C4 photosynthesis, suggestive of higher water-use efficiencies and growth advantage in warm arid environments. Plant cover was commonly below the threshold of dune stabilization. Increasing sand movement with continued aridity will select for plants adapted to burial, deflation, and abrasion. The study indicates plants tolerant of increased sand mobility and burial but more investigation is needed to identify the plants adapted to establish and regenerate under these conditions. In addition, the role of Salsola spp. in promoting decline of perennial grasses and shrubs needs clarification.     

Seed rain and soil seed bank compensatory roles on Nassella tenuis (Phil.) Barkworth seedling recruitment in ungrazed and grazed sites

In semi-arid lands, vegetation is distributed in shrub patches immersed in a less vegetated interpatch matrix. Grazing affects perennial grass seed bank through a decrease in seed rain and an increase in seed predation and soil compaction. Nevertheless, some species with anchorage mechanisms in their seeds might overcome this, such as Nassella tenuis (Phil.) Barkworth. This is an important species in grazing paddocks because it has an intermediate palatability and its relatively tolerant to grazing. These characteristics allow N. tenuis to increase its abundance in grazed sites. Our objective was to assess how grazing affects the key palatable species from seeds to seedlings: i.e., seed rain, soil seed bank, and seedling recruitment in different microsites along a windward-leeward transect across shrub canopy. We hypothesized that: (1) the negative effects of grazing on N. tenuis fructification are reflected in its seed rain, soil seed bank, and seedling recruitment, especially in interpatches; (2) Nassella tenuis seed rain reduction, soil compaction by cattle in grazed sites, and removal of seeds by wind decrease its soil seed bank, especially in microsites exposed to the predominant wind; and (3) the decrease in N. tenuis soil seed bank and cover increase in annual species in grazed sites have negative effects on its seedling recruitment, especially in microsites exposed to predominant wind. We placed seed traps, collected soil samples, and monitored seedling recruitment in different locations around shrub canopy to address our hypotheses. Also, we established a manipulative experiment in which we sow N. tenuis seeds and followed its recruitment in different microsites. We compared the seed rain, soil seed bank, natural seedling recruitment, and sown seeds recruitment of N. tenuis between grazed and ungrazed sites. We analyzed differences between microsites along a windward-leeward transect across shrubs patches. Seed rain and soil seed bank had the same density in patches and interpatches both in ungrazed and grazed sites. But seed rain was higher, and soil seed bank was lower in ungrazed sites than in grazed sites. Almost all under-canopy microsites showed greater soil seed bank abundance and natural seedling recruitment in ungrazed sites. Sown seeds recruitment was the same between grazed and ungrazed sites, but it showed protective effects of shrubs in leeward microsites under grazed sites. As a conclusion, seed rain and soil seed bank are complementary under grazed sites.     

Ecological biomass allocation strategies in plant species with different life forms in a cold desert,China

Biomass allocation patterns among plant species are related to their adaptive ecological strategies. Ephemeral, ephemeroid and annual plant life forms represent three typical growth strategies of plants that grow in autumn and early spring in the cold deserts of China. These plants play an important role in reducing wind velocity in the desert areas. However, despite numerous studies, the strategies of biomass allocation among plant species with these three life forms remain contentious. In this study, we conducted a preliminary quadrat study during 2014-2016 in the southern part of the Gurbantunggut Desert, China, to investigate the allocation patterns of above-ground biomass (AGB) and below-ground biomass (BGB) at the individual level in 17 ephemeral, 3 ephemeroid and 4 annual plant species. Since ephemeral plants can germinate in autumn, we also compared biomass allocation patterns between plants that germinated in autumn 2015 and spring 2016 for 4 common ephemeral species. The healthy mature individual plants of each species were sampled and the AGB, BGB, total biomass (TB), leaf mass ratio (LMR) and root/shoot ratio (R/S) were calculated for 201 sample quadrats in the study area. We also studied the relationships between AGB and BGB of plants with the three different life forms (ephemeral, ephemeroid and annual). The mean AGB values of ephemeral, ephemeroid and annual plants were 0.806, 3.759 and 1.546 g/plant, respectively, and the mean BGB values were 0.106, 4.996 and 0.166 g/plant, respectively. The mean R/S value was significantly higher in ephemeroid plants (1.675) than in ephemeral (0.154) and annual (0.147) plants. The mean LMR was the highest in annual plants, followed by ephemeroid plants and ephemeral plants, reflecting the fact that annual plants allocate more biomass to leaves, associated with their longer life span. Biomass of ephemeral plants that germinated in autumn was significantly higher than those of corresponding plants that germinated in spring in terms of AGB, BGB and TB. However, the R/S value was similar in plants that germinated in autumn and spring. The slope of regression relationship between AGB and BGB differed significantly among the three plant life forms. These results support different biomass allocation hypotheses. Specifically, at the individual level, the AGB and BGB partitioning supports the allometric hypothesis for ephemeroid and annual plants and the isometric hypothesis for ephemeral plants.     

Phytogeography of the northeastern coast of the Caspian Sea： native flora and recent colonizations

The northeastern coast of the Caspian Sea is one of the youngest territories for plant colonization in Kazakhstan,and the flora of the most recent portion of this coastal area,the New Caspian marine plain,was chosen to study phytogeographical characteristics of plant species,especially as related to alien origin and invasive potential.Because of the recent formation of this flora,I expected that a large proportion of the species may be alien and invasive.After compiling a comprehensive species list from previous research,I identified the taxonomic,life form,ecological,and geographical structures of the flora.The area belongs to the northern type of deserts with continental climate and low annual precipitation.Taxonomic and life form structures show that the flora is specific to Central Asian deserts.Ecological structure demonstrates a high percentage of halophytes,which resulted from their adaptation to soil salinity and shallow ground waters that occur throughout the study area.Geoelements of the flora indicate allochtonous properties of the flora(i.e.species derived from areas outside the study area) with a low proportion of native(Caspian) plants.Alien species are estimated to comprise 12%-19% of the flora.Although some species have invasive features,severe arid environmental conditions and high salinity of soils and ground waters decrease invasive capacity of exotic plants.However,a threat of expansion of potentially invasive plants exists in the New Caspian marine plain due to the fast growth of anthropogenic habitats associated with recent oil developments.     

外来植物有害生物入侵及其对策

分析了外来植物有害生物传入我国蔓延危害的主要特点、发展态势及潜在风险.我国防范外来植物有害生物入侵,主要存在管理体制、法规制度、检疫手段和技术、人员素质和资金投入等诸方面问题.加强植物检疫职能、整合检疫管理力量、构建快速反应机制、确保安全服务贸易等是有效防范外来生物入侵的重要组织步骤;完善植物检疫立法和管理体制、重视技术标准研制和采用国际标准惯例、加快有害生物风险分析和重新确定检疫性有害生物名录、改进植物检疫检验手段和技术、加强非疫区和非疫生产基地建设、设立植物检疫专项基金、加强国际合作与交流等尤为迫切.     

棉田黄萎病菌致病型结构初步研究

棉花黄萎病是棉花生产中的主要病害之一,广泛分布于世界各产棉国.控制该病的猖獗危害,已成为棉花生产可持续发展的主要问题[1].利用不同抗性的棉花品种对棉黄萎病菌的选择作用,从棉田中分离获得不同的黄萎病菌菌系,在温室中采用2个抗病性差异明显的品种对其致病力进行测定,以明确同一块棉田是否存在不同致病力菌系.     

北疆棉田非作物生境食蚜蝇种群消长动态

2016—2017年，利用扫网法系统调查了北疆棉田周边的非作物生境中9科13种常见植物上的食蚜蝇种群发生情况。研究发现，食蚜蝇种群密度在不同植物上有显著差异，种群发生高峰主要集中在各种植物开花期，种群消长还与这些植物上的蚜虫发生有明显跟随关系。5—6月，食蚜蝇在大部分植物上都有发生，但主要集中于新疆大蒜芥和罗布麻等；7—8月，在碱蓬、大麻、顶羽菊等上种群密度高；9月，主要在甘草、顶羽菊、罗布麻等上。本研究为今后充分利用棉田周边非作物生境，提升对食蚜蝇种群保育功能及棉花害虫生态控制水平提供了科学依据。     

Domestication of plants for sustainable agriculture in drylands: Experience from the Negev Desert

With globalization in the last century, introduction of exotic plant species for commercial use has become more accessible. Such attempts may involve extreme land changes. We stress that domestication of native species should be preferred to the introduction of exotic species. We took the initial steps in domesticating several species by examining commercial uses and studying aspects of plant physiology. The following desert plants were considered: Bassia indica, for salt phytoremediation and for livestock feed; Commiphora gileadensis, as an agent against cancer cells; Artemisia sieberi and A. judaica, as plants with allopathic traits; Ficus palmate, as a stand for fig plantation; Balanites aegyptiaca, as a medicinal plant and for other uses; Portulaca oleracea and Scorzonera judaica, as food crops with added values; and Pistacia atlantica, as rootstock for P. vera.     

Is bi-seasonal germination an optimal choice for an ephemeral plant living in a cold desert?

Research on germination strategies has been proposed as a tool for understanding the evolutionary patterns of plant species living in extreme climate conditions. Previous research has concentrated on spring-germinated plants, while there has been little investigation on the ecological significance of ephemeral plants that germinate in both autumn and spring. The biological characteristics and life history strategies of autumn-and spring-germinated plants of Hypecoum erectum L. that belongs to Hypecoum in Papaveraceae family in the southern part of the Gurbantunggut Desert, China, were investigated from 2016 to 2017. Results showed that:(1) the interval from seedling emergence to the end of the life cycle in autumn-germinated plants(202–208 d) was significantly longer than that in spring-germinated plants(53–65 d);(2) the height, crown, principal axis and the number of leaves of autumn-germinated plants were much greater than those of spring-germinated plants;(3) allocation of dry mass to reproduction was 30.24%(±2.41%) and 10.12%(±0.68%) in autumn-and spring-germinated plants, respectively. Autumn-germinated seedlings of H. erectum had an advantage in avoiding the competition between annual and perennial herbs that had longer periods of vegetative growth.Spring-germinated seedlings need to ensure the survival of population when only a fewer autumn-germinated seedlings successfully overwinter. In an unpredictable environment, the germination strategy of bet hedging not only utilizes the resources and reduces the competition intensity in offspring,but also ensures the survival of the plant population.     

Outbreak of a new alien invasive plant Salvia reflexa in north‐east China

The establishment of invasive species is widely recognised as a pivotal issue in the preservation of biodiversity. Salvia reflexa, a species native to the south‐central United States and Mexico, has been widely introduced in Argentina, Australia, New Zealand and Japan. In China, the first population of this plant was found growing adjacent to a grain depot in Shahai village, Jianping County, Liaoning Province, on 25 July 2007. Since the grain depot imported foodstuffs from regions where the plant is native, we infer that S. reflexa was introduced into China via imported foodstuff in the early to mid‐2000s. Based on field observations, at least seven populations of this plant were observed in north‐east China. The plants displayed vigorous growth in midsummer and produced prolific seeds to overcome the cold environment in winter. Salvia reflexa occurred in both dense monocultures and in mixed stands with native plants. In order to validate a system for recognising and categorising non‐native plants in China, the Australian Weed Risk Assessment system was used to assess the invasiveness status of 19 exotic and 16 native plants in north‐east China. Salvia reflexa exhibited a high score of 10, suggesting it is a potentially pernicious alien invasive plant. Although the current distribution of S. reflexa is restricted to Liaoning province and thus far has limited impact on local environments, local regulatory authorities should pay close attention to this plant and take measures to stop its expansion. This is the first time that an invasive plant from the Lamiaceae (mint family) has been documented from cold environments in China.     

Predicting weed distribution at the regional scale in the native range: environmental determinants and biocontrol implications of Phyla nodiflora (Verbenaceae)

Alien plants produce severe environmental and economic losses in the territories they invade. Modelling the spatial distribution of alien species as a function of the environment in the native range has therefore become an essential first step in the struggle against invasions. Phyla nodiflora var. minor is a fast‐growing perennial herb native to South America that has spread through three continents, where it poses a major threat to biodiversity and significantly impacts on conservation and grazing systems, mainly in riparian areas. To assess the distribution of native Argentine populations of P. nodiflora as a function of the environment, we conducted long‐term roadside surveys and associated the occurrence of the plant with climatic, geographical, demographical and vegetation cover variables in a generalised linear mixed model. The plant was recorded in 230 of 431 sites, mostly east of 66°W and north of 39°S. According to the best model, which predicted the data 58% better than random assignment, its occurrence was associated with temperature variables (mean annual values and daytime range) and relative humidity. Based on these associations, we generated a presence probability map for the occurrence of P. nodiflora in southern South America. Understanding the environmental determinants of the distribution of weeds in their native range provides valuable baseline data to further manage the spread of alien species.