Vegetation zonation along the desert-wetland ecosystem of Taif Highland,Saudi Arabia

Saudi Arabia has no permanent lakes or rivers but has wet meadows, which are desert wetlands temporarily formed due to the seasonal rainfall. This work investigates the environmental variables' impact on the vegetation pattern in the desert-wetland ecosystem in Taif highlands. Forty-one stands were randomly selected representing three main habitats (wet meadows, slopes, and terraces) to study their floristic features and vegetation analysis. A total of 142 species were recorded belonging to 111 genera and 45 families in the desert wetlands of Taif Province. About 64.1% were natural plants, while 25.4% were segetal weeds, 7.7% were aquatic plants, and 2.8% were plants that escaped from cultivation. Therophytes dominated over the other life forms, and mono-regional taxa were the dominant chorotype. Multivariate analysis of the recorded plants produced eight vegetation groups; four of them (A: Potamogeton nodosus-Nasturtium officinale, B: Lemna gibba-Leptochloa fusca, C: Typha domingensis- Xanthium strumarium and D: Conyza stricta- Cyperus longus) represented the wet meadows, while two (E: Acacia gerrardii- Commicarpus plumbagineus and H: Osteospermum vaillantii- Eragrostis Pilosa) for slopes and other two (F: Argemone ochroleuca-Cyperus rotundus and G: Pulicaria undulata- Solanum incanum) for the desert terraces. The vegetation zonation was clear, which started from real aquatic species in the wet meadows passing through mixed vegetation in the slopes and ended with proper xerophytic vegetation in the terraces. Conyza stricta- Cyperus longus community had the highest species diversity, while that of Potamogeton nodosus-Nasturtium officinale had the lowest. The principal component analysis indicated that HCO₃, NO₃, Mg, Cl, Ca, and pH values were the most effective soil variable. The presence of several segetal weeds suggests the alteration of the natural status of the desert-wetland ecosystem, and thus the conservation of these natural habitats becomes urgent.     

The Survival of Transplants of Rare Ligularia sibirica is Enhanced by Neighbouring Plants

Reintroduction programs are often initiated to restore the viability of endangered plant populations, whose decline is usually caused by loss of suitable habitats. Ligularia sibirica is a species associated with wetlands. It is endangered in Europe and has declined considerably in Estonia since the cessation of traditional management and, in addition, drainage leading to the overgrowth of habitats. The purpose of this work was to estimate the extent of the impact of competition from neighbouring plants and habitat change caused by overgrowing on the survival of transplants of L. sibirica and thereby assess the effectiveness of reinforcement. Laboratory-grown transplants were planted back into their original populations in plots arranged in a two × two (vegetation intact or removed × open or overgrown habitat) factorial experimental design, and their survival was followed for three years. The survival differed notably among populations, but the percentage of surviving plants per plot was on average higher in plots with intact vegetation and in open habitats. The latter indicates that overgrowing indeed decreases habitat quality for this species, despite the fact that plants of L. sibirica can often be found in forested habitats. The lower survival in plots where vegetation had been removed can largely be explained by increased damage caused by animals. In intact plots, by contrast, neighbouring plants provide shelter and protection. Our results stress the importance of restoration and preservation of habitat quality for the protection of this rare species, for which reinforcement may be effective.     

Rocks and Walls: Natural Versus Secondary Habitats

Walls are often considered secondary habitats for vegetation of natural rock surfaces. Compared with rocks, walls differ in many features, for example the presence of a binding material (mainly calcareous mortar), location in settlements and exposure to human impact. A data set of 1,205 phytosociological relevés recorded on horizontal wall tops, wall verticals and rock verticals in the Czech Republic was used to compare their vegetation with regard to i) species composition (frequent species, species diversity, endangered and alien species) and ii) the ecological requirements of the respective species. Gamma diversity of vascular plant species was comparable in all habitat types (242 species on wall tops, 212 species on wall verticals and 197 species on rock verticals). Wall verticals had higher beta diversity, but lower alpha diversity than rocks. Remarkable differences were found comparing the diversity of alien species. Whereas alpha and gamma diversities of aliens were higher on both wall habitats, beta diversity of aliens was the highest on rocks. The high floristic heterogeneity of walls is mainly attributable to the large pool of species from the surrounding urbanized landscape (e.g., cultivated ornamental species and synanthropic weeds) that are favoured by high nutrient inputs. In contrast, species characteristic of rocks are mainly substrate specialists. Walls and rocks share the frequent occurrence of ferns, grasses and herbs typical of forest understorey and clearings. Compared with rocks, walls are generally colonized by species requiring higher nutrient content, soil reaction, temperature and moisture. Secondary wall habitats might be suitable for some rare and endangered species, but contrary to rocks their occurrences are only accidental and temporary. The representation of aliens was considerably higher on walls (approximately 35%) than on rocks (9%).     

Composition of stem borer communities in selected vegetation mosaics in Kenya

Busseola fusca (Fuller), Sesamia calamistis Hampson, Chilo partellus (Swinhoe) and Chilo orichalcociliellus (Strand) are important stem borer pests of maize and sorghum in East Africa. Persistence of these pests in crop fields is blamed on the influx of diaspore populations from the neighbouring natural habitats. In addition to pest species, natural habitats support numerous non-economic stem borer species, some not known to science. However, due to growing human populations and accompanying global change, some of the natural habitats are undergoing rapid changes, a process that may result in the evolution of “new” pest species. In this study, we investigated stem borer species diversity in four different vegetation mosaics in Kenya, with an aim of establishing the differences in species composition and distributions in both wild and cultivated habitats. We identified 33 stem borer species belonging to 14 different genera in the four families; Noctuidae, Crambidae, Pyralidae and Tortricidae from 37 plant species. In addition to the above stem borer pest species, we found three more species, Busseola segeta Bowden, Pirateolea piscator Fletcher and Eldana saccharina Walker, in the cultivated fields. Together, stem borer pests varied in distribution among vegetation mosaics, suggesting differences in ecological requirement. Despite the variations in distribution patterns, stem borer pests co-existed with non-economic species in the natural habitats, communities that are facing threats due to ongoing habitat changes. This paper discusses the likely impacts of habitat changes on both pest and non-economic species.     

Effects of bird seed dispersal on diversity of the invaded plants in several hedge types

The plants that invaded as weeds including woody weeds were surveyed in three hedge types, Euonymus japonicus(HEa), Viburnum awabuki (HV), and Deutzia scabra (HD), respectively, and two hedge types, Buxus microphylla var. sinica (HBa, HBb) cultivated in different habitats in Nanjing Botanical Garden Mem. Sun Yat-Sen (NBG), Nanjing of East China, from April 2001 to November 2002. Another hedge type, Euonymus japonicus (HEb) was also investigated as a contrast, cultivated in Nanjing Agricultural University (NAU), about 3 km away from NBG, between April and November 2003. In total, 1230 plant indi-viduals were found to have invaded these six hedge types, and were identified as belonging to 70 species in 57 genera and 42 fami-lies. Among these plants, 1047 individuals of 55 species were adapted for bird seed dispersal, and 161 individuals of 10 species were adapted for wind seed dispersal, but the seed dispersal mode of the other 22 individuals of five species was uncertain. Among the six hedge types, we found a significantly higher occurrence of bird-dispersed plant species than that of wind-dispersed species ( t = 5.086, df = 10, P < 0.0001) or that of species with the unknown dispersal mode ( t = 8.446, df = 10, P < 0.0001). However, the difference of occurrence between wind-dispersed species and species with the unknown dispersal mode was not significant ( t = 1.977, df = 10, P = 0.076). The number of bird-dispersed plant species recorded in the five hedge types of NBG varied from 15 to 36, M ± SD = 25.6 ± 8.1, and the Shannon-Wiener indices were between 2.151 and 2.917, M ± SD = 2.671 ± 0.306. In contrast with NBG, only 12 species of bird-dispersed plants occurred in the hedge of NAU, with a lower Shannon-Wiener index of 1.679. As a result of cluster analysis, based on Bray-Curtis similarity indices of the invaded plant species adapted for bird seed dispersal, the similarity of species composition of bird-dispersed plants between hedges was influenced to a large extent by the surrounding habitat characteristics, e.g., locality, seed source diversity, distances from seed sources, seed dispersing birds, and frequency of human disturbance, rather than simply being dependent on the hedge tree species themselves. This research suggests that hedges could attract birds to utilize their interior shelter as habitats, and therefore, would have enhanced the deposition of bird-dispersed seeds, as well as have favored seed-ling survival under hedges. Consequently, avian seed dispersal has enriched the species composition of each of the six hedge types consisting of just a single tree species. Although survival and colonization of the migrated plants will inevitably cause some influ-ences on the aesthetic view of hedges, these invaded weeds or woody weeds could be managed and suppressed through regular arti-ficial pruning and by eradication. The results indicate the ecological significance of seed sources, bird seed dispersal, and shrub patches in promoting the successional development of woody vegetation.     

Utilization of harvester ant nest sites by Persian goitered gazelle in steppes of central Iran

Ants are among the most important elements in many ecosystems and known as famous ecosystem engineers. By changing physical and chemical properties of soil, ants may provide suitable habitats for other species. Based on previous observations, we hypothesized that Persian goitered gazelles (Gazella subgutturosa subgutturosa) exhibit a preference for utilizing sites close to seed harvester ant (Messor spp.) nests. We tested our hypothesis by (1) mapping the occurrence of harvester ant nests and aggregated gazelle pellet groups along 31 strip transects, (2) monitoring pellet group accumulation bimonthly at 56 pairs of permanent plots established on ant nests and at adjacent control sites for a complete year, and (3) comparing vegetation and soil parameters between ant nest sites used by gazelles and paired control plots without ant nests. Although the area of Messor spp. nest sites covered only about 0.29% of the sampled transects, 84% of the gazelle pellet group aggregation sites were positioned upon ant nests, suggesting that gazelles actively selected Messor spp. nest sites. Pair-wise comparisons between ant nest plots and paired control plots also confirmed higher use of ant nest sites by gazelles compared to sites without ant nests in all time periods. Percent soil organic matter, percent cover of gravel, and annual herb vegetation significantly differed between ant nest and paired control plots in all the vegetation communities. We suggest that the alterations brought about by harvester ants on soil and vegetation make these sites attractive to gazelles. Gazelle territoriality behaviour and use of ant nests as bedding sites may be the reasons for selection of ant nest sites by gazelles.     

Induced climate change impairs photosynthetic performance in Echinocactus platyacanthus, an especially protected Mexican cactus species

The responses of desert plants to climate warming have been poorly assessed, perhaps due to the overall expectation that desert vegetation will expand as a consequence of this component of climate change. However, determining what plant species will tolerate the expected increase in temperature is a question that remains unanswered. The Chihuahuan Desert is the largest warm desert of North America, and predictive models of climate change indicate that summer temperatures in this desert will increase by 1–2 °C in the next decade. This study experimentally assessed the performance of an endangered cacti species from the Chihuahuan Desert under simulated warming conditions. Hexagonal open top-chambers (OTCs) were used to simulate the effects of global warming on five-years-old individuals of the specially protected species Echinocactus platyacanthus. Temperature was 1.9 °C higher in open top-chambers than in control plots. In contrast, relative humidity was 3.1% higher in control plots than in open top-chambers. E. platyacanthus showed 100% survival for 14 weeks in both OTC and control plots. However, induced warming negatively affected the photosynthetic performance of this species. Cacti located within OTCs displayed lower maximum quantum efficiency of photosystem II (F_v/F_m), effective quantum yield of photosystem II (Φ_PSII), and electron transport rate (ETR) values, but higher non-photochemical quenching (NPQ) values, than cacti from control plots. This is the first study focused on the potential impact of climate warming on survival and photosynthetic performance of young individuals of a succulent species from American deserts. Induced warming negatively affected the photosynthetic performance of young E. platyacanthus, but it also increased non-photochemical quenching, a mechanism for avoiding photoinhibition.     

人工柠条-荒漠草地交错带拟步甲昆虫群落多样性

选取宁夏东部盐池县人工柠条灌丛-荒漠草地交错带为研究样地,以距离梯度形式,利用巴氏诱罐法对拟步甲科昆虫群落多样性进行了调查,研究了边缘效应对拟步甲昆虫群落多样性的影响。共采集拟步甲昆虫1405只,分属8属13种。结果表明,克小鳖甲和弯齿琵甲个体数量分别占总个体数的32.74%和43.27%,为该地区的优势种类。拟步甲昆虫在人工柠条灌丛-荒漠草地交错带的分布可分为3种类型,优势种克小鳖甲和弯齿琵甲属于栖息地广布型,但二者并没有表现出十分均匀的适应性,而且他们在各样带的分布呈显著负相关,克小鳖甲的分布趋向于沙生荒漠环境,弯齿琵甲的分布趋向于柠条灌丛;常见种蒙古漠王、小皮鳖甲的分布偏向于喜好荒漠草地;异距琵甲、奥氏真土甲、网目土甲和淡红毛隐甲的分布则偏向于喜好柠条灌丛。拟步甲昆虫丰富度与Shannon-Wiener多样性沿边缘分别向柠条灌丛和荒漠草地内部降低,个体数量总体上沿柠条灌丛、交错带向荒漠草地内部降低,但各样带差异不显著。从季节动态看,荒漠草地和柠条灌丛物种多样性季节变化相似,3种生境拟步甲活动密度季节变化相似。边缘效应强度分析呈现边缘正效应。CCA排序图显示分类地位相近的物种在生态适应上具有趋同性。多元回归分析表明,植被密度影响拟步甲昆虫群落的优势种和个体数量,植被盖度和高度分别影响拟步甲群落的均匀度和丰富度。主坐标分析(PCo A)排序表明人工柠条灌丛-荒漠草地交错带的拟步甲昆虫群落组成与柠条灌丛内部没有明显分化,但趋于向柠条灌丛生境演替。     

Cross-spatial-scale patterns in the facilitative effect of shrubs and potential for restoration of desert steppe

Facilitation (positive plant–plant interactions) is a potential means to accelerate vegetation restoration in arid areas. Shrubs can accelerate vegetation recovery by means of soil amelioration, but this effect has not been evaluated at large spatial scales or across scales. Here, we examined the facilitative function of shrub change across spatial scales at a desert steppe in Mongolia. Using a high-resolution satellite image, we established five 2500 m² plots in each of three shrub density classes (low, moderate, high) in a desert steppe in Mongolia. To evaluate the facilitative functions of shrubs at multiple spatial scales, we recorded the total number of plant species at three nested spatial scales in each plot: 25, 400, and 2500 m². The facilitative effect of shrubs on plant species richness was more pronounced at larger scales. Denser shrub communities increased plant species diversity at a larger scale. However, the increased taxonomic diversity was not clearly related to increased functional diversity in this system. This scale dependency in species diversity can be explained by the degree to which spatial heterogeneity of habitats within the plots increased as plot size increased. These results support the hypothesis of scale-dependent changes in the balance between facilitation and competition. Therefore, transplanting shrub saplings at high-density and a larger scale could potentially improve the success of vegetation restoration in arid regions.     

Soil seed bank in different habitats of the Eastern Desert of Egypt

The floristic composition and species diversity of the germinable soil seed bank were studied in three different habitats (desert salinized land, desert wadi, and reclaimed land) in the Eastern Desert of Egypt. Moreover, the degree of similarity between the seed bank and the above-ground vegetation was determined. The seed bank was studied in 40 stands representing the three habitats. Ten soil samples (each 25 × 20 cm and 5 cm depth) were randomly taken per stand. The seed bank was investigated by the seedling emergence method. Some 61 species belonging to 21 families and 54 genera were identified in the germinable seed bank. The recorded species include 43 annuals and 18 perennials. Ordination of stands by Detrended Correspondence Analysis (DCA) indicates that the stands of the three habitats are markedly distinguishable and show a clear pattern of segregation on the ordination planes. This indicates variations in the species composition among habitats. The results also demonstrate significant associations between the floristic composition of the seed bank and edaphic factors such as CaCO₃, electrical conductivity, organic carbon and soil texture. The reclaimed land has the highest values of species richness, Shannon-index of diversity and the density of the germinable seed bank followed by the habitats of desert wadi and desert salinized land. Motyka’s similarity index between the seed bank and the above-ground vegetation is significantly higher in reclaimed land (75.1%) compared to desert wadi (38.4%) and desert salinized land (36.5%).     

Shrubs and species identity effects on the distribution and diversity of ground-dwelling arthropods in a Gobi desert

Disentangling the relationship between shrub vegetation and ground-dwelling arthropods at multiple levels of taxonomic resolution is essential to developing a suitable management strategy for the conservation of shrub-associated arthropod biodiversity in shrubland ecosystems. Using Gobi desert (dominated by shrub species Nitraria sphaerocarpa and Reaumuria soongorica) occurring widely in inland arid areas of northwest China as a model system, we sampled ground-dwelling arthropods by pitfall trapping method under canopies of both shrubs and in intershrub bare areas during spring, summer and autumn. Our aim was to determine whether the presence and species identity of shrubs influence the distribution of ground-dwelling arthropods and whether the influence of shrub presence and species identity differs among trophic and taxonomic groups. At the community level, total arthropod abundance and species richness were significantly greater under shrubs than in intershrub bare habitats, whereas more arthropods were captured under N. sphaerocarpa than under R. soongorica. At the trophic group level, the abundance of predator and decomposer arthropods was significantly greater under shrubs than in intershrub bare habitats, whereas herbivore and decomposer arthropods were more abundant under N. sphaerocarpa than under R. soongorica. At the family level, the abundance of Carabidae, Gnaphosidae, Karschiidae, Tenebrionidae and Thomisidae was consistently much greater under shrubs than in intershrub bare habitats, whereas that of Formicidae, Philodromidae and Tettigoniidae did not differ between the shrub microhabitats and the intershrub bare habitats. However, the abundance of Curculionidae under R. soongorica and the abundance of Geotrupidae under N. sphaerocarpa were significantly lower than that in intershrub bare habitats. N. sphaerocarpa was commonly preferred by arthropods in the families of Curculionidae and Tenebrionidae, whereas R. soongorica was commonly preferred by arthropods in the family Geotrupidae, but shrub species identity did not affect the abundance of the remaining families. Our results suggest that shrubs and species identity play important roles in structuring ground-dwelling arthropod communities, but the response of arthropods differed among trophic or taxonomic groups. This study may have important implications for the conservation of invertebrate biodiversity in Gobi desert ecosystems.     

Distribution and spread of environmental weeds along New?Zealand roadsides

Most non-native weeds and other naturalised plants are in the early stages of invasion into New Zealand landscapes. For this invasion to be controlled, even partially, it is important to understand the dominant routes, mechanisms, and rates of weed spread across landscapes. With their linear corridors of disturbed habitats, roadsides are thought to play a large role in the spread of some weeds. We used both new surveys and existing data to assess which of the 328 environmental weeds listed by the Department of Conservation are most frequently found and where on roadsides, and whether distribution patterns are consistent with linear dispersal. We also analysed historical survey data for relationships between reserve weediness and proximity to roads. We surveyed 340 plots of 100-m-long stretches of roadside across four regions and found between 2 and 19 environmental weeds per plot; 128 species in total (Chao estimate 148). Especially abundant were agricultural (weeds and cultivated) species, species that have been naturalised for well over 50 years, and species that disperse externally attached to vertebrates. While we purposefully sampled within 10 km of town limits, we found no strong effect of distance from town on roadside weed richness, including richness of just ornamentally sourced weeds. Instead, number of houses within 250?m and presence of an adjacent house or other residential structure were both important, as was presence of woody vegetation on and adjacent to roadsides. Reserves adjacent to roads had significantly higher weed richness than reserves further from roads, although the causal mechanisms are unclear. Our results suggest that while roadsides include suitable habitats for most environmental weeds, distributions are patchy and roads show little sign of acting as linear dispersal corridors, instead they largely reflect neighbouring land uses. As such, roadside weeds should best be managed as part of the wider landscape.     

Colonisation by native species of abandoned farmland adjacent to a remnant patch of Mediterranean steppe

We studied plant distribution at the margins (0–10 m) of three formerly cultivated plots adjacent to a remnant patch of the only Mediterranean steppe of France: La Crau. We sampled above-ground vegetation, seed bank, seed rain and seed dispersal by ants in order to assess the colonisation of steppe species at margins. Our results showed that (1) present day above-ground vegetation of formerly cultivated plots is influenced more by former agricultural practices (duration of melon cultivation, fertilisation) and time since abandonment than their position in relation to the steppe. (2) An edge effect was identified as the vegetation of the steppe (e.g. Thymus vulgaris, Salvia verbenaca, Linaria arvensis) colonises the formerly cultivated plots (coefficients of similarity between vegetation on margins and steppe vegetation decreased with distance from boundaries (r = -0.65, p < 0.001)). (3) Permanent deep seed bank (10-20 cm) did not contribute to either site or edge effects and was characterised by weed species from previous melon cultivation (e.g. Chenopodium album, Kicksia elatine, Portulaca oleracea, Solanum nigrum). (4) Seed rain density decreased with distance from edges (r = -0.39, p < 0.001) and seemed positively correlated to T. vulgaris cover. (5) The number of seeds in ant-traps seemed correlated to T. vulgaris cover. We concluded that after 19 years of abandonment, only about half of the steppe species have colonised just the few meters of the margins of the formerly cultivated plots and that restoration from seed bank, seed rain or seed dispersal by ants is unlikely. Our results are thus discussed within the context of restoring the steppe plant community on formerly cultivated plots.

     

High-Level Diversity of Tailed Phages,Eukaryote-Associated Viruses,and Virophage-Like Elements in the Metaviromes of Antarctic Soils

The metaviromes of two distinct Antarctic hyperarid desert soil communities have been characterized. Hypolithic communities, cyanobacterium-dominated assemblages situated on the ventral surfaces of quartz pebbles embedded in the desert pavement, showed higher virus diversity than surface soils, which correlated with previous bacterial community studies. Prokaryotic viruses (i.e., phages) represented the largest viral component (particularly Mycobacterium phages) in both habitats, with an identical hierarchical sequence abundance of families of tailed phages (Siphoviridae > Myoviridae > Podoviridae). No archaeal viruses were found. Unexpectedly, cyanophages were poorly represented in both metaviromes and were phylogenetically distant from currently characterized cyanophages. Putative phage genomes were assembled and showed a high level of unaffiliated genes, mostly from hypolithic viruses. Moreover, unusual gene arrangements in which eukaryotic and prokaryotic virus-derived genes were found within identical genome segments were observed. Phycodnaviridae and Mimiviridae viruses were the second-most-abundant taxa and more numerous within open soil. Novel virophage-like sequences (within the Sputnik clade) were identified. These findings highlight high-level virus diversity and novel species discovery potential within Antarctic hyperarid soils and may serve as a starting point for future studies targeting specific viral groups.     

Pollen and non-pollen palynomorph evidence of medieval farming activities in southwestern Greenland

Radiocarbon dating, pollen and non-pollen palynomorph analyses from a lake core were used to establish the timing and effects of farming activities around Lake Igaliku, Eastern Settlement, Greenland. The absence of agro-pastoral impact before the medieval colonization by Europeans provides an opportunity to understand the development of farming activity in a pristine landscape. The results show that the first phase of clearance and grazing pressure, without the expansion of the Norse apophyte (native plant, in habitats created by humans) Rumex acetosa type, could have occurred in the 9–10th century a.d. The presence of Norse settlers and livestock is clearly recorded from the 11–12th century a.d. with increasing frequencies of the Norse apophytes Rumex acetosa type and Ranunculus acris type, and coprophilous fungi. This colonization phase is followed by a period of decreasing human impact at the beginning of the 14th century, with a decrease in weeds, apophytes and coprophilous fungi suggesting a reduced grazing pressure. The regrowth of Salix and Betula and the disappearance of anthropogenic indicators except Rumex acetosa type between the 15th and 18th century demonstrate the abandonment of the settlement, until the development of contemporary agriculture in the 20th century.     

准噶尔盆地典型地段植物群落及其与环境因子的关系

沿88°E线,南北纵穿新疆北部准噶尔盆地,选择环境梯度明显的典型地段,设置33个具有代表性的野外样方,应用TWINSPAN与DCCA分析样方的物种数据和环境数据。研究结果表明:(1)样方TWINSPAN分类结果的第一级分类将分布于流动、半流动沙丘(垄)上的白梭梭群落与固定、半固定沙地上的梭梭群落区分开来,进一步的分类,可将33个样方划分为12个组。35种优势植物种TWINSPAN第1级分类把沙漠内部植物种与外缘物种分开。第2级分类把沙漠内部垄上与垄间植物种以及沙漠外缘旱生、中生和盐生植物种分开。(2)在各种环境因子中,土壤水分与相对高度(或地面活动性)是影响植物群落分布的最主要环境因子,DCCA第一排序轴反映生境水分环境条件,第2轴反映土壤结构梯度的变化。(3)除相对高度(或地面活动性)与土壤水分外,在沙漠南部外缘的山前冲积、洪积扇扇缘,土壤盐分状况亦为植物生长的重要胁迫因子;在沙漠北部外缘的砾石戈壁平原,基质的机械组成对群落分布格局有重要影响;在沙漠内部,土壤质地、地面坡度对植物群落的分布有较大影响。(4)以沙漠为中心的准噶尔盆地地势相对高度与地面活动性、土壤有机质与土壤粘粒、土壤水分与土壤总盐、pH值、有机质、相对高度之间存在显著相关关系。     

Testing bespoke management of foraging habitat for European turtle doves Streptopelia turtur

Agri-environment schemes (AES) are increasingly being employed to mitigate biodiversity loss in agricultural environments. The European Turtle Dove Streptopelia turtur is an obligate granivorous bird in rapid decline within both the UK (−96% since 1970) and across continental Europe (−77% since 1980), despite widespread uptake of AES. Here, we assess the efficacy of a potentially new, sown agri-environment option designed to provide abundant, accessible seed for S. turtur during the breeding season. During summer 2011 we compared vegetation structure and seed provision on trial plots to control habitat types (existing agri-environment options thought to potentially provide S. turtur foraging habitat) to assess whether trial plots performed better for foraging S. turtur than control habitats. In September 2011 all trial plots were topped (cut) and half of a subset of trial plots were then scarified (60% of soil surface disturbed). Vegetation structure on topped, and topped and scarified trial plots was measured during summer 2012 to determine which management regime was most effective in maintaining suitable sward structure and seed provision into the second year. No control habitat type produced as much seed important in S. turtur diet as trial plots at any point during year one. Trial plots provided accessible vegetation structure early in the season with no difference in vegetation metrics between trial plots and previously published data on S. turtur foraging locations. However, to allow later access, management is required during mid-June to open up the sward through localized topping or scarification. Vegetation structure during year two was generally too dense to attract foraging S. turtur. However, scarifying trial plots during the September following sowing encouraged self-seeding of Fumaria. officinalis (a plant species historically forming a significant proportion of S. turtur diet during the breeding season) into the second year, with this species present in 16% of scarified trial plots compared to only 4% of topped trial plots during year two. Thus, autumn scarification, possibly followed by topping or scarification of part of the trial plots in June, is necessary for trial plots to provide more seed and access for S. turtur than existing agri-environment options during year two. We recommend modifications to our original seed mix in order to reduce vegetation density and improve vegetation structure. The study provides an example of the need to strike the right balance between food abundance and accessibility, through vegetation structure, when designing agri-environment scheme management options that provide food for birds.     

Gap size and regeneration in a New Zealand dairy pasture

Abstract Seedling emergence of three weeds (Carduus nutans, Cirsium vulgare and Rumex obtusifolius) and three clovers (Trifolium repens, T. subterraneum and T. pratense) was monitored in gaps of different sizes (0, 2, 6 and 10 cm diameter, plus a 3 m² bare plot), which were created in a Loliumperenne/T. repens pasture. Clover emergence was greatest in the bare plots, in contrast with the weeds, whose emergence peaked in small or intermediate-sized gaps. Relationships between weed emergence and gap size in glasshouse swards were poorly denned. As a result of trampling by cattle, seedling mortality occurred most rapidly for all species in the bare plots. Very few weeds survived in the other gaps, where there was no detectable effect of gap size upon survivorship. Naturally occurring gaps were most abundant during summer, but their size frequency distributions varied little between spring and autumn. The sizes of almost 95% of the natural gaps were within the range of the experimentally-created gaps. Poor survivorship of weeds within this range, however, suggests that larger gaps are required for regeneration.     

Interspecific variations in the habitats of Reichardia tingitana (L.) Roth leading to changes in its bioactive constituents and allelopathic activity

Reichardia tingitana is an annual plant growing in different habitats of the Egyptian deserts. Little is known about variation among the habitats occupied by this species, its distribution, chemical composition, and allelopathic activity. The present study aimed to (a) assess the vegetation composition of three different habitats (Western Coast, Delta Coast, and Wadi Hagoul) of R. tingitana in Egypt, (b) determine their correlation to soil factors, (c) identify the changes in the bioactive constituents of R. tingitana in the three regions, and (d) evaluate the allelopathic activity regarding the variation in the habitat. Density and cover of all plant species associated with R. tingitana were estimated within 52 plots, representing three regions. Physical and chemical parameters of soil were analyzed in each plot. R. tingitana aboveground biomass was collected from each habitat, and the bioactive composition was analyzed using HPLC. The allelopathic effect against two weeds (Amaranthus lividius and Chenopodium murale) was assessed. The floristic composition showed the presence of 133 species belonging to 27 families. In the Delta Coast habitat of R. tingitana, Zygophyllum aegyptium and Calligonum polygonoides co-dominate, while Lycium shawii dominate the Western Coast habitat and finally the habitat of Wadi Hagoul was dominated by Haloxylon salicornicum. Soil analysis revealed little variations among habitats, especially salinity and organic matter. Fifteen compounds, mainly phenolics (60% of the total identified compounds) were identified from all R. tingitana samples. The major compounds were quercetin, naringenin, ellagic, gallic, chlorogenic, and caffeic acids. These compounds varied in diversity or quantity among different habitats. The Western Coast sample was the richest in species, followed by Delta Coast sample. Our study showed that salinity is the crucial factor that induces the production of bioactive constituents in R. tingitana, especially phenolics and flavonoids. The R. tingitana extracts significantly reduced the germination and growth of Chenopodium and Amaranthus. However, the Western Coast sample showed potent allelopathic activity, where the germination was wholly inhibited at 75 mg L⁻¹ and 50 mg L⁻¹, respectively. Thereby, this extract could be used as eco-friendly bioherbicide and may be integrated into weed control strategies.