Measuring succession: methods for establishing long-term vegetation monitoring sites

Successional stages are often characterized by dominant plant species (species with the highest cover) and their effect on the structure and function of an area through time. However, the plant species determining the ecosystem properties and plant community dynamics may not be the dominant, especially when it is exotic. Understanding plant community dynamics in ecosystems that are uncharacterized and/or affected by invasive plant species requires a data-driven approach and proper placement of monitoring plots. To generate robust datasets on vegetation change through time, monitoring plot placement must consider the scale of ecological variation for both vegetation and soils and plots would ideally be replicated within similar ecological site types to quantify the consistency of successional transitions. We characterized soil and vegetation across and within seven floodplains affected by Russian olive (Elaeagnus angustifolia L.) along the Yellowstone River in southeastern Montana, USA. Using modern Classification and Regression Trees (CART) and multivariate net differentiation, we identified five distinct plant community types, or classes, characterized by their tertiary woody plant cover, not the primary species, Russian olive. Our findings indicate that Russian olive communities differ across space, and these riparian areas can be classified into distinct plant community types. Characterizing plant community types via this analytical approach should allow practitioners to modify management decisions and forecast succession within relevant plant communities.     

Segregation,nestedness and homogenisation in plant communities dominated by native and alien species

ABSTRACT

Background: Highly modified landscapes offer the opportunity to assess how environmental factors influence the integration of alien plant species into native vegetation communities and determine the vulnerability of different communities to invasion.

Aims: To examine the importance of biotic and abiotic drivers in determining whether alien plant species segregate spatially from native plant communities or become integrated and lead to biotic homogenisation.

Methods: Ordination and classification of a floristic survey of over 1200 systematically located 6 m × 6 m plots were used to examine how plant community segregation, nestedness and homogenisation varied in relation to climate, environmental and human-related factors across Banks Peninsula, New Zealand.

Results: The analyses of community structure indicated that native and alien plant communities were spatially and ecologically segregated due to different responses primarily to an anthropogenic impact gradient and secondly to environmental factors along an elevation gradient. Human-land use appeared most strongly linked to the distribution of alien species and was associated with increased vegetation homogenisation. However, despite spatial segregation of alien and native plant communities, biotic homogenisation not only occurred in highly managed grasslands but also in relatively less managed shrublands and forest.

Conclusions: The role played by anthropogenic factors in shaping alien and native plant species community structure should not be ignored and, even along a marked environmental gradient, if the recipient sites have a long history of human-related disturbance, biotic homogenisation is often strong.     

Colonisation of experimentally immersed wood in south eastern Australia: responses of feeding groups to changes in riparian vegetation

We investigated macroinvertebrate abundance and functional feeding groups colonising experimentally-positioned woody substrates of different species in streams with three different riparian vegetation types. Native Eucalyptus forest formed a dense closed canopy over our streams; introduced (exotic, alien) pine plantation forest did not fully shade the streams, and grassland streams were completely open, although with woody riparian vegetation well upstream of our sites. Macroinvertebrate assemblages varied taxonomically and functionally with both wood species and riparian vegetation composition. Two specialist feeding groups responded clearly to riparian vegetation: wood gougers were most common in forested streams, and algal grazers in more open streams. Gougers colonised native Eucalyptus wood in preference to alien species. Other feeding groups responses showed complex interactions between vegetation and wood type. Our results indicate the importance of sampling appropriate substrates when assessing questions of this type – if seeking shifts in functional organisation, the substrates on which the feeding groups of interest occur must be sampled. The composition of the riparian strip may influence xylophilous communities as much as the structure (i.e. whether closed or open).     

Do riparian plant community characteristics differ between <Emphasis Type="Italic">Tamarix</Emphasis> (L.) invaded and non-invaded sites on the upper Verde River,Arizona?

Invasion by Tamarix (L.) can severely alter riparian areas of the western U.S., which are globally rare ecosystems. The upper Verde River, Arizona, is a relatively free-flowing river and has abundant native riparian vegetation. Tamarix is present on the upper Verde but is a minor component of the vegetation (8% of stems). This study sought to determine whether riparian vegetation characteristics differed between sites where Tamarix was present and sites where Tamarix was absent during the invasion of the upper Verde. We hypothesized that herbaceous understory and woody plant communities would differ between Tamarix present and absent sites. Our hypothesis was generally confirmed, the two types of sites were different. Tamarix present sites had greater abundance of all vegetation, native understory species, graminoids, and native trees, and a positive association with perennial native wetland plant species. Tamarix absent sites had greater abundance of exotic plants and upland adapted plants and an association with greater abiotic cover and litter. These results are contrary to other reports of Tamarix association with depauperate riparian plant communities, and suggest that Tamarix invasion of a watershed with a relatively natural flow regime and a robust native plant community follows similar establishment patterns as the native riparian plant community.     

Under the shadow of a big plane tree: Why Platanus orientalis should be considered an archaeophyte in Italy

In Italy, Platanus orientalis L. is judged as an endangered species by some authors and non-native by others: these contrasting assessments can mislead the prioritization of management actions to preserve the species and the riparian vegetation that is its host. Based on a multidisciplinary approach, including palaeobotanical and ecological information, we assessed its status in Italy including the ecological and conservation value of the riparian plant communities hosting it in the Cilento National Park (S-Italy). Palaeobotanical data showed that P. orientalis in Italy should be considered an archaeophyte. According to the ecological assessment of the riparian plant communities hosting P. orientalis, the presence of the species can be interpreted as an indicator of an unfavourable state for the conservation of riparian vegetation. Knowing the status of a species remains one of the first steps to take to correctly propose scientifically based solutions for the conservation of plant diversity. However, there are no absolute criteria for conservation because all conservation objectives can be considered as cultural values. In this context, P. orientalis should be protected as a symbolic tree, an archaeophyte testifying an ancient common Mediterranean cultural heritage, worthy of preservation but outside of natural habitats.     

水淹干扰对水库水滨带植物群落稳定性与种间关系的影响

受城市化与人类活动等因素影响而退化的水滨带植被的恢复与重建是近年来生态环境的热点问题。植物群落的种间关系直接影响植被的演替与恢复。以南水北调中线一期工程通水前的丹江口水库原有水滨带植被为研究对象，对年均多于9个月（海拔142 m以下）、6-9个月（海拔142-147 m）、3-6个月（海拔147-151 m）和少于3个月（海拔151-157 m）的4种不同强度水淹干扰的水滨带植物群落的稳定性和种间关系进行分析，探讨不同水淹干扰强度对水库水滨带植物群落稳定性及种间关系的影响。采用M.Godron稳定性测定法对植物群落稳定性进行分析，通过方差比率（VR）、χ²检验、联结系数（AC）以及Spearman秩相关检验对不同水淹干扰强度下的植物群落优势种进行种间关联分析。结果表明：（1）水库水滨带植物群落稳定性从高到低依次为水淹时长3-6个月、水淹时长6-9个月、水淹时长少于3个月和水淹时长多于9个月。中度水淹干扰下的植物群落稳定性要好于重度和轻度水淹干扰的植物群落；（2）不同水淹干扰强度下水滨带植物群落总体性关联表现为显著正相关。随着水淹时间增加，群落中正联结种对占总对数的比例呈下降趋势，负联结种对比例呈增加趋势，正负联结比值降低，群落内种间联结强度逐渐降低，说明水淹干扰强度增加会导致水滨带植物群落种群间相互依存关系减弱或竞争关系加剧。在此基础上，探讨不同水淹干扰强度下物种的空间分布和生态习性，并提出针对不同水淹干扰强度的水滨带植被恢复的物种选择建议。     

Consequences of exotic host use: impacts on Lepidoptera and a test of the ecological trap hypothesis

Investigating the effects of invasive species on native biodiversity is one of the most pressing challenges in ecology. Our goal in this study was to quantify the effects of invasive plants on butterfly and moth communities. In addition, we sought to elucidate the fitness consequences of non-native hosts on lepidopterans. We conducted a meta-analysis on a total of 76 studies which provided data on larval performance, survival, oviposition preference, abundance, and species richness of Lepidoptera on native and exotic plants. Overwhelmingly, we found that performance and survival were reduced for larvae developing on exotic hosts, relative to native hosts. At the community level, alien plant invasion was associated with a reduction in the overall abundance and richness of lepidopteran communities. We found that lepidopterans did not show strong oviposition preference for native hosts. This result suggests that many invasive plant species may decrease lepidopteran abundance by providing a target for oviposition where larvae have a relatively poor chance of survival. Among studies that tested both survival and preference on exotic hosts, 37.5 % found evidence for novel hosts that could function as ecological traps (the figure was 18 % when considering studies that only assayed larval performance). Thus, although the majority of novel hosts included in our analyses are not likely to act as ecological traps, the potential clearly exists for this effect, and the role of ecological traps should be considered along with other aspects of global change impacting natural communities.     

Altitudinal distribution of native and alien plant species in roadside communities from central Argentina

Roadsides may homogenize the distribution of native species and act as corridors for the spread of alien taxa. We examined the variation in native and alien plant species richness and composition at two spatial scales defined by altitude and habitat type (edges and fill slopes), as well as the relationship between native and exotic species richness in roadside plant communities in mountains from central Argentina. Following a gradient from 1100 to 2200 m a.s.l. along a mountain road, plant species cover was recorded within sample plots of 30 m × 10 m systematically located at 100‐m altitude intervals on both roadside habitats. Although native species richness decreased with altitude and composition changed accordingly, the number of alien species peaked at both extremes of the elevation gradient and did not reflect an altitudinal replacement of chorological groups. The number of both native and alien species was higher in roadside edges, but a negative association between the richness of native and alien species occurred only on fill slopes, suggesting that roadside habitats differ in their susceptibility to plant species colonization and in the mechanisms driving native and alien species richness. Our results highlight the importance of altitude and roadside habitat as factors controlling plant species richness and composition along roadside communities in central Argentina. Although altitude acts as a filter for native plants, it apparently did not constrain the establishment of alien species along the studied roadsides, indicating that the influence of this road as a plant species corridor may increase with time, promoting the opportunities for aliens to expand their current distribution.     

Importance of scale,land‐use,and stream network properties for riparian plant communities along an urban gradient

相似文献   

Evaluation of the Degraded Riparian Ecosystems in the Geum River Watershed in Korea

Riparian vegetation, an important mediator of land–water interactions, provides habitat for animals and other organisms; however, riparian vegetation zones have been altered by agricultural and urban development in Korea. This riparian vegetation survey was conducted to obtain information vital for the ecological restoration and management of the Korean Geum River ecosystem. At 100 study sites, along the Geum River, we recorded the vegetation of the Geum riparian zone. We then surveyed the riparian vegetation associations in the area and overlaid those areas corresponding to trees, shrubs, perennial herbs, annual herbs, exotic plants, cultivated lands, and damaged lands on a geographical map. We also reconstructed the cross-sectional landscape. The mean values of vegetation diversity, exotic plant area (%), annual plant area (%), and species richness were 6.47 ± 0.26, 5.44 ± 1.01, 11.98 ± 1.20, and 22.69 ± 0.93, respectively. The landscape elements of the herbaceous plants were more spread out, compared with those of the woody plants, and 23 sites were composed strictly of herbs. Our results indicate significant differences in vegetation structure among the study sites. For example, at some sites, exotic plants, cultivated lands, and damaged lands dominated the landscape comprising 25.7, 62, and 68.9%, respectively, of the area. The riparian landscape reference model suggested by these results may be applied to studies of other well-conserved riparian zones. We propose that the material pathways and transport of organisms from land to water at Geum River depend on the patchy distribution of these diverse landscape elements.     

Grazing, Environmental Heterogeneity, and Alien Plant Invasions in Temperate Pampa Grasslands

Temperate humid grasslands are known to be particularly vulnerable to invasion by alien plant species when grazed by domestic livestock. The Flooding Pampa grasslands in eastern Argentina represent a well-documented case of a regional flora that has been extensively modified by anthropogenic disturbances and massive invasions over recent centuries. Here, we synthesise evidence from region-wide vegetation surveys and long-term exclosure experiments in the Flooding Pampa to examine the response of exotic and native plant richness to environmental heterogeneity, and to evaluate grazing effects on species composition and diversity at landscape and local community scales. Total plant richness showed a unimodal distribution along a composite stress/fertility gradient ranging several plant community types. On average, more exotic species occurred in intermediate fertility habitats that also contained the highest richness of resident native plants. Exotic plant richness was thus positively correlated with native species richness across a broad range of flood-prone grasslands. The notion that native plant diversity decreases invasibility was supported only for a limited range of species-rich communities in habitats where soil salinity stress and flooding were unimportant. We found that grazing promoted exotic plant invasions and generally enhanced community richness, whereas it reduced the compositional and functional heterogeneity of vegetation at the landscape scale. Hence, grazing effects on plant heterogeneity were scale-dependent. In addition, our results show that environmental fluctuations and physical disturbances such as large floods in the pampas may constrain, rather than encourage, exotic species in grazed grasslands.     

Assigning plant communities to a successional phase: Time trends in abandoned limestone quarries

We investigated spontaneous vegetation succession and the relationship between time and vegetation patterns in several abandoned quarries of the Botticino extraction basin (Lombardy, Italy) and then assigned plant assemblages to a predetermined theoretical successional phase using an original procedure. To recognise and validate the gradient due to time, an ordination approach of vegetation plots linked to constant variables and time since last mining Canonical Correspondence Analysis was conducted first. Then, to determine the durations of the vegetation succession phases and trends between the colonisers and late successional species, we used an original six-step procedure based primarily on the regression curve of the percent relative abundance of life forms (RALFs) over time. The results demonstrated that time is the primary factor that significantly affects life form turnover during succession. Vegetation establishment and development in the “pioneer phase” (0–6 years) were affected by abiotic filters, which determined the dominance of a few ruderal and annual/alien species, mostly therophytes. The successive phases were characterised by an increasing presence of perennial species (mostly phanerophytes) with a consequent influence of biotic filters. The RALF procedure may be applied to other environments to investigate the time trends of plant communities during successions.     

Community-level consequences of invasion: impacts of exotic clonal plants on riparian vegetation

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.     

Exotic plant invasions over 40 years of old field successions: community patterns and associations

While exotic plant species often come to dominate disturbed communities, long-term patterns of invasion are poorly known. Here we present data from 40 yr of continuous vegetation sampling, documenting the temporal distribution of exotic plant species in old field succession. The relative cover of exotic species decreased with time since abandonment, with significant declines occurring ≥20 yr post-abandonment. The number of exotic species per plot also declined with time since abandonment while field-scale richness of exotics did not change. This suggests displacement occurring at small spatial scales. Life history types changed from short-lived herbaceous species to long-lived woody species for both native and exotic plant species. However, shrubs and lianas dominated woody cover of exotic plants while trees dominated native woody cover. The species richness of exotic and native species was positively correlated at most times. In abandoned hay fields, however, the proportion of exotic plant cover per plot was inversely related to total species richness. This relationship suggests that it is not the presence, but the abundance of exotic species that may cause a reduction in community diversity. While the development of closed-canopy forest appears to limit most introduced plant species, several shade-adapted exotic species are increasing within the fields. These invasions may cause a reversal of the patterns seen in the first 40 yr of succession and may result in further impacts on community structure.     

How Does Restoration of Native Canopy Affect Understory Vegetation Composition? Evidence from Riparian Communities of the Hunter Valley Australia

Restoration of native vegetation often focuses on the canopy layer species, with the assumption that regeneration of the understory elements will occur as a consequence. The goal of this study was to assess the influence of canopy restoration on the composition and abundance of understory plant species assemblages along riparian margins in the Hunter Valley, NSW, Australia. We compared the floristic composition (richness, abundance, and diversity) of understory species between nonrevegetated (open) and canopy revegetated plots across five sites. A number of other factors that may also influence understory vegetation, including soil nutrients, proximity to main channel, and light availability, were also measured. We found that sites where the canopy had been restored had lower exotic species richness and abundance, as well as higher native species cover, but not native species richness, compared with open sites. Multivariate analysis of plots based on plant community composition showed that revegetated sites were associated with lower total species diversity, light availability, and exotic cover. This study has found that the restoration of the canopy layer does result in lower exotic species richness and cover, and higher native species cover and diversity in the understory, a desirable restoration outcome. Our results provide evidence that restoration of native canopy species may facilitate restoration of native understory species; however, other interventions to increase native species richness of the understory should also be considered as part of management practice.     

Riparian zones as havens for exotic plant species in the central grasslands

In the Central Grasslands of the United States, we hypothesized that riparian zones high in soil fertility would contain more exotic plant species than upland areas of low soil fertility. Our alternate hypothesis was that riparian zones high in native plant species richness and cover would monopolize available resources and resist invasion by exotic species. We gathered nested-scale vegetation data from 40 1 m²subplots (nested in four 1000 m² plots) in both riparian and upland sites at four study areas in Colorado, Wyoming, and South Dakota (a total of 320 1 m² subplots and 32 1000 m² plots). At the 1 m² scale, mean foliar cover of native species was significantly greater (P<0.001) in riparian zones (36.3% ± 1.7%) compared to upland sites (28.7% ± 1.5%), but at this small scale there were no consistent patterns of native and exotic species richness among the four management areas. Mean exotic species cover was slightly higher in upland sites compared to riparian sites (9.0% ± 3.8% versus 8.2% ± 3.0% cover). However, mean exotic species richness and cover were greater in the riparian zones than upland sites in three of four management areas. At the 1000 m² scale, mean exotic species richness was also significantly greater (P<0.05) in riparian zones (7.8 ± 1.0 species) compared to upland sites (4.8 ± 1.0 species) despite the heavy invasion of one upland site. For all 32 plots combined, 21% of the variance in exotic species richness was explained by positive relationships with soil % silt (t =1.7, P=0.09) and total foliar cover (t = 2.4, P=0.02). Likewise, 26% of the variance in exotic species cover (log₁₀ cover) was explained by positive relationships with soil % silt (t =2.3, P=0.03) and total plant species richness (t = 2.5, P=0.02). At landscape scales (four 1000 m² plots per type combined), total foliar cover was significantly and positively correlated with exotic species richness (r=0.73, P<0.05) and cover (r=0.74, P<0.05). Exotic species cover (log₁₀ cover) was positively correlated with log₁₀% N in the soil (r=0.61, P=0.11) at landscape scales. On average, we found that 85% (±5%) of the total number of exotic species in the sampling plots of a given management area could be found in riparian zones, while only 50% (±8%) were found in upland plots. We conclude that: (1) species-rich and productive riparian zones are particularly invasible in grassland ecosystems; and (2) riparian zones may act as havens, corridors, and sources of exotic plant invasions for upland sites and pose a significant challenge to land managers and conservation biologists.     

哈尔滨市主要城市绿地特征和耦合关系

采用样方法调查了哈尔滨市17块绿地的植物多样性,研究城市绿地生态系统中本土植物多样性对外来植物的影响规律。结果如下:哈尔滨市绿地有75种外来植物,外来栽培植物42种,外来非栽培植物33种。在哈尔滨市绿地植物群落中,外来栽培植物的平均盖度、平均重要值和平均出现频度均较高;外来非栽培种的平均盖度、平均重要值较低,而平均出现频度较高。绿地本土植物物种数与外来栽培种、外来非栽培种的物种数极显著正相关(P<0.01),与外来非栽培种的平均出现频度显著负相关(P<0.05)。绿地乔木层本土植物的香农威尔指数、物种丰富度与外来栽培种、外来非栽培种的物种数均显著负相关(P<0.05),乔木层本土植物的均匀度与外来非栽培种的平均出现频度极显著负相关(P<0.01);灌木层本土植物的物种丰富度与外来栽培种的平均重要值显著负相关(P<0.05);草本层本土植物的均匀度与外来非栽培种的平均相对盖度显著正相关(P<0.05)。随绿地总面积的增加,外来栽培种和外来非栽培种的物种数增加,平均出现频度均呈现显著降低的趋势。随建成时间增加,外来栽培种的平均出现频度呈非线形变化,外来非栽培种的平均出现频度呈现降低的趋势。应提高哈尔滨市绿地本土植物的多样性,严格控制新建成的、总面积较小的绿地中外来植物的引种栽培管理,以防止外来植物发展成为危害本地生态系统的入侵植物。     

鄂尔多斯高原沙地植被和两种优势克隆半灌木的空间格局

群落优势种重要值的变化可以表征植被的演替状况。研究了鄂尔多斯高原飞播后不同演替阶段的沙地植被 ,以及两种优势克隆植物羊柴 (H edysarum laeve)和油蒿 (Artemisia ordosica)种群的空间格局。结果表明 :在调查的尺度内 ,群落水平上 ,演替前期和演替中期的植被盖度空间自相关发生的尺度远小于演替后期。随着植被的演替和发育 ,小于抽样尺度 (<1m)的随机变异逐渐增加。暗示着植被盖度空间格局的变化与羊柴种群和油蒿种群在群落中的地位的变化有关。种群水平上 ,小尺度的空间自相关控制着羊柴种群在 3个演替阶段的空间格局 ;处于前 2个演替阶段的油蒿种群 ,空间格局受更大尺度的过程控制 ,并在自身为建群种的群落随机分布。对于 3个演替阶段的油蒿种群而言 ,发生在小于抽样尺度 (<1m)的随机变异都高于相应的羊柴种群。这两种克隆半灌木的种群空间格局的差异可能与二者克隆构型和克隆性的不同有关。本文还根据这两种植物的生物学特性探讨了二者对鄂尔多斯高原沙地植被恢复的不同作用     

Identifying Native Vegetation for Reducing Exotic Species during the Restoration of Desert Ecosystems

There is currently much interest in restoration ecology in identifying native vegetation that can decrease the invasibility by exotic species of environments undergoing restoration. However, uncertainty remains about restoration's ability to limit exotic species, particularly in deserts where facilitative interactions between plants are prevalent. Using candidate native species for restoration in the Mojave Desert of the southwestern U.S.A., we experimentally assembled a range of plant communities from early successional forbs to late‐successional shrubs and assessed which vegetation types reduced the establishment of the priority invasive annuals Bromus rubens (red brome) and Schismus spp. (Mediterranean grass) in control and N‐enriched soils. Compared to early successional grass and shrub and late‐successional shrub communities, an early forb community best resisted invasion, reducing exotic species biomass by 88% (N added) and 97% (no N added) relative to controls (no native plants). In native species monocultures, Sphaeralcea ambigua (desert globemallow), an early successional forb, was the least invasible, reducing exotic biomass by 91%. However, the least‐invaded vegetation types did not reduce soil N or P relative to other vegetation types nor was native plant cover linked to invasibility, suggesting that other traits influenced native‐exotic species interactions. This study provides experimental field evidence that native vegetation types exist that may reduce exotic grass establishment in the Mojave Desert, and that these candidates for restoration are not necessarily late‐successional communities. More generally, results indicate the importance of careful native species selection when exotic species invasions must be constrained for restoration to be successful.     

Short‐term vegetation recovery after alien plant clearing along the Rondegat River,South Africa

The outcomes of ecosystem restoration projects should be periodically monitored to inform subsequent adaptive management decisions. In 2012, a project was begun to remove both invasive alien plants and fish from the Rondegat River in South Africa. Although the initial post‐intervention dynamics of aquatic fauna have been documented, the results of the simultaneous clearing of dense riparian stands of alien trees and shrubs have not been reported. We examined native riparian vegetation recovery over 3 years after alien plant clearing. We documented increased cover of native riparian shrubs, but a simultaneous increase of alien and native weedy grass cover. Secondary invasions, especially by grasses, can have strong effects on ecosystem dynamics and achieving the goals of restoration may therefore require additional active management. Our findings provide an initial baseline reference for future monitoring and adaptive management decisions.