南滇池国家湿地公园外来园林植物生态风险评价

[目的]通过构建南滇池国家湿地公园外来园林植物生态风险评价体系,推进外来园林植物的有效判定、有利运用和有别管控,探讨国家湿地公园前期建设中存在外来植物科学防控问题,为各类生态湿地公园的建设和发展提供参考.[方法]对南滇池国家湿地公园园林植物物种组成和外来植物入侵现状进行全面普查,通过文献研究和专家咨询,构建南滇池国家湿...     

Fire and Litter Effects on Seedling Establishment in Western Oregon Upland Prairies

Prescribed burning is an important tool for managing and restoring prairies and other ecosystems. One effect of fire is plant litter removal, which can influence seedling establishment. Four experimental treatments (burned, clipped and raked to remove litter, burned with litter reapplied, and unmanipulated) were applied to 2 × 2.5–m plots in three western Oregon, United States, upland prairies to determine how burning affects seedling establishment. Seeds of common exotic and native prairie species were sowed into the experimental plots after treatments. Seedlings were censused the following spring. The experiment was repeated on each of the three sites, representing three common types of prairie vegetation: an Annual Exotic Grass site, a Perennial Exotic Grass site, and a Native Bunchgrass site. In both the Annual Exotic Grass and the Perennial Exotic Grass sites, burning significantly improved native, but not exotic, seedling establishment over those on unburned plots. Litter removal was a significant component of this burn effect, particularly on the Perennial Exotic Grass site. In these winter‐moist systems, the net effect of litter is to inhibit seedling establishment. Burning treatments on the Native Bunchgrass site significantly increased seedling establishment only of short‐lived exotic species. These results suggest that in prairie ecosystems similar to the Annual and Perennial Exotic Grass sites, prescribed burning followed by sowing native seeds can be an effective restoration technique. Burning alone or sowing alone would be counter‐productive, in the first case because increased establishment would come from exotic species and in the second case because establishment rates are low in unburned plots.     

Disturbance of biological soil crust increases emergence of exotic vascular plants in California sage scrub

Biological soil crusts (BSCs) are comprised of soil particles, bacteria, cyanobacteria, green algae, microfungi, lichens, and bryophytes and confer many ecosystem services in arid and semiarid ecosystems worldwide, including the highly threatened California sage scrub (CSS). These services, which include stabilizing the soil surface, can be adversely affected when BSCs are disturbed. Using field and greenhouse experiments, we tested the hypothesis that mechanical disturbance of BSC increases emergence of exotic vascular plants in a coastal CSS ecosystem. At Whiting Ranch Wilderness Park in southern California, 22 plots were established and emergence of exotic and native plants was compared between disturbed and undisturbed subplots containing BSC. In a separate germination study, seed fate in disturbed BSC cores was compared to seed fate in undisturbed BSC cores for three exotic and three native species. In the field, disturbed BSCs had significantly (>3×) greater exotic plant emergence than in undisturbed BSC, particularly for annual grasses. Native species, however, showed no difference in emergence between disturbed and undisturbed BSC. Within the disturbed treatment, emergence of native plants was significantly, and three times less than that of exotic plants. In the germination study, seed fates for all species were significantly different between disturbed and undisturbed BSC cores. Exotic species had greater emergence in disturbed BSC, whereas native plants showed either no response or a positive response. This study demonstrates another critical ecosystem service of BSCs—the inhibition of exotic plant species—and underscores the importance of BSC conservation in this biodiversity hotspot and possibly in other aridland ecosystems.     

Grouping plant species by shared native range, and not by native status, predicts response to an exotic herbivore

Differences among exotic species can be as large as differences between native and exotic species. Typically, however, only the distinction between native and exotic is made when predicting responses in a community. In this paper, I examine the response of plant species to experimental disturbance and exclusion of invasive European rabbits (Oryctolagus cuniculus) in a grassland community with exotic plants originating from five continents. I explore group responses based on native status, shared native range with rabbits, having a congener from the native range of rabbits, life-history (e.g., annual), and life-form (e.g., grass). Individual species responses to rabbits were idiosyncratic, but group responses were predicted by continent of origin, not native status. Native status did predict response to disturbance with almost uniform responses within groups. Exotic species, regardless of origin, were positively affected by disturbance. Native species, in contrast, were negatively affected by disturbance. These results suggest that grouping plant species by native status is valid for questions of disturbance, but when analyzing outcomes of interactions, factors other than native status, such as shared evolutionary history, should be considered.     

Site‐specific responses of native and exotic species to disturbances in a mesic grassland community

Abstract. Grassland communities are increasingly recognized as disturbance‐dependent ecosystems, yet there are few replicated, multi‐site studies documenting vegetation responses to varying frequencies and types of grassland disturbance. Even so, land managers frequently manipulate disturbance regimes in an attempt to favour native grassland plants over exotic species. We conducted a factorial experiment testing three frequencies of clipping combined with litter accumulation, litter removal, and soil disturbance within the highly threatened California coastal prairie plant community. We monitored the response of native/exotic, grass/forb plant guilds once a year for four years. More frequent clipping reduced cover of exotic grasses and favoured exotic forbs, whereas native species were largely unaffected by clipping frequency. Litter accumulation, litter removal, and soil disturbance did not affect vegetation composition. Effects of litter accumulation may take longer than our experiment allowed, and soil disturbance due to our treatments was not sufficiently strong to show consistent effects relative to mammalian soil disturbance. Treatment response of some plant guilds differed among sites, highlighting the importance of replicating experiments at several sites before recommending conservation management practices.     

Biotic resistance to plant invasions? Native herbivores prefer non‐native plants

In contrast to expectations of the enemy release hypothesis, but consistent with the notion of biotic resistance, we found that native generalist crayfishes preferred exotic over native freshwater plants by a 3 : 1 ratio when plants were paired by taxonomic relatedness. Native crayfishes also preferred exotic over native plants when tested across 57 native and 15 exotic plants found growing sympatrically at 11 sites throughout the southeastern USA. Exotic grass carp that share little evolutionary history with most of these plants exhibited no preference for native vs. exotic species. Analyses of three terrestrial data sets showed similar patterns, with native herbivores generally preferring exotic plants, while exotic herbivores rarely exhibited a preference. Thus, exotic plants may escape their coevolved herbivores only to be preferentially consumed by the native generalist herbivores in their new ranges, suggesting that native herbivores may provide biotic resistance to plant invasions.     

Nutrient enrichment increases plant biomass and exotic plant proportional cover independent of warming in freshwater wetland communities

Anthropogenic environmental change can increase exotic species performance and reduce native biodiversity. Nutrient enrichment may favor exotic plants with higher growth rates. Warming may increase the performance of exotic species from warmer native ranges and/or decrease the performance of locally adapted native species. However, community level impacts of nutrient enrichment and warming may depend on their combined effects on individual species and species interactions. We conducted a factorial 11-month field experiment that manipulated 1) plant origin: native, exotic (species from warmer and nutrient rich habitats), or native-&-exotic; 2) nutrients: ambient or high; and 3) temperature: ambient, +1 °C, or +2 °C. Elevated nutrients increased biomass and exotic plant proportional cover. Exotic diversity was higher with elevated nutrients. Native and exotic biomass responses to elevated nutrients were smaller in native-&-exotic treatments. Elevated nutrients increased the relative abundance of two exotic and decreased one exotic and three native species in native-&-exotic treatments. The predicted exotic to native biomass ratio was higher than the observed ratio, indicating that native plants reduced the potential growth of exotic plants in native-&-exotic treatments. Warming had no effect on plant biomass or diversity. These results suggest that nutrient enrichment increases the performance of some exotic plants and that it is critical to consider native and exotic plant interactions when assessing anthropogenic factor and exotic plant effects on native plant communities.     

丛枝菌根真菌（AMF）对外来植物入侵反馈机制的研究进展

丛枝菌根真菌（AMF）在植物群落竞争演替、物种多样性的形成及群落空间分布格局、植物群落对全球变化的响应中均起着重要的调节作用;同样也能影响外来植物与本地植物的互作,影响外来植物入侵过程中植物群落演替进程,甚至决定入侵的成败。因此,AMF与外来植物共生及其对外来植物入侵的反馈已成为国际上外来植物入侵机制研究的一个热点。本文基于外来植物的入侵过程,从AMF对外来植物生长、外来植物与本地植物竞争关系的影响,以及外来植物入侵对AMF的影响及AMF对入侵的反馈3个方面综述了AMF对外来植物入侵的反馈机制。外来植物可以通过多种途径改变土著AMF的群落结构和功能,而土著AMF也能直接或间接地改变甚至逆转外来植物与入侵地植物的互作关系。未来的研究不仅需要考虑AMF与外来植物共生的菌根特性和对竞争关系的影响,还需要通过大尺度条件下的野外试验及室内补充试验深入探究影响AMF在外来植物与本地植物竞争演替中的作用的生物和非生物因子,以全面解释AMF影响外来植物入侵的反馈机制。     

Non-native plant invasions of United States National Parks

The United States National Park Service was created to protect and make accessible to the public the nation’s most precious natural resources and cultural features for present and future generations. However, this heritage is threatened by the invasion of non-native plants, animals, and pathogens. To evaluate the scope of invasions, the USNPS has inventoried non-native plant species in the 216 parks that have significant natural resources, documenting the identity of non-native species. We investigated relationships among non-native plant species richness, the number of threatened and endangered plant species, native species richness, latitude, elevation, park area and park corridors and vectors. Parks with many threatened and endangered plants and high native plant species richness also had high non-native plant species richness. Non-native plant species richness was correlated with number of visitors and kilometers of backcountry trails and rivers. In addition, this work reveals patterns that can be further explored empirically to understand the underlying mechanisms.     

Exotic plant species in a C4-dominated grassland: invasibility, disturbance, and community structure

We used data from a 15-year experiment in a C₄-dominated grassland to address the effects of community structure (i.e., plant species richness, dominance) and disturbance on invasibility, as measured by abundance and richness of exotic species. Our specific objectives were to assess the temporal and spatial patterns of exotic plant species in a native grassland in Kansas (USA) and to determine the factors that control exotic species abundance and richness (i.e., invasibility). Exotic species (90% C₃ plants) comprised approximately 10% of the flora, and their turnover was relatively high (30%) over the 15-year period. We found that disturbances significantly affected the abundance and richness of exotic species. In particular, long-term annually burned watersheds had lower cover of exotic species than unburned watersheds, and fire reduced exotic species richness by 80–90%. Exotic and native species richness were positively correlated across sites subjected to different fire (r = 0.72) and grazing (r = 0.67) treatments, and the number of exotic species was lowest on sites with the highest productivity of C₄ grasses (i.e., high dominance). These results provide strong evidence for the role of community structure, as affected by disturbance, in determining invasibility of this grassland. Moreover, a significant positive relationship between exotic and native species richness was observed within a disturbance regime (annually burned sites, r = 0.51; unburned sites, r = 0.59). Thus, invasibility of this C₄-dominated grassland can also be directly related to community structure independent of disturbance. Received: 9 February 1999 / Accepted: 12 May 1999     

Responses of exotic plant species to fires in Pinus ponderosa forests in northern Arizona

Abstract. Changes in disturbance due to fire regime in southwestern Pinus ponderosa forests over the last century have led to dense forests that are threatened by widespread fire. It has been shown in other studies that a pulse of native, early‐seral opportunistic species typically follow such disturbance events. With the growing importance of exotic plants in local flora, however, these exotics often fill this opportunistic role in recovery. We report the effects of fire severity on exotic plant species following three widespread fires of 1996 in northern Arizona P. ponderosa forests. Species richness and abundance of all vascular plant species, including exotics, were higher in burned than nearby unburned areas. Exotic species were far more important, in terms of cover, where fire severity was highest. Species present after wildfires include those of the pre‐disturbed forest and new species that could not be predicted from above‐ground flora of nearby unburned forests.     

Exotic thistles increase native ant abundance through the maintenance of enhanced aphid populations

Exotic species change the structure and composition of invaded communities in multiple ways, but the sign of their impact on native species is still controversial. We evaluated the effects of the thistles Carduus thoermeri and Onopordum acanthium—two of the most abundant exotic plant species in disturbed areas of the Patagonian steppe—on the native tending ant assemblage. Exotic thistles showed an increased number of plants with aphids and had greater aphid density than native plants. Since native tending ants were present only in plants with aphids, their abundance was higher in infested thistles than in native plants. Path analyses confirmed that ant activity depended more on aphid density than on thistle traits. Our results suggest that the presence of exotic thistles in disturbed areas of NW Patagonia indirectly benefit the native ant assemblage through the maintenance of an increased aphid population. This illustrates how the impact of exotic on native species can depend on the ecological context.     

How environmental and disturbance factors influence species composition in temperate Australian grasslands

Abstract. A distinctive feature of Australian vegetational history is the abruptness of change since European settlement, involving the influx of exotic species and the imposition of exogenous disturbances which are novel in both intensity and character. This can produce two sources of habitat variability: the natural patterns arising from environmental variation, as well as an overlying effect of disturbance. The relative importance of these two types of variables were compared in temperate herbaceous vegetation. Canonical Correspondence Analysis showed that environment and disturbance had similar contributions to floristic variability. Individually, lithology, altitude and soil disturbance were the strongest variables while slope position, grazing and water enrichment were slightly less important. Despite generally low levels of site specificity, groups of species associated with lithology, slope position, altitude and different disturbance regimes were identified. Exotic species were associated with higher levels of disturbance, but showed levels of environmental specialization similar to the native component. Through combination of this analysis with a previous analysis of species richness for the same data set, it became evident that environmental variation mostly resulted in species substitutions while disturbances led to losses of species, with partial replacement by exotics. Synthesizing these results, we identified three broad groups in relation to tolerance of levels of exogenous disturbance: (1) intolerant species - native taxa intolerant of severe disturbances and constituting the species - rich component of the vegetation; (2) tolerant species - exotic and native taxa occurring at both disturbed and undisturbed habitats and (3) disturbance specialists - predominantly exotic species, correlated with high levels of disturbance.     

Bee Preference for Native versus Exotic Plants in Restored Agricultural Hedgerows

Habitat restoration to promote wild pollinator populations is becoming increasingly common in agricultural lands. Yet, little is known about how wild bees, globally the most important wild pollinators, use resources in restored habitats. We compared bee use of native and exotic plants in two types of restored native plant hedgerows: mature hedgerows (>10 years from establishment) designed for natural enemy enhancement and new hedgerows (≤2 years from establishment) designed to enhance bee populations. Bees were collected from flowers using timed aerial netting and flowering plant cover was estimated by species using cover classes. At mature hedgerow sites, wild bee abundance, richness, and diversity were greater on native plants than exotic plants. At new sites, where native plants were small and had limited floral display, abundance of bees was greater on native plants than exotic plants; but, controlling for floral cover, there was no difference in bee diversity and richness between the two plant types. At both mature and new hedgerows, wild bees preferred to forage from native plants than exotic plants. Honey bees, which were from managed colonies, also preferred native plants at mature hedgerow sites but exhibited no preference at new sites. Our study shows that wild bees, and managed bees in some cases, prefer to forage on native plants in hedgerows over co‐occurring weedy, exotic plants. Semi‐quantitative ranking identified which native plants were most preferred. Hedgerow restoration with native plants may help enhance wild bee abundance and diversity, and maintain honey bee health, in agricultural areas.     

Takahe Valley Hut: a focal point for weed invasion in an isolated area of Fiordland National Park, New Zealand

The role of backcountry huts as focal points for weed establishment and spread into New Zealand’s national parks has received little attention. In this study we describe the pattern of weed spread around Takahe Valley Hut, Murchison Mountains, Fiordland National Park. Established in 1948, the hut is located at 900 m a.s.l. at the ecotone between Nothofagus forest and valley floor shrubland/grassland. We recorded the distribution of vascular plants in quadrats (110) placed by restricted randomisation around the hut, and measured relative irradiance and distance from the hut. Nine exotic species, mostly grasses, were recorded, the most frequent being Agrostis capillaris (34%). The majority of occurrences of exotic plant species were located in the immediate vicinity (less than 5 m) of the hut but two exotic species (Agrostis capillaris and Dactylis glomerata) ranged more widely. Exotic species were present in well-drained shrubland and grassland but did not extend far into Nothofagus forest or onto infertile wetlands. The percentage of exotic species in quadrats declined significantly with distance from the hut. There was no linear relationship between the percentage of exotic species and relative irradiance. When forest quadrats were excluded, the number of native species in quadrats was negatively correlated with the number of exotic species, suggesting competitive displacement of native species by exotics in non-forest habitats. Long-term persistence of most exotic species at this site depends on physical disturbance and nutrient enrichment associated with human activities at the hut site. However the maintenance of this species pool has provided sufficient propagule pressure for some exotic species to disperse into the wider area. Weed accumulation around huts can be reduced by locating huts in vegetation types that are more resistant to invasion, and maintaining facilities to eliminate local weed infestations.     

Linear declines in exotic and native plant species richness along an increasing altitudinal gradient in the Snowy Mountains,Australia

Abstract Declines in plant species richness with increasing altitude are common, but the form of the relationship can vary, with both monotonic decreasing relationships and humped relationship recorded. However, these different richness to altitude relationships may be due to methods that used different plot sizes/areas and survey efforts. To explore native and exotic plant richness along an altitudinal gradient in the Snowy Mountains of Australia, we consistently surveyed plots that were 120 m² in area at 39 sites ranging from 540 to 2020 m. To relate exotic plant richness to disturbance, we surveyed plots at 16 sites along main roads and 23 sites along minor roads and also compared these 39 roadside plots to 120‐m² plots located in undisturbed vegetation adjacent to the roadside (native plant richness was only surveyed in 25 of these 39 adjacent plots). We found a negative linear relationship between total, exotic and native species richness and altitude for plots on the side of main roads (16 sites) and minor roads (23 sites). For adjacent plots negative linear relationships were significant for all measures of species richness except for native species adjacent to major roads. As the pattern occurred for exotics it is less likely to be due to historical constraints on the species pools. The pattern could be influenced by difference in levels of disturbance along the gradient, although any such gradient in disturbance would have to apply to roadside and adjacent plots on major and minor roads. Therefore, it may be due to other factors such as changes in climate along the altitudinal gradient, although additional sampling including direct measures of climatic conditions, soil and disturbance factors would be needed to determine if this was the case.     

Population,community and ecosystem effects of exotic herbivores: A growing global concern

Exotic herbivores represent a serious threat to native biodiversity, producing large scale changes in native communities and altering ecosystem processes. In this special issue, we present a series of case studies and reviews from different areas of the world that highlight (1) the consequences of herbivore introductions are a global problem; (2) they can result in wholesale shifts in the distribution of dominant plants on the landscape and; (3) the effects of herbivore introductions extend from the population to the community and ecosystem level. These studies suggest that introduced herbivores often retard ecosystem recovery after disturbance, facilitate invasion of plant species and can act as selective agents on native plant communities. These studies also suggest that several topics, including facilitation between exotic herbivores and exotic plants and animals (i.e., invasional meltdown) and the effect of exotic herbivores on ecosystem processes, require more research attention. Overall the papers in this special feature suggest that introduced herbivores are a global problem with wide-ranging ecological and evolutionary effects.     

Co‐adapting societal and ecological interactions following large disturbances in urban park woodlands

The responses of urban park woodlands to large disturbances provide the opportunity to identify and examine linkages in social‐ecological systems in urban landscapes. We propose that the Panarchy model consisting of hierarchically nested adaptive cycles provides a useful framework to evaluate those linkages. We use two case studies as examples – Cherokee Park in Louisville, Kentucky, USA and Tijuca Forest in Rio de Janeiro, Brazil. In the Cherokee Park case study, the disturbance, a destructive tornado, triggered bottom‐up societal responses that created new institutions that influenced park management and shifted the woodland community from a successional pathway dominated by invasive exotic plants to one where native plant species are regaining importance. In the Tijuca Forest example, the disturbance, large scale land‐use changes during the 18th century, triggered primarily top‐down societal responses to create the world's largest urban forest through a transformative programme of intensive multispecies forest replanting and management. Currently, fine scale disturbances – primarily anthropogenically caused fire – threaten portions of Tijuca Forest through loss of forest structure and establishment of flammable invasive plants, and again elicited top‐down societal responses to stop further destruction and promote greater native plant regeneration. These case studies illustrate that either natural or anthropogenic disturbances to natural systems can alter the direction and magnitude of interactions between social and natural domains in urban landscapes in a co‐adaptive manner that alters structures and processes in both system components.     

Promotion of exotic weed establishment by endangered giant kangaroo rats (Dipodomys ingens) in a California grassland

Giant kangaroo rats (Dipodomys ingens) continually modify their burrow precincts by digging tunnels, clipping plants, and other activities. In the valley grasslands of the Carrizo Plain Natural Area (San Luis Obispo County, California), this chronic disturbance to soil and vegetation promoted the establishment of exotic ruderal and early successional plant species. Erodium cicutarium, Bromus madritensis ssp. rubens, and other Mediterranean annuals were found to constitute a very large proportion of the vegetation on giant kangaroo rat precincts. When vegetation on precincts was compared with the vegetation in less disturbed intermediate areas located between precincts, species richness, cover and frequency of exotic plants were significantly greater on precincts. The reverse was found for native species. In addition, exotic species encountered in this study had significantly larger seeds than did native species, suggesting that these granivorous kangaroo rats preferentially cache large weed seeds on their precincts. Since the kangaroo rats depend on exotic plants for food and the exotic plants depend upon the kangaroo rats to disturb their habitat continually, the weed-kangaroo rat relationship is mutualistic. This strong relationship may also inhibit population growth of native grassland plants which occupy disturbed habitats but have difficulty competing with exotic weeds for resources. From a conservation perspective, this mutualism presents an intractable management dilemma. Restoration of valley grasslands where endangered giant kangaroo rats occur, to conditions where native species dominate, may be impossible.