Plant Species Density Research Articles

Conservation opportunities across the world's anthromes

AbstractAimBiologists increasingly recognize the roles of humans in ecosystems. Subsequently, many have argued that biodiversity conservation must be extended to environments that humans have shaped directly. Yet popular biogeographical frameworks such as biomes do not incorporate human land use, limiting their relevance to future conservation planning. ‘Anthromes’ map global ecological patterns created by sustained direct human interactions with ecosystems. In this paper, we set to understand how current conservation efforts are distributed across anthromes.LocationGlobal.MethodsWe analysed the global distribution of IUCN protected areas and biodiversity hotspots by anthrome. We related this information to density of native plant species and density of previous ecological studies. Potential conservation opportunities in anthromes were then identified through global analysis and two case studies.ResultsProtected areas and biodiversity hotspots are not distributed equally across anthromes. Less populated anthromes contain a greater proportion of protected areas. The fewest hotspots are found within densely settled anthromes and wildlands, which occur at the two extremes of human population density. Opportunities for representative protection, prioritization, study and inclusion of native species were not congruent.Main conclusionsResearchers and practitioners can use the anthromes framework to analyse the distribution of conservation practices at the global and regional scale. Like biomes, anthromes could also be used to set future conservation priorities. Conservation goals in areas directly shaped by humans need not be less ambitious than those in ‘natural areas’.

Time since fire influences food resources for an endangered species, Carnaby’s cockatoo, in a fire-prone landscape

Where threatened species persist in multiple use landscapes, management activities, such as prescribed burning, may influence the availability of resources for those species. We examined how time since fire can influence food resources for the endangered Carnaby’s cockatoo (Calyptorhynchus latirostris) in banksia woodlands of southwestern Australia. Tree density and cone productivity of dominant plant species, Banksia attenuata and Banksia menziesii, were compared across 44 sites of varying post-fire aged vegetation. The number of Carnaby’s cockatoos that could be supported in banksia woodlands was estimated using the bird’s energetic requirements and seed energy content. Banksia attenuata produced more cones at sites aged 10–30years since fire in both survey years, while cone productivity for B. menziesii was highest in very old sites (>35years since fire) in one year only. Higher numbers of Carnaby’s cockatoos were predicted to be supported in vegetation aged between 14–30years since fire, peaking in vegetation aged 20–25years. The current distribution of post-fire aged vegetation within this area (>60% burnt within the last 7years) is predicted to support ∼2725 Carnaby’s cockatoos, representing 25–35% of the estimated birds reliant on the area. Our results indicate that food resources are influenced by time since fire and, consequently, if optimising food resources was an objective, may be manipulated by altering burning patterns. While human and asset protection is a priority for prescribed burning, management of landscapes for improved persistence of threatened species is also important and complex trade-offs will have to be considered.

The outcome of shared pollination services is affected by the density and spatial pattern of an attractive neighbour

Summary Interactions among neighbouring plants are often mediated by foraging choices of pollinators. For example, the presence of a conspicuous species may increase the number of pollinators attracted to its vicinity, indirectly increasing visitation rates also to neighbouring plants. Because pollinator choices are frequently density‐dependent, the presence of a conspicuous species at high densities may also increase competition for pollination services. Additionally, models predict that plant density will interact with spatial distribution in manipulating the pollinator behaviour, yet experimental evidence for this effect is missing. We performed a field experiment in which we introduced a highly conspicuous species in different densities and spatial configurations in a full‐factorial manner into a species‐rich meadow and studied its effect on neighbouring plants. We showed that the highly conspicuous species strongly contributed to the attractiveness of its local patch and thus benefited its neighbours. However, because of the strong density effect, the conspicuous species changed its role and became a competitor for pollinators when its density increased. We supported our theoretical assumptions and showed that when the introduced conspicuous species was regularly distributed among other plants in the patch, it increased visitation rate, and in some cases also seed set, to conspicuous neighbours relative to when it was aggregated, at least at low densities. Synthesis. We suggest that complex interactions between density and spatial distribution of plant species at the patch scale are highly relevant for the interpretation of pollinator behaviour and therefore should be treated as factors of floral attractiveness in future studies.

A global analysis of the impacts of urbanization on bird and plant diversity reveals key anthropogenic drivers

Urbanization contributes to the loss of the world's biodiversity and the homogenization of its biota. However, comparative studies of urban biodiversity leading to robust generalities of the status and drivers of biodiversity in cities at the global scale are lacking. Here, we compiled the largest global dataset to date of two diverse taxa in cities: birds (54 cities) and plants (110 cities). We found that the majority of urban bird and plant species are native in the world's cities. Few plants and birds are cosmopolitan, the most common being Columba livia and Poa annua. The density of bird and plant species (the number of species per km(2)) has declined substantially: only 8% of native bird and 25% of native plant species are currently present compared with estimates of non-urban density of species. The current density of species in cities and the loss in density of species was best explained by anthropogenic features (landcover, city age) rather than by non-anthropogenic factors (geography, climate, topography). As urbanization continues to expand, efforts directed towards the conservation of intact vegetation within urban landscapes could support higher concentrations of both bird and plant species. Despite declines in the density of species, cities still retain endemic native species, thus providing opportunities for regional and global biodiversity conservation, restoration and education.

The weed and alien plants of Yakutia

On the basis of published data and the author’s own observations, the data on invasion of vascular plants into the territory of Yakutia are provided. It was established that the composition of flora of Yakutia includes 155 species and 1 subspecies of alien plants which are representatives of 29 families. It was found that, over a period close to a century, the number of alien elements of the flora of this region increased by 99 species. Considering the big size of the territory of Yakutia, the density of weed and alien plant species per unit area is relatively low. This is caused by severe physical and geographical conditions of this region. Nevetheless, considering the trends of climate warming, it is necessary to expect additional invasion of undesirable elements of flora into Yakutia and to provide measures for protection against them.

Herbivores shape woody plant communities in the Kruger National Park: Lessons from three long-term exclosures

The role of grazers in determining vegetation community compositions and structuring plant communities is well recognised in grassy systems. The role of browsers in affecting savanna woody plant communities is less clear. We used three long-term exclosures in the Kruger National Park to determine the effect of browsers on species compositions and population structures of woody communities. Species assemblages, plant traits relating to browsing and soil nutrients were compared inside and outside of the exclosures. Our results showed that browsers directly impact plant species distributions, densities and population structures by actively selecting for species with traits which make them desirable to browsers. Species with high leaf nitrogen, low total phenolic content and low acid detergent lignin appeared to be favoured by herbivores and therefore tend to be rare outside of the exclosures. This study also suggested that browsers have important indirect effects on savanna functioning, as the reduction of woody cover can result in less litter of lower quality, which in turn can result in lower soil fertility. However, the magnitude of browser effects appeared to depend on inherent soil fertility and climate.Conservation implications: Browsers were shown to have significant impacts on plant communities. They have noticeable effects on local species diversity and population structure, as well as soil nutrients. These impacts are shown to be related to the underlying geology and climate. The effects of browsers on woody communities were shown to be greater in low rainfall, fertile areas compared to high rainfall, infertile soils.

Seasonal controls on grassland microbial biogeography: Are they governed by plants, abiotic properties or both?

Temporal dynamics create unique and often ephemeral conditions that can influence soil microbial biogeography at different spatial scales. This study investigated the relation between decimeter to meter spatial variability of soil microbial community structure, plant diversity, and soil properties at six dates from April through November. We also explored the robustness of these interactions over time. An historically unfertilized, unplowed grassland in southwest Germany was selected to characterize how seasonal variability in the composition of plant communities and substrate quality changed the biogeography of soil microorganisms at the plot scale (10 m × 10 m). Microbial community spatial structure was positively correlated with the local environment, i.e. physical and chemical soil properties, in spring and autumn, while the density and diversity of plants had an additional effect in the summer period. Spatial relationships among plant and microbial communities were detected only in the early summer and autumn periods when aboveground biomass increase was most rapid and its influence on soil microbial communities was greatest due to increased demand by plants for nutrients. Individual properties exhibited varying degrees of spatial structure over the season. Differential responses of Gram positive and Gram negative bacterial communities to seasonal shifts in soil nutrients were detected. We concluded that spatial distribution patterns of soil microorganisms change over a season and that chemical soil properties are more important controlling factors than plant density and diversity. Finer spatial resolution, such as the mm to cm scale, as well as taxonomic resolution of microbial groups, could help determine the importance of plant species density, composition, and growth stage in shaping microbial community composition and spatial patterns.

荒漠草原区柠条固沙人工林地表草本植被季节变化特征

研究荒漠草原人工林固沙区地表草本植被季节变化特征及其和柠条林龄的关系，对于分析柠条人工林地表草本植物的季节适应性和制订合理的人工林管理措施均具有重要的科学意义。选择6、15、24年生和36年生柠条人工林为研究对象，通过调查每个样地5月、8月和10月地表草本植物密度、物种数、盖度和高度，分析了荒漠草原区柠条人工固沙林生长过程中地表草本植被季节变化特征及其影响因素。结果表明，地表草本植物物种数在柠条林龄6和15a时受季节改变的影响较小，在24a之后受到季节变化的显著影响（<em>P</em><0.05）。地表草本植物密度在柠条林龄6a时受季节改变的影响较小，但在15a之后季节变化显著影响地表草本植物个体数分布（<em>P</em><0.05），而且在10月具有最多的地表草本植物个体数。地表草本植被盖度和高度均受到季节变化的显著影响（<em>P</em><0.05），而受林龄的影响较小；不同年龄林地地表草本植被盖度和高度均表现为10月和8月较高，5月较低。研究表明，荒漠草原柠条人工林固沙区，柠条林发育生长和灌木形态的改变不仅影响土壤营养条件，而且还可以调控由于季节改变而引起的土壤温湿度变化，柠条林龄和季节更替二者交互作用，共同影响地表草本植被的季节变化特征。;It is a very valuable study on seasonal changes of ground vegetation characteristics under artificially plantations and its relation to stand age in desert steppe. These results will be beneficial to understand the adaptation of ground vegetation under artificial plantations to seasonal changes, and to give rational management on these artificial plantations. An investigation on ground vegetation characteristics including herbaceous plant species richness, density, cover and height, was carried out in May, August and October, in four artificial plantations (<em>C. intermedia</em>) at age of 6, 15, 24 and 36 yeas respectively. The seasonal changes of ground vegetation under artificial plantations during stand development were discussed, together with the related affecting factors. As the results were shown, there were marked different seasonal adaptations of ground vegetation to varying artificial plantations with age. There was a significant impact of seasonal changes on herbaceous plant species richness, not at age of 6 or 15 years but at age of 24 and 36 years (<em>P</em><0.05). When (at age of 24 and 36 years), herbaceous plant species were significantly lower in May than in October (<em>P</em><0.01). There was also a significant impact of seasonal changes on herbaceous plant density not at age of 6 years but at age of 15, 24 and 36 years (<em>P</em><0.05), when there was a significantly higher herbaceous plant density in October than in May (<em>P</em><0.05). Whiles ground vegetation cover and height were not affected by stand age, but by seasonal changes (<em>P</em><0.05). There was a significantly higher ground cover and height in October and August than in May (<em>P</em><0.05), irrespective of stand age. Pearson correlation analysis implied that the main forces were shrub height and basal diameter on herbaceous plant species richness, and shrub morphological characteristics and soil moisture on herbaceous plant density. While soil moisture and temperature with seasonal changes was the main limiting factors on ground vegetation cover and height, respectively. It was suggested that the changing shrub characteristics during stand development not only facilitated soil nutrient conditions, but regulated soil moisture and temperature due to seasonal changes in these artificial plantations. The interaction between stand age and seasonal changes (soil moisture and temperature) co-affected the seasonal dynamics of ground vegetation under artificial plantation in desert steppe.

Impact of &amp;lt;i&amp;gt;Parthenium hysterophorus&amp;lt;/i&amp;gt; L. Invasion on Species Diversity of Cultivated Fields of Bilaspur (C.G.) India

In present study invasion of Parthenium hysterophorus L. and its impacts on agriculture fields will be done in different cultivated crops in Bilaspur. The present work deals with diversity and distribution of weeds species in cultivated fields of Bilaspur C.G. A total number of 28 species under 27 genera and 16 families was distributed in three study sites (Koni, Sakri & Kota) of cultivated fields in Bilaspur C.G. These study sites were located in different altitudinal zones responding different conditions in the this study. The number of species per sites ranged from 13 to 24. In the Sakri, number of species was ranged from 17 to 27, and the relative density of plant species ranged between 0.77 (Heteropogon contortus, Solanum surratense, Vernonia cinneria and Leucas aspera) and 22.92 (Parthenium hysterophorus). In the Kota, number of species was ranged from 14 to 28, and the relative density of plant species ranged between 0.85 (Ageratum conyzoides, Heteropogon contortus, Triticum aestivum) and 29.06 (Zea mays) and 30.91 (Parthenium hysterophorus). In the Agriculture field, number of species was ranged from 15 to 28, and the relative density of plant species ranged between 0.58 (Leucas aspera) and 26.23 (Triticum aestivum). Present work will give the information that weeds are harmful to herbs, crops and medicinal plants. Parthenium weed can suppress and crowd out other weed species, and could form a single dominant population in the invasion area, causing serious threat to plant community biological diversity.

Classification and Determination of Indicator Environmental Properties in Western Iran Rangelands

How soil characteristics affecting plant species density was investigated through the one-way ANOVA method in typical rangelands of Iran in Zagros Mountains region. All of present species were identified, studied, tagged and named. Four plant types were identified based on two-way indicator species analysis (TWINSPAN). Survey was done at two depths of soil (0-30 and ≥30 cm). In each plot canopy related factors were measured and to determine chemical and physical properties of soil, at primary and end points of each transect profiles were dug. For each profile eight factors at two depths were measured inclusive: soil texture, Organic matter, total nitrogen percent, absorbable phosphorus, absorbable potassium, Lime, pH and EC. Means of squares comparison showed that organic matter, phosphorus, potassium, EC, sand and lime were more effective on species density at two depths in such rangeland ecosystems.

Relationships between Plant Diversity and the Abundance and α-Diversity of Predatory Ground Beetles (Coleoptera: Carabidae) in a Mature Asian Temperate Forest Ecosystem

A positive relationship between plant diversity and both abundance and diversity of predatory arthropods is postulated by the Enemies Hypothesis, a central ecological top-down control hypothesis. It has been supported by experimental studies and investigations of agricultural and grassland ecosystems, while evidence from more complex mature forest ecosystems is limited. Our study was conducted on Changbai Mountain in one of the last remaining large pristine temperate forest environments in China. We used predatory ground beetles (Coleoptera: Carabidae) as target taxon to establish the relationship between phytodiversity and their activity abundance and diversity. Results showed that elevation was the only variable included in both models predicting carabid activity abundance and α-diversity. Shrub diversity was negatively and herb diversity positively correlated with beetle abundance, while shrub diversity was positively correlated with beetle α-diversity. Within the different forest types, a negative relationship between plant diversity and carabid activity abundance was observed, which stands in direct contrast to the Enemies Hypothesis. Furthermore, plant species density did not predict carabid α-diversity. In addition, the density of herbs, which is commonly believed to influence carabid movement, had little impact on the beetle activity abundance recorded on Changbai Mountain. Our study indicates that in a relatively large and heterogeneous mature forest area, relationships between plant and carabid diversity are driven by variations in environmental factors linked with altitudinal change. In addition, traditional top-down control theories that are suitable in explaining diversity patterns in ecosystems of low diversity appear to play a much less pronounced role in highly complex forest ecosystems.

Positive Plant Diversity-Soil Stability Relationships are Mediated through Roots in the Songnen Grassland: Chronosequence Evidence

Living plant diversity (excluding the litter issue) may affect below-ground properties and processes, which is critical to obtaining an integrated biodiversity-ecosystem functioning theory. However, related patterns and underlying mechanisms have rarely been examined, especially lacking long-term evidence. We conducted a factorial crossed sample survey to examine the effects of plant diversity on soil stability over succession based on space-for-time substitution in the Songnen Steppes, North-Eastern China. The results indicate that, under natural colonizing conditions, species-poor systems achieved lower soil stability than species-rich systems, regardless of successional stage. However, soil stability was significantly regulated by plant species richness (number), composition (identity), density (abundance), and functional roles. Our results confirm that a long-term positive plant diversity-soil stability relationship exists in steppe succession. In particular, this enhanced effect of biodiversity on soil stability may operate via diversifying plant root traits. Our results may underpin an integrated biodiversity-ecosystem functioning theory, and improve human use and conservation management of natural resources at an integrated ecosystem level.

Vegetation composition and structure influences bird species community assemblages in the highland agricultural landscape of Nyandarua, Kenya

We examined the effects of vegetation composition and structure on bird species diversity and richness of foraging guilds in the highland agricultural landscape of Nyandarua, Kenya. Bird point counts and vegetation surveys were undertaken during four sampling periods. Linear mixed models were used to examine the effects of vegetation variables on bird species diversity and richness of respective foraging guilds, and logistic generalised linear models used to examine vegetation effects on the presence/absence of the 17 most common bird species. Bird species diversity increased with increasing density of woody plant species and vegetation structural heterogeneity. Two gradients of increasing vegetation structural heterogeneity were most important in influencing bird community composition and had positive effects on species diversity and the presence of most of the species assessed: (1) increasing closed cover due to woody plant density, which also had positive effects on species richness of frugivores and nectarivores, but negative effects on carnivores, and (2) increasing fallow and cultivation versus decreasing grassland/pasture cover, which also had a positive effect on species richness of granivores and omnivores. This study reaffirms the need to maintain a structurally rich agricultural landscape for it to support agrobiodiversity.

Plant management and biodiversity conservation in Náhuatl homegardens of the Tehuacán Valley, Mexico

BackgroundThe Tehuacán Valley is one of the areas of Mesoamerica with the oldest history of plant management. Homegardens are among the most ancient management systems that currently provide economic benefits to people and are reservoirs of native biodiversity. Previous studies estimated that 30% of the plant richness of homegardens of the region are native plant species from wild populations. We studied in Náhuatl communities the proportion of native plant species maintained in homegardens, hypothesizing to find a proportion similar to that estimated at regional level, mainly plant resources maintained for edible, medicinal and ornamental purposes.MethodsWe analysed the composition of plant species of homegardens and their similarity with surrounding Cloud Forest (CF), Tropical Rainforest (TRF), Tropical Dry forest (TDF), and Thorn-Scrub Forest (TSF). We determined density, frequency and biomass of plant species composing homegardens and forests through vegetation sampling of a total of 30 homegardens and nine plots of forests, and documented ethnobotanical information on use, management, and economic benefits from plants maintained in homegardens.ResultsA total of 281 plant species was recorded with 12 use categories, 115 ornamental, 92 edible, and 50 medicinal plant species. We recorded 49.8 ± 23.2 (average ± S.D.) woody plant species (shrubs and trees) per homegarden. In total, 34% species are native to the Tehuacán Valley and nearly 16% are components of the surrounding forests. A total of 176 species were cultivated through seeds, vegetative propagules or transplanted entire individual plants, 71 tolerated, and 23 enhanced. The highest species richness and diversity were recorded in homegardens from the CF zone (199 species), followed by those from the TRF (157) and those from the TDF (141) zones.ConclusionHomegardens provide a high diversity of resources for subsistence of local households and significantly contribute to conservation of native biodiversity. The highest diversity was recorded in homegardens where the neighbouring forests had the least diversity, suggesting that management of homegardens aims at compensating scarcity of naturally available plant resources. Cultivated species were markedly more abundant than plants under other management forms. Diversity harboured and management techniques make homegardens keystones in strategies for regional biodiversity conservation.

Changes in plant species density in an experimentally fragmented forest landscape: Are the effects scale-dependent?

The establishment of commercial tree plantations is a common cause of habitat fragmentation globally, yet the influence of this land use on plant species density in fragmented native forests requires further understanding. Theory predicts species density will be highest in large areas of habitat, and should decline as area is reduced, but whether these effects are scale-dependent is largely unknown. We assessed plant species density (total, common and uncommon species) in experimentally fragmented eucalypt forest remnants (0.25, 0.88, 3.06 ha) surrounded by a pine plantation, at three spatial scales using nested quadrats. Specifically, we consider how plant species density varies across three different sized fragments, and whether the response of species density is magnified in common or uncommon species. Species density in small fragments was higher than continuous forest for all species groupings at the smallest spatial scale (1 m2), and for total and common species at the next smallest spatial scale (16 m2). No species groupings responded to reductions in habitat area at the largest spatial scale (144 m2). We suggest that pine plantations may cause higher species density in small fragments via two mechanisms, either by allowing species to infill unoccupied areas within small fragments, or by buffering small fragments from species losses during a severe and prolonged drought. In both cases we suspect reduced moisture stress (e.g. increased soil moisture, higher shading and reduced temperature) in small fragments has led to the observed changes in species density.

Mapping sub-antarctic cushion plants using random forests to combine very high resolution satellite imagery and terrain modelling.

Monitoring changes in the distribution and density of plant species often requires accurate and high-resolution baseline maps of those species. Detecting such change at the landscape scale is often problematic, particularly in remote areas. We examine a new technique to improve accuracy and objectivity in mapping vegetation, combining species distribution modelling and satellite image classification on a remote sub-Antarctic island. In this study, we combine spectral data from very high resolution WorldView-2 satellite imagery and terrain variables from a high resolution digital elevation model to improve mapping accuracy, in both pixel- and object-based classifications. Random forest classification was used to explore the effectiveness of these approaches on mapping the distribution of the critically endangered cushion plant Azorella macquariensis Orchard (Apiaceae) on sub-Antarctic Macquarie Island. Both pixel- and object-based classifications of the distribution of Azorella achieved very high overall validation accuracies (91.6–96.3%, κ = 0.849–0.924). Both two-class and three-class classifications were able to accurately and consistently identify the areas where Azorella was absent, indicating that these maps provide a suitable baseline for monitoring expected change in the distribution of the cushion plants. Detecting such change is critical given the threats this species is currently facing under altering environmental conditions. The method presented here has applications to monitoring a range of species, particularly in remote and isolated environments.

Characteristics of Vegetation Growing in Indeterminate Fallows in South-Central Zimbabwe

Despite widespread food insecurity in Zimbabwe, there is an increasing amount of agricultural land being left fallow for indeterminate periods of time. The objective of the study was to assess the characteristics of vegetation growing in indeterminate fallows in Chivi district in south-central Zimbabwe. One metre by one metre quadrats were used to assess the species composition of herbaceous species while 8 m × 8 m quadrats were used for woody species. Attributes that were assessed included frequency, abundance, density of different plant species from which were computed diversity indices (Shannon-Weiner index and Shannon evenness index). The density, Shannon-Weiner index and Shannon Evenness index), and species richness of the fallow land sites were significantly lower than those of the uncultivated land. However, there were no significant differences among fallow treatments. Species richness, Shannon Index, and Shannon’s Evenness Index showed a weak and non significant correlation with length of the fallow period. Woody species which were cleared during land preparation and repeated weeded during the cultivation years were absent in all fallows regardless of the fallow period.

Biological control and precipitation effects on spotted knapweed (Centaurea stoebe): empirical and modeling results

The literature is inconsistent regarding the ability of herbivory to control or reduce densities of a major invasive plant species of North America, spotted knapweed (Centaurea stoebe). Here, findings from experimental manipulations of spotted knapweed and long‐term monitoring of seed production and insect abundance were used to parameterize a population matrix model for this species. Model predictions were compared against spotted knapweed densities observed in permanent transects, which were established after the release of biological controls. The model incorporated population‐level compensation for adult mortality (increased growth from juveniles to adults). The model also incorporated newly reported results showing an interaction between precipitation and biological control impacts. We compared predictions from four alternate models against the observed population densities; models were: conspecific density‐dependence, the effects of biological controls, precipitation, and biological control‐precipitation interaction. The best model to explain population declines included the effects of biological control agents. Declines in population growth rates (λ &lt; 1) were only predicted when reduced seed production and increased plant mortality due to biological controls were included. Results suggest that biological controls contributed to declines observed in field studies, and support the contention that biological control attenuates the ability of spotted knapweed to exploit favorable climatic conditions. The results also demonstrate that spotted knapweed control (i.e., conditions where λ &lt; 1) depends upon a relatively large impact of biological control agents through high densities or large per capita impact; both of which are known to vary at our site and elsewhere. At our site spotted knapweed in certain habitats (e.g., disturbed riparian areas) is unlikely to be eradicated by insect herbivory, but spotted knapweed densities found in most other habitats can be reduced by biological control agents. Regardless, the management implications from these findings are that biological controls can intensify the efficacy of other control methods.

Plant Invasions in China – Challenges and Chances

Invasive species cause serious environmental and economic harm and threaten global biodiversity. We set out to investigate how quickly invasive plant species are currently spreading in China and how their resulting distribution patterns are linked to socio-economic and environmental conditions. A comparison of the invasive plant species density (log species/log area) reported in 2008 with current data shows that invasive species were originally highly concentrated in the wealthy, southeastern coastal provinces of China, but they are currently rapidly spreading inland. Linear regression models based on the species density and turnover of invasive plants as dependent parameters and principal components representing key socio-economic and environmental parameters as predictors indicate strong positive links between invasive plant density and the overall phytodiversity and associated climatic parameters. Principal components representing socio-economic factors and endemic plant density also show significant positive links with invasive plant density. Urgent control and eradication measures are needed in China's coastal provinces to counteract the rapid inland spread of invasive plants. Strict controls of imports through seaports need to be accompanied by similarly strict controls of the developing horticultural trade and underpinned by awareness campaigns for China's increasingly affluent population to limit the arrival of new invaders. Furthermore, China needs to fully utilize its substantial native phytodiversity, rather than relying on exotics, in current large-scale afforestation projects and in the creation of urban green spaces.

Phytotoxic Sulfide More Important than Nutrients for Plants Within a Groundwater-Fed Wetland

Plant diversity in groundwater-fed wetland ecosystems is typically extraordinarily high, yet the biogeochemical controls of this diversity are still incompletely understood. We hypothesized that fine-scale variation in sulfide would influence plant community composition via direct phytotoxicity and indirect mediation of phosphorus release from iron, coupled with gradients in other chemicals such as calcium. We measured porewater chemistry and plant species composition at 400 locations within a calcareous rich fen in central New York State. Groundwater-derived calcium (Ca2+) and sulfate and redox-sensitive sulfide and ferrous iron (Fe2+) showed high heterogeneity. Phosphorus availability was limited and not readily traceable to toxic sulfide, whereas nitrogen (TDN) was more abundant than expected. Using the corrected Akaike information criterion to select between competing models of toxic, nutrient, and mixed-chemistry influences on vegetation, we found that hydrogen sulfide explained decreases in total plant cover, cover of the three most frequently occurring species, dicot species density, plant height, and litter accumulation. Furthermore, sulfide coupled with calcium and phosphorus to explain plant species density and composition. Sulfide was more likely to explain decreased cover of dominant species than rare species. The presence and cover of uncommon species was often unexpectedly explained best by Fe2+ and sulfate, but all models of plant responses with environmental predictor variables were better than the “null” model of mean plant response that lacked environmental variables. An integrated geochemical assessment of coupled groundwater chemistry, redox-sensitive chemistry, and nutrient influences on plants demonstrated the importance of phytotoxic sulfide in explaining plant species density and composition.