Native Plant Species Richness Research Articles

Exclosure from browsing by invasive ungulates increases species richness and diversity of ground flora in rainforests of New Caledonia

Introduced ungulates can impact forest structure and composition. We tested in rainforests of New Caledonia if exclosure of invasive ungulates (Javan rusa deer Rusa timorensis russa and feral pigs Sus (scrofa) domesticus) increased abundance, species richness and diversity of native plants by comparing 19 plots of 10 m2 in four study areas that were protected from browsing for 7 years with 76 unprotected plots. Abundance, species richness and diversity of native plants of 20–60 cm of height were higher in protected plots compared to unprotected plots. We attribute the measured negative impact mainly to deer as the positive effect of exclosures was highest in the study area with the highest deer abundance and browsing rate. The exclosures were also beneficial in a secondary forest with medium deer abundance whereas in old-growth forest with medium deer abundance we could not detect an effect of the exclosures. We conclude that protecting even small areas from browsing by invasive ungulates can increase biodiversity and that exclosures are most beneficial at high deer abundance and in secondary habitats.

Environmental thresholds for plant species richness of black alder (Alnus glutinosa) forests in Central Europe

The diversity of vascular plants in temperate floodplain forests varies between biogeographical regions of Europe. Our study aims to identify the key environmental drivers of plant species richness in forests dominated by black alder (Alnus glutinosa) in Central Europe with four regions: Pannonian lowland, Matricum as the southern part of the Western Carpathians, High Western Carpathians and Polish Plain. We analysed plant species richness and quantified 15 environmental characteristics (soil, climatic and landscape characteristics) in 140 vegetation plots (35 per region). We used model-based regression trees to test the influence of predictors on the richness of both native and alien species. The regression tree analysis identified eight significant variables controlling species richness in three regions and all bioregions together but found no significant predictor in Matricum. The analysis of the joint dataset indicates that native plant richness was controlled by the effects of catchment slope, soil reaction and precipitation of the warmest quarter. In contrast, the richness of alien species was influenced by the precipitation of the warmest quarter, soil phosphorous and temperature. The species richness of native plants in the High Western Carpathians was driven by soil reaction and the presence of artificial surfaces around the plots, while the richness trend in the Pannonain lowland was determined by annual temperature. Alien richness was affected by the proportion of agricultural areas in the High Western Carpathians, by the stream power index in the Polish Plain and by soil reaction in the Pannonian lowland. The explanatory power of the tree models ranged from 22 to 36%. Our results suggest that the predictability of the richness patterns is contingent upon the specific regions, which differ in the length of environmental gradients.

Distribution of native plants and birds on 27 remote Tuamotu atolls (South Pacific Ocean): a contribution to the Island species-area relationship

ABSTRACT Island species-area relationship (ISAR) is the most documented pattern in island biogeography. Different hypotheses were advanced to explain this pattern. In this study, I selected 27 remote Tuamotu atolls in the South Pacific Ocean with complete surveys of native species richness of birds and vascular plants to test the influence of four abiotic predictors on species richness (atoll emerged area, habitat diversity, mean elevation, and number of islets). Linear regressions were used to assess the relative influence of predictors on native species richness while stepwise regression was then used to identify the best model. Atoll area was a significant predictor to explain native bird and plant species richness, attesting ISAR on the remote surveyed atolls. Stepwise model demonstrated that both habitat diversity and atoll area explained bird species richness, whereas atoll area and mean elevation were the best predictors for native plants. These results suggest that ISAR can be related to different hypotheses, depending on the taxon studied. Among hypotheses, the simple “target-area” hypothesis was a suitable framework to explain ISAR of native birds, while the “disturbance” hypothesis was relevant to support ISAR of native plants observed on the atolls.

Revegetation of disturbed land reclaimed with suboptimal topsoil replacement depth and organic amendments

AbstractSuccessful reclamation and revegetation of disturbed sites depends on the availability of sufficient topsoil. Current regulations in western Canada require the replacement of ≥80% of the original topsoil depth (TRD) to restore pre‐disturbance productivity. However, salvaged topsoil at many legacy and other disturbed sites is often insufficient to achieve the 80% TRD (TRD80). This 5‐year study examined vegetation responses to 50% TRD without organic amendment (TRD50) or amended with either peat (PTRD50) or biochar (BTRD50), relative to the TRD80 treatment, following borrow site reclamation in northeastern Alberta, Canada. Amendments were applied once at rates calculated to bring organic carbon in the topsoil to concentrations approximating those in the TRD80 treatment. Tree and shrub seedling mixes were transplanted following amendment application and vegetation attributes were measured annually thereafter. Results showed that PTRD50 performed as well as TRD80 and outperformed BTRD50 with respect to native species' canopy cover and tree seedling height. Canopy covers of forb and non‐native species decreased significantly whereas those of graminoid and native species increased over time for all treatments. Across treatments, native plant species richness increased by 5% per year while non‐native species richness decreased by 19% per year. Overall, peat showed a satisfactory rate of recovery and a trajectory toward the natural boreal forest, indicating its potential to improve reclamation success at disturbed boreal sites where salvaged soil is insufficient to attain equivalent land capability. This finding will provide an additional tool for regulators seeking to refine land reclamation guidelines for such sites in boreal forest regions.

Climate-induced tree-mortality pulses are obscured by broad-scale and long-term greening.

Vegetation greening has been suggested to be a dominant trend over recent decades, but severe pulses of tree mortality in forests after droughts and heatwaves have also been extensively reported. These observations raise the question of to what extent the observed severe pulses of tree mortality induced by climate could affect overall vegetation greenness across spatial grains and temporal extents. To address this issue, here we analyse three satellite-based datasets of detrended growing-season normalized difference vegetation index (NDVIGS) with spatial resolutions ranging from 30 m to 8 km for 1,303 field-documented sites experiencing severe drought- or heat-induced tree-mortality events around the globe. We find that severe tree-mortality events have distinctive but localized imprints on vegetation greenness over annual timescales, which are obscured by broad-scale and long-term greening. Specifically, although anomalies in NDVIGS (ΔNDVI) are negative during tree-mortality years, this reduction diminishes at coarser spatial resolutions (that is, 250 m and 8 km). Notably, tree-mortality-induced reductions in NDVIGS (|ΔNDVI|) at 30-m resolution are negatively related to native plant species richness and forest height, whereas topographic heterogeneity is the major factor affecting ΔNDVI differences across various spatial grain sizes. Over time periods of a decade or longer, greening consistently dominates all spatial resolutions. The findings underscore the fundamental importance of spatio-temporal scales for cohesively understanding the effects of climate change on forest productivity and tree mortality under both gradual and abrupt changes.

Direct topsoil transfer to already planted reforestation sites increases native plant understory and not ruderals

Forests restored passively or by tree planting can take many decades to be recolonized by native forest understory plant species, if at all. Our study tested (1) the ability of forest topsoil transfer to accelerate the recovery of native forest plant communities in post‐agricultural reforestation sites after tree‐planting and without previous topsoil removal and (2) the effect of adding combinations of woody debris (WD), shrub plantings, and shade shelters (SS) on top of the transferred topsoil. Five 12.5 × 10 m treatment blocks were established in each of three recipient sites, which included two post‐agricultural reforestation sites, and one abandoned gravel pit site. Each treatment blocks received forest topsoil and a combination of additional treatments. Treatment and control plots were sampled for all vascular species in spring and summer. Native forest plant species richness in topsoil recipient plots was similar (p > 0.05) to that of mature donor forest sites, and significantly higher (p < 0.05) than that of passive control plots in the recipient sites. The plant community composition of all topsoil recipient plots had also become more like the donor forests and less like recipient site controls. Only the unplanted gravel pit‐site increased in non‐native ruderal plant species after topsoil transfer. The addition of WD, shrub plantings, or SS had no significant effect after two growing seasons. We recommend that topsoil should when possible be added where trees have already been planted, allowing for shorter time to canopy closure and thereby higher survival of shade‐adapted understory species.

Passive restoration of fynbos after afforestation with exotic pines, South Africa

Plantations, and associated invasions, of exotic Pinus trees occur extensively in the southern hemisphere, threatening the persistence of biodiverse Mediterranean‐climate vegetation. Large‐scale decommissioning of such plantations in the eastern Cape Floristic Region (South Africa) enabled a wide‐ranging study showing successful passive restoration of fynbos vegetation after afforestation. Using a paired study design, we compared the diversity, and floristic and growth‐form composition of post‐fire recovering fynbos in former plantations with that in recently burnt neighboring fynbos in a natural state within the Garden Route National Park. The fynbos of the study area showed good autogenic recovery after several decades of pine afforestation and a fire subsequent to the clearcutting of these trees. On average, native plant abundance and species richness (particularly of shrubs) were significantly lower, and non‐native plant species richness significantly higher, in former plantation areas than in natural fynbos, but these differences were small. Species diversity (Shannon–Wiener index) did not differ significantly between the two vegetation states. The former plantations harbored 91% of the number of native species that the natural fynbos had, while the similarity of the two floras was 65%. Non‐metric multidimensional scaling ordination and multivariate generalized linear models accordingly showed no clear distinction in community composition between the two vegetation states. We concluded that the restoration potential of the montane grassy fynbos in the study area is superior to that previously documented in montane proteoid fynbos, and that fire and invasive alien plant control after clearcutting of the plantations is essential to promote fynbos restoration.

Intervention intensity predicts the quality and duration of prairie restoration outcomes

Restoration of grassland ecosystems is essential for mitigating global losses of biodiversity and is typically initiated to foster persistent, long‐term increases in biodiversity. Yet, evaluating long‐term impacts of restoration on biodiversity is rare, especially across sites restored using consistent methods. Evaluation of restoration outcomes is particularly important for increasing predictive capacity in restoration ecology to determine the level of restoration effort that is required to achieve both short‐ and long‐term restoration goals. We conducted a multisite study that explicitly compared the impacts of no intervention (“passive” or “natural” recovery), low intervention (seeding native plants), and moderate intervention (seeding native plants and using fire management) at 32 restored prairies differing in the age of restoration (3–23 years). Grasslands with natural recovery have equivalent native plant species richness compared to sites with low and moderate restoration intervention, however, they have significantly lower‐quality vegetation, as measured by Floristic Quality (mean C). We found that managing restored prairies with fire maintains native plant richness over time and is correlated with higher vegetation quality and presence of seeded species. Seed mixes with a high mean C score are positively correlated with plant community quality. However, seed mixes with more species are negatively correlated with the proportion of seeded species present. We found that while the degree of restoration intervention has no effect on the number of native plant species, greater levels of assisted recovery are required to produce restored prairies that resemble high‐quality remnant vegetation and, especially, to maintain these successes over the long term.

Promoting Beneficial Arthropods in Urban Agroecosystems: Focus on Flowers, Maybe Not Native Plants.

(1) Urbanization threatens biodiversity, yet urban native plants support native biodiversity, contributing to conservation and ecosystem services. Within urban agroecosystems, where non-native plants are abundant, native plants may boost the abundance and richness of beneficial arthropods. Nevertheless, current information focuses on pollinators, with little attention being paid to other beneficials, like natural enemies. (2) We examined how the species richness of native plants, garden management, and landscape composition influence the abundance and species richness of all, native, and non-native bees, ladybeetles, ants, and ground-foraging spiders in urban agroecosystems (i.e., urban community gardens) in California. (3) We found that native plants (~10% of species, but only ~2.5% of plant cover) had little influence on arthropods, with negative effects only on non-native spider richness, likely due to the low plant cover provided by native plants. Garden size boosted native and non-native bee abundance and richness and non-native spider richness; floral abundance boosted non-native spider abundance and native and non-native spider richness; and mulch cover and tree and shrub abundance boosted non-native spider richness. Natural habitat cover promoted non-native bee and native ant abundance, but fewer native ladybeetle species were observed. (4) While native plant richness may not strongly influence the abundance and richness of beneficial arthropods, other garden management features could be manipulated to promote the conservation of native organisms or ecosystem services provided by native and non-native organisms within urban agroecosystems.

Native vegetation structure, landscape features and climate shape non‐native plant richness and cover in New Zealand native shrublands

AbstractAimStudies investigating the determinants of plant invasions rarely examine multiple factors and often only focus on the role played by native plant species richness. By contrast, we explored how vegetation structure, landscape features and climate shape non‐native plant invasions across New Zealand in mānuka and kānuka shrublands.LocationNew Zealand.MethodWe based our analysis on 247 permanent 20 × 20‐m plots distributed across New Zealand surveyed between 2009 and 2014. We calculated native plant species richness and cumulative cover at ground, understorey and canopy tiers. We examined non‐native species richness and mean species ground cover in relation to vegetation structure (native richness and cumulative cover), landscape features (proportion of adjacent anthropogenic land cover, distance to nearest road or river) and climate. We used generalized additive models (GAM) to assess which variables had greatest importance in determining non‐native richness and mean ground cover and whether these variables had a similar effect on native species in the ground tier.ResultsA positive relationship between native and non‐native plant species richness was not due to their similar responses to the variables examined in this study. Higher native canopy richness resulted in lower non‐native richness and mean ground cover, whereas higher native ground richness was associated with higher native canopy richness. Non‐native richness and mean ground cover increased with the proportion of adjacent anthropogenic land cover, whereas for native richness and mean ground cover, this relationship was negative. Non‐native richness increased in drier areas, while native richness was more influenced by temperature.Main ConclusionsAdjacent anthropogenic land cover seems to not only facilitate non‐native species arrival by being a source of propagules but also aids their establishment as a result of fragmentation. Our results highlight the importance of examining both cover and richness in different vegetation tiers to better understand non‐native plant invasions.

The designation of a historical site to maintain plant diversity in the Tokyo metropolitan region

Although urban habitats contribute to the conservation of species diversity, urbanization has significantly reduced biodiversity by causing environmental changes such as habitat loss and fragmentation. Therefore, research on urban biodiversity studies has become increasingly important. Historical heritage sites are recognized as important habitats in remnant green spaces in urban areas. We aimed to evaluate the role of historical sites in conserving biodiversity in urban areas. As the land in these historical sites is not modified, they have the potential to conserve biodiversity through continued maintenance activities such as mowing and tree cutting. In Japan, Tamagawa-josui, a waterway that runs from west to east through the Tokyo megacity (35° 40′ N, 139° 25′ E), has been recognized as a civil engineering heritage landmark that preserves water utilization technology from the early modern period (1600s, Edo-era). The present study examined the relationships between plant diversity and green space in a historic site of a megacity (i.e., Tamagawa-josui) and determined the factors that influence plant diversity. Specifically, we examined the relationships between plant species indices (species richness and species compositions) and environmental factors (management, environmental conditions, and landscape factors). The present study analyzed spatial changes in the plant species composition in Tamagawa-josui. We demonstrated that tree canopy openness was positively correlated with plant species richness, and the increased disturbance associated with developing historical sites as urban parks was negatively correlated with native plant species richness. In addition, there was significant species turnover in the plant community from upstream to downstream in Tamagawa-josui, which could largely be explained by spatial factors. We demonstrated that historical sites can provide potential habitats for the conservation of the plant species diversity, which is based on the effectiveness of the management of their vegetation.

Invasion of a Horticultural Plant into Forests: Lamium galeobdolon argentatum Affects Native Above-Ground Vegetation and Soil Properties

Horticultural trade is considered the most important pathway for the introduction of non-native plant species. Numerous horticultural plants are spreading from private gardens and public green space into natural habitats and have the potential to alter native biodiversity and ecosystem functioning. We assessed the invasiveness of the horticultural plant Lamium galeobdolon subsp. argentatum. We documented its spread in semi-natural habitats in the surroundings of Basel, Switzerland, over the past decades. We compared the performance of L. g. argentatum with that of the native subspecies Lamium galeobdolon galeobdolon based on surveys in forests and a pot experiment under standardized conditions. We also assessed whether the two subspecies differentially affect native forest vegetation and various physical, chemical and biological soil properties. The horticultural L. g. argentatum has tripled its occurrence in forests in the region of Basel in the last four decades. Lamium g. argentatum had both a higher growth rate and regeneration capacity than the native subspecies. Furthermore, L. g. argentatum reduced native plant species richness and changed the species composition of the ground vegetation, in addition to altering several soil properties in deciduous forests. Lamium g. argentatum should therefore be considered an invasive taxon.

Increased Leaf Bacterial Network Complexity along the Native Plant Diversity Gradient Facilitates Plant Invasion?

Understanding the mechanisms of biological invasion is critical to biodiversity protection. Previous studies have produced inconsistent relationships between native species richness and invasibility, referred to as the invasion paradox. Although facilitative interactions among species have been proposed to explain the non-negative diversity-invasibility relationship, little is known about the facilitation of plant-associated microbes in invasions. We established a two-year field biodiversity experiment with a native plant species richness gradient (1, 2, 4, or 8 species) and analyzed the effects of community structure and network complexity of leaf bacteria on invasion success. Our results indicated a positive relationship between invasibility and network complexity of leaf bacteria of the invader. Consistent with previous studies, we also found that native plant species richness increased the leaf bacterial diversity and network complexity. Moreover, the results of the leaf bacteria community assembly of the invader suggested that the complex bacteria community resulted from higher native diversity rather than higher invader biomass. We concluded that increased leaf bacterial network complexity along the native plant diversity gradient likely facilitated plant invasion. Our findings provided evidence of a potential mechanism by which microbes may affect the plant community invasibility, hopefully helping to explain the non-negative relationship between native diversity and invasibility.

Pinus contorta Alters Microenvironmental Conditions and Reduces Plant Diversity in Patagonian Ecosystems

Pinus contorta is considered one of the most invasive tree species worldwide, generating significant impacts on biodiversity and ecosystems. In several Patagonian ecosystems in southern Chile, it has escaped from plantations established mainly in the 1970s, and is now invading both forests and treeless environments. In this study, we evaluated the impact of the invasion of P. contorta on microenvironmental conditions in Araucaria araucana forest and Patagonian steppe ecosystems, and assessed how these changes related to the richness and abundance of native and non-native plant species. In each ecosystem, 24 plots of 100 m2 were established along a gradient of P. contorta biomass, where 18 environmental variables and the composition of native and non-native vegetation were measured at a local scale. Our results indicated that increased pine biomass was associated with differences in microclimatic conditions (soil and air temperature, photosynthetically active radiation (PAR), and soil moisture) and soil properties (potassium, nitrate, pH, and litter accumulation). These changes were ecosystem dependent, however, as well as associated with the level of invasion. Finally, the reduction in the richness and abundance of native plants was associated with the changes in soil properties (accumulation of leaf litter, pH, and organic matter) as well as in the microclimate (minimum air temperature, PAR) generated by the invasion of P. contorta. Overall, our results confirm that the invasion of P. contorta impacts microenvironmental conditions (i.e., canopy cover, litter accumulation, minimum air temperature, and maximum soil temperature) and reduces native plant diversity. For future restoration plans, more emphasis should be given to how environmental changes can influence the recovery of invaded ecosystems even after the removal of the living pine biomass (i.e., legacy of the invasion).

Cultural Landscape as Both a Threat and an Opportunity to Preserve a High Conservation Value of Vascular Flora: A Case Study

This study aimed to show the influence of cultural landscape structure on species richnessand the conservation value of vascular flora.The analyses are based on 3201 original floristic lists (relevés) and 83,875 floristic data collected since 1994 within Gopło Millennium Park (Nadgoplański Park Tysiąclecia) in a rural area in central Poland. Descriptions of landscape composition in grid cells (0.5 km × 0.5 km) include land use structure, mean deviation of uneven proportions of various land use types, and Shannon index of diversity (H’). Vascular plant diversity was described using total species richness and contributions of groups of native and alien species. Assessment of floristic conservation value was based on qualitative and quantitative floristic index (Wfj and Wfi), mean coefficient of conservatism (C), and floristic quality index (FQI). Floristic analyses were conducted in relation to the whole study area and within grid cells, basing on numbers of species and number of floristic data. The results suggest that species richness in grid cells depends more strongly on diversity and evenness of contributions of land use types, irrespective of which land use types were present. Species richness is strongly dependent on land use structure. Larger contributions of arable fields and built-up areas are linked with a decrease in species richness of nonsynanthropic native plants and species of floristic conservation value. Regularity in this respect is very well illustrated by indices excluding the influence of species richness on floristic value (quantitative floristic index Wfi and mean coefficient of conservatism C). According to the algorithm of FQI, the most valuable floras are characterized by a large number of species with a high contribution of conservative ones. In the study area, this condition was met by floras of surface waters and wetlands.

Comparative diversity of vascular plants in black alder floodplain and swamp forests of Central European biogeographical regions.

Plant species diversity of black alder-dominated forests was studied in three biogeographical regions (Alpine, Continental and Pannonian) of Central Europe. They were represented by regions of the Polish Plain (Continental), the High Western Carpathians and Matricum of the Western Carpathians (Alpine) and the Pannonian lowland (Pannonian). We analysed 35 plots per region in order to identify: i) local alpha (α) diversity defined as the counted number of plant taxa occurring in a single sampling plot, ii) amongst-site beta (β) diversity, iii) regional (γ) diversity defined as the total species richness of all sampling plots and iv) zeta diversity (ζ) as a generalisation of beta diversity. We recorded a total of 432 vascular plant taxa in all bioregions; more than 13% were alien plants. Statistically significant differences in species richness (α) of both native and alien plants were found between assemblages of the regions. The High Western Carpathians showed the highest native and the lowest alien plant species richness. Total β-diversity was high in all regions, but significantly differed amongst regions only for alien plant species. Cumulative native and alien species richness (γ) was the highest and lowest in the High Western Carpathians and Matricum of Western Carpathians, respectively. Our results identified the High Western Carpathians as a hotspot for diversity of native plants in Central European black alder-dominated forests.

Effects of Pine Plantation on Native Ecuadorian Páramo Vegetation

Exotic pine plantations, installed mainly for timber production and carbon sequestration purposes, cover an ever-expanding area of equatorial and tropical regions; however, their economic and environmental benefits are under debate due to their potential negative effects on native plant species conservation. The native understory plant species richness and cover under pine (Pinus radiata D. Don) plantations were compared with natural grasslands in the Ecuadorian Páramo. We analyzed the vegetation in four zones: Antisana (8-year-old pines), Cajas (16-year-old pines), Tisaleo (41-year-old pines) and Cotopaxi (53-year-old pines). The total understory plant cover decreased between 29% and 90% under pine plantations in all zones. The mean species richness in the pine plantations decreased by 44% in Antisana, Cajas and Tisaleo but not in Cotopaxi. Pine plantations strongly reduced the abundance of herbaceous light-demanding species (59%), except small herbs whose cover increased under pine (17.6%). Shrub cover was also negatively affected in Tisaleo and Cotopaxi (7.4%). Pine afforestation effects on Páramo vegetation depend mainly on canopy cover which changes with age and growing conditions (altitude) and secondarily on the vegetation state at the time of planting, resulting from land use history and ecological conditions. The pine effect was therefore more pronounced in the young and dense plantations of Antisana and Cajas than in the old and open stand of Cotopaxi, whose understory vegetation was more similar to that of grasslands.

Reintroducing bison results in long-running and resilient increases in grassland diversity

The widespread extirpation of megafauna may have destabilized ecosystems and altered biodiversity globally. Most megafauna extinctions occurred before the modern record, leaving it unclear how their loss impacts current biodiversity. We report the long-term effects of reintroducing plains bison (Bison bison) in a tallgrass prairie versus two land uses that commonly occur in many North American grasslands: 1) no grazing and 2) intensive growing-season grazing by domesticated cattle (Bos taurus). Compared to ungrazed areas, reintroducing bison increased native plant species richness by 103% at local scales (10 m2) and 86% at the catchment scale. Gains in richness continued for 29 y and were resilient to the most extreme drought in four decades. These gains are now among the largest recorded increases in species richness due to grazing in grasslands globally. Grazing by domestic cattle also increased native plant species richness, but by less than half as much as bison. This study indicates that some ecosystems maintain a latent potential for increased native plant species richness following the reintroduction of native herbivores, which was unmatched by domesticated grazers. Native-grazer gains in richness were resilient to an extreme drought, a pressure likely to become more common under future global environmental change.

Floristic homogenization as a result of the introduction of exotic species in China

AbstractAimThe introduction of exotic plants can both increase (homogenize) and decrease (differentiate) floristic similarity between areas. We have a poor understanding of the degree to which plant species introductions tend to homogenize or differentiate floras, and relevant studies covering large spatial extent are scarce. China has been heavily invaded by exotic plants. Here, we analyse a comprehensive dataset of vascular plants to determine whether the introduction of exotic plant species has homogenized or differentiated species composition in regions across China.LocationChina.MethodsWe calculated the Jaccard index and Simpson index of similarity for each pair of province‐level regions for native and exotic species separately and jointly, and calculated a homogenization index for each pair of regional floras. We correlated species richness of native and exotic plants to climatic factors, and correlated the Jaccard index and Simpson index to geographic and climatic distances. We used variation partitioning analysis to determine the relative importance of geographic and climatic distances on species turnover. We also examined the effect of human population density on florisitic similarity of exotic species.ResultsWe found that the geographic range of each species was, on average, larger for exotics than for natives; floristic similarity between regions was greater for exotics than for natives; the vast majority of pairwise regional floras have been homogenized; the introduction of exotic species has caused stronger biotic homogenization for pairwise floras with greater dissimilarity in their species composition; geographic distributions of exotic and native species were determined by different sets of climatic factors; and distributions of exotic species were determined by climatic factors more strongly, compared to those of native species. Human population density had a moderate effect on florisitic similarity of exotic species.Main conclusionsThe introduction of exotic plant species has homogenized regional floras across China. Because strong international trades between China and other countries and dramatic development of transportation systems are continuing in China, which help spread of exotic species, we predict that exotic species will continue to spread and will strengthen biotic homogenization in China.

Grazing of Reed Canarygrass (Phalaris arundinacea) in Restored Wet Meadows

Reed canarygrass (Phalaris arundinacea) is a grass species that can dominate wet meadow plant communities. This study investigated if grazing by cattle on restored wet meadows suppresses reed canarygrass, thereby promoting the restored plant community. This study was conducted at two locations in northwest Minnesota, one managed by The Nature Conservancy (TNC) and the other a Minnesota Board of Water and Soil Resources (BWSR) wetland bank site. Management practices used were a patch-burn grazing treatment on the TNC site and a high-density, short-duration grazing rotation system on the BWSR site. A pretreatment survey of total species canopy coverage was conducted before grazing followed by periodic surveys up to 7 y after grazing started. Both the patch-burn grazing and the grazing rotation system reduced reed canarygrass canopy cover by 49% compared to non-grazed control sites 5–7 y after grazing. With a reduction in reed canary grass canopy coverage due to grazing, the plant community moved toward a community with higher canopy coverage of Carex pellita that met restoration goals. Some of the species change was to grasses like Kentucky bluegrass (Poa pratensis), which is an exotic, invasive grass in prairies. The changed plant community held steady in native plant species richness or had an increase in native plant species richness. This study demonstrates grazing reduces the cover of reed canarygrass, while meeting restoration goals for wet meadows.