GEOGRAFISKA ANNALER SERIES A: PHYSICAL GEOGRAPHY, Issue 4 2009
NATALIE S. HAUSSMANN
ABSTRACT. Through changing soil thermal regimes, soil moisture and affecting weathering and erosion processes plants can have an important effect on the physical properties and structure of soils. Such physical soil changes can in turn lead to biological facilitation, such as vegetation-banked terrace formation or differential seedling establishment. We studied the fine scale variability in soil temperature and moisture parameters, specifically focusing on frost cycle characteristics around cushions of the dominant, vascular plant species, Azorella selago, on sub-Antarctic Marion Island. The frost season was characterised by numerous low intensity and very shallow frost cycles. Soils on eastern cushion sides were found to have lower mean and maximum temperatures in winterthan soils on western cushion sides. In addition, lower variability in temperature was found on eastern cushion sides in winterthan on western cushion sides, probably as a result of higher wind speeds on western cushion sides and/or eastern, lee-side snow accumulation. Despite the mild frost climate, extensive frost heave occurred in the study area, indicating that needle ice forms at temperatures above ,2°C. Our results demonstrate the effectiveness of frost pull as a heave mechanism under shallow frost conditions. The results highlight the importance of Azorella cushions in modifying site microclimates and of understanding the consequences of these modifications, such as potentially providing microhabitats. Such potential microhabitats are particularly important in light of current climate change trends on the island, as continued warming and drying will undoubtedly increase the need for thermal and moisture refugia. [source]

Susceptibility of Common and Rare Plant Species to the Genetic Consequences of Habitat Fragmentation

CONSERVATION BIOLOGY, Issue 3 2007
OLIVIER HONNAY
diversidad genética; endogamia; fragmentación de hábitat; sistema reproductivo; tamaño poblacional Abstract:,Small plant populations are more prone to extinction due to the loss of genetic variation through random genetic drift, increased selfing, and mating among related individuals. To date, most researchers dealing with genetic erosion in fragmented plant populations have focused on threatened or rare species. We raise the question whether common plant species are as susceptible to habitat fragmentation as rare species. We conducted a formal meta-analysis of habitat fragmentation studies that reported both population size and population genetic diversity. We estimated the overall weighted mean and variance of the correlation coefficients among four different measures of genetic diversity and plant population size. We then tested whether rarity, mating system, and plant longevity are potential moderators of the relationship between population size and genetic diversity. Mean gene diversity, percent polymorphic loci, and allelic richness across studies were positively and highly significantly correlated with population size, whereas no significant relationship was found between population size and the inbreeding coefficient. Genetic diversity of self-compatible species was less affected by decreasing population size than that of obligate outcrossing and self-compatible but mainly outcrossing species. Longevity did not affect the population genetic response to fragmentation. Our most important finding, however, was that common species were as, or more, susceptible to the population genetic consequences of habitat fragmentation than rare species, even when historically or naturally rare species were excluded from the analysis. These results are dramatic in that many more plant species than previously assumed may be vulnerable to genetic erosion and loss of genetic diversity as a result of ongoing fragmentation processes. This implies that many fragmented habitats have become unable to support plant populations that are large enough to maintain a mutation-drift balance and that occupied habitat fragments have become too isolated to allow sufficient gene flow to enable replenishment of lost alleles. Resumen:,Las poblaciones pequeñas de plantas son más propensas a la extinción debido a la pérdida de variación genética por medio de la deriva génica aleatoria, el incremento de autogamia y la reproducción entre individuos emparentados. A la fecha, la mayoría de los investigadores que trabajan con erosión genética en poblaciones fragmentadas de plantas se han enfocado en las especies amenazadas o raras. Cuestionamos si las especies de plantas comunes son tan susceptibles a la fragmentación del hábitat como las especies raras. Realizamos un meta análisis formal de estudios de fragmentación que reportaron tanto tamaño poblacional como diversidad genética. Estimamos la media general ponderada y la varianza de los coeficientes de correlación entre cuatro medidas de diversidad genética y de tamaño poblacional de las plantas. Posteriormente probamos si la rareza, el sistema reproductivo y la longevidad de la planta son moderadores potenciales de la relación entre el tamaño poblacional y la diversidad genética. La diversidad genética promedio, el porcentaje de loci polimórficos y la riqueza alélica en los estudios tuvieron una correlación positiva y altamente significativa con el tamaño poblacional, mientras que no encontramos relación significativa entre el tamaño poblacional y el coeficiente de endogamia. La diversidad genética de especies auto compatibles fue menos afectada por la reducción en el tamaño poblacional que la de especies exogámicas obligadas y especies auto compatibles, pero principalmente exogámicas. La longevidad no afectó la respuesta genética de la población a la fragmentación. Sin embargo, nuestro hallazgo más importante fue que las especies comunes fueron tan, o más, susceptibles a las consecuencias genéticas de la fragmentación del hábitat que las especies raras, aun cuando las especies histórica o naturalmente raras fueron excluidas del análisis. Estos resultados son dramáticos porque muchas especies más pueden ser vulnerables a la erosión genética y a la pérdida de diversidad genética como consecuencia de los procesos de fragmentación que lo se asumía previamente. Esto implica que muchos hábitats fragmentados han perdido la capacidad para soportar poblaciones de plantas lo suficientemente grandes para mantener un equilibrio mutación-deriva y que los fragmentos de hábitat ocupados están tan aislados que el flujo génico es insuficiente para permitir la reposición de alelos perdidos. [source]

Exclusion of Natural Enemies as a Tool in Managing Rare Plant Species

CONSERVATION BIOLOGY, Issue 5 2000
S. M. Louda
No abstract is available for this article. [source]

Reaction of Certain Solanaceous and Asteraceous Plant Species to Inoculation with Phytophthora infestans in Cameroon

JOURNAL OF PHYTOPATHOLOGY, Issue 6 2004
D. A. Fontem
Abstract Experiments were conducted to detect potential hosts of Phytophthora infestans, causal agent of potato late blight among weeds occurring in Cameroon. Isolates of P. infestans isolated from garden huckleberry (Solanum scabrum), potato (S. tuberosum) and tomato (S. lycopersicon) were inoculated on detached leaves of 12 solanaceous and 14 asteraceous species collected from the potato agroecosystem in the western highlands of Cameroon. Isolates of P. infestans from huckleberry and potato infected the same host plants as well as gboma eggplant (S. macrocarpon) and two asteraceous weeds; Billy goatweed (Ageratum conyzoides) and Dichrocephala (Dichrocephala integrifolia). Inoculum from potato caused late blight symptoms on haemorrhage plant (Aspilia africana); while inoculum from tomato resulted in late blight on worowo (Solanecio biafrae). This is the first report of late blight infection on S. macrocarpon, A. conyzoides, Sol. biafrae and Asp. africana in Cameroon. The research results indicate that some asteraceous and solanaceous weeds may be alternative hosts of P. infestans in the potato agroecosystem. [source]

Herbivore-Mediated Competition between Defended and Undefended Plant Species: A Model to Investigate Consequences of Climate Change

PLANT BIOLOGY, Issue 5 2002
C. F. Dormann
Abstract: Optimal levels of anti-herbivore defence are determined not only by grazing pressure on the target plant, but also by the efficiency of the defence and by competitive interactions with neighbours. In the high Arctic on Svalbard, grazing by reindeer is a process that can be modelled without plant-to-herbivore feedback, as reindeer population sizes are not correlated with plant growth. However, growing conditions are extreme: a short season and low temperatures inhibit optimal growth. Therefore, it is possible to model anti-herbivore defence in competition in this system, assess how its optimum depends on grazing intensity and defence efficiency, and, finally, how global climate change will effect plant-plant interactions. This model, based on a Lotka-Volterra type competition and temperature-dependent growth, indicates that competition is of considerable importance even in extreme environments. Herbivory mediates displacement of the defended plant by releasing it from competition. This process is more pronounced under high grazing pressure than under low pressure. In other words, competition potentially magnifies the effect of herbivory. Elevated temperatures and a longer growing season have no qualitative impact on these processes, as the dominant defended plant profits most. [source]

Toward detoxifying mercury-polluted aquatic sediments with rice genetically engineered for mercury resistance

ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 12 2003
Andrew C. P. Heaton
Abstract Mercury contamination of soil and water is a serious problem at many sites in the United States and throughout the world. Plant species expressing the bacterial mercuric reductase gene, merA, convert ionic mercury, Hg(II), from growth substrates to the less toxic metallic mercury, Hg(0). This activity confers mercury resistance to plants and removes mercury from the plant and substrates through volatilization. Our goal is to develop plants that intercept and remove Hg(II) from polluted aquatic systems before it can undergo bacterially mediated methylation to the neurotoxic methylmercury. Therefore, the merA gene under the control of a monocot promoter was introduced into Oryza sativa L. (rice) by particle gun bombardment. This is the first monocot and first wetland-adapted species to express the gene. The merA -expressing rice germinated and grew on semisolid growth medium spiked with sufficient Hg(II) to kill the nonengineered (wild-type) controls. To confirm that the resistance mechanism was the conversion of Hg(II) to Hg(0), seedlings of merA -expressing O. sativa were grown in Hg(II)-spiked liquid medium or water-saturated soil media and were shown to volatilize significantly more Hg(0) than wild-type counterparts. Further genetic manipulation could yield plants with increased efficiency to extract soil Hg(II) and volatilize it as Hg(0) or with the novel ability to directly convert methylmercury to Hg(0). [source]

Leaf litter flammability in some semi-arid Australian woodlands

FUNCTIONAL ECOLOGY, Issue 5 2006
F. R. SCARFF
Summary 1Wildfires strongly influence the biotic composition and carbon cycle of many ecosystems. Plant species provide the fuel for wildfires, but vary widely in their flammability. This study aimed to determine what plant characteristics control leaf litter flammability and to clarify how they are related to other functional traits. 2Litter flammability varied across 14 tree species occurring in a mosaic of five floristic associations. 3Differences in heat-release rate between species were driven by leaf size, from small-leaved conifers, casuarinas and acacias to large-leaved eucalypts and Brachychiton. 4Large leaves created an open litter-bed structure that burned more rapidly because it was better ventilated. The results on heat-release rate were partitioned according to fundamental principles for the transport of oxygen through a packed fuel bed, showing that heat-release rate scaled linearly with estimated gas-flow rates, as expected in ventilation-controlled fires. 5Species that were able to resprout after fire had litter that burned more intensely and was more likely to sustain a spreading fire than litter from obligate seeders, and were correspondingly larger-leaved. 6Many fire-prone wooded ecosystems in the region consist of large-leaved resprouting tree species co-occurring with small-leaved obligate seeders. [source]

Spatial scale affects bioclimate model projections of climate change impacts on mountain plants

GLOBAL CHANGE BIOLOGY, Issue 5 2008
MANDAR R. TRIVEDI
Abstract Plant species have responded to recent increases in global temperatures by shifting their geographical ranges poleward and to higher altitudes. Bioclimate models project future range contractions of montane species as suitable climate space shifts uphill. The species,climate relationships underlying such models are calibrated using data at either ,macro' scales (coarse resolution, e.g. 50 km × 50 km, and large spatial extent) or ,local' scales (fine resolution, e.g. 50 m × 50 m, and small spatial extent), but the two approaches have not been compared. This study projected macro (European) and local models for vascular plants at a mountain range in Scotland, UK, under low (+1.7 °C) and high (+3.3 °C) climate change scenarios for the 2080s. Depending on scenario, the local models projected that seven or eight out of 10 focal montane species would lose all suitable climate space at the site. However, the European models projected such a loss for only one species. The cause of this divergence was investigated by cross-scale comparisons of estimated temperatures at montane species' warm range edges. The results indicate that European models overestimated species' thermal tolerances because the input coarse resolution climate data were biased against the cold, high-altitude habitats of montane plants. Although tests at other mountain ranges are required, these results indicate that recent large-scale modelling studies may have overestimated montane species' ability to cope with increasing temperatures, thereby underestimating the potential impacts of climate change. Furthermore, the results suggest that montane species persistence in microclimatic refugia might not be as widespread as previously speculated. [source]

Plant species as indicators of the extent of desertification in four sandy rangelands

AFRICAN JOURNAL OF ECOLOGY, Issue 1 2007
Ping An
Abstract We examined the distribution of plants in sandy rangelands with different degrees of desertification in (i) Horqin and Mu Us sandy lands in north China, (ii) Darfur district in north-west Sudan and (iii) southern Tunisia. The severity of desertification in these areas was classified as light, moderate, severe or extreme. The following vegetation changes were observed with increasing severity of desertification: a decrease in the number of plant species, an increase in drought-tolerant plants, a decrease in the proportion of palatable grasses and the occurrence of some species in only one category of desertification, whereas other species occurred in several categories. Plant species with unique niche requirements were identified and recommended as indicators of the degree of desertification for particular areas. We discuss the characteristics of species in areas with severe desertification and the method of using plant species as indicators of the extent of desertification. Résumé Nous avons examiné la distribution des plantes dans des régions sableuses touchées à différents degrés par la désertification 1) dans les terres sableuses de Horqin et de Mu Us, dans le nord de la Chine, 2) dans le district du Darfur, au nord-ouest du Soudan et 3) dans le sud de la Tunisie. La gravité de la désertification était classifiée comme légère, modérée, sévère ou extrême. Les changements de végétation suivants ont été observés en fonction de l'accroissement de la désertification: une diminution du nombre d'espèces de plantes, une augmentation des plantes supportant la sécheresse, une diminution de la proportion de plantes appétantes, et l'occurrence de certaines espèces qui ne vivent que dans une catégorie de désertification, alors que d'autres espèces apparaissent dans plusieurs catégories. On a identifié les espèces végétales qui exigent une niche précise et on les a recommandées comme indicateurs du degré de désertification dans des zones particulières. Nous discutons des caractéristiques des espèces dans des régions où la sécheresse est sévère et de la méthode pour utiliser les espèces végétales comme indicateurs de la gravité de la désertification. [source]

Linkages of plant traits to soil properties and the functioning of temperate grassland

JOURNAL OF ECOLOGY, Issue 5 2010
Kate H. Orwin
Summary 1.,Global change is likely to alter plant community structure, with consequences for the structure and functioning of the below-ground community and potential feedbacks to climate change. Understanding the mechanisms behind these plant,soil interactions and feedbacks to the Earth-system is therefore crucial. One approach to understanding such mechanisms is to use plant traits as predictors of functioning. 2.,We used a field-based monoculture experiment involving nine grassland species that had been growing on the same base soil for 7 years to test whether leaf, litter and root traits associated with different plant growth strategies can be linked to an extensive range of soil properties relevant to carbon, nitrogen and phosphorus cycling. Soil properties included the biomass and structure of the soil microbial community, soil nutrients, soil microclimate and soil process rates. 3.,Plant species with a high relative growth rate (RGR) were associated with high leaf and litter quality (e.g. low toughness, high nitrogen concentrations), an elevated biomass of bacteria relative to fungi in soil, high rates of soil nitrogen mineralization and concentrations of extractable inorganic nitrogen, and to some extent higher available phosphorus pools. 4.,In contrast to current theory, species with a high RGR and litter quality were associated with soils with a lower rate of soil respiration and slow decomposition rates. This indicates that predicting processes that influence carbon cycling from plant traits may be more complex than predicting processes that influence nitrogen and phosphorus cycling. 5.,Root traits did not show strong relationships to RGR, leaf or litter traits, but were strongly correlated with several soil properties, particularly the biomass of bacteria relative to fungi in soil and measures relating to soil carbon cycling. 6.,Synthesis. Our results indicate that plant species from a single habitat can result in significant divergence in soil properties and functioning when grown in monoculture, and that many of these changes are strongly and predictably linked to variation in plant traits associated with different growth strategies. Traits therefore have the potential to be a powerful tool for understanding the mechanisms behind plant,soil interactions and ecosystem functioning, and for predicting how changes in plant species composition associated with global change will feedback to the Earth-system. [source]

Plant species and functional group effects on abiotic and microbial soil properties and plant,soil feedback responses in two grasslands

JOURNAL OF ECOLOGY, Issue 5 2006
T. MARTIJN BEZEMER
Summary 1Plant species differ in their capacity to influence soil organic matter, soil nutrient availability and the composition of soil microbial communities. Their influences on soil properties result in net positive or negative feedback effects, which influence plant performance and plant community composition. 2For two grassland systems, one on a sandy soil in the Netherlands and one on a chalk soil in the United Kingdom, we investigated how individual plant species grown in monocultures changed abiotic and biotic soil conditions. Then, we determined feedback effects of these soils to plants of the same or different species. Feedback effects were analysed at the level of plant species and plant taxonomic groups (grasses vs. forbs). 3In the sandy soils, plant species differed in their effects on soil chemical properties, in particular potassium levels, but PLFA (phospholipid fatty acid) signatures of the soil microbial community did not differ between plant species. The effects of soil chemical properties were even greater when grasses and forbs were compared, especially because potassium levels were lower in grass monocultures. 4In the chalk soil, there were no effects of plant species on soil chemical properties, but PLFA profiles differed significantly between soils from different monocultures. PLFA profiles differed between species, rather than between grasses and forbs. 5In the feedback experiment, all plant species in sandy soils grew less vigorously in soils conditioned by grasses than in soils conditioned by forbs. These effects correlated significantly with soil chemical properties. None of the seven plant species showed significant differences between performance in soil conditioned by the same vs. other plant species. 6In the chalk soil, Sanguisorba minor and in particular Briza media performed best in soil collected from conspecifics, while Bromus erectus performed best in soil from heterospecifics. There was no distinctive pattern between soils collected from forb and grass monocultures, and plant performance could not be related to soil chemical properties or PLFA signatures. 7Our study shows that mechanisms of plant,soil feedback can depend on plant species, plant taxonomic (or functional) groups and site-specific differences in abiotic and biotic soil properties. Understanding how plant species can influence their rhizosphere, and how other plant species respond to these changes, will greatly enhance our understanding of the functioning and stability of ecosystems. [source]

Plant species and growth form richness along altitudinal gradients in the southwest Ethiopian highlands

JOURNAL OF VEGETATION SCIENCE, Issue 4 2010
Wana Desalegn
Abstract Questions: Do growth forms and vascular plant richness follow similar patterns along an altitudinal gradient? What are the driving mechanisms that structure richness patterns at the landscape scale? Location: Southwest Ethiopian highlands. Methods: Floristic and environmental data were collected from 74 plots, each covering 400 m2. The plots were distributed along altitudinal gradients. Boosted regression trees were used to derive the patterns of richness distribution along altitudinal gradients. Results: Total vascular plant richness did not show any strong response to altitude. Contrasting patterns of richness were observed for several growth forms. Woody, graminoid and climber species richness showed a unimodal structure. However, each of these morphological groups had a peak of richness at different altitudes: graminoid species attained maximum importance at a lower elevations, followed by climbers and finally woody species at higher elevations. Fern species richness increased monotonically towards higher altitudes, but herbaceous richness had a dented structure at mid-altitudes. Soil sand fraction, silt, slope and organic matter were found to contribute a considerable amount of the predicted variance of richness for total vascular plants and growth forms. Main Conclusions: Hump-shaped species richness patterns were observed for several growth forms. A mid-altitudinal richness peak was the result of a combination of climate-related water,energy dynamics, species,area relationships and local environmental factors, which have direct effects on plant physiological performance. However, altitude represents the composite gradient of several environmental variables that were interrelated. Thus, considering multiple gradients would provide a better picture of richness and the potential mechanisms responsible for the distribution of biodiversity in high-mountain regions of the tropics. [source]

Biological performance of Myzus persicae and Macrosiphum euphorbiae (Homoptera: Aphididae) on seven wild Solanum species

ANNALS OF APPLIED BIOLOGY, Issue 3 2010
Y. Pelletier
Resistance level of seven accessions of wild Solanum species (Solanaceae) to Myzus persicae and Macrosiphum euphorbiae (Homoptera: Aphididae) was evaluated by measuring survival and fecundity during sleeve cage experiments and population growth on whole plants in a controlled environment. The survival was lowest on the Solanum circaeifolium spp. capsicibaccatum, Solanum pinnatisectum and Solanum trifidum accessions for M. persicae and on the S. circaeifolium spp. capsicibaccatum, Solanum okadae and S. trifidum, accessions with M. euphorbiae. Plant species significantly influenced the fecundity of both aphid species. Aphid population growth on whole plants was negatively affected by the age of the plant, but generally followed the levels of net reproductive rate on different plant species observed during the sleeve cage experiment. The population of M. persicae varied among the seven wild potato accessions with the lowest growth rates on S. circaeifolium spp. capsicibaccatum, Solanum polyadenium, Solanum tarijense and S. trifidum. The number of M. euphorbiae also varied among accessions but the smallest population was collected from S. polyadenium. The results can be used to identify sources of resistance to aphids within those accessions already known to be resistant to the Colorado potato beetle. This study highlights the difficulties involved in developing a high-throughput screening test for aphid resistance compatible with a potato breeding programme. [source]

Classifying the fire-response traits of plants: How reliable are species-level classifications?

AUSTRAL ECOLOGY, Issue 3 2010
LYNDSEY MARIE VIVIAN
Abstract Plant species in fire-prone environments possess specific traits which allow them to survive fire. Species are commonly classified according to whether they survive fire and resprout or whether they are killed by fire and regenerate from seed. However, different populations of the same species have been shown to vary in their responses. Therefore, the classification of a species into a single category based on fire-response traits may not necessarily be representative of every population under every circumstance. This study examined the extent of within-species variation in fire-response traits of woody plants in south-eastern Australia after the 2003 fires. Species were then classified using two approaches: (i) using data from a field survey of fire-response traits, taking into account within-species variation; and (ii) using species' fire responses listed in a pre-existing fire-response database compiled from a variety of primary sources. Field data showed that the majority of species in the study area resprouted after fire with around one in 10 species variable in their resprouting response. Almost half of all species varied from site to site according to whether they regenerated from seed, either solely or in addition to resprouting. The numbers of species classified as resprouters and seed regenerators varied according to the classification method used. Differences were also found between the classification method when calculating the mean proportion of resprouters and seed regenerators across sites. The fire-response traits for some species from the database were found to differ from the observed field responses. This study demonstrated that the application of a fire-response trait, reported in a trait database, to an entire species, may not adequately represent the actual fire responses of the populations of interest. Rather than considering the fire-response traits of a species, accurate prediction may be better achieved by considering how different populations of plants will respond to fire. [source]

Scaling-up from leaf to canopy-aggregate properties in sclerophyll shrub species

AUSTRAL ECOLOGY, Issue 3 2006
CASSIA READ
Abstract: Plant species vary widely in their average leaf lifespan (LL) and specific leaf area (SLA, leaf area per dry mass). The negative LL,SLA relationship commonly seen among species represents an important evolutionary trade-off, with higher SLA indicating greater potential for fast growth (higher rate of return on a given investment), but longer LL indicating a longer duration of the revenue stream from that investment. We investigated how these leaf-economic traits related to aggregate properties of the plant crown. Across 14 Australian sclerophyll shrub species, those with long LL accumulated more leaf mass and leaf area per unit ground area. Light attenuation through their canopies was more severe. Leaf accumulation and light attenuation were more weakly related to SLA than to LL. The greater accumulation of foliage in species with longer LL and lower SLA may counterbalance their generally lower photosynthetic rates and light-capture areas per gram of leaf. [source]

Global patterns in plant height

JOURNAL OF ECOLOGY, Issue 5 2009
Angela T. Moles
Summary 1. ,Plant height is a central part of plant ecological strategy. It is strongly correlated with life span, seed mass and time to maturity, and is a major determinant of a species' ability to compete for light. Plant height is also related to critical ecosystem variables such as animal diversity and carbon storage capacity. However, remarkably little is known about global patterns in plant height. Here, we use maximum height data for 7084 plant Species × Site combinations to provide the first global, cross-species quantification of the latitudinal gradient in plant height. 2. ,The mean maximum height of species growing within 15° of the equator (7.8 m) was 29 times greater than the height of species between 60° and 75° N (27 cm), and 31 times greater than the height of species between 45° and 60° S (25 cm). There was no evidence that the latitudinal gradient in plant height was different in the northern hemisphere than in the southern hemisphere (P = 0.29). A 2.4-fold drop in plant height at the edge of the tropics (P = 0.006) supports the idea that there might be a switch in plant strategy between temperate and tropical zones. 3. ,We investigated 22 environmental variables to determine which factors underlie the latitudinal gradient in plant height. We found that species with a wide range of height strategies were present in cold, dry, low productivity systems, but there was a noticeable lack of very short species in wetter, warmer, more productive sites. Variables that capture information about growing conditions during the harsh times of the year were relatively poor predictors of height. The best model for global patterns in plant height included only one term: precipitation in the wettest month (R2 = 0.256). 4. ,Synthesis. We found a remarkably steep relationship between latitude and height, indicating a major difference in plant strategy between high and low latitude systems. We also provide new, surprising information about the correlations between plant height and environmental variables. [source]

Activation of defence reactions in Solanaceae: where is the specificity?

CELLULAR MICROBIOLOGY, Issue 1 2007
Sabine Desender
Summary When a potential pathogen attempts to infect a plant, biochemical and molecular communication takes place and leads to the induction of plant defence mechanisms. In the case of efficient defence, visible symptoms are restricted and the pathogen does not multiply (incompatible interaction); when defence is inefficient, the plant becomes rapidly infected (compatible interaction). During the last 30 years, a growing body of knowledge on plant,pathogen interactions has been gathered, and a large number of studies investigate the induction of various plant defence reactions by pathogens or by pathogen-derived compounds. However, as most papers focus on incompatible interactions, there is still a lack of understanding about the similarities and differences between compatible and incompatible situations. This review targets the question of specificity in Solanaceae,pathogen interactions, by comparing defence patterns in plants challenged with virulent or avirulent pathogens (or with pathogen-associated molecular patterns from these). A special emphasis is made on analysing whether defence reactions in Solanaceae depend primarily on the type of elicitor, on the plant genotype/species, or on the type of interaction (compatible or incompatible). [source]

Susceptibility of Common and Rare Plant Species to the Genetic Consequences of Habitat Fragmentation

A Nationwide Assessment of the Biodiversity Value of Uganda's Important Bird Areas Network

CONSERVATION BIOLOGY, Issue 1 2006
HERBERT TUSHABE
AIAs; complementariedad; congruencia trans-taxón; selección de sitios de conservación Abstract:,BirdLife International's Important Bird Areas (IBA) program is the most developed global system for identifying sites of conservation priority. There have been few assessments, however, of the conservation value of IBAs for nonavian taxa. We combined past data with extensive new survey results for Uganda's IBAs in the most comprehensive assessment to date of the wider biodiversity value of a tropical country's IBA network. The combined data set included more than 35,000 site × species records for birds, butterflies, and woody plants at 86 Ugandan sites (23,400 km2), including 29 of the country's 30 IBAs, with data on additional taxa for many sites. Uganda's IBAs contained at least 70% of the country's butterfly and woody plant species, 86% of its dragonflies and 97% of its birds. They also included 21 of Uganda's 22 major vegetation types. For butterflies, dragonflies, and some families of plants assessed, species of high conservation concern were well represented (less so for the latter). The IBAs successfully represented wider biodiversity largely because many have distinctive avifaunas and, as shown by high cross-taxon congruence in complementarity, such sites tended to be distinctive for other groups too. Cross-taxon congruence in overall species richness was weaker and mainly associated with differences in site size. When compared with alternative sets of sites selected using complementarity-based, area-based, or random site-selection algorithms, the IBA network was efficient in terms of the number of sites required to represent species but inefficient in terms of total area. This was mainly because IBA selection considers factors other than area, however, which probably improves both the cost-effectiveness of the network and the persistence of represented species. Resumen:,El programa de Áreas de Importancia para las Aves (AIAs) de Birdlife International es el sistema global más desarrollado para la identificación de sitios de prioridad para la conservación. Sin embargo, ha habido pocas evaluaciones del valor de conservación de las AIAs para taxa no aviares. En la evaluación más integral, hasta la fecha, del valor de la biodiversidad en general de la red de AIAs de un país tropical, combinamos datos antiguos con los resultados de muestreos extensivos recientes de las AIAs de Uganda. El conjunto de datos combinados incluyó más de 35000 registros de sitios x especies de aves, mariposas y plantas leñosas en 86 sitios en Uganda (23400 km2), incluyendo 29 de las 30 AIAs del país, con datos sobre taxa adicionales en muchos sitios. Las AIAs de Uganda contenían por lo menos un 70% de las especies de mariposas y plantas leñosas del país, 86% de sus libélulas y 97% de sus aves. También incluyeron 21 de los 22 principales tipos de vegetación. En las mariposas, libélulas y algunas de las familias de plantas evaluadas, la representación de especies de alto interés para la conservación fue buena (menor en las plantas). Las Áreas de Importancia para las Aves representaron exitosamente a la biodiversidad en general principalmente porque muchas tienen avifaunas distintivas y, como muestra la alta congruencia trans-taxón en complementariedad, tales sitios tendieron a ser distintivos para otros grupos también. La congruencia trans-taxón en la riqueza de especies total fue más débil y se asoció principalmente con diferencias en el tamaño del sitio. Cuando se compara con conjuntos alternativos de sitios seleccionados mediante algoritmos basados en complementariedad, área o selección aleatoria de sitios, la red de AIAs fue eficiente en términos del número de sitios requeridos para representar especies, pero ineficiente en términos del área total. Sin embargo, esto se debió principalmente a que la selección de AIA considera factores distintos al área que probablemente mejoran tanto la efectividad de la red como la persistencia de las especies representadas. [source]

From Red Lists to Species of Conservation Concern

CONSERVATION BIOLOGY, Issue 6 2004
VERENA KELLER
aves; conservación de especies; listas rojas; prioridades de conservación; Suiza Abstract:,National red lists of threatened animal and plant species prepared according to the criteria of the World Conservation Union (IUCN) adequately reflect the extinction risk of species within a country but cannot be used directly to set conservation priorities. In particular, the significance of national populations for the conservation of the species as a whole is not taken into account. We present a procedure that can be used to assess national responsibility based on the national red-list status of a species, the international importance of the national population, and the species' "historical rarity" status. We distinguished five responsibility classes for breeding birds: B1, threatened species with internationally important populations in Switzerland; B2, threatened species with internationally less important populations; B3, nonthreatened species with internationally important populations; B4, nonthreatened species with internationally less important populations; and B5, species that have never been common in Switzerland. Two responsibility classes were distinguished for birds occurring in Switzerland as visitors: G1, species with large concentrations in Switzerland and an unfavorable conservation status in Europe, and G2, species with large concentrations in Switzerland and a favorable conservation status in Europe. Two additional classes (G3 and G4) for visiting species occurring in internationally less important numbers are possible but were not analyzed in detail. Responsibility classes B1, B2, B3, G1, and G2 were defined as species of national conservation concern. We developed the method for birds in Switzerland, but it can be used in other countries and for other taxonomic groups as well. It is particularly suitable where national red lists are established according to IUCN guidelines. Resumen:,Las listas rojas nacionales de especies de animales y plantas amenazadas que siguen los criterios de la World Conservation Union (IUCN) reflejan adecuadamente el riesgo de extinción de especies en un país pero no pueden ser utilizadas directamente para definir prioridades de conservación. En particular, no se toma en cuenta el significado de poblaciones nacionales para la conservación de especies como tales. Presentamos un procedimiento que se puede utilizar para evaluar la responsabilidad nacional con base en el estatus de lista roja de una especie en un país, la importancia internacional de la población nacional y el estatus de "rareza histórica" de la especie. Distinguimos cinco clases de responsabilidad para aves residentes: B1, especies amenazadas con poblaciones internacionalmente importantes en Suiza; B2, especies amenazadas con poblaciones internacionalmente menos importantes; B3, especies no amenazadas con poblaciones internacionalmente importantes; B4, especies no amenazadas con poblaciones internacionalmente menos importantes; y B5, especies que nunca han sido comunes en Suiza. Se distinguieron dos clases de responsabilidad para aves que ocurren como visitantes en Suiza: G1, especies con grandes concentraciones en Suiza y un estatus de conservación desfavorable en Europa y G2, especies con grandes concentraciones en Suiza y un estatus de conservación favorable en Europa. Son posibles dos clases más, (G3 y G4) para especies visitantes que ocurren en números menos importantes internacionalmente, pero no fueron analizados en detalle. Las clases de responsabilidad B1, B2, B3, G1 y G2 fueron definidas como especies de interés nacional para la conservación. Desarrollamos el método para aves en Suiza, pero también se puede utilizar en otros países y con otros grupos taxonómicos, Es particularmente adecuado donde las listas rojas nacionales se establecen de acuerdo con lineamientos de IUCN. [source]

Role of Corridors in Plant Dispersal: an Example with the Endangered Ranunculus nodif lorus

CONSERVATION BIOLOGY, Issue 2 2003
Florian Kirchner
But the few experimental studies supporting the usefulness of corridors have all concerned animal species. We investigated the role of corridors in seed dispersal, studying population genetic and demographic structure in metapopulations of the rare, pond-dwelling, autogamous plant species Ranunculus nodiflorus L. in the Fontainebleau Forest ( France ). Differentiation on three polymorphic isozyme markers was strong among local populations ( ponds ) within metapopulations ( sites ) and moderate among metapopulations. Partial Mantel tests revealed that the connection of ponds through temporarily flooded natural corridors, facilitating seed migration, had a strong negative effect on genetic differentiation between local populations and that a pond was more likely to be colonized when connected by corridors to other occupied ponds. Thus, corridors are probably a key element of landscape structure for metapopulation dynamics in R. nodiflorus. From a conservation perspective, our results suggest that corridors could increase the chance of persistence of plant species living in fragmented habitats by promoting seed dispersal between habitat patches. Resumen: La propuesta de que la migración de organismos entre parches de hábitat puede ser incrementada por corredores ha sido muy discutida en biología de la conservación. Pero los pocos estudios experimentales que apoyan la utilidad de los corredores han sido enfocados hacia especies de animales. Investigamos el papel de los corredores en la dispersión de semillas, estudiando la genética poblacional y la estructura demográfica en metapoblaciones de la especie de planta rara, autógama, habitante de estanques Ranunculus nodiflorus L. en el bosque Fontainebleau ( Francia ). La diferenciación de tres isozimas polimórficas marcadoras fue fuerte entre las poblaciones locales ( estanques ) dentro de metapoblaciones ( sitios ) y fue moderada entre metapoblaciones. Las pruebas parciales de Mantel revelaron que la conexión de estanques a través de corredores naturales inundados facilitando la migración de semillas, tuvo un efecto negativo fuerte en la diferenciación genética entre poblaciones locales y que un estanque fue más probable de ser colonizado cuando se conectaba por corredores con otros estanques ocupados. Por lo tanto, los corredores probablemente son un factor clave de la estructura del paisaje para dinámicas metapoblacionales en R. nodiflorus. Desde una perspectiva de conservación, nuestros resultados sugieren que los corredores podrían incrementar la probabilidad de persistencia de especies de plantas que viven en hábitats fragmentados al promover la dispersión de semillas entre parches de hábitats. [source]

Extinction-Rate Estimates for a Modern Neotropical Flora

CONSERVATION BIOLOGY, Issue 5 2002
Nigel C. A. Pitman
We present the first quantitative estimates of extinction rate in a complete Neotropical flora based on historical plant-collection records, quantitative measurements of forest loss and plant diversity, and the conservation status of endemic plant species in Ecuador. Our analyses suggest that 19,46 endemic plant species have gone extinct in Ecuador over the last 250 years, mostly because of habitat loss, and therefore are now globally extinct. An additional 282 species, nearly 7% of Ecuador's endemic flora, qualify as critically endangered. We found evidence of impending large-scale plant extinctions in the country's coastal and Andean forests, but little extinction and low potential for extinction in the Amazonian lowlands. Resumen: Las preocupaciones sobre las elevadas tasas de extinción en los trópicos son una característica común en la literatura sobre conservación, pero las mediciones directas son escasas. Presentamos las primeras estimaciones cuantitativas de la tasa de extinción en una flora neotropical completa basada en los expedientes históricos de colecciones de plantas, las mediciones cuantitativas de la pérdida de bosque y de diversidad y el estado de conservación de especies de plantas endémicas en Ecuador. Nuestro análisis sugiere que 19,46 especies de plantas se han extinguido en el Ecuador a lo largo de los últimos 250 años, debido principalmente a la pérdida de hábitat y por lo tanto son ahora extintas a nivel mundial. Además 282 especies, cerca del 7% de la flora endémica del Ecuador califica como críticamente amenazada. Encontramos indicaciones de inminentes extinciones de gran escala en el país, tanto en los bosques costeros como en los bosques de los Andes, pero poca extinción y bajo potencial de extinción en las tierras bajas del Amazonas. [source]

Implications of Climatic Warming for Conservation of Native Trees and Shrubs in Florida

CONSERVATION BIOLOGY, Issue 4 2001
David W. Crumpacker
Climatic-envelope models are useful for simultaneous investigation of many plant species whose range-limiting mechanisms are poorly known. They are most effectively applied in regions with strong temperature and moisture gradients and low relief. Their required databases are often relatively easy to obtain. We provide an example involving the effect of six annual warming scenarios, ranging from +1° C to +2° C and from +10% to ,20% annual precipitation (some have greater warming in winter than in summer), on 117 native woody species in Florida (U.S.A.). Tree species at their southern range boundaries in several parts of Florida are likely to be negatively affected by as little as 1° C warming if it is greater in winter than in summer or is accompanied by a 20% decrease in annual precipitation. Potential species responses to an identical type of 1° C warming may be different for some conservation areas in the same region of Florida. Potentially extensive disruption of some major woody ecosystems is predicted under certain types of 1° C annual warming and under all types of 2° C annual warming that were investigated. Additional consideration of nonclimatic factors suggests that many potential effects on species and ecosystems are not underestimates of actual effects over a 100-year period of warming. We recommend monitoring for decreased fertility and viability of ecologically important, temperate woody species near their southern range limits in Florida. Early detection of such changes in fitness might then provide time for mitigations designed to alleviate more serious subsequent effects on biodiversity. Control of invasive, non-native plant species and prevention of their additional introduction, human-assisted translocation of native subtropical plant species into previously temperate parts of Florida, and restoration of more natural hydrological regimes are examples of potentially useful mitigations if climatic warming continues. Resumen: Los modelos de procesos ecológicos y los modelos empíricos han sido usados para relacionar predicciones de cambio climático con los efectos en especies de plantas y vegetación. Los modelos climáticos son útiles para la investigación simultánea de muchas especies de plantas cuyos mecanismos limitantes de rango son poco conocidos. Estos modelos son más eficientemente aplicados en regiones con gradientes de temperatura y humedad fuertes y con relieve bajo. Las bases de datos requeridas son a menudo relativamente fáciles de adquirir. Proveemos un ejemplo que involucra el efecto de seis escenarios anuales de calentamiento con un rango de +1° C a +2° C y de +10% a ,20% de precipitación anual (algunos con rangos de calentamiento mayores en el invierno que en el verano), en 117 especies leñosas nativas de Florida ( E.U.A.). Las especies de árboles en sus límites de rango al sur en diversas partes de Florida son más factibles de ser negativamente afectadas por tan poco como 1° C de calentamiento, si este es mayor en el invierno que en el verano o si es acompañado por una disminución de un 20% de precipitación anual. Las respuestas potenciales de las especies a un tipo idéntico de calentamiento de 1° C puede ser diferente para algunas áreas de conservación en la misma región de Florida. Se predicen perturbaciones potencialmente extensivas en algunos ecosistemas leñosos principales investigados bajo ciertos tipos de calentamiento anual de 1° C y bajo todos los tipos de calentamiento anual de 2° C. Las consideraciones adicionales de factores no climáticos sugieren que muchos efectos potenciales sobre las especies y ecosistemas no son subestimaciones de los efectos actuales sobre un período de calentamiento de 100 años. Se recomienda el monitoreo de la disminución de la fertilidad y viabilidad de especies leñosas templadas ecológicamente importantes cerca de los límites sureños de sus rangos en la Florida. La detección temprana de estos cambios en adaptabilidad pueden proveer tiempo para mitigaciones diseñadas para aliviar efectos posteriores más serios en la biodiversidad. Algunos ejemplos de mitigaciones potencialmente útiles en caso de que el calentamiento global continúe incluyen el control de especies de plantas invasoras no nativas y la prevención de su introducción adicional, la translocación asistida por humanos de plantas nativas subtropicales en partes previamente templadas de Florida y la restauración de regimenes hidrológicos más naturales. [source]

BIODIVERSITY RESEARCH: Population expansion in an invasive grass, Microstegium vimineum: a test of the channelled diffusion model

DIVERSITY AND DISTRIBUTIONS, Issue 5 2010
Nathaniel P. Miller
Abstract Aim, The greatest biodiversity impact of non-native plant species is caused by rapid expansion of colonist populations. Unfortunately, invasion has rarely been documented in real time at a population scale, and demographic mechanisms of invasion remain unclear. Our goal is to describe real-time expansion of populations, using channelled diffusion as a null model. Location, The study examined three populations of the invasive annual grass Microstegium vimineum in mature second-growth forests of south-eastern Ohio and nearby West Virginia, USA. Methods, Distributions were recorded in belt transects perpendicular to population edges over a period of 3 years. A second group of belt transects documented spread along five types of potential movement corridor. Observed changes in distribution were compared with predictions from a diffusion model. A seed-sowing experiment tested seed availability, microsite quality and proximity to potential movement corridors as factors controlling population spread. Results, Population boundaries showed little change over the study period. Colonization was limited by propagule availability over distances as little as 0.25 m, and to a lesser extent by litter cover. Populations did not advance along several potential movement corridors including unpaved roads, off-road vehicle trails and footpaths. Advance was observed along deer trails and stream courses but did not conform to the wave-form distribution predicted by diffusion theory. During the study, seeds were moved out of experimental plots by sheet flow and minor flooding events along small streams. Main conclusion, At a population level, invasion is driven by processes that are episodic in time and non-random in space , probably a common condition in non-native plant species. Spatially realistic models are likely to be more useful than diffusive models in managing invasions at these scales. [source]

Disentangling the relative effects of environmental versus human factors on the abundance of native and alien plant species in Mediterranean sandy shores

DIVERSITY AND DISTRIBUTIONS, Issue 4 2010
Marta Carboni
Abstract Aim, Mediterranean coastal sand dunes are characterized by both very stressful environmental conditions and intense human pressure. This work aims to separate the relative contributions of environmental and human factors in determining the presence/abundance of native and alien plant species in such an extreme environment at a regional scale. Location, 250 km of the Italian Tyrrhenian coast (Region Lazio). Methods, We analysed alien and native plant richness and fitted generalized additive models in a multimodel-inference framework with comprehensive randomizations to evaluate the relative contribution of environmental and human correlates in explaining the observed patterns. Results, Native and alien richness are positively correlated, but different variables influence their spatial patterns. For natives, human population density is the most important factor and is negatively related to richness. Numbers of natives are unexpectedly lower in areas with a high proportion of natural land cover (probably attributable to local farming practices) and, to a lesser degree, affected by the movement of the coastline. On the other hand, alien species richness is strongly related to climatic factors, and more aliens are found in sectors with high rainfall. Secondarily, alien introductions appear to be related to recent urban sprawl and associated gardening. Main conclusions, Well-adapted native species in a fragile equilibrium with their natural environment are extremely sensitive to human-driven modifications. On the contrary, for more generalist alien species, the availability of limited resources plays a predominant role. [source]

Using multi-scale species distribution data to infer drivers of biological invasion in riparian wetlands

DIVERSITY AND DISTRIBUTIONS, Issue 1 2010
Jane A. Catford
Abstract Aim, Biological invasion is a major conservation problem that is of interest to ecological science. Understanding mechanisms of invasion is a high priority, heightened by the management imperative of acting quickly after species introduction. While information about invading species' ecology is often unavailable, species distribution data can be collected near the onset of invasion. By examining distribution patterns of exotic and native plant species at multiple spatial scales, we aim to identify the scale (of those studied) that accounts for most variability in exotic species abundance, and infer likely drivers of invasion. Location, River Murray wetlands, south-eastern Australia. Methods, A nested, crossed survey design was used to determine the extent of variation in wetland plant abundance, grazing intensity and water depth at four spatial scales (reaches, wetland clumps, wetlands, wetland sections), and among three Depth-strata. We examined responses of exotic and native species groups (grouped into terrestrial and amphibious taxa), native weeds and 10 individual species using hierarchical ANOVA. Results, As a group dominated by terrestrial taxa, exotic species cover varied at reach-, wetland- and section-scales. This likely reflects differences in abiotic characteristics and propagule pressure at these scales. Groups based on native species did not vary at any scale examined. Cover of 10 species mostly varied among and within wetlands (patterns unrelated to species' origin or functional group), but species' responses differed, despite individual plants being similar in size. While flora mostly varied among wetlands, exotic cover varied most among reaches (26%), which was attributed to hydrological modification and human activities. Main conclusions, Multi-scale surveys can rapidly identify factors likely to affect species' distributions and can indicate where future research should be directed. By highlighting disproportionate variation in exotic cover among reaches, this study suggests that flow regulation and human-mediated dispersal facilitate exotic plant invasion in River Murray wetlands. [source]

Phylogenetic relatedness and plant invader success across two spatial scales

DIVERSITY AND DISTRIBUTIONS, Issue 3 2009
Marc W. Cadotte
ABSTRACT Aim, Successful invaders often possess similar ecological traits that contribute to success in new regions, and thus under niche conservatism, invader success should be phylogenetically clustered. We asked if the degree to which non-native plant species are phylogenetically related is a predictor of invasion success at two spatial scales. Location, Australia , the whole continent and Royal National Park (south-eastern Australia). Methods, We used non-native plant species occupancy in Royal National Park, as well as estimated continental occupancy of these species from herbarium records. We then estimated phylogenetic relationships using molecular data from three gene sequences available on GenBank (matK, rbcL and ITS1). We tested for phylogenetic signals in occupancy using Blomberg's K. Results, Whereas most non-native plants were relatively scarce, there was a strong phylogenetic signal for continental occupancy, driven by the clustering of successful species in Asteraceae, Caryophyllaceae, Poaceae and Solanaceae. However, we failed to detect a phylogenetic signal at the park scale. Main Conclusions, Our results reveal that at a large spatial scale, invader success is phylogenetically clustered where ecological traits promoting success appear to be shared among close relatives, indicating that phylogenetic relationships can be useful predictors of invasion success at large spatial scales. At a smaller, landscape scale, there was no evidence of phylogenetic clustering of invasion success, and thus, relatedness plays a much reduced role in determining the relative success of invaders. [source]

A latitudinal gradient of beta diversity for exotic vascular plant species in North America

DIVERSITY AND DISTRIBUTIONS, Issue 3 2008
Hong Qian
ABSTRACT Determining relationships between the ranges of introduced species and geographical and environmental factors is an important step in understanding the mechanisms and processes of the spread of introduced species. In this study, I examined the beta diversity and latitude relationship for all naturalized exotic species of vascular plants in North America at a continental scale. Beta diversity was calculated as the absolute value of the slope of the relationship between the natural logarithm of the Simpson index of similarity (lnS) and spatial distance between pairs of state-level exotic floras within four latitudinal zones examined. Relative contributions of spatial distance and environmental difference to species turnover between exotic floras were examined. I found that beta diversity decreased monotonically from low to high latitudes: beta diversity for the southernmost zone was shallower than that for the northernmost zone by a factor of 2.6. Regression models of lnS in relation to spatial distance and environmental (climatic and topographical) difference for each latitudinal zone demonstrated that the explanatory power of these variables diminishes monotonically with latitude: the explained variance in lnS is 70.4%, 62.1%, 53.9%, and 33.9%, respectively, for the four latitudinal zones from south to north. For the southernmost zone, 58.3% of the variance in lnS is explained by climate variables and topography, and spatial distance explains only 2.3% of the variance. In contrast, for the northernmost zone, more than half the amount (22.5%) of the explained variance in lnS is attributable to spatial distance, and the remaining (18.9%) of the explained variance is attributable to climate variables and topography. [source]

Distribution of myrmecochorous species over the landscape and their potential long-distance dispersal by emus and kangaroos

DIVERSITY AND DISTRIBUTIONS, Issue 1 2008
María Calviño-Cancela
ABSTRACT Topographical heterogeneity can create a mosaic of substrate types leading to the formation of isolated plant populations. Seed dispersal then becomes crucial for the colonization of such suitable but remote substrate types. We surveyed the distribution of seven elaiosome-bearing species (myrmecochores) over 5 km2 of natural heathland in southwestern Australia. Ants are the standard means of dispersal of these species, which provide limited dispersal (usually of a few metres). Six species were associated with particular substrate types (dune or swale) and all occurred as discrete populations, on average 270,500 m apart, with closest dune edges 280 m apart. We evaluated the possible roles of emus and kangaroos as alternative agents of long-distance seed dispersal between substrate types. Their droppings contained viable seeds of three of the target species, as well as other myrmecochores, and were evenly distributed over the substrate types. While migration of these plant species between preferred substrate types seems unlikely when considering only their standard dispersal agents (ants), it is highly likely in the presence of emus (in particular) and kangaroos that act as non-standard dispersers. This may have important consequences for plant species conservation by increasing habitat connectivity and favouring regional persistence. [source]

Do cities export biodiversity?

DIVERSITY AND DISTRIBUTIONS, Issue 1 2008
Traffic as dispersal vector across urban, rural gradients
ABSTRACT Urban areas are among the land use types with the highes richness in plant species. A main feature of urban floras is the high proportion of non-native species with often divergent distribution patterns along urban,rural gradients. Urban impacts on plant species richness are usually associated with increasing human activity along rural-to-urban gradients. As an important stimulus of urban plant diversity, human-mediated seed dispersal may drive the process of increasing the similarity between urban and rural floras by moving species across urban,rural gradients. We used long motorway tunnels as sampling sites for propagules that are released by vehicles to test for the impact of traffic on seed dispersal along an urban,rural gradient. Opposite lanes of the tunnels are separated by solid walls, allowing us to differentiate seed deposition associated with traffic into vs. out of the city. Both the magnitude of seed deposition and the species richness in seed samples from two motorway tunnels were higher in lanes leading out of the city, indicating an ,export' of urban biodiversity by traffic. As proportions of seeds of non-native species were also higher in the outbound lanes, traffic may foster invasion processes starting from cities to the surrounding landscapes. Indicator species analysis revealed that only a few species were confined to samples from lanes leading into the city, while mostly species of urban habitats were significantly associated with samples from the outbound lanes. The findings demonstrate that dispersal by traffic reflects different seed sources that are associated with different traffic directions, and traffic may thus exchange propagules along the urban,rural gradient. [source]