Distance to suburban/wildland border interacts with habitat type for structuring exotic plant communities in a natural area surrounding a metropolitan area in central Chile

Background: The explosive growth of urbanisation in Mediterranean ecosystems in Chile has favoured the rapid expansion of exotic plant species, yet factors driving these invasion patterns in adjacent natural areas remain poorly assessed.

Aims: To assess how distance to a suburban/wildland border, habitat type, site-scale disturbance and woody plant cover of native species influences the diversity of exotic species in a natural area surrounding the city of Santiago, Chile.

Methods: Three watersheds were chosen, and the diversity of exotic species was assessed in 36 100-m-long transects, equally distributed over two distance categories and three habitats. For each transect, we measured woody plant cover of native species and frequency of rabbit faeces as a measure of competitive exclusion and site-scale disturbance, respectively.

Results: Species diversity decreased as the distance from the suburban/wildland border increased, and it was found to be higher in north-facing habitats compared to south-facing and alluvial habitats. Neither native woody plant cover nor frequency of rabbit faeces had an effect on species diversity.

Conclusions: The current pattern of exotic plant species in this natural area is mainly influenced by the distance to suburban border and habitat type. An adequate management of conditions favouring exotic species in suburban/wildland border may prevent the spread of these into natural areas next to urban settings.     

The impact of red deer on liverwort-rich oceanic heath vegetation

Background: There is concern about increasing numbers of large herbivores including red deer (Cervus elaphus), but little is known about their impact on bryophytes.

Aims: This study set out to determine the effect of different localised densities of red deer on the internationally important Northern Atlantic hepatic mat, characteristic of oceanic heath vegetation, at four locations in the Scottish Highlands where sheep have been absent for decades.

Methods: Thirty 7 m × 7 m plots were randomly located in each study area. The standing crop dung pellet group count method was used to estimate red deer density. Species richness, diversity and cover of hepatic mat liverworts were obtained from 1 m × 1 m quadrats placed at random within the sample plots. Calluna vulgaris cover, ericoid height, rock cover, gradient and altitude were also recorded.

Results: Model simplification in analysis of covariance revealed a consistent pattern of decreasing cover of hepatic mat and Calluna with increasing red deer density at all four study areas. Northern Atlantic hepatic mat cover, diversity and species richness were positively correlated with Calluna cover.

Conclusions: The data suggest that Calluna cover is reduced (through trampling and browsing) at high local densities of red deer which has had cascading effects on the Northern Atlantic hepatic mat. Alternative explanations are discussed.     

Giant stem rosettes have strong facilitation effects on alpine plant communities in the tropical Andes

ABSTRACT

Background: Giant rosettes constitute one of the most distinctive growth-forms in tropical alpine ecosystems. However, their interactions with other plant species remain unexplored in high Andean páramos.

Aims: Quantify the effect of a dominant rosette (Coespeletia timotensis) on soil and microclimatic conditions and relate the impacts to plant community structure.

Methods: We analysed topsoil temperatures, soil organic matter (SOM) and plant species cover in areas adjacent to C. timotensis and paired areas outside, at three sites (4250–4360 m a.s.l.) in La Culata National Park, Venezuela. Species richness, total vegetation cover and percent cover of each species near and away from the rosettes were compared.

Results: Topsoil temperature amplitudes were lower and SOM greater near C. timotensis stems, compared to areas away from them. C. timotensis had a consistent positive effect on species richness, vegetation cover and the cover of many abundant species (including cushions and herbs).

Conclusions: The facilitation effects of C. timotensis on abiotic conditions and community structure indicate they play a key role as nurse plants, pointing to giant rosettes as foundation species for the maintenance of plant diversity in the alpine tropics.     

Contrasting response of native and alien plant species richness to environmental energy and human impact along alpine elevation gradients

Aim We tested whether the species–energy and species–human relationships vary between native and both naturalized and casual alien species richness when other environmental variables had been taken into account. Location Trento Province, a region (c. 6200 km²) on the southern border of the European Alps (Italy), subdivided into 156 contiguous (c. 37.5 km²) cells and ranging in elevation from 66 to 3769 m. Methods Data were separated into three subsets, representing richness of natives, naturalized aliens and casual aliens and separately related to temperature, human population and various environmental correlates of plant species diversity. We applied ordinary least squares and simultaneous autoregressive regressions to identify potential contrasting responses of the three plant status subsets and hierarchical partitioning to evaluate the relative importance of the predictor variables. Results Variation in alien plant species richness along the region was almost entirely explained by temperature and human population density. The relationships were positive but strongly curvilinear. Native species richness was less strongly related to either factor but was positively related to the presence of calcareous bedrock. Native species richness had a decelerating positive relationship with temperature (R²= 55%), whereas naturalized and casual aliens had a positive accelerating relationship explaining 86% and 62% of the variation in richness, respectively. Native species richness had a positive decelerating relationship with population density (R²= 42%), whilst both alien subsets had a positive accelerating relationship. Main conclusions Alien species richness was higher in areas with the most rich and diverse assemblages of native species. Areas at high altitudes are not especially prone to alien invasion due to energy constraints, low propagule pressure and disturbance, even considering a potential increased in temperature. Thus, if we consider future environmental change, we should expect a stronger response of aliens than natives in the currently warm, urbanized, low‐altitude areas than in cold, high‐altitude areas where human population density is low.     

Research Symposium—Aberdeen

ABSTRACT

Background: Climate change may increase the risk of biological invasions. However, current knowledge of this interaction is limited.

Aims: We aimed to quantify (1) the effect of climate change on the potential distribution of invasive plant species in Spain, (2) the importance of the area of origin of such species and (3) the vulnerability of different biogeographic provinces to future changes in climatic suitability for invaders.

Methods: We applied six methods of species distribution modelling to assess the variation of climatically suitable areas for 40 alien plants. We developed a Potential Area Change Index and used it as the response variable in modelling for three future emissions scenarios and three global circulation models over three time periods. The area of origin and biogeographic province in Spain were also considered.

Results: We found a highly specific response for each plant species rather than a clear trend for the entire set of species. Predicted climate suitability increased over higher emission scenarios and longer projected time lags. Neotropical species showed the greatest potential climatic range expansion. We detected a strong interaction between the geographic origin of a species and the biogeographic province.

Conclusions: Special attention should be given to the areas where aridification of climate is projected and where introduced neotropical species are likely to expand their range. Future work should develop accurate species-specific approaches that allow the management invasive plant species.     

Floristic diversity and the richness of locally endangered plant species of semi-natural grasslands under different management practices,southern Kyushu,Japan

Background: The rapid decline of semi-natural grasslands in Japan threatens many relic and endemic plant species. There is insufficient knowledge on how the impacts of land-use changes and management of grasslands have been affecting grassland ecosystems and what conservation measures may be taken to conserve as much of the existing plant diversity as possible.

Aim: We assessed the existing management regimes for their suitability for conserving Red Data Book (RDB) species.

Methods: We conducted our study in four districts of Kushima, Kyushu, south-west Japan, with different land-use histories. We compared species richness, plant density and abundance in six grassland types: regularly burnt, regularly mown, paddy levee, roadside, landslip and wetland communities in a total of 289 1 m x 1 m quadrats, recorded in172 grassland patches. Species richness plant density and abundance were analysed with special reference to RDB species under different land use history.

Results: Species richness of grasslands did not differ across different land use histories, yet our analysis showed that the reduced area of grasslands markedly affected the density of RDB species. Grassland types differed in their ability to support RDB species: regularly burnt grasslands were the richest in RDB species and poorest in alien species, followed by regularly mown grasslands, paddy levees, landslip, wetland and roadside communities.

Conclusions: Traditional management regimes, such as regular burning or mowing of grasslands have the best potential for conserving RDB species, and thus should be part of conservation management practices of semi-natural grasslands.     

Winter use of wild bird cover crops by passerines on farmland in northeast England

Capsule Declining farmland species were more abundant in these crops which can be matched to the birds' requirements.

Aims To assess the use of seed-bearing crop by a range of bird species in winter.

Methods The study was carried out over three winters at a site in County Durham (England). Eleven bird species were represented, five of which are nationally targeted for conservation action.

Results Bird abundance was significantly higher where wild bird cover crops were present. Kale Brassica napus and Quinoa Chenopodium quinoa were the most used crop species, although cereals and linseed were also used.

Conclusion Simple crop mixtures can be designed to meet the needs of farmland bird communities. Our results suggest that seed production may be limited within government agri-environment schemes by restrictions on fertilizer use. The agronomy of seed-bearing crops for birds requires further investigation.     

Invasibility of an inland area in NE Spain by alien plants

This study examines the alien flora of a representative zone of the continental northeast region of the Iberian Peninsula, in the Huesca province. Its aims were to determine the biological and ecological factors responsible for the invasive behaviour of the alien species, along with factors related to the environment and land use that could increase the vulnerability of the different habitats towards invasion. Results were then compared with previous observations made in the coastal areas closest to this inland region. Relationships between the invasive nature and the biological and ecological characteristics of the species were evaluated by logistic analysis. General linear model analysis was used to correlate environmental factors with the capacity of the region's habitats to accept these invaders. Perhaps the most noticeable feature was the high number of alien plants growing as crop weeds in the continental study area. The factors found to be most related to the invasive behaviour of the alien species were biological type, route of introduction and the disturbance degree of the habitat. Human population density, average yearly rainfall and temperature, and to a lesser extent, land use were the environmental factors most significantly associated with the number of alien species present. Our findings indicate that the invasibility of continental areas of the NE Iberian Peninsula by alien plants is notably lower compared to the closest coastal zones, the degree of naturalisation of alien species within the native flora also being lower. Differences between the coast and interior in terms of the origins and introduction routes of the alien plants were also evident. Environments showing the greatest capacity to accommodate alien plant species were coastal areas, where the land is mostly given over to urban use and there is a predominance of fluvial and riparian ecosystems.     

Seed mass,seed number and evolutionary trade-off across geographic distribution: do they explain invasiveness in Eschscholzia californica,central Chile?

Background: Seed mass is a life history trait that is related to invasiveness. Under limiting conditions, a trade-off is observed whereby an increase in seed mass occurs at the expense of seed numbers; if the above trade-off holds across climatic gradients it can provide an opportunity to assess the fitness/invasive potential of exotic plants.

Aims: To examine the variation in the life history traits of Eschscholzia californica populations across climatic gradients and to relate these traits to observed invasiveness.

Methods: We examined 19 populations in Chile. For each population we related seed mass, seed number, the slope of trade-off between seed mass and number and plant density with annual precipitation and mean annual temperature.

Results: Seed number and the coefficient of variation in seed mass were positively correlated with climatic variables. Trade-off was detected in 26% of the populations and no relationship was detected with climatic gradient. Plant density was negatively associated with precipitation.

Conclusions: The results suggest that for E. californica producing seeds with a variety of sizes is an optimal strategy to face geographic heterogeneity and hence to increase its invasiveness. Increased production of seeds at the cool and wet southern limit of the current range of the species does not contribute to an increase in its invasiveness.     

The identification of the seeds and fruits of common Scottish aquatic herbs

Background: There have been few quantitative observations of the attributes of native animal paths and no studies of their variation between vegetation types. These paths may be important in extending the local ranges of plant species.

Aims: To determine the incidence, cover and characteristics of native animal paths in different vegetation types, their relationships with other variables and the influence of paths on plant species distributions.

Methods: Randomly located line transects, and paired quadrats on and adjacent to paths, were used to record path and environmental attributes at 10 sites in each of 10 vegetation types. The relationships between path cover, number, width and depth and potential predictor variables were determined by using Pearsons product moment correlation.

Results: The mean cover of paths in plant communities varied between 6.5% and 12.6%. Path cover, number, width and depth varied between vegetation types. Penetration resistance, bare ground, scat density and plant species richness had higher values in path quadrats than in controls. Within particular vegetation types, several plant species were restricted to paths.

Conclusions: Animal trampling is an important influence on vegetation structure and the distribution of plant species in the study area.     

Obituaries

Background: Although impacts of edge effects on forest ecosystems are well known, their consequences on savannas have rarely been explored.

Aims: To investigate the influence of edge effects on the plant community and microclimate of a cerrado fragment in south-eastern Brazil.

Methods: Several plant community variables (density, basal area, richness and cover by each vegetation layer) and microclimatic variables (light, air temperature and humidity), were measured in 10 transects across a savanna fragment surrounded by exotic grasses, and were used to fit semi-parametric models relating these variables with the distance from the habitat edge.

Results: Differences in microclimate and tree communities were poorly related to distance from the edge. On the other hand, there were detectable edge effects on the ground layer community (i.e. plants less than 50 cm in height). Edges had a negative effect on native plants of this layer (density and richness of all species and cover of native grasses), while favouring invasive grasses.

Conclusions: Unlike reports for edge effects in forest ecosystems, microclimate does not explain changes in this cerrado fragment. The most significant edge effect threatening the conservation of cerrado vegetation is the widespread invasion by African grasses. Starting from the fragment borders, this invasion causes changes in the structure and composition of the native plant community, thus jeopardising the population dynamics and persistence of native species.     

Grazing in remnant wetland habitats in an arid region: direct and indirect effects on two specialist bird species

Capsule: Grazing by livestock can have complex effects on drivers of population change in the Clamorous Reed Warbler Acrocephalus stentoreus and Dead Sea Sparrow Passer moabiticus.

Aims: To investigate the effect on two specialist bird species on wetland degradation in the Jordan Valley.

Methods: The direct and indirect effects of grazing on the probability of occurrences of two specialist bird species, Clamorous Reed Warbler A. stentoreus and Dead Sea Sparrow P. moabiticus, were analysed during the breeding season at the patch scale, using path analysis.

Results: Tamarix shrub density was a strong predictor for the presence of both species. Grazing had a negative total effect on both; a significant indirect effect on Dead Sea Sparrow via its impact on the mean height of shrubs, and a significant, negative indirect effect on Clamorous Reed Warbler by reducing reed cover. Intensive grazing and browsing by livestock including goats, sheep and camels, apparently had a negative effect on the overall density of native Tamarix shrubs, while promoting encroachment by invasive Prosopis juliflora.

Conclusion: This may be part of a long-term cascade leading to an ecological transition and loss of important wetland habitats in the arid Jordan Valley.     

Abundance of the rose-grain aphid,Metopolophium dirhodum,on barley in Canterbury,New Zealand, 1984–87

Abstract

Spring populations of Metopolophium dirhodum (Walker) (Hemiptera: Aphididae) on barley, at Lincoln and elsewhere in Canterbury, New Zealand, declined markedly during 1984–87. Spring suction-trap catches of M. dirhodum also declined at the same time. Numbers of immigrant M. dirhodum on young barley, and maximum aphid population density on the crop, were positively correlated with suction-trap catches of M. dirhodum during the preceding week or month, respectively. Egg numbers of the most abundant predator, Micromus tasmaniae Walker (Neuroptera: Hemerobiidae), and mummy numbers of the parasitoid, Aphidius rhopalosiphi De Stefani-Perez (Hymenoptera: Aphidiidae), increased relative to aphid numbers during the study. Entomophagous fungus-disease incidence could not be related to monthly rainfall, and the decline in aphid numbers during the study period was apparently not related to disease incidence. It is suggested that aphid population regulation by predators and parasitoids in the wider habitat of M. dirhodum could reduce the rate of immigration, and hence aphid population growth, in a given crop.     

Correlates of distribution and nesting success in a Welsh upland Eurasian Curlew Numenius arquata population

Capsule: Habitat structure and composition explained spatial variation in breeding distribution and nesting success in a declining upland Eurasian Curlew Numenius arquata population in North Wales.

Aims: To identify environmental correlates of Curlew breeding distribution, nesting success and change in distribution.

Methods: Thirty random 1?km squares stratified by historical population trend were surveyed for Curlew density and nesting success, and habitat- and predation-related variables in a landscape containing agriculturally improved farmland, and moorland that was partly protected and subject to grazing reductions for nature conservation. Analyses tested for associations between Curlew measures and environmental variables.

Results: Curlew breeding density declined by 29% between 1994 and 2008, and was highest in squares comprising a mixture of moorland and agriculturally improved farmland, and in squares with lower vegetation density and higher cover of Nardus stricta (characteristic of rough grazing). Nesting success was positively associated with cover of Trichophorum germanicum (characteristic of mire). Vegetation density was lower than average in squares with the highest Curlew densities, while in the protected area vegetation density was higher than average.

Conclusion: Habitat and vegetation variables influenced Curlew distribution and nesting success in North Wales, largely in line with previous results but with no evidence for predator-related influences. Habitat condition for Curlew in the protected area could probably be increased through targeted increases in grazing alongside the protection of priority habitats.     

Restoration of three forest herbs in the Liliaceae family by manipulating deer herbivory and overstorey and understorey vegetation

Background: Research on herbaceous vegetation restoration in forests characterised by overstorey tree harvests, excessive deer herbivory, and a dominant fern understorey is lacking. Most of the plant diversity found in Eastern hardwood forests in the United States is found in the herbaceous understorey layer. Loss of forest herbaceous species is an indicator of declining forest conditions.

Aims: The combined effects of deer herbivory, competitive understorey vegetation removal, and overstorey tree removal on the abundance and reproductive capacity of three understorey herbs in the Liliaceae family were evaluated.

Methods: A split-plot randomised block design was used with three replicates. Treatments included three harvest intensities, fenced/unfenced, herbicide/no herbicide-treated, prescribed burn/no prescribed burn, and all combinations. A generalised linear model was used to compare treatment effects over 8 years.

Results: Both fruit production and cover increased significantly in fenced areas for all three species. There was a significant 6-year recovery period for cover of the three species in response to herbicide. There was a significant 4-year recovery period of fire-treated plots for fruit production of the three species. The most intensively cut, fenced, and herbicide-treated plots had the greatest increases in sapling and Rubus spp. cover. Cover and fruit production of the three herbs were significantly greatest in the moderate-cut treatment.

Conclusions: Restoration of these three liliaceous species is most likely to occur in Eastern deciduous forests and similar forests using a combined fenced and moderate-cut treatment.     

Energy metabolism in green cells

Background: Although fire is an important factor in determining cerrado vegetation, information about its effect on seed banks is sparse. Cerrado fires are rapidly moving surface fires with low residence time, producing only short-term heating of the uppermost centimetres of the soil. However, the reduction in vegetation cover and deposition of ashes increases the daily amplitude of soil temperature by as much as 35 °C.

Aims: To assess the effect of post-fire daily soil temperatures on the germination of one alien and nine native grasses.

Methods: Seeds were stored at alternating temperatures of 45 ºC/10 ºC (10 h/14 h) for 7 d or 30 d, simulating two different storage times in the soil seed bank before the onset of the rainy season. Germination was monitored over 30 d.

Results: The variation in temperature had a significant effect on the rate of seed germination in some species, either enhancing it (Aristida setifolia) or reducing it (Schizachyrium sanguineum). Increased storage time reduced the viability of S. sanguineum and Echinolaena inflexa. The invasive Melinis minutiflora had the highest germination rate and it also showed the best toleration of post-fire conditions (45 ºC/10 ºC) after 7 d, with significant reduction in the germination time after 30 d.

Conclusions: Fire seems to have a significant effect in the early life of cerrado grasses. Some native species responded positively to temperature oscillation, suggesting that they should be better prepared to compete with alien species after a fire, with more of their seeds germinating and/or at a more rapid rate.     

Landscape-dependent use of a seed-rich habitat by farmland passerines: relative importance of game cover crops in a grassland versus an arable region of Scotland

Capsule Game cover crops in a pastoral region of southwest Scotland supported passerines at more than twice the density found in similar crops in an arable region.

Aims To investigate the use of seed-rich habitats (game cover crops) by farmland passerines in the agricultural grasslands of southwest Scotland relative to the arable east.

Methods Birds were counted in game cover crops and conventional crops on nine farms in Dumfries and Galloway, and Ayrshire, during the winters of 2003/04 and 2004/05. Similar data from eastern Scotland were re-analysed to compare the relative use of the two crop types in the contrasting regions.

Results Passerine densities in game cover crops in southwest Scotland were two orders of magnitude greater than in conventional crops. Furthermore, densities within grassland game cover crops were more than double those in arable areas and densities in grassland conventional crops were just 14% of those in equivalent arable habitats.

Conclusion The significantly greater difference between passerine densities in game cover crops and conventional crops in a grassland versus an arable region of Scotland could not be explained by differences in the bird communities, crop types, boundary habitats, weather, observer effects or survey methods used. We suggest that game cover crops may be more attractive in grassland regions because alternative food sources are rarer than in arable regions.     

Density and productivity of breeding Skylarks Alauda arvensis in relation to crop type on agricultural lands in western France

Capsule Small field size and the maintenance of set-aside and lucerne are important to ensure high breeding pair densities and productivity.

Aims To investigate the effects of crop types and their attributes on density and productivity of breeding Skylark.

Methods At each of four selected study sites in western France, territory density, vegetation height, vegetation cover and field size was estimated by field and attempts were made to find nests. Crop types included winter and spring cereals, oilseed rape, sunflower, maize, grass, lucerne, set-aside, and bare ground.

Results About 80% of Skylark territories included more than one crop type. Birds preferred small fields and territory density decreased with increasing field size. Density was highest in crops with low vegetation height and cover. Set-aside, lucerne and grass supported highest territory density. Fledging productivity was highest in set-aside and lucerne, and was zero on bare ground. Skylark density decreased throughout the breeding season (-26% in 1999 and -29% in 2000), suggesting an instability in territory distribution or activity in intensive farmland.

Conclusions Farming systems that decrease field size and increase set-aside and lucerne instead of oilseed rape, maize and sunflower will benefit Skylark and other declining farmland species.     

Cover crop mixtures including legume produce ecosystem services of nitrate capture and green manuring: assessment combining experimentation and modelling

Background and aims

During the fallow period, non-legume cover crop species can capture mineral nitrogen (N) and thus decrease nitrate leaching, whereas legume cover crop species can provide a green manuring service that increases N availability for the subsequent crop. The aim of our study was to investigate the ability of bispecific mixtures to simultaneously produce these two services of N management in relation to their interspecific interactions.

Methods

Three field experiments were conducted at contrasting sites from summer to autumn to evaluate 25 mixtures and 10 sole crops. We measured biomass, N acquisition, C:N ratio and soil mineral N. Ecosystem services were assessed using both experimental data and simulation model predictions.

Results

Overall, prediction of N mineralized from cover crop residues was significantly higher for mixtures than for non-legume sole crops. Predictions of nitrate leached after mixtures did not differ significantly from those after non-legume sole crops and remained significantly lower than those under bare soil, especially for mixtures with turnip rape which benefitted greatly from being in mixtures.

Conclusions

Some of the mixtures provided a choice of compromises between the two ecosystem services, which helps define solutions for adapting mixture choice according to the site’s soil and climate characteristics and to fallow period management.

     

Environmental correlates of breeding abundance and population change of Eurasian Curlew Numenius arquata in Britain

Capsule: Across Britain, breeding Eurasian Curlew Numenius arquata are less numerous and have shown greater population declines in areas with more arable farming, woodland cover and higher generalist predator abundance.

Aims: We present the first national-scale analysis of the potential drivers of Curlew population change in Britain, which is needed to guide conservation action for this globally near-threatened, declining species.

Methods: Breeding Bird Survey data and environmental predictors were used to model variation in Curlew abundance in 1995–99 and 2007–11, and population change between these periods.

Results: Arable farming and woodland cover were negatively associated with Curlew abundance and population declines. Curlew abundance was positively associated with extent of protected area coverage and gamebird numbers. Abundance and population change were positively associated with cooler temperatures and higher summer rainfall, but negatively associated with numbers of generalist predators.

Conclusions: We found support for the negative effects of intensive agriculture, forestry, increases in generalist predator populations and climate warming on Curlew abundance and population change. Effective site protection and measures to reduce generalist predator abundance may be important conservation measures, together with improving breeding habitat quality in the wider countryside.