COLONIZING PLANTS ON THE PUMICE PLAINS,MOUNT ST. HELENS,WASHINGTON

Initial colonization on the devastated Pumice Plains on the northern flank of Mount St. Helens, Washington, was monitored in two large grids seven seasons after the eruptions of 1980. The Pumice Plains is composed primarily of deep pumice, but contains a few large mudflow channels and numerous small erosion gullies. Over 45% of 1,600 10 by 10 m quadrats (Willow Spring site) and over 35% of 875 quadrats (Lupine Patch site) were devoid of vascular plants. The most common species were the weedy natives, Anaphalis margaritacea and Epilobium angustifolium, as well as Lupinus lepidus var. lobbii, a native with poor dispersal usually found at subalpine elevations. The first two species invaded by long-distance dispersal; a few individuals of the latter somehow established by 1981 from surviving rootstocks or seeds, and dense populations have developed from these survivors. Other species are typically found at low densities in favorable microsites. Species richness averaged 1.03 per 100 m² at Willow Spring and 1.82 at Lupine Patch. There are 32 species at Willow Spring and 26 at Lupine Patch. Species richness was concentrated in sites with high soil moisture and where topographic irregularities permitted accumulation of seeds. Colonists are an unusual mix of natives, drawn from an array of open habitats, and introduced weeds originating in fields and clearcuts at lower elevations. Colonizing species are primarily herbaceous, perennial, and wind-dispersed, though seedlings of woody “climax” species occur. Three distributional patterns are recognized: hydrophiles, found near streams; facultative hydrophiles, concentrated in wet sites but successfully colonizing upland sites; and species distributed at random or in xeric sites. We predict that the course of succession will continue to be slow and herbs-dominated. Patches of Lupinus lepidus at present do not appear to facilitate colonization. Colonists will continue to be rare and be confined to favorable microsites for several years.     

Forest pattern,climate and vulcanism in central North Island,New Zealand

Abstract. A quantitative study of relationships between forest pattern and environment in the central North Island, New Zealand, is based on forest composition data from ca. 2000 existing plots distributed throughout the forests of the region. Estimates of mean annual temperature, rainfall, and solar radiation are derived for each plot from mathematical surfaces fitted to climate station data. Estimates of the depth of the last major rhyolitic eruption, (Taupo Pumice, ca. 130 AD) are derived from isopach maps. A classification procedure is used to identify broad compositional groups. Generalised linear models are used to examine relationships between major species and climatic and other physical factors. Significant relationships are identified between the distributions of both plot groups and species, and climate, vulcanism, topography and drainage. Among these factors, temperature and/or solar radiation are indicated as major determinants of the regional forest pattern, with rainfall, topography, and drainage acting at a secondary level. The role of the Taupo Pumice eruption is more difficult to interpret, and its effects seem to have been greatly influenced by topography. Deep extensive deposits of tephra on flat-to-rolling sites close to the eruption centre have probably favoured the current dominance of these sites by more rapidly dispersing conifers. In contrast, on adjacent steep sites where forest destruction was likely to be less severe, slow-dispersing Nothofagus species are largely dominant. Further work is needed to understand the factors favouring conifer dominance of the central basins and the degree to which Nothofagus species might expand their range in the future.     

Simplifying understory complexity in oil palm plantations is associated with a reduction in the density of a cleptoparasitic spider,Argyrodes miniaceus (Araneae: Theridiidae), in host (Araneae: Nephilinae) webs

Expansion of oil palm agriculture is currently one of the main drivers of habitat modification in Southeast Asia. Habitat modification can have significant effects on biodiversity, ecosystem function, and interactions between species by altering species abundances or the available resources in an ecosystem. Increasing complexity within modified habitats has the potential to maintain biodiversity and preserve species interactions. We investigated trophic interactions between Argyrodes miniaceus, a cleptoparasitic spider, and its Nephila spp. spider hosts in mature oil palm plantations in Sumatra, Indonesia. A. miniaceus co‐occupy the webs of Nephila spp. females and survive by stealing prey items caught in the web. We examined the effects of experimentally manipulated understory vegetation complexity on the density and abundance of A. miniaceus in Nephila spp. webs. Experimental understory treatments included enhanced complexity, standard complexity, and reduced complexity understory vegetation, which had been established as part of the ongoing Biodiversity and Ecosystem Function in Tropical Agriculture (BEFTA) Project. A. miniaceus density ranged from 14.4 to 31.4 spiders per square meter of web, with significantly lower densities found in reduced vegetation complexity treatments compared with both enhanced and standard treatment plots. A. miniaceus abundance per plot was also significantly lower in reduced complexity than in standard and enhanced complexity plots. Synthesis and applications: Maintenance of understory vegetation complexity contributes to the preservation of spider host–cleptoparasite relationships in oil palm plantations. Understory structural complexity in these simplified agroecosystems therefore helps to support abundant spider populations, a functionally important taxon in agricultural landscapes. In addition, management for more structurally complex agricultural habitats can support more complex trophic interactions in tropical agroecosystems.     

Changing Community States in the Gulf of Maine: Synergism Between Invaders, Overfishing and Climate Change

Human activities, including overfishing and species introductions, have had a dramatic impact on benthic communities in the Gulf of Maine within the past two decades. Prior to the 1970s, the climax community in the shallow subtidal was composed of Laminaria spp. kelp beds with an understory of arborescent red algae. In the 1980s, a population explosion of the green sea urchin, Strongylocentrotus droebachiensis, created an alternate community state, urchin barrens. Recently, a new community has been observed in former urchin barrens and kelp beds. This assemblage is principally composed of the introduced species: Codium fragile subsp. tomentosoides (green alga), Membranipora membranacea (bryozoan), Diplosoma listerianum (tunicate), Bonnemaisonia hamifera (red alga) and the opportunistic species Mytilus edulis (mussel) and Desmarestia aculeata (brown alga). In addition to changes in relative abundance, many of these species have greatly expanded their distribution and habitat selection. A model detailing mechanisms for the transition of the traditional kelp bed and urchin barren communities to others is presented and implications for this new community are discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Current distribution and potential extent of the most invasive alien plant species on La Réunion (Indian Ocean,Mascarene islands)

Abstract La Réunion Island has the largest area of intact vegetation of the islands in the Mascarene archipelago. Biological invasions are the primary threat to biodiversity in the intact habitats of the island (those not already transformed by agriculture and urbanization). Our study aimed to identify areas to prioritize in managing invasive alien plants for biodiversity conservation. We used extensive surveys of 238 distinct untransformed areas on La Réunion to define the current distribution patterns of all invasive species. Using expert knowledge, we compiled maps of the current distribution of the 46 most widespread/important invasive plants at the habitat scale (identified according to vegetation structure). Data from 440 botanical relevés for the 20 most threatening invasive alien plant species across the island and climatic envelope models were used to derive climatic suitability surfaces; these were used to map potential distributions for these species. More than 10 species invade 16.7% of the remaining habitat. Five habitat types are invaded by 25 or more species, and eight have fewer than 10 invasive alien plant species. Cluster analysis based on presence/absence of species in the 18 habitat types produced eight groups of species that invade particular habitats. Potential distribution models show that some species have invaded large parts of their potential range (e.g. Fuchsia magellanica, Furcraea foetida, Hiptage benghalensis), whereas others have the potential to increase their range substantially (e.g. Clidemia hirta, Strobilanthes hamiltonianus, Ulex europaeus). Management implications are identified for both groups. Three broad groups of habitats were identified: (i) intact habitats with a low level of invasion (e.g. subalpine shrubland); (ii) moderately invaded habitats with varying levels of intactness (ranging from windward submountain rainforest to the Acacia heterophylla forest); and (iii) habitats with little remaining intact area and high levels of invasion (e.g. lowland rainforest). Different management interventions are appropriate for these three groups.     

Micro-Scale Restoration: A 25-Year History of a Southern Illinois Barrens

We studied vegetation change of a remnant barrens in southern Illinois over twenty‐five years. The study area was periodically burned between 1969 and 1993, but fire was excluded for a 16‐year period (1974–1989). During the study, the barrens supported a mixture of species whose preferred habitats ranged from prairie and open woodlands to closed forest communities. The herbaceous vegetation may be on a trajectory characterized by increasing dominance of woodland species and declining prairie species. Fire management temporarily reversed this trend, but it continued once fire was excluded. Reintroduction of prescribed burning in 1990–1993 altered the vegetation trajectory but not back toward a species composition comparable to that present on the site before cessation of fire management after 1973. Following interruption of prescribed burning, tree basal area more than doubled, and density showed a 67% increase between premanagement conditions in 1968 and 1988. Salix humilis (prairie willow) density had significant negative correlations with tree density and basal area. However, there was no consistency in response of shrub species on the site to the varied site conditions over time. Fire management on the site may not recover the historic barrens that occurred on the site. Nevertheless, consistent fire management will drive vegetation changes toward increasing abundance of prairie and open woodland species that would otherwise be lost without burning.     

Density and habitat associations of Henslow's Sparrows wintering in saline soil barrens in southern Arkansas

ABSTRACT Although the habitat requirements of breeding populations of Henslow's Sparrow (Ammodramus henslowii) have been examined, less is known about their habitat requirements and ecology during the nonbreeding season. We estimated population densities and quantified habitat associations of Henslow's Sparrows wintering in saline soil barrens in southern Arkansas. Densities of Henslow's Sparrows in the saline soil barrens were similar to those in the Longleaf Pine (Pinus palustris) Ecosystem of the southeastern United States, considered by many to be their primary wintering habitat. Henslow's Sparrows were closely associated with open areas with greater cover of Aristida spp. and globe beaksedge (Rhynchospora globularis), greater stem density at 11–20 cm above ground, more lichens, more herbaceous cover, more bare ground, greater occurrence of little bluestem (Schizacyrium scoparium) as the tallest vegetation, less moss, and less shrub cover than randomly selected sites. In contrast to the results of studies conducted in the Longleaf Pine Ecosystem, the presence of Henslow's Sparrows in our study was not correlated with the height of the tallest vegetation. Our results indicate that saline soil barrens of southern Arkansas support a high density of wintering Henslow's Sparrows and do so for longer postdisturbance periods than longleaf pine savanna. We also found that stem density near the ground was similar to that reported from longleaf pine savanna, but only about half that observed on their breeding grounds. Areas used by Henslow's Sparrows had more lichen and less moss cover, suggesting that those areas were drier than random sites within the barrens. Further research is needed to determine if large populations of Henslow's Sparrows winter in other saline soil barrens and if fire influences habitat associations and densities in the barrens.     

Seasonal abundance and habitat use of bird species in and around Wondo Genet Forest,south‐central Ethiopia

The habitat use and seasonal migratory pattern of birds in Ethiopia is less explored as compared to diversity studies. To this end, this study aimed at investigating the patterns of distribution related to seasonality and the effect of habitat characteristics (elevation, slope, and average vegetation height) on habitat use of birds of Wondo Genet Forest Patch. A stratified random sampling design was used to assess the avian fauna across the four dominant habitat types found in the study area: natural forest, wooded grassland, grassland, and agroforestry land. A point transect count was employed to investigate avian species richness and abundance per habitat type per season. Ancillary data, such as elevation above sea level, latitude and longitude, average vegetation height, and percent slope inclination, were recorded with a GPS and clinometers per plot. A total of 33 migratory bird species were recorded from the area, of which 20 species were northern (Palearctic) migrants while 13 were inter‐African migrants. There was a significant difference in the mean abundance of migratory bird species between dry and wet seasons (t = 2.13, p = .038, df = 44). The variation in mean abundance per plot between the dry and wet seasons in the grassland habitat was significant (t = 2.35, p = .051, df = 7). In most habitat types during both dry and wet seasons, omnivore birds were the most abundant. While slope was a good predictor for bird species abundance in the dry season, altitude and average vegetation height accounted more in the wet season. The patch of forest and its surrounding is an important bird area for migratory, endemic, and global threatened species. Hence, it is conservation priority area, and the study suggests that conservation coupled with ecotourism development is needed for its sustainability.     

Status of a Relocated Population of Endangered Iguana pinguis on Guana Island, British Virgin Islands

Eight individual rock iguanas (Iguana pinguis) from Anegada Island were relocated to Guana Island by Lazell, 1984–1987, in order to establish a second population reservoir for this endangered species. The species may have originally occupied the entire Puerto Rico Bank. The relocation has been successful and, in the area currently providing the best habitat, we estimate a density of 9 or 12 animals of various age classes per 19 ha. The optimal area contains a sheep exclosure with relatively dense understory vegetation and numerous exotic as well as native species of plants. Iguana activity is concentrated on east facing slopes and ridge-tops that get morning sun. Outside the exclosure most edible ground cover and shrubs have been eaten by sheep, leaving toxic or noxious species, such as Croton or Lantana, in the understory where I. pinguis adults generally forage. Removal of sheep may be critical to continued population growth of these reptiles. Views on relocation or repatriation of other endangered Antillean Iguana species are advanced, with some ideas on minimum viable population sizes and a possible explanation for the extirpation of I. pinguis from much of its former range.     

The cascading effects of elephant presence/absence on arthropods and an Afrotropical thrush in Arabuko‐Sokoke Forest,Kenya

Although studies have explored how habitat structure and disturbance affect arthropod communities, few have explicitly tested the effects of both structure and disturbance level across trophic levels and phyla. We present here the results of a study conducted in the Arabuko‐Sokoke Forest (ASF) of coastal Kenya, in which abundance of arthropods and one of their avian predators, the East Coast Akalat Sheppardia gunning sokokensis was compared in relatively undisturbed habitat (outside elephant roaming areas) and in disturbed habitat (inside elephant roaming areas). Vegetation structure in both areas was measured using several metrics, including leaf litter depth, understory vegetation density, animal disturbance and fallen log counts. Leaf litter and coleopteran abundance were higher outside the elephant roaming areas, whereas understory visibility, animal disturbance and dipteran diversity were much higher inside the elephant areas. Species composition of several arthropod taxa (e.g. Hymenoptera, Coleoptera, Diptera, Hemiptera and Araneae) was also influenced by degree of disturbance, whereas akalat abundance was inversely related to understory visibility. Our results suggest that differences in species sensitivity to habitat disturbance and vegetation structure across trophic levels should be incorporated into the management and conservation of rare and endangered species.     

Short‐term efficacy and nontarget effects of aerial glyphosate applications for controlling Lonicera maackii (Amur honeysuckle) in oak‐hickory forests of Eastern Missouri,U.S.A.

Lonicera maackii (Amur honeysuckle) is a non‐native species that has invaded forest stands throughout the eastern United States. This research examined using aerially applied glyphosate in autumn 2013 to control L. maackii in oak‐hickory forest stands in Missouri, U.S.A. We targeted the spraying time period when L. maackii was still green and most native plants were dormant. Across treatment units, the mean difference in L. maackii stem density significantly declined (p = 0.004) by 5.4 stems per plot from spring 2013 to summer 2014 when compared to control units which increased by 1.8 stems per plot. Treated units with a high initial infestation level of L. maackii (>50% cover) had a significant (p = 0.004) decline in the mean difference in L. maackii cover of ?50.0% per plot between spring 2013 and summer 2014 compared to an average increase of 9.2% in the controls. Similar results were found for treated units with a low initial infestation level of L. maackii (10–50% cover). Mortality of native overstory and understory trees post‐treatment was negligible. In the ground layer of forest stands with a low initial L. maackii infestation level, native non‐spray‐sensitive forb cover per plot significantly increased (p = 0.023) relative to controls between summer 2013 and summer 2014 while native spray‐sensitive species cover significantly decreased (p = 0.021) during the same period. These results suggest that an aerial application of glyphosate can provide an L. maackii control option, but with trade‐offs in compositional shifts in the native ground‐layer vegetation.     

Temporal variation in the woody understory of an old-growth Fagus-Acer forest and implications for overstory recruitment

Abstract. Changes in woody vegetation were examined over eight years, using a 1.05-ha permanent plot in which the location of every shrub and tree > 1m height was mapped. There was little change in the overstory vegetation, as expected for an old-growth forest. Much greater change occurred in the understory, primarily related to a 40 % increase in density. Differences occurred among species in the under-story, as Acer saccharum and Prunus serotina increased and Fraxinus americana and Fagus grandifolia decreased. Canopy gap dynamics are implicated in differences among species in the establishment and growth of individuals in the understory and their recruitment into the overstory. It is concluded that because understory is temporally variable, overstory recruitment from the understory may take different courses at different times in the same forest.     

Understory Invasion by <Emphasis Type="Italic">Acacia longifolia</Emphasis> Alters the Water Balance and Carbon Gain of a Mediterranean Pine Forest

In water-limited ecosystems, where potential evapotranspiration exceeds precipitation, it is often assumed that plant invasions will not increase total ecosystem water use, because all available water is evaporated or transpired regardless of vegetation type. However, invasion by exotic species, with high water use rates, may potentially alter ecosystem water balance by reducing water available to native species, which may in turn impact carbon assimilation and productivity of co-occurring species. Here, we document the impact of invasion by an understory exotic woody species (Acacia longifolia) in a semi-arid Mediterranean dune pine forest. To quantify the effects of this understory leguminous tree on the water use and carbon fixation rates of Pinus pinaster we compare an invaded and a non-invaded stand. A. longifolia significantly altered forest structure by increasing plant density and leaf area index in the mid-stratum of the invaded forest. A. longifolia contributed significantly to transpiration in the invaded forest (up to 42%) resulting in a slight increase in stand transpiration in the invaded relative to non-invaded forest. More importantly, both water use and carbon assimilation rates of P. pinaster were significantly reduced in the invaded relative to non-invaded stand. Therefore, this study shows that exotic plant invasions can have significant impacts on hydrological and carbon cycling even in water-limited semi-arid ecosystems through a repartitioning of water resources between the native and the invasive species.     

How does Reynoutria invasion fit the various theories of invasibility?

Questions: 1. How does species richness of recipient communities affect Reynoutria invasion? 2. How does Reynoutria invasion change host community structure? 3. Are there any differences in habitat preferences among three closely related Reynoutria taxa? 4. How does the genetic structure of Reynoutria populations change along the course of a river? Location: River Jizera basin, north Bohemia, Czech Republic. Methods: Nine 0.25 km² plots were chosen along the river. Within each plot all main habitat types were determined and sampled using the Braun‐Blanquet scale to determine the invasibility of various communities. The patches invaded by Reynoutria taxa and surrounding Reynoutria‐free vegetation in the same habitat type were sampled as relevé pairs to compare the composition of invaded and non‐invaded vegetation. In addition, to characterize the genetic structure of Reynoutria populations along the river, 30 samples from different clones were collected. Results and conclusions: 1. The species richness of communities has no influence on the success of Reynoutria invasion in the area studied. The combination of environmental conditions and propagule spread is more important to the invasion success than the number of species in the host community. 2. Reynoutria invasion greatly reduces species diversity. 3. R. japonica invaded more habitat types than R. sachalinensis and R.×bohemica. The hybrid R.×bohemica outcompetes the parental taxa at sites where both taxa co‐occur. 4. Isozyme analysis revealed phenotype variability in the hybrid in contrast to the parental taxa. Different hybrid phenotypes are distributed randomly on the middle and lower reaches of the River Jizera; one of them dominates and the other three occur occasionally. This pattern supports the hypothesis that sexual reproduction occasionally occurs within Reynoutria taxa.     

Conifer Regeneration Problems in Boreal and Temperate Forests with Ericaceous Understory: Role of Disturbance,Seedbed Limitation,and Keytsone Species Change

Conifer regeneration failure in the presence of dense ericaceous cover resulting from the removal of canopy trees by forest harvesting observed in boreal and temperate forest has been attributed to allelopathy, competition, and soil nutrient imbalance. Ecosystem-level alleopathic effect has been argued as a cause for conifer regeneration failure by citing examples from a species-poor boreal forest in northern Sweden with ground vegetation dominated by crowberry (Empetrum hermaphroditum, Ericales) and New Zealand dairy pastures invaded by nodding or musk thistle (Carduus nutans). This article aims to explain the phenomenon of vegetation shift from conifer forest to ericaceous heath by extending the argument of ecosystem-level impact of ericaceous plants and linking the disturbance-mediated regeneration strategies of the dominant conifer species and the understory ericaceous species with the quality of seedbed substrate that influence the direction of secondary succession. It has been argued that fire severity plays a pivotal role in controlling seedbed quality and the regeneration mechanisms of conifers, which in turn determines the direction of post-disturbance succession. The post-fire-dominated ericaceous plants and their habitat-modifying effects have been explained from the point of view of keystone species concept and their role as ecosystem engineers. In the absence of high severity natural fires the canopy keystone species (conifer) fails to regenerate successfully mainly due to limitation of favorable seedbed. On the other hand, the understory ericaceous plants regenerate vigorously by vegetative methods from the belowground components that survived the fire. Forest harvesting by clearcutting or selective cutting also create similar vigorous vegetative regrowth of ericaceous plants, but conifer regeneration suffers from the lack of a suitable seedbed. Thus in the absence of successful conifer regeneration, the vigorously growing understory ericaceous plants become the new keystone species. The new keystone ericaceous species bring about a significant long-term habitat change by rapid accumulation of plyphenol-rich humus. Ericaceous phenolic compounds have been found to inhibit seed germination and seedling growth of conifers. By forming protein-phenol complexes they cause a further reduction of available nitrogen of the already nutrient-stressed habitat. A low pH condition in the presence of phenolic compounds causes the leaching of metallic ions and forms hard iron pans that impair soil water movement. The phenolic allelochemicals of ericaceous humus are also inhibitory to many conifer ectomycorrhizae. On the other hand, ericaceous plants perpetuate in the community by their stress-tolerating strategies as well as their ability to acquire nutrients through ericoid mycorrhizae. Three mechanisms working at the ecosystem level can be suggested as the cause of vegetation shift from forest to ericaceous heath. These are (1) the absence of high severity natural fire and the limitation of suitable conifer seedbed in the presence of thick humus, (2) increased competition resulting from the rapid vegetative regeneration of understory ericaceous plants after forest canopy opening by harvesting or nonsevere fire, and (3) habitat degradation by phenolic allelochemicals of ericaceous plants causing a soil nutrient imbalance and iron pan formation. Thus, a shift in keystone species from conifer to ericaceous plant in the post-disturbance habitat may induce a retrogressive succession due to ecosystem-level engineering effects of the new keystone species. Vegetation management in conifer-ericaceous communities depends on land management objectives. If the objective is to produce timber and other forest products then the control of ericaceous plants and site preparation is necessary after forest harvesting. Ploughing and liming followed by conifer planting and repeated N fertilization has been applied successfully to promote afforestation of Calluna heathlands in Britain. However, such practice has not been proven successful in the reforestation of Kalmia-dominated sites in eastern Canada. If, on the other hand, the land management objective is to maintain heathlands for herbivore production or conservation of cultural landscape, as in the case of certain Calluna-dominated heathland in Western Europe, then moderately hot prescribed burning is useful as a management tool.     

不同生境下濒危植物膝柄木幼树的生态适应性

膝柄木是我国极度濒危植物,也是广西滨海过渡带天然植被的重要组成树种.为了解光因子对膝柄木天然更新的限制影响,该文对林缘、林窗、林下三种不同光照生境下膝柄木幼树的生理和生长指标的年际变化特征进行了研究.结果表明:(1)光合有效辐射不足影响了膝柄木幼树的生长.林下幼树的地径、株高和叶面积增长量显著降低,而生长于光照充足林缘...     

Plant invasion alters trait composition and diversity across habitats

Increased globalization has accelerated the movement of species around the world. Many of these nonnative species have the potential to profoundly alter ecosystems. The mechanisms underpinning this impact are often poorly understood, and traits are often overlooked when trying to understand and predict the impacts of species invasions on communities. We conducted an observational field experiment in Canada's first National Urban Park, where we collected trait data for seven different functional traits (height, stem width, specific leaf area, leaf percent nitrogen, and leaf percent carbon) across an abundance gradient of the invasive Vincetoxicum rossicum in open meadow and understory habitats. We assessed invasion impacts on communities, and associated mechanisms, by examining three complementary functional trait measures: community‐weighted mean, range of trait values, and species’ distances to the invader in trait space. We found that V. rossicum invasion significantly altered the functional structure of herbaceous plant communities. In both habitats V. rossicum changed the community‐weighted means, causing invaded communities to become increasingly similar in their functional structure. In addition, V. rossicum also reduced the trait ranges for a majority of traits indicating that species are being deterministically excluded in invaded communities. Further, we observed different trends in the meadow and understory habitats: In the understory, resident species that were more similar to V. rossicum in multivariate trait space were excluded more, however this was not the case in the meadow habitat. This suggests that V. rossicum alters communities uniquely in each habitat, in part by creating a filter in which only certain resident species are able to persist. This filtering process causes a nonrandom reduction in species' abundances, which in turn would be expected to alter how the invaded ecosystems function. Using trait‐based frameworks leads to better understanding and prediction of invasion impacts. This novel framework can also be used in restoration practices to understand how invasion impacts communities and to reassemble communities after invasive species management.     

Effects of grazing by re-introduced Equus hemionus on the vegetation in a Negev desert erosion cirque

Abstract. Asiatic wild asses, Equus hemionus, were driven to extinction in Israel in the early 20th century. In 1983, a herd of these animals was re-introduced to the wild in Makhtesh Ramon, a large erosion cirque in the central Negev desert, Israel. The population has grown steadily ever since and now numbers some 100 animals. In order to determine whether the wild asses are having a significant impact on the vegetation, we have monitored the plant communities in Makhtesh Ramon since 1992, using McAuliffe's log-series survey method. Our study involves 11 pairs of plots along the length of the altitudinal gradient in Makhtesh Ramon. The altitudinal gradient results in a rainfall gradient from an average of 95 mm rain per year to an average of about 40 mm per year. Each pair of plots consists of: (1) an unfenced plot, and (2) a fenced plot that excludes wild asses but not the other large mammalian herbivore, the dorcas gazelle Gazella dorcas. The wild asses have not had a significant impact on vegetation cover, species richness, diversity or dominance. Three plant species showed significant increases in percentage cover in fenced plots, while one species showed a significant increase in percentage cover in unfenced plots. Furthermore, eight plant species invaded fenced plots, three species invaded unfenced plots and one species disappeared from unfenced plots during the study. Using Detrended Correspondence Analysis, we found that the major differences among plots are due to position along the altitudinal gradient. The Detrended Correspondence Analyses indicated that the wild asses have had no significant effect on vegetation community structure.     

Photosynthetic properties of an orchid community in central Italy

Abstract

Chlorophyllous Mediterranean orchids share a habitat endangered by climate change and land use change. These orchids are characterized by two mechanisms of carbon assimilation, being autotrophic carbon fixation through photosynthesis supplemented by heterotrophic carbon fixation from mycorrhizal fungi. We investigated whether photosynthesis may sustain autotrophy of several species of orchids co-occurring in the same habitat (the understory of a chestnut forest in the Apennines range) along a vegetative season, and how photosynthesis responds to environmental parameters in the different species. Combined analysis of gas-exchange, chlorophyll fluorescence, optical properties, chlorophylls concentration, and Ribulose 1,5 bisphosphate carboxylase/oxygenase (Rubisco) activity were carried out to characterize the photosynthetic apparatus of the orchid species. Both in vivo and in vitro measurements indicated that in all orchids, in natural conditions and over the entire vegetative season (May to July), a detectable amount of carbon, typical of autotrophic shade leaves, is fixed. It is therefore suggested that these orchids are predominantly autotrophic. As an exception, however, Limodorum abortivum, a co-occurring orchid in the examined habitat, is unable to photosynthesize at rates compatible with autotrophy. At the low light intensity experienced in the understory habitat all orchids exhibited a similar quantum yield, but photosynthesis of Dactylorhiza saccifera and Cephalanthera longifolia was stimulated by light intensities higher than ambient, indicating that these species may better use sunflecks reaching the understory vegetation. Photosynthesis of all orchids, including Limodorum, positively responded to increasing CO₂ concentration and temperature. Whether this will lead to a larger photosynthetic carbon fixation because of present and future climate change needs to be assessed with long-term experiments also including the impacts of climate on mychorrizal activity and host plants.