Local vs regional factors as determinants of the invasibility of indigenous forest fragments by alien plant species

Both local and regional filters can determine the invasion of alien species into native plant communities. However, their relative importance is essentially unknown. We used plot data from fragments of indigenous forests in southeastern New Zealand to infer which factors are important in explaining invasibility, measured as alien species richness. Twenty-eight predictor variables comprising both local factors (stand structure and soil) and regional ones (climate and land cover) were assessed. Reduction or increase in deviance in linear models was assessed, both individually and with a forward and backward stepwise variable selection procedure using the Akaike information criterion (AIC).
We found that higher alien species richness was mainly associated with forest fragments of small area in warm and dry climates and where there were only small areas of surrounding indigenous forest. Local soil and stand structure variables had considerably smaller effects on alien species richness than the regional land cover and climate variables. Alien species richness showed no relationship with native species richness. We conclude that in the forest fragments investigated here, of the variables included in the analyses, regional land cover and climate variables are potentially important drivers for alien species richness at plot level. This has implications for projections of alien species spread in the future under different climate change and land use scenarios.     

A continent under stress: interactions, feedbacks and risks associated with impact of modified land cover on Australia's climate

Global climate change is the major and most urgent global environmental issue. Australia is already experiencing climate change as evidenced by higher temperatures and more frequent and severe droughts. These impacts are compounded by increasing land use pressures on natural resources and native ecosystems. This paper provides a synthesis of the interactions, feedbacks and risks of natural climate variability, climate change and land use/land cover change (LUCC) impacting on the Australian continent and how they vary regionally. We review evidence of climate change and underlying processes resulting from interactions between global warming caused by increased concentration of atmospheric greenhouse gases and modification of the land surface. The consequences of ignoring the effect of LUCC on current and future droughts in Australia could have catastrophic consequences for the nation's environment, economy and communities. We highlight the need for more integrated, long-term and adaptive policies and regional natural resource management strategies that restore the beneficial feedbacks between native vegetation cover and local-regional climate, to help ameliorate the impact of global warming.     

The Altitudinal Patterns of Leaf C∶N∶P Stoichiometry Are Regulated by Plant Growth Form,Climate and Soil on Changbai Mountain,China

Understanding the geographic patterns and potential drivers of leaf stoichiometry is critical for modelling the nutrient fluxes of ecosystems and to predict the responses of ecosystems to global changes. This study aimed to explore the altitudinal patterns and potential drivers of leaf C∶N∶P stoichiometry. We measured the concentrations of leaf C, N and P in 175 plant species as well as soil nutrient concentrations along an altitudinal transect (500–2300 m) on the northern slope of Changbai Mountain, China to explore the response of leaf C∶N∶P stoichiometry to plant growth form (PGF), climate and soil. Leaf C, N, P and C∶N∶P ratios showed significant altitudinal trends. In general, leaf C and C∶N∶P ratios increased while leaf N and P decreased with elevation. Woody and herbaceous species showed different responses to altitudinal gradients. Trees had the largest variation in leaf C, C∶N and C∶P ratios, while herbs showed the largest variation in leaf N, P and N∶P ratio. PGF, climate and soil jointly regulated leaf stoichiometry, explaining 17.6% to 52.1% of the variation in the six leaf stoichiometric traits. PGF was more important in explaining leaf stoichiometry variation than soil and climate. Our findings will help to elucidate the altitudinal patterns of leaf stoichiometry and to model ecosystem nutrient cycling.     

Alien and native plants show contrasting responses to climate and land use in Europe

Aim We tested whether the distribution and cover of alien plant species in Europe was related to human disturbance and microclimate. Location Surveys were conducted at 13 sites across Europe, each containing a pair of landscapes with different land‐use intensities. Methods Sampling locations were chosen based on land use and microclimate at two scales: land use was characterized at the patch and landscape scale; climate was expressed as regional and local temperature. The slope of each sample location was derived from a digital elevation model. Cover of plant species was measured using point counts and analysed using mixed effect models. Species were classified as native, archaeophytes and neophytes (pre‐ versus post‐ad 1500 immigrants). Due to the zero inflation observed in the alien groups, their cover was analysed conditional on their presence. Results Anthropogenic disturbance was a significant explanatory variable, increasing the presence and cover of alien species and decreasing the cover of native species. Alien presence was increased in sites under agricultural management, while their cover responded to land use at both local and landscape scales (and to their interaction), such that only natural habitats in semi‐natural landscapes had low alien cover. Microclimate was important for neophytes, with presence concentrated around mesic conditions. Slope was relevant for archaeophytes and native species, suppressing the former group and promoting the latter one. Main conclusions We found that, at the European scale, the distribution of alien plants is related to anthropogenic disturbance more than to microclimatic differences. The presence of neophytes, however, was influenced by climate at local and regional scales, with the highest incidence under mesic conditions. The different patterns observed for the presence and cover of alien species suggest different mechanisms acting during their establishment and spread. They also suggest that to counteract the expansion of alien species natural habitats may need to be maintained at landscape scales.     

The relative importance of climatic effects, wildfires and management for future forest landscape dynamics in the Swiss Alps

Forest landscape dynamics result from the complex interaction of driving forces and ecological processes operating on various scales. Projected climate change for the 21st century will alter climate‐sensitive processes, causing shifts in species composition and also bringing about changes in disturbance regimes, particularly regarding wildfires. Previous studies of the impact of climate change on forests have focused mainly on the direct effects of climate. In the present study, we assessed the interactions among forest dynamics, climate change and large‐scale disturbances such as fire, wind and forest management. We used the Land Clim model to investigate the influence, interactions and the relative importance of these different drivers of landscape dynamics in two case study areas of the European Alps. The simulations revealed that projected future climate change would cause extensive forest cover changes, beginning in the coming decades. Fire is likely to become almost as important for shaping the landscape as the direct effects of climate change, even in areas where major wildfires do not occur under current climatic conditions. The effects of variable wind disturbances and harvesting regimes, however, are less likely to have a considerable impact on forest development compared with the direct effects of climate change coupled with the indirect effects of increased fire activity. We conclude that the joint direct and indirect effects of climate change are likely to have major consequences for mountain forests in the European Alps, including their ability to provide protection against natural hazards.     

Anomalous droughts,not invasion,decrease persistence of native fishes in a desert river

Changing climate extremes and invasion by non‐native species are two of the most prominent threats to native faunas. Predicting the relationships between global change and native faunas requires a quantitative toolkit that effectively links the timing and magnitude of extreme events to variation in species abundances. Here, we examine how discharge anomalies – unexpected floods and droughts – determine covariation in abundance of native and non‐native fish species in a highly variable desert river in Arizona. We quantified stochastic variation in discharge using Fourier analyses on >15 000 daily observations. We subsequently coupled maximum annual spectral anomalies with a 15‐year time series of fish abundances (1994–2008), using Multivariate Autoregressive State‐Space (MARSS) models. Abiotic drivers (discharge anomalies) were paramount in determining long‐term fish abundances, whereas biotic drivers (species interactions) played only a secondary role. As predicted, anomalous droughts reduced the abundances of native species, while floods increased them. However, in contrast to previous studies, we observed that the non‐native assemblage was surprisingly unresponsive to extreme events. Biological trait analyses showed that functional uniqueness was higher in native than in non‐native fishes. We also found that discharge anomalies influenced diversity patterns at the meta‐community level, with nestedness increasing after anomalous droughts due to the differential impairment of native species. Overall, our results advance the notion that discharge variation is key in determining community trajectories in the long term, predicting the persistence of native fauna even in the face of invasion. We suggest this variation, rather than biotic interactions, may commonly underlie covariation between native and non‐native faunas, especially in highly variable environments. If droughts become increasingly severe due to climate change, and floods increasingly muted due to regulation, fish assemblages in desert rivers may become taxonomically and functionally impoverished and dominated by non‐native taxa.     

The impact of human pressure on landscape patterns and plant species richness in Mediterranean coastal dunes

We analyze the spatial patterns of natural dune cover patches and their plant richness, comparing coastal sites with different levels of human pressure in central Italy. We created a detailed land cover map of dune sites. The spatial pattern of natural dune cover types was characterized by computing a set of patch-based metrics. To quantify patch plant richness, we used 16 m² vegetation plots, randomly distributed on coastal dune cover types. For each patch, the richness of the entire pool of species and of three guilds (i.e., typical dune, ruderal, and alien species) was considered. We compared different levels of human pressure on coastal dunes focusing on pattern metrics and floristic information by using the nonparametric Kruskal–Wallis test. In sites with high human pressure, we have observed a general simplification in the natural dune spatial pattern and a decline of plant richness but with a specific response for each cover type. Alien and ruderal species presented low richness in all patches. In coastal dunes, the harsh ecological conditions and the strong sea–inland gradient shape the distribution of human activities and control the number of ruderal species. The approach effectively describes fragmentation and biodiversity in dune ecosystems.     

Wetlands in flux: looking for the drivers in a central European case

Planet Earth is undergoing significant changes which are driven by natural and anthropogenic factors. However, it is difficult to identify the drivers and their effect on the environment and ecosystems because there are many interdependencies. In this study we present a multi-parameter approach to assess the effect of changes in human-induced and natural drivers on a wetland ecosystem. The study area is one of the most prominent European wetlands: the Biebrza Basin, located in north-eastern Poland. We analysed long-term (ca. 1960–2000) changes in meteorology, hydrology, soil and vegetation, and also conservation history. This approach enabled us to identify interactions between environmental change and management. We found significant trends (1960–2012) indicating climate change: increases in temperature, evapotranspiration and earlier start of spring floods. We identified (1970–2000) a shift towards drier vegetation types after drainage. However, we also found that restoration measures that were implemented have mitigated climate change effects and have led to increases in soil moisture and wetter vegetation types. We conclude that, if carried out sufficiently frequently, the management measures implemented in the Biebrza Basin, which are a combination of different restoration measures (blocking drainage, not clearing aquatic vegetation, bush removal, mowing), can to some extent mitigate the effects of climate change.     

Interactions between rainfall, deforestation and fires during recent years in the Brazilian Amazonia

Understanding the interplay between climate and land-use dynamics is a fundamental concern for assessing the vulnerability of Amazonia to climate change. In this study, we analyse satellite-derived monthly and annual time series of rainfall, fires and deforestation to explicitly quantify the seasonal patterns and relationships between these three variables, with a particular focus on the Amazonian drought of 2005. Our results demonstrate a marked seasonality with one peak per year for all variables analysed, except deforestation. For the annual cycle, we found correlations above 90% with a time lag between variables. Deforestation and fires reach the highest values three and six months, respectively, after the peak of the rainy season. The cumulative number of hot pixels was linearly related to the size of the area deforested annually from 1998 to 2004 (r2=0.84, p=0.004). During the 2005 drought, the number of hot pixels increased 43% in relation to the expected value for a similar deforested area (approx. 19000km2). We demonstrated that anthropogenic forcing, such as land-use change, is decisive in determining the seasonality and annual patterns of fire occurrence. Moreover, droughts can significantly increase the number of fires in the region even with decreased deforestation rates. We may expect that the ongoing deforestation, currently based on slash and burn procedures, and the use of fires for land management in Amazonia will intensify the impact of droughts associated with natural climate variability or human-induced climate change and, therefore, a large area of forest edge will be under increased risk of fires.     

An empirical test of the relative and combined effects of land‐cover and climate change on local colonization and extinction

Land‐cover and climate change are two main drivers of changes in species ranges. Yet, the majority of studies investigating the impacts of global change on biodiversity focus on one global change driver and usually use simulations to project biodiversity responses to future conditions. We conduct an empirical test of the relative and combined effects of land‐cover and climate change on species occurrence changes. Specifically, we examine whether observed local colonization and extinctions of North American birds between 1981–1985 and 2001–2005 are correlated with land‐cover and climate change and whether bird life history and ecological traits explain interspecific variation in observed occurrence changes. We fit logistic regression models to test the impact of physical land‐cover change, changes in net primary productivity, winter precipitation, mean summer temperature, and mean winter temperature on the probability of Ontario breeding bird local colonization and extinction. Models with climate change, land‐cover change, and the combination of these two drivers were the top ranked models of local colonization for 30%, 27%, and 29% of species, respectively. Conversely, models with climate change, land‐cover change, and the combination of these two drivers were the top ranked models of local extinction for 61%, 7%, and 9% of species, respectively. The quantitative impacts of land‐cover and climate change variables also vary among bird species. We then fit linear regression models to test whether the variation in regional colonization and extinction rate could be explained by mean body mass, migratory strategy, and habitat preference of birds. Overall, species traits were weakly correlated with heterogeneity in species occurrence changes. We provide empirical evidence showing that land‐cover change, climate change, and the combination of multiple global change drivers can differentially explain observed species local colonization and extinction.     

Predicting Plant Diversity Patterns in Madagascar: Understanding the Effects of Climate and Land Cover Change in a Biodiversity Hotspot

Climate and land cover change are driving a major reorganization of terrestrial biotic communities in tropical ecosystems. In an effort to understand how biodiversity patterns in the tropics will respond to individual and combined effects of these two drivers of environmental change, we use species distribution models (SDMs) calibrated for recent climate and land cover variables and projected to future scenarios to predict changes in diversity patterns in Madagascar. We collected occurrence records for 828 plant genera and 2186 plant species. We developed three scenarios, (i.e., climate only, land cover only and combined climate-land cover) based on recent and future climate and land cover variables. We used this modelling framework to investigate how the impacts of changes to climate and land cover influenced biodiversity across ecoregions and elevation bands. There were large-scale climate- and land cover-driven changes in plant biodiversity across Madagascar, including both losses and gains in diversity. The sharpest declines in biodiversity were projected for the eastern escarpment and high elevation ecosystems. Sharp declines in diversity were driven by the combined climate-land cover scenarios; however, there were subtle, region-specific differences in model outputs for each scenario, where certain regions experienced relatively higher species loss under climate or land cover only models. We strongly caution that predicted future gains in plant diversity will depend on the development and maintenance of dispersal pathways that connect current and future suitable habitats. The forecast for Madagascar’s plant diversity in the face of future environmental change is worrying: regional diversity will continue to decrease in response to the combined effects of climate and land cover change, with habitats such as ericoid thickets and eastern lowland and sub-humid forests particularly vulnerable into the future.     

Land use changes and conservation threats in the eastern Selous–Niassa wildlife corridor,Nachingwea, Tanzania

Selous–Niassa miombo woodland ecosystem has been and continues to face conservation threats. Understanding of changes happening in such ecosystem overtime is important for establishing management baseline data. This study identified land use changes, socio‐economic factors and conservation threats to the Selous–Niassa wildlife corridor across Nachingwea district, Tanzania. Landsat images of 1978, 1993 and 2000 were used to assess land use changes. Household survey was conducted to obtain socio‐economic data; logistic regression model was used to analyse the data. In 15 years (1978–1993) cultivated land only increased by 131% while forestlands decreased by 8.7%. In 12 years (1993–2005) cultivated land increased by 65.6% while forestland decreased by 10.7%. Land cover change per year has been found 0.54% relatively low compared to national land cover change of 45%per year. Land tenure, shifting cultivation and crops prices were major factors influencing land use changes while wildfires, farm encroachment and illegal timber harvesting were major conservation threats. Basing on the results, it was recommended that there is a need for a government to introduce community‐based natural resource management plans to improve natural resource utilization and reduce human stress to the corridor.     

Shielded environments reduce stress in alien Asteraceae species during hot and dry summers along urban‐to‐rural gradients

Urban environments often host a greater abundance and diversity of alien plant species than rural areas. This is frequently linked to higher disturbance and propagule pressure, but could also be related to the additional establishment of species from warmer native ranges in cities, facilitated by the latter''s higher air temperatures and drier soils. A hitherto unresolved question is how stressful the urban environments become during climate extremes such as heatwaves and droughts. Do such episodes still favor alien plant species, or set them back? We used in situ measured phenotypic leaf and development trait responses of the six most widespread alien Asteraceae species from various native climates along Belgian urban‐to‐rural gradients, measured during two unusually warm and dry summers. Urbanization was characterized by three factors: the percentage of artificially sealed surfaces (urbanity, measured at three spatial scales from in situ to satellite‐based), the vegetation cover and the sky view factor (SVF, fraction of the hemisphere not blocked by buildings or vegetation). Across species, either from colder or warmer native climates, we found a predominant protective effect of shielded environments that block solar radiation (low SVF) along the entire urban‐to‐rural gradient. Such environments induced lower leaf anthocyanins and flavonols indices, indicating heat stress mitigation. Shielded environments also increased specific leaf area (SLA), a typical shade response. We found that vegetated areas had a secondary importance, increasing the chlorophyll content and decreasing the flavonols index, but these effects were not consistent across species. Finally, urbanity at the organism spatial scale decreased plant height, while broader‐scale urbanity had no significant influence. Our results suggest that sealed surfaces constrain alien Asteraceae during unusually warm and dry summers, while shielded environments protect them, possibly canceling out the lack of light. These findings shed new light on alien plant species success along urban‐to‐rural gradients in a changing climate.     

Effects of land use and environment on alien and native macrophytes: lessons from a large‐scale survey of Australian rivers

Aim We sampled riverine macrophyte communities and environmental conditions to compare drivers of alien and native abundance and to provide a general set of environmental correlates of invasion by aquatic macrophytes. Location Streams adjacent to three land‐use types (intensive, agricultural and natural) across a large latitudinal gradient (approximately 27° S–43° S) in Australia. Sites were located near Brisbane (Queensland), Sydney (New South Wales), Canberra (Australian Capital Territory), Melbourne (Victoria) and Hobart (Tasmania). Methods Alien and native aquatic plant species cover, water quality, forest canopy and adjacent land use were measured in three catchment locations (low‐, mid‐ and upper‐catchment) in all cities. Mean richness and cover of native and alien macrophytes were compared in the five cities, three catchment locations, and three land‐use types. Correlation tests examined relationships between alien and native richness at transect, site and city scales. Canonical correspondence analysis (CCA) determined the effects of environment on cover and richness of native and alien plant groups (emergents, floating, forbs/other, graminoids and submerged). Results Variation existed in the aquatic plant community at all scales, but strong patterns emerged with respect to land use and environmental gradients. Alien abundance was more responsive to anthropogenic disturbance (e.g. greater in intensive and agricultural land‐use types, and greater where dissolved nutrients and conductivity were high) than natives, which were unaffected by land‐use type and less responsive overall to environmental gradients. Native and alien richness were uncorrelated at all scales. Main conclusions Natives and aliens of the same life form did not respond similarly to the environment, suggesting inherent differences in their ability to capitalize on anthropogenic disturbance. Our results suggest invasion‐susceptible habitats are those that receive nutrient pollutants and that occur in urban and agricultural areas low in the catchment. Our confidence in these patterns is strengthened by their consistency across a large latitudinal gradient.     

The impact of grazing by macropods on coastal foredune vegetation in southeast Queensland

Abstract The extent of grazing by two macropodids, the agile wallaby (Macropus agilis) and the swamp wallaby (Wallabia bicolor) on coastal foredunes on South Stradbroke Island in southeast Queensland was investigated to determine potential impacts on the principal sand colonizing species, sand spinifex grass (Spinifex sericeus). Grazing on spinifex grass on the foredunes of South Stradbroke island can be attributed principally to agile wallabies. Foraging activity by wallabies was higher in areas of high spinifex abundance, however, grazing intensity and impact on spinifex was only important on foredunes with low spinifex abundance. Spinifex consumption by wallabies was also related to a number of factors, especially composition and structure of vegetation in adjacent habitats. Spinifex consumption increased when the abundance of ground cover components (grasses, sedges, forbs) in adjacent habitats was low and structural complexity was high. Grazing on foredunes by wallabies significantly affects the species composition of the foredune community by excluding the establishment of a number of perennial foredune plant species. This may have implications for community succession in coastal ecosystems.     

Tree growth in the aftermath of A flood: A tree-ring based reconstruction of the impacts of the 1996-Biescas catastrophe

Catastrophic floods and large debris flows are natural hazards common in mountain areas. They cause injuries and impact the radial growth of trees growing in the affected basins. Reconstructing how these catastrophic events impact trees by using dendrochronology improves our understanding of natural hazards. The 1996-Biescas (Central Spanish Pyrenees) flood was a catastrophic event causing the loss of many lives in a campsite located on an active alluvial fan. We investigated using tree rings how this catastrophic flood impacted planted trees (poplars, cedars) located in the campsite. Conspicuous scars in the stem were more abundant in cedar trees (75 %) than in poplar (36 %) trees. Scarred cedar trees formed traumatic resin ducts after the flood. In cedar tree perimeter influenced the size of the wound formed after the flood, but this was not observed in poplar. On average, 63 % of trees showing scars formed them in the side of the stem (N-NW) where the impact of the flood was assumed to be strongest. We also detected sharp reductions of tree-ring width after the flood (–56 % and –16 % in poplar and cedar, respectively). However, this was not found when using basal area increment, which suggests there was an age effect on the post-flood growth changes. The two species mean chronologies were also more coupled after the flood in agreement with an increased responsiveness to climate, particularly a higher dependence of growth on June precipitation. To adequately reconstruct responses to flood and to assess the actual vulnerability of forests to debris flow impacts tree features such as species, age, growth rate and responsiveness to climate must be considered.     

Microbe-mediated plant–soil feedback and its roles in a changing world

Plants affect soil conditions, which in turn alter plant growth and interspecific competition, forming plant?Csoil feedback (PSF) systems. PSF is a good example of bidirectional interactions between biomes and the non-living environments, acting as a major driving force of community structure and ecosystem function. Among the major types of PSF mediated by various soil components, there are many holes in our knowledge of the interactions between PSF mediated by plant species-specific litter and PSF mediated by soil microbes. Here I discuss the role of the functional diversity of microbial decomposers in litter-mediated PSF and also propose new hypotheses on the role of microbial diversity in PSF mediated by pathogenic and mutualistic soil microbes. I also review how PSF interacts with human-induced environmental change, i.e., direct drivers of change in the ecosystem (e.g. climate change and the invasion of alien species). Many authors have suggested that the impact of alien plant species on ecosystems is mediated by PSF, which also interacts with other direct drivers, such as climate change. Using a simple model of litter-mediated PSF with microbial decomposers, I confirm that the interactions between PSF and other direct drivers affect the invasion process of alien species. The model also demonstrates that the functional diversity of microbial decomposers accelerates or decelerates the speed of the invasion depending on the environmental change scenarios. Further theoretical and empirical studies are needed to derive general predictions on how exogenous environmental change induced by human activities alters communities and ecosystems through disturbance or modification of endogenous community?Cecosystem interactions, such as the functioning of PSF.     

The vulnerability of animal and human health to parasites under global change

The term 'global change' is used to encompass all of the significant drivers of environmental change as experienced by hosts, parasites and parasite managers. The term includes changes in climate and climate variability, atmospheric composition, land use and land cover including deforestation and urbanisation, bio-geochemistry, globalisation of trade and transport, the spread of alien species, human health and technology. A subset of land use issues relates to the management of protective technologies in relation to residues in food and the environment and the emergence of resistance. Another is the question of changing biodiversity of both parasites and their associated natural enemies, and the effects on the host--parasite relationship and on parasite management. A framework for studying impacts of global change is proposed and illustrated with field data, and CLIMEX and simulation modelling of the cattle tick Boophilus microplus in Australia. Parasitology suffers from the perception that the key impacts of global change will be driven by changes at lower trophic levels, with parasitic interactions being treated as secondary effects. This is incorrect because the environment mediates host-parasite interactions as much as it affects parasites directly. Parasitologists need to strive for holistic solutions to the management of animal and human health, within a wider context of overall management of those systems, if they are to make a meaningful contribution to global efforts aimed at coping with global change.