Franz Essl

Global trade will accelerate plant invasions in emerging economies under climate change

Trade plays a key role in the spread of alien species and has arguably contributed to the recent enormous acceleration of biological invasions, thus homogenizing biotas worldwide. Combining data on 60-year trends of bilateral trade, as well as on biodiversity and climate, we modeled the global spread of plant species among 147 countries. The model results were compared with a recently compiled unique global data set on numbers of naturalized alien vascular plant species representing the most comprehensive collection of naturalized plant distributions currently available. The model identifies major source regions, introduction routes, and hot spots of plant invasions that agree well with observed naturalized plant numbers. In contrast to common knowledge, we show that the imperialist dogma, stating that Europe has been a net exporter of naturalized plants since colonial times, does not hold for the past 60xa0years, when more naturalized plants were being imported to than exported from Europe. Our results highlight that the current distribution of naturalized plants is best predicted by socioeconomic activities 20xa0years ago. We took advantage of the observed time lag and used trade developments until recent times to predict naturalized plant trajectories for the next two decades. This shows that particularly strong increases in naturalized plant numbers are expected in the next 20xa0years for emerging economies in megadiverse regions. The interaction with predicted future climate change will increase invasions in northern temperate countries and reduce them in tropical and (sub)tropical regions, yet not by enough to cancel out the trade-related increase.

Phenology predicts the native and invasive range limits of common ragweed

Accurate models for species distributions are needed to forecast the progress and impacts of alien invasive species and assess potential range-shifting driven by global change. Although this has traditionally been achieved through data-driven correlative modelling, robustly extrapolating these models into novel climatic conditions is challenging. Recently, a small number of process-based or mechanistic distribution models have been developed to complement the correlative approaches. However, tests of these models are lacking, and there are very few process-based models for invasive species. We develop a method for estimating the range of a globally invasive species, common ragweed (Ambrosia artemisiifolia L.), from a temperature- and photoperiod-driven phenology model. The model predicts the region in which ragweed can reach reproductive maturity before frost kills the adult plants in autumn. This aligns well with the poleward and high-elevation range limits in its native North America and in invaded Europe, clearly showing that phenological constraints determine the cold range margins of the species. Importantly, this is a forward prediction made entirely independently of the distribution data. Therefore, it allows a confident and biologically informed forecasting of further invasion and range shifting driven by climate change. For ragweed, such forecasts are extremely important as the species is a serious crop weed and its airborne pollen is a major cause of allergy and asthma in humans. Our results show that phenology can be a key determinant of species range margins, so integrating phenology into species distribution models offers great potential for the mechanistic modelling of range dynamics.

Biological Flora of the British Isles: Ambrosia Artemisiifolia

This account presents information on all aspects of the biology of Ambrosia artemisiifolia L. (Common ragweed) that are relevant to understanding its ecology. The main topics are presented within the standard framework of the Biological Flora of the British Isles: distribution, habitat, communities, responses to biotic factors, responses to environment, structure and physiology, phenology, floral and seed characters, herbivores and disease, and history, conservation, impacts and management. n nAmbrosia artemisiifolia is a monoecious, wind-pollinated, annual herb native to North America whose height varies from 10 cm to 2.5 m, according to environmental conditions. It has erect, branched stems and pinnately lobed leaves. Spike-like racemes of male capitula composed of staminate (male) florets terminate the stems, while cyme-like clusters of pistillate (female) florets are arranged in groups in the axils of main and lateral stem leaves. n nSeeds require prolonged chilling to break dormancy. Following seedling emergence in spring, the rate of vegetative growth depends on temperature, but development occurs over a wide thermal range. In temperate European climates, male and female flowers are produced from summer to early autumn (July to October). nAmbrosia artemisiifolia is sensitive to freezing. Late spring frosts kill seedlings and the first autumn frosts terminate the growing season. It has a preference for dry soils of intermediate to rich nutrient level. n nAmbrosia artemisiifolia was introduced into Europe with seed imports from North America in the 19th century. Since World War II, it has become widespread in temperate regions of Europe and is now abundant in open, disturbed habitats as a ruderal and agricultural weed. n nRecently, the North American ragweed leaf beetle (Ophraella communa) has been detected in southern Switzerland and northern Italy. This species appears to have the capacity to substantially reduce growth and seed production of A. artemisiifolia. n nIn heavily infested regions of Europe, A. artemisiifolia causes substantial crop-yield losses and its copious, highly allergenic pollen creates considerable public health problems. There is a consensus among models that climate change will allow its northward and uphill spread in Europe.

Delayed biodiversity change: no time to waste

Delayed biodiversity responses to environmental forcing mean that rates of contemporary biodiversity changes are underestimated, yet these delays are rarely addressed in conservation policies. Here, we identify mechanisms that lead to such time lags, discuss shifting human perceptions, and propose how these phenomena should be addressed in biodiversity management and science.

Naturalization of ornamental plant species in public green spaces and private gardens

Ornamental horticulture is the most important pathway for alien plant introductions worldwide, and consequently, invasive spread of introduced plants often begins in urban areas. Although most introduced ornamental garden-plant species are locally not naturalized yet, many of them have shown invasion potential elsewhere in the world, and might naturalize when climate changes. We inventoried the planted flora of 50 public and 61 private gardens in Radolfzell, a small city in southern Germany, to investigate whether local naturalization success of garden plants is associated with their current planting frequency, climatic suitability (as assessed with climatic niche modelling) and known naturalization status somewhere in the world. We identified 954 introduced garden-plant species, of which 48 are already naturalized in Radolfzell and 120 in other parts of Germany. All currently naturalized garden plants in Radolfzell have a climatic suitability probability of ≥xa00.75 and are naturalized in ≥xa013 out of 843 regions globally. These values are significantly higher than those of garden plants that have not become locally naturalized yet. Current planting frequencies, however, were not related to current naturalization success. Using the identified local naturalization thresholds of climatic suitability and global naturalization frequency, and climate projections for the years 2050 and 2070, we identified 45 garden-plant species that are currently not naturalized in Radolfzell but are likely to become so in the future. Although our approach cannot replace a full risk assessment, it is well-suited and applicable as one element of a screening or horizon scanning-type approach.

Accounting for imperfect observation and estimating true species distributions in modelling biological invasions

The documentation of biological invasions is often incomplete with records lagging behind the species’ actual spread to a spatio-temporally heterogeneous extent. Such imperfect observation bears the risk of underestimating the already realised distribution of the invading species, misguiding management efforts and misjudging potential future impacts. In this paper, we develop a hierarchical modelling framework which disentangles the determinants of the invasion and observation processes, models spatio-temporal heterogeneity in detection patterns, and infers the actual, yet partly undocumented distribution of the species at any particular time. We illustrate the model with a case study application to the invasion of Common ragweed Ambrosia artemisiifolia in Austria. The invasion part of the model reconstructs the historical spread of this species across a grid of ~ 6×6 km2 cells as driven by spatio-temporal variation in physical site conditions, propagule production, dispersal, and ‘background’ introductions from unknown sources. The observation part models the detection of the species occurrences based on heterogeneous sampling efforts, human population density, and estimated local invasion level. We fitted the hierarchical model using a Bayesian inference approach with parameters estimated by Markov Chain Monte Carlo (MCMC). The actual spread of A. artemisiifolia concentrated on the climatically well-suited lowlands and was mainly driven by spatio-temporal propagule pressure from source cells with long-distance dispersal occurring rather frequently. Annual detection probabilities were estimated to vary between about 1% and up to 28%, depending mainly on sampling intensity. The model suggested that by 2005 about half of the actual distribution of the species was not yet documented. Our hierarchical model offers a flexible means to account for imperfect observation and spatio-temporal variability in detection efficiency. Inferences can be used to disentangle aspects of the invasion dynamics itself from patterns of data collection, develop improved future surveying schemes, and design more efficient invasion management strategies. n nThis article is protected by copyright. All rights reserved.

Wie könnten unsere Lebensräume und Landschaften zukünftig aussehen

Die Auswirkungen vieler Umweltbelastungen auf das Wasser sind fur uns Menschen unsichtbar. Wahrend der Boden Schadstoffe oft jahrhundertelang verfugbar halten kann, scheinen Gewasser aufgrund ihrer Dynamik rascher in der Lage nach Storungen wieder in den Ursprungszustand zuruckkehren zu konnen. Dies mag fur manche Schadstoffe und besonders fur Fliesgewasser tatsachlich zutreffen. Die tiefgreifenden Anderungen, die aquatische und gewassernahe Lebensraume in den letzten Jahrzehnten durch den steigenden Nutzungsdruck erfahren haben, sind jedoch nur mit hohem Aufwand wieder gut zu machen. Zunehmend wird erkannt, dass naturliche Stromungsdynamik, ausreichende Retentionsraume und verringerte Nahrstoffeintrage nicht nur fur den Naturschutz, sondern auch nach okonomischen Masstaben wertvoll sind.

Handlungsoptionen und -erfordernisse

Naturliche Okosysteme, die organismische Vielfalt, die sie beherbergen, und ihre Leistungen sind von grundlegender Bedeutung fur den Menschen.

Was leistet die Biodiversität für die Anpassung der vom Klimawandel betroffenen menschlichen Gesellschaft

Das Konzept der Okosystemleistungen wurde in den 1990er-Jahren entwickelt (Myers 1996, Costanza et al. 1997, Daily 1997), wobei Westman (1977) mit seinem Konzept der Nature’s services einen Grundstein dafur legte. Mit der breiten Nutzung dieses methodischen Zugangs im Millenium Ecosystem Assessment (MA 2005, Abb. 6-1) wurde die Diskussion uber Biodiversitatsverluste neu ausgerichtet: Seither ist der Verlust von Biodiversitat nicht mehr nur Inhalt von Naturschutzdebatten, sondern wird als Einfl ussfaktor mit zentraler Bedeutung fur das menschliche Wohlergehen gesehen, woraus sich das Erfordernis eines nachhaltigen Lebensstils begrunden und allgemein verstandlich aufzeigen lasst.

Klima als Umwelt- und Überlebensfaktor

Das Klima ist hauptverantwortlich fur die Auspragung unterschiedlicher Okozonen, in denen sich spezialisierte Faunen und Floren entwickelt haben und die daher eine grose Ahnlichkeit mit den Klimazonen der Erde zeigen (Kap. 1). Als Folge von Klimaanderungen in der erdgeschichtlichen Vergangenheit haben sich Lage und Ausdehnung der globalen Okozonen mehrfach stark geandert. So pragte im Tertiar subtropischer Wald die Vegetation in Mitteleuropa.