To better manage invasive populations, it is vital to understand the environmental drivers underlying spatial variation in demographic performance of invasive individuals and populations. The invasive common ragweed, Ambrosia artemisiifolia, has severe adverse effects on agriculture and human health, due to its vast production of seeds and allergenic pollen. Here, we identify the scale and nature of environmental factors driving individual performance of A. artemisiifolia, and assess their relative importance. We studied 39 populations across the European continent, covering different climatic and habitat conditions. We found that plant size is the most important determinant in variation of per-capita seed and pollen production. Using plant volume as a measure of individual performance, we found that the local environment (i.e. the site) is far more influential for plant volume (explaining 25% of all spatial Published in "Biological Invasions doi: 10.1007/s10530-017-1640-9, 2018" which should be cited to refer to this work. variation) than geographic position (regional level; 8%) or the neighbouring vegetation (at the plot level; 4%). An overall model including environmental factors at all scales performed better (27%), including the weather (bigger plants in warm and wet conditions), soil type (smaller plants on soils with more sand), and highlighting the negative effects of altitude, neighbouring vegetation and bare soil. Pollen and seed densities varied more than 200-fold between sites, with highest estimates in Croatia, Romania and Hungary. Pollen densities were highest on arable fields, while highest seed densities were found along infrastructure, both significantly higher than on ruderal sites. We discuss implications of these findings for the spatial scale of management interventions against A. artemisiifolia.

Time to cut: population models reveal how to mow invasive common ragweed cost-effectively 53Time to cut: population models reveal how to mow invasive common ragweed cost-effectively AbstractRoadsides are an important habitat for invasive common ragweed, Ambrosia artemisiifolia L., by facilitating seed dispersal. Reducing the size of roadside populations is therefore essential for confining this highly allergenic species. Here, we aim to determine the cost-effectiveness of mowing regimes varying in frequency and timing, by analysing population-level effects and underlying demographic processes. We constructed population models of A. artemisiifolia parameterised by demographic data for four unmanaged reference populations across Europe in two years. We integrated the effects of four experimental mowing regimes along Austrian road sides on plant performance traits of five years and experimental data on seed viability after cutting. All four experimental regimes reduced the projected intrinsic population growth rates (r) compared to the unmanaged controls by reducing plant height and seed viability, thereby counteracting increased size-dependent fecundity. The prevailing 2-cut regime in Austria (cutting during vegetative growth, here in June and just before seed ripening, here in September) performed least well and the reduction in r was mainly due to reduced seed viability after the second cut. The efficacy of the two best experimental regimes (alternative schemes for 2 or 3 cuts) was mainly due to cutting just before female flowering (here in August) by decreasing final adult plant height dramatically and thereby reducing seed numbers. Patterns were consistent across reference populations and years. Whether regimes reduced r below replacement level, however, varied per population, year and the survival rate of the seeds in the soil bank. Our model allowed RESEARCH ARTICLE Advancing research on alien species and biological invasions A peer-reviewed open-access journal NeoBiotaSuzanne T. E. Lommen et al. / NeoBiota 39: 53-78 (2018) 54 projecting effects of five theoretical mowing regimes with untested combinations of cuts on r. By plotting r-cost relationships for all regimes, we identified the most cost-effective schemes for each cutting frequency (1-3 cuts). They all included the cut just before female flowering, highlighting the importance of cutting at this moment (here in August). Our work features i) the suitability of a modelling approach for the demography of an annual species with a seed bank, ii) the importance of seed viability in assessing mowing effects, iii) the use of population models in designing cost-effective mowing regimes.

Background: Common ragweed, Ambrosia artemisiifolia, is one of the economically most important worldwide plant invaders, due to its huge production of seeds and allergenic pollen, while its range and impact are expected to increase in future. Knowledge of the population dynamics is essential to understand what factors drive spatio-temporal variation in population growth, and can help assessing efficacy of management interventions at the population level. Detailed demographic surveys over multiple years are labour-intensive, but when multiple research groups join forces and work according to standardized protocols, it may be feasible to collect such in-depth data in multiple habitat types across a large geographic range and over larger time spans. Aim: We developed this field survey protocol to monitor the population dynamics of common ragweed (Ambrosia artemisiifolia L., Asteraceae) across Europe. It is designed to estimate all vital rates of a population (establishment of plants, plant survival, plant growth, reproduction, and seed survival), and study how they relate to plant density and individual plant size. It targets unmanaged field populations (to create a baseline), but could also be used for assessing managed populations with some adaptations. Methods: Plots of 0.25m2 are established in a field population of common ragweed. The population, plots and (randomly selected) marked common ragweed plants within these are monitored early in the growing season and are re-assessed at seed set, when in addition soil samples and reproductive plants are collected (outside the plots) for further analysis in the laboratory. Repeating this procedure in multiple years is essential to derive estimates of seed survival in the soil seed bank from year to year. Replicated monitoring in time and/or space is needed to relate the dynamics to environmental variables. Protocols provided: i) list of materials, ii) the selection of a site, iii) setting up the survey, iv) monitoring, v) sampling of plants, soil and seeds, vii) lab analyses of samples (plant biomass, soil seed bank, soil texture and content, cleaning of aerial seed samples) Record forms provided: i) for registration of meta-data of the site, ii) for all measures taken in the field and in the lab; all in a pdf-version for printout to use in the field and in an excel-version for digitising data Other material provided: i) field sheets (checklist for field work, legend to the record forms), ii) help tools (for mapping plants, for assigning unique numbers to plants) Optimisation: The protocol has been used to monitor over 50 populations across the European continent in 2014-2016 by members of the SMARTER Task Force Population Dynamics, within the framework of the EU-funded COST Action 'SMARTER' (FA1203, ‘Sustainable management of Ambrosia artemisiifolia in Europe’, 2013-2016). By yearly Task Force meetings, the protocol has been evaluated and improved to the current version.

Background: Common ragweed, Ambrosia artemisiifolia L., isan economically important worldwide plant invader, due to its huge production of seeds and allergenic pollen, while its range and impact are expected to increase in future. Knowledge of the population dynamics of this annual species is essential to understand what factors drive spatio-temporal variation in population growth, and can help assessing efficacy of management interventions at the population level. Detailed demographic surveys over multiple years are labour-intensive, but when multiple research groups join forces and work according to standardized protocols, it may be feasible to collect such in-depth data in multiple habitat types across a large geographic range and over larger time spans. Aim: We developed this field survey protocol to monitor the population dynamics of common ragweed (Ambrosia artemisiifolia L., Asteraceae) across Europe. It is designed to estimate all vital rates of a population (establishment of plants, plant survival, plant growth, reproduction, and seed survival), and study how they relate to plant density and individual plant size. It targets unmanaged field populations (to create a baseline), but could also be used for assessing managed populations with some adaptations. Methods: Plots of 0.25m2 are established in a field population of common ragweed. The population, plots and (randomly selected) marked common ragweed plants within these are monitored early in the growing season and are re-assessed at seed set, when in addition soil samples and reproductive plants are collected (adjacent to but outside the plots) for further analysis in the laboratory. Repeatingthe procedure on the same plots in multiple years is essential to derive estimates of seed survival in the soil seed bank from year to year. Replicated monitoring in time (multiple years) and/or space (multiple populations), and measuring (additional) environmental factors, is needed to relate the dynamics to environmental variables. Protocols provided: i) list of materials, ii) the selection of a site, iii) setting up the survey, iv) monitoring, v) sampling of plants, soil and seeds, vii) lab analyses of samples (plant biomass, soil seed bank, soil texture and content, cleaning of aerial seed samples) Record forms provided: i) for registration of meta-data of the site, ii) for all measures taken in the field and in the lab; all in a pdf-version for printout to use in the field and in an excel-version for digitising data Other material provided: i) field sheets (checklist for field work, legend to the record forms), ii) help tools (for mapping plants, for assigning unique numbers to plants) Optimisation: The protocol has been used to monitor over 50 populations across the European continent in 2014-2016 by members of the SMARTER Task Force Population Dynamics, within the framework of the EU-funded COST Action 'SMARTER' (FA1203, ‘Sustainable management of Ambrosia artemisiifolia in Europe’, 2013-2016). By yearly Task Force meetings, the protocol has been evaluated and improved to the current version.