The new Kr-86 excess ice core proxy for synoptic activity: West Antarctic storminess possibly linked to Intertropical Convergence Zone (ITCZ) movement through the last deglaciation

Here we present a newly developed ice core gas-phase proxy that directly samples a component of the large-scale atmospheric circulation: synoptic-scale pressure variability. Surface pressure changes weakly disrupt gravitational isotopic settling in the firn layer, which is recorded in krypton-86 excess (86Krxs). The 86Krxs may therefore reflect the time-averaged synoptic pressure variability over several years (site “storminess”), but it likely cannot record individual synoptic events as ice core gas samples typically average over several years. We validate 86Krxs using late Holocene ice samples from 11 Antarctic ice cores and 1 Greenland ice core that collectively represent a wide range of surface pressure variability in the modern climate. We find a strong spatial correlation (, p<0.01) between site average 86Krxs and time-averaged synoptic variability from reanalysis data. The main uncertainties in the analysis are the corrections for gas loss and thermal fractionation and the relatively large scatter in the data. Limited scientific understanding of the firn physics and potential biases of 86Krxs require caution in interpreting this proxy at present. We show that Antarctic 86Krxs appears to be linked to the position of the Southern Hemisphere eddy-driven subpolar jet (SPJ), with a southern position enhancing pressure variability. We present a 86Krxs record covering the last 24 kyr from the West Antarctic Ice Sheet (WAIS) Divide ice core. Based on the empirical spatial correlation of synoptic activity and 86Krxs at various Antarctic sites, we interpret this record to show that West Antarctic synoptic activity is slightly below modern levels during the Last Glacial Maximum (LGM), increases during the Heinrich Stadial 1 and Younger Dryas North Atlantic cold periods, weakens abruptly at the Holocene onset, remains low during the early and mid-Holocene, and gradually increases to its modern value. The WAIS Divide 86Krxs record resembles records of monsoon intensity thought to reflect changes in the meridional position of the Intertropical Convergence Zone (ITCZ) on orbital and millennial timescales such that West Antarctic storminess is weaker when the ITCZ is displaced northward and stronger when it is displaced southward. We interpret variations in synoptic activity as reflecting movement of the South Pacific SPJ in parallel to the ITCZ migrations, which is the expected zonal mean response of the eddy-driven jet in models and proxy data. Past changes to Pacific climate and the El Niño–Southern Oscillation (ENSO) may amplify the signal of the SPJ migration. Our interpretation is broadly consistent with opal flux records from the Pacific Antarctic zone thought to reflect wind-driven upwelling. We emphasize that 86Krxs is a new proxy, and more work is called for to confirm, replicate, and better understand these results; until such time, our conclusions regarding past atmospheric dynamics remain speculative. Current scientific understanding of firn air transport and trapping is insufficient to explain all the observed variations in 86Krxs. A list of suggested future studies is provided

Invasive exotic aoudad (Ammotragus lervia) as a major threat to native Iberian ibex (Capra pyrenaica): A habitat suitability model approach

The introduction of alien species to new environments is one of the main threats to the conservation of biodiversity. One particularly problematic example is that of wild ungulates which are increasingly being established in regions outside their natural distribution range due to human hunting interests. Unfortunately, we know little of the effects these large herbivores may have on the host ecosystems. This study deals with a first comparative analysis of the habitat requirements of two ungulate species that may be facing competition for resources in the south of Europe: the native Iberian ibex (Capra pyrenaica) and the exotic aoudad (Ammotragus lervia). The aoudad is a North African caprid introduced in 1970 as a game species in south-eastern Spain. It has adapted well, and populations have been freely expanding since then. Ecological Niche Factor Analysis is used to describe the realized niche of both species where their distribution ranges merge. Both species occupy marginal areas of rugged terrain in the region. Marginality is higher for the Iberian ibex, which also presents a higher tolerance of secondary environmental gradients than the aoudad. Highly suitable areas for each species are secondarily suitable for the other. Reclassified and cross-tabulated habitat suitability maps showing the areas of potential spatial coexistence and differences in ecological traits between both species are provided. The results obtained do not allow inferring resource competition between these species. However, current aoudad expansion could result in it invading the favoured habitats of the ibex. Inadequate hunting policy and monitoring, and increasing climatic resemblance of the study region to the native aoudad areas, due to a strong desertification process, are facilitating a high rate of expansion. We strongly recommend to eradicate or, at least, monitor these exotic populations, and promote active conservation practices, if one wants to preserve the unique natural resources present in this European region.We acknowledge financial supported by the project PBI-05-010 granted by Junta de Comunidades de Castilla-La Mancha. Finally, JH was supported by a Portuguese FCT (Fundação para a Ciência e Tecnologia) grant (BPD/20809/2004), and also by the Spanish MEC project CGL2004-0439/BOS.Peer reviewe

Chromolaena odorata (Siam Weed) in eastern Africa: distribution and socio-ecological impacts

Invasive alien plant species such as Chromolaena odorata have negative impacts on biodiversity, ecosystem services and human well-being. Ecological impacts of this shrub are relatively well understood, but its impacts on local livelihoods and perceptions are poorly documented. We mapped C. odorata distribution in eastern Africa (Ethiopia, Kenya, Rwanda, Tanzania and Uganda) and compared perceptions and quantified the impacts of this species across Tanzanian villages with varying degrees of invasion density. Data were collected through 240 household questionnaires. Results indicate that C. odorata is a relatively new invader that already has severe negative impacts and is threatening livelihoods and the environment. Impacts include reductions in native biodiversity and the amount of available forage for livestock, reduced crop and water yields, and impaired mobility. Continued spread will cause additional negative impacts on poor rural communities. Implementation of a biological control programme targeting C. odorata is needed as a cost effective management approach along with other control and restoration measures

Social-ecological drivers and impacts of invasion-related regime shifts: consequences for ecosystem services and human wellbeing

There are growing concerns that increasing global environmental pressures could lead to the exceedance of critical ecological thresholds that could trigger long-lasting regime shifts that will affect the structure and function of ecosystems and the broader social-ecological systems in which they are embedded. Biological invasions are a major driver of global change, and a number of invasive species alter key ecological feedbacks in ways that lead to regime shifts, with consequences for biodiversity, ecosystem services, livelihoods and human wellbeing. We present four case studies, chosen to represent a diverse range of ecosystems and invasive taxa, to illustrate invasion-driven regime shifts in a variety of social-ecological systems globally. The case studies are: i) wattle trees (Australian Acacia species) in fynbos shrublands in South Africa; ii) Nile perch (Lates niloticus) in Lake Victoria in East Africa; iii) chestnut blight fungus (Cryphonectria parasitica) within broad-leaved forests of eastern North America; and iv) the floating macrophytes salvinia (Salvinia molesta) and water hyacinth (Eichhornia crassipes) in East Sepik Province of Papua New Guinea. For each case we identify the social and ecological drivers and feedbacks underlying the shift, the impacts on ecosystem services and human wellbeing, and the management options for reducing impacts. We discuss the value of using causal-loop diagrams to improve our understanding of the complex dynamics of shifts, and explore how concepts associated with regime shifts can inform guidelines for enhancing adaptive governance of biological invasions. Identifying species that have the potential to generate high-impact regime shifts, understanding the diversity of consequences for different environments and stakeholders, and developing robust management methods to reduce impacts and restore systems to improve social-ecological resilience and reduce vulnerability are priorities for further research

Identifying barriers to effective management of widespread invasive alien trees: Prosopis species (mesquite) in South Africa as a case study.

Biological invasions are a major driver of ecological and social change globally. The negative effects of these invasions have led to the initiation of programs to manage these invasions across the world. Management aims to reduce impacts and in some cases improve the benefits that some invasive species can provide. This study assesses the barriers that hinder the effective management of widespread tree invasions, drawing insights from a case study of invasions of Prosopis species (mesquite) in South Africa. We used questionnaire surveys and focussed workshops to identify barriers and adaption responses in four key stakeholder groups involved in different stages of management. More than 100 barriers were identified, most of them relating to social issues. Key barriers related to limited knowledge, insufficient funds, conflicts of interest, the ecology of the genus and the nature of the invaded land, as well as poor planning, co-ordination and co-operation, and a lack of prioritisation. There were marked differences in how stakeholders perceived the importance of some barriers. Most Farmers (>80%) placed high importance on a lack of planning, and poor management as important barriers, while few Managers (<20%) regarded these as important; this reflects different views about the context in which management projects operate. Workshops identified more barriers and, overall, provided greater insights into the dimensions of barriers. The questionnaires were, however, useful for providing quantitative data which helped to rank the importance of barriers amongst stakeholders. Although adaptation responses were identified, not all barriers are conducive to simple solutions. Among the most intractable barriers were the lack of adequate funds and factors relating to the ecology of Prosopis species. Problems such as adopting new clearing methods and strategic planning need to be overcome to improve the effectiveness of control with the available funds

The impact of invasive alien Prosopis species (mesquite) on native plants in different environments in South Africa

Many Prosopis species have been introduced to South Africa; some taxa and their hybrids have naturalised and become widespread invasive trees. These invasions have detrimental effects on biodiversity, ecosystem services and human livelihoods. Although several studies have documented these impacts, the studies have been limited to single sites or restricted areas. This study assessed the Prosopis population across the full invasive range of the genus in South Africa, and quantified the effects of invasions on native woody and herbaceous species. Basal areas of invasive Prosopis stands reached 9 m2/ha, and were on average higher along perennial rivers than along ephemeral rivers (mean basal areas of 3.2 vs. 1.4 m2/ha). Native woody species density, basal area, richness and diversity all decreased significantly as the basal area of Prosopis stands increased. For example, up to eight native woody species occurred at basal area of b2 m2/ha, this decreased to three native species or fewer at basal areas of N4 m2/ha. The cover of native perennial grasses and herbaceous plants declined from 15–20% where the basal area of Prosopis was b2 m2/ha to zero where the basal area of Prosopis was N4.5 m2/ha. The results highlight the widespread nature of the impacts across all invaded biomes. Current control of Prosopis has had limited success, and alternative, potentially more effective, options are controversial. In the light of the widespread impacts, we recommend that a thorough assessment of the problem be undertaken to inform policy