Soil Chemical Analysis

CITATION: Downey, P. O. & Richardson, D. M. 2016. Alien plant invasions and native plant extinctions : a six-threshold framework. AoB PLANTS, 8:1-21, doi:10.1093/aobpla/plw047.

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Alien plant invasions and native plant extinctions: a six-threshold framework.

The categorization of invasive alien species based on their impact is an important way of improving the management of biological invasions. The impact of 128 alien species of plants in Europe was evaluated using the Generic Impact Scoring System (GISS) originally developed for mammals. Based on information in the literature their environmental and socioeconomic impacts were assessed and assigned to one of six different categories. In each category, the impact was classified on a five-degree scale, which reflects the impact intensity. To identify species with the greatest impacts, we used the maximum score recorded in each category and their sums. Data from the whole invaded range were considered, which resulted in scoring the potential impact of each species, not necessarily currently realized in Europe. Environmental impacts are most often manifested via competition with native species (recorded for 83 % of the species), while socioeconomic impacts are associated mostly with human health (78 %). The sums of environmental and socioeconomic impacts were significantly correlated, which indicates that the same suite of species traits is associated with both types of impacts. In terms of plant life forms, annual plants have on average lower environmental impacts than perennial plants, and aquatic species have a higher socioeconomic impact than other life forms. Applying the GISS to plants, the most species-rich taxonomic group of alien organisms in Europe, is an important step towards providing managers and policymakers with a robust tool for identifying and prioritizing alien species with the highest impact.

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Scoring environmental and socioeconomic impacts of alien plants invasive in Europe

In an era of climate change, predictive distribution modelling and niche dynamics of invasive species can help in understanding current and future invasion potential. Parthenium hysterophorus (Congress grass), native to tropical America, is one of the world’s worst weeds with huge ecological and economic impacts, including in India. Here we report the current and future potential distribution of P. hysterophorus in India under climate change scenarios and describe its niche dynamics. The results revealed that under current climate, 65% of the total area in India is suitable for its potential invasion with three invasion hotspots identified: Western Himalaya, North-East and parts of Peninsular India. The study predicts an overall decrease in habitat suitability for this invasive species under climate change with about half of the suitable habitat reduced under RCP 8.5-2070; but some of the currently invaded regions will remain equally (North-East) or become highly vulnerable (Western Himalaya) to its invasion under future climate. Interestingly, niche dynamics results revealed that P. hysterophorus has shifted its climatic niche in the invaded range in India, more due to niche unfilling. Based on univariate analysis, niche dynamic processes in the analogous (expansion) and non-analogous (abandonment and pioneering) environments were also evident. The results from present study can help in developing climate change-integrated and region-specific invasion management strategies in India. More importantly, results of niche dynamics between native and invaded ranges of P. hysterophorus offer novel insights to understand the nature of niche shifts in invasive species and to predict the invasion potential under climate change.

Predicting invasion potential and niche dynamics of Parthenium hysterophorus (Congress grass) in India under projected climate change.

Long-term research in ecology and evolution (LTREE) is considered fundamental for understanding complex ecological and evolutionary dynamics. However, others have argued for revision of LTREE efforts given perceived limitations in current research priorities and approaches. Yet most arguments about the benefits and failings of LTREE could be argued to reflect the views of only the limited number of scientists who have authored reports on the field, and not the wider community of ecological and evolutionary scientists. To more systematically and quantitatively assess the views of the community on LTREE contributions and future activities, we conducted and here report the results of a survey of ecological and evolutionary scientists at primarily U.S.-based institutions, completed by 1,179 respondents. The survey objectives were to (1) identify and prioritize research questions that are important to address through long-term, ecological field experiments and (2) understand the role that these experiments might play in generating and applying ecological and evolutionary knowledge. Almost 80% (n = 936) of respondents said that long-term experiments had contributed “a great deal” to ecological understanding. Compared to other research approaches (e.g., short-term, single-site, modeling, or lab), there was overwhelming support that multi-site, long-term research was very important for advancing theory, and that both observational and experimental approaches were required. Respondents identified a wide range of research questions for LTREE to address. The most common topic was the impact of global change (n = 1,352), likely because these processes play out over many years, requiring LTREE approaches to fully understand. Another recurrent theme was the potential of LTREE approaches to build evolutionary understanding across all levels of ecological organization. Critical obstacles preventing some scientists from engaging in LTREE included short-term funding mechanisms and fewer publications, whereas the longer-term value for advancing knowledge and an individual’s career were widely recognized. Substantive advances in understanding ecological and evolutionary dynamics then seem likely to be made through engagement in long-term observational and experimental research. However, wider engagement seems dependent on a more supportive research environment and funding structure, through increased institutional acknowledgement of the contributions of long-term research, and greater program support during the establishment and maintenance of research.

Long-term research in ecology and evolution: a survey of challenges and opportunities

Terrestrial invasive plants are a global problem and are becoming ubiquitous components of most ecosystems. They are implicated in altering disturbance regimes, reducing biodiversity, and changing ecosystem function, sometimes in profound and irreversible ways. However, the ecological impacts of most invasive plants have not been studied experimentally, and most research to date focuses on few types of impacts, which can vary greatly among studies. Thus, our knowledge of existing ecological impacts ascribed to invasive plants is surprisingly limited in both breadth and depth. Our aim was to propose a standard methodology for quantifying baseline ecological impact that, in theory, is scalable to any terrestrial plant invader (e.g., annual grasses to trees) and any invaded system (e.g., grassland to forest). The Global Invader Impact Network (GIIN) is a coordinated distributed experiment composed of an observational and manipulative methodology. The protocol consists of a series of plots located in (1) an invaded area; (2) an adjacent removal treatment within the invaded area; and (3) a spatially separate uninvaded area thought to be similar to pre-invasion conditions of the invaded area. A standardized and inexpensive suite of community, soil, and ecosystem metrics are collected allowing broad comparisons among measurements, populations, and species. The method allows for one-time comparisons and for long-term monitoring enabling one to derive information about change due to invasion over time. Invader removal plots will also allow for quantification of legacy effects and their return rates, which will be monitored for several years. GIIN uses a nested hierarchical scale approach encompassing multiple sites, regions, and continents. Currently, GIIN has network members in six countries, with new members encouraged. To date, study species include representatives of annual and perennial grasses; annual and perennial forbs; shrubs; and trees. The goal of the GIIN framework is to create a standard yet flexible platform for understanding the ecological impacts of invasive plants, allowing both individual and synthetic analyses across a range of taxa and ecosystems. If broadly adopted, this standard approach will offer unique insight into the ecological impacts of invasive plants at local, regional, and global scales.

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Peter Leipzig‐Scott

Papers

Global Invader Impact Network (GIIN): toward standardized evaluation of the ecological impacts of invasive plants