Showing papers by "Marcel Rejmánek published in 2014"

Conflicting values: ecosystem services and invasive tree management

Abstract: Tree species have been planted widely beyond their native ranges to provide or enhance ecosystem services such as timber and fibre production, erosion control, and aesthetic or amenity benefits. At the same time, non-native tree species can have strongly negative impacts on ecosystem services when they naturalize and subsequently become invasive and disrupt or transform communities and ecosystems. The dichotomy between positive and negative effects on ecosystem services has led to significant conflicts over the removal of non-native invasive tree species worldwide. These conflicts are often viewed in only a local context but we suggest that a global synthesis sheds important light on the dimensions of the phenomenon. We collated examples of conflict surrounding the control or management of tree invasions where conflict has caused delay, increased cost, or cessation of projects aimed at invasive tree removal. We found that conflicts span a diverse range of taxa, systems and countries, and that most conflicts emerge around three areas: urban and near-urban trees; trees that provide direct economic benefits; and invasive trees that are used by native species for habitat or food. We suggest that such conflict should be seen as a normal occurrence in invasive tree removal. Assessing both positive and negative effects of invasive species on multiple ecosystem services may provide a useful framework for the resolution of conflicts.

A standardized set of metrics to assess and monitor tree invasions

Abstract: Scientists, managers, and policy-makers need functional and effective metrics to improve our understanding and management of biological invasions. Such metrics would help to assess progress towards management goals, increase compatibility across administrative borders, and facilitate comparisons between invasions. Here we outline key characteristics of tree invasions (status, abundance, spatial extent, and impact), discuss how each of these characteristics changes with time, and examine potential metrics to describe and monitor them. We recommend quantifying tree invasions using six metrics: (a) current status in the region; (b) potential status; (c) the number of foci requiring management; (d) area of occupancy (AOO) (i.e. compressed canopy area or net infestation); (e) extent of occurrence (EOO) (i.e. range size or gross infestation); and (f) observations of current and potential impact. We discuss how each metric can be parameterised (e.g. we include a practical method for classifying the current stage of invasion for trees following Blackburn’s unified framework for biological invasions); their potential management value (e.g. EOO provides an indication of the area over which management is needed); and how they can be used in concert (e.g. combining AOO and EOO can provide insights into invasion dynamics; and we use potential status and threat together to develop a simple risk analysis tool). Based on these metrics, we propose a standardized template for reporting tree invasions that we hope will facilitate cross-species and inter-regional comparisons. While we feel this represents a valuable step towards standardized reporting, there is an urgent need to develop more consistent metrics for impact and threat, and for many specific purposes additional metrics are still needed (e.g. detectability is required to assess the feasibility of eradication).

Invasive trees and shrubs: where do they come from and what we should expect in the future?

Abstract: The global database of invasive trees and shrubs has been updated, resulting in a total of 751 species (434 trees and 317 shrubs) from 90 families (Rejmanek and Richardson 2013 Divers Distrib 19:1093–1094). This database is used to assess major trends in human-assisted exchanges of dendrofloras among 15 major geographical regions. Areas most invaded by non-native trees are Pacific Islands (136 species), Southern Africa (118), Australia (116), and North America (114). Areas most invaded by non-native shrubs are North America (98), Australia (87), Pacific Islands (71), and Europe (61). The most important sources of invasive trees are Asia (122–146 species, depending on how many Eurasian species are considered to have been introduced only from Europe), Australia (81), and South America (81). The most important sources of invasive shrubs are Asia (103–118), Europe (68), and South America (54). Mean number of native geographical regions for invasive trees is 1.64, while the mean number of invaded regions by trees is 2.51. The difference is smaller for shrubs: 1.60 versus 2.11. Asia is the major source of invasive Rosaceae shrubs, as well as invasive Arecaceae and Oleaceae species. South America and Australia are major sources of invasive Fabaceae trees. North America and Europe are major sources of invasive Pinaceae. Most of the invasive Salicaceae are of Eurasian origin. The identified trends will very likely continue in this century. Because of increasing interactions with many states in Asia, even more invasive woody species will be introduced from this part of the world.

The number of vegetation types in European countries: major determinants and extrapolation to other regions

Abstract: Questions: How many vegetation classes and alliances are described in European countries? What are the main factors driving the number of these vegetation types? What would be the estimated number of vegetation types in so far under-explored regions outside Europe? Location: Twenty-three countries and regions in Europe. Fourteen regions outside Europe. Methods: We compiled lists of vegetation types (phytosociological classes as broader units and alliances as narrower ones) described in European countries with a well-developed vegetation classification. The delimitation and nomenclature of classes and alliances were standardized according to a unified classification system for Europe. Generalized linear models were used to test the influence of floristic richness, area, sampling effort, altitudinal range and geological diversity on the number of vegetation types. Best predictors were used to estimate the number of classes and alliances in selected regions over the world. Results: In agreement with broadly recognized diversity patterns, we found the highest numbers of vegetation types in countries with a mediterranean climate. The numbers of classes and alliances per country did not depend on the country size, while country's floristic richness was identified as the main explanatory variable, accounting for up to 67% of explained deviance. The number of alliances increased in countries with broad altitudinal range and large geological diversity, but these variables did not influence the number of classes. Accordingly, estimates of the number of alliances for other (mostly non-European) regions were adjusted when including altitudinal range as an additional predictor. Conclusions: At broad scales, the number of vegetation types can be predicted from floristic richness, which indirectly accounts for the effect of area, and from environmental heterogeneity. Furthermore, this overview demonstrates that the number of phytosociological alliances reflects biogeographic patterns in Europe better than the number of classes. We also estimate, for the first time, the number of vegetation types that may be expected in so far poorly surveyed regions worldwide, using procedures of vegetation classification analogous to those used in European phytosociology.

Biological invasions and ecological hypotheses

Abstract: At the time of an enormous inflation of edited volumes on biological invasions (many of them claiming their uniqueness), this is clearly an outstanding book. It is exceptional for two reasons. First, it deals with both ancient (nine studies) and modern (nine studies) migrations and/or invasions of plants and animals to, or from, Australasia (mostly Australia). Second, each study is consistently built around a set of 11 central hypotheses from population and community ecology: H1 – a species will not be able to invade an area that has abiotic conditions that are outside its physiological tolerance levels; H2 – the extent of an invasion is negatively correlated with the species diversity of functional guild competitors in the invaded environment; H3 – an invasive species will not be able to replace a native species if they occupy the same niche and are in all other ways equal; H4 – a species will not be able to invade an area that harbors pathogens (that cause disease) or predators (that prey on the invading species) that it has not encountered before (the opposite of this hypothesis is stated as the Enemy Release Hypothesis); H5 – a species will not be able to invade an area if its coevolutionary species (necessary for parts of the invader's life cycle) is/are not present in the area; H6 – species that occur at low population densities in their native range will not be invasive; H7 – a species will not be able to invade an area if it has a lower use efficiency of its limiting resource than a native species that occupies the same location; H8 – species can more easily invade highly disturbed areas; H9 – species from older lineages are more vulnerable to being replaced by invasive species that occupy a similar niche; H10 – a species will be able to invade an area only if it has a life-history strategy that is more r selected than that of the species that is already occupying the niche; and H11 – there are no rules concerning whether a species is invasive or not, it all happens by chance.