Modelling native and alien vascular plant species richness: at which scales is geodiversity most relevant?

Aim: To explore the scale-dependency of relationships between novel geodiversity measures and 26 both native and alien vascular plant species richness. Location: Great Britain Time period: Data collected 1995-2015 Major taxa: Vascular plants Methods: We calculated terrestrial native and alien vascular plant species richness (6,932 species in total) across the island of Great Britain at 1km2 (N=219,964) and 100km2 (N=2,121) grain sizes and regional extents 25-250 km in diameter, centred around each 100km2 cell. We compiled geodiversity data on landforms, soils, hydrological and geological features using existing national datasets, and used a newly developed geomorphometric method to extract landform coverage data (e.g. hollows, ridges, valleys, peaks). We used these as predictors of species richness, alongside climate, commonly used topographic metrics, land-cover variety and human population. We analysed species richness across scales using boosted regression tree (BRT) modelling and compared models with and without geodiversity data. Results: Geodiversity significantly improved models over and above widely used topographic metrics, particularly at smaller extents and the finer grain size, and slightly more so for native species richness. For each increase in extent, the contribution of climatic variables increased and that of geodiversity decreased. Of the geodiversity variables, automatically extracted landform data added the most explanatory power, but hydrology (rivers, lakes) and materials (soil, superficial deposits, geology) were also important. Main conclusions Geodiversity improves our understanding of, and ability to model, the relationship between species richness and abiotic heterogeneity at multiple spatial scales by allowing us to get closer to the real-world physical processes that affect patterns of life. Greatest benefit comes from measuring the constituent parts of geodiversity separately, rather than one combined variable (as for most of the few studies to date). Automatically extracted landform data, the use of which is novel in ecology and biogeography, proved particularly valuable in our study

Do urban areas act as foci for the spread of alien plant species? An assessment of temporal trends in the UK

Aim Given that urban landscapes often act as a point of entry for many non-native species and urban development continues to increase as the human population rapidly expands, an understanding of the interaction between urbanization and non-native plant species is important both in the control of potentially invasive species and in the conservation of native biodiversity. We investigated the spatial and temporal relationship between urban land cover and the distribution of non-native species in Britain using two floristic data sets collected at two different time periods: 1987–88 and 2003–04. Location UK. Methods Using floristic data collected by the Botanical Society of the British Isles in 1987–88 (Monitoring Scheme) and 2003–04 (Local Change) in conjunction with habitat data obtained from the Land Cover Map of the UK, we conducted multiple regression analyses both within and between years on both groups of species (natives, neophytes and archaeophytes) and individual species. Results Neophytes (alien species introduced after 1500) were very strongly associated with urban land cover in both time periods and do not appear to be spreading out of urban habitats into the wider countryside. Archaeophytes (alien species introduced before 1500), however, showed a strong association with urban habitats in the earlier 1988 data set but no longer showed this association in the 2004 data set. Analysis at the individual species level showed that a large percentage of alien plant species, particularly archaeophytes, were not strongly associated with urban land cover or were negatively associated with such habitats. Main conclusions Our results suggest that there has been a reduction in the urban association of archaeophytes that is likely to have resulted from the recovery of archaeophytes associated with non-urban (especially arable) habitats, following their decline in mid-20th century, rather than from the movement of aliens into the wider countryside from urban habitats

Habitat invasions by alien plants: a quantitative comparison among Mediterranean, subcontinental and oceanic regions of Europe

1. Although invasions by alien plants are major threats to the biodiversity of natural habitats, individual habitats vary considerably in their susceptibility to invasion. Therefore the risk assessment procedures, which are used increasingly by environmental managers to inform effective planning of invasive plant control, require reliable quantitative information on the extent to which different habitats are susceptible to invasion. It is also important to know whether the levels of invasion in different habitats are locally specific or consistent among regions with contrasting climate, flora and history of human impact. 2. We compiled a database of 52 480 vegetation plots from three regions of Europe: Catalonia (Mediterranean–submediterranean region), Czech Republic (subcontinental) and Great Britain (oceanic). We classified plant species into neophytes, archaeophytes and natives, and calculated the proportion of each group in 33 habitats described by the European Nature Information System (EUNIS) classification. 3. Of 545 alien species found in the plots, only eight occurred in all three regions. Despite this large difference in species composition, patterns of habitat invasions were highly consistent between regions. None or few aliens were found in environmentally extreme and nutrient-poor habitats, e.g. mires, heathlands and high-mountain grasslands. Many aliens were found in frequently disturbed habitats with fluctuating nutrient availability, e.g. in man-made habitats. Neophytes were also often found in coastal, littoral and riverine habitats. 4. Neophytes were found commonly in habitats also occupied by archaeophytes. Thus, the number of archaeophytes can be considered as a good predictor of the neophyte invasion risk. However, neophytes had stronger affinity to wet habitats and disturbed woody vegetation while archaeophytes tended to be more common in dry to mesic open habitats. 5. Synthesis and applications. The considerable inter-regional consistency of the habitat invasion patterns suggests that habitats can be used as a good predictor for the invasion risk assessment. This finding opens promising perspectives for the use of spatially explicit information on habitats, including scenarios of future land-use change, to identify the areas of highest risk of invasion

Plant species richness and environmental heterogeneity in a mountain landscape: effects of variability and spatial configuration

The loss of biodiversity has become a matter of urgent concern and a better understanding of local drivers is crucial for conservation. Although environmental heterogeneity is recognized as an important determinant of biodiversity, this has rarely been tested using field data at management scale. We propose and provide evidence for the simple hypothesis that local species diversity is related to spatial environmental heterogeneity. Species partition the environment into habitats. Biodiversity is therefore expected to be influenced by two aspects of spatial heterogeneity: 1) the variability of environmental conditions, which will affect the number of types of habitat, and 2) the spatial configuration of habitats, which will affect the rates of ecological processes, such as dispersal or competition. Earlier, simulation experiments predicted that both aspects of heterogeneity will influence plant species richness at a particular site. For the first time, these predictions were tested for plant communities using field data, which we collected in a wooded pasture in the Swiss Jura mountains using a four-level hierarchical sampling design. Richness generally increased with increasing environmental variability and "roughness" (i.e. decreasing spatial aggregation). Effects occurred at all scales, but the nature of the effect changed with scale, suggesting a change in the underlying mechanisms, which will need to be taken into account if scaling up to larger landscapes. Although we found significant effects of environmental heterogeneity, other factors such as history could also be important determinants. If a relationship between environmental heterogeneity and species richness can be shown to be general, recently available high-resolution environmental data can be used to complement the assessment of patterns of local richness and improve the prediction of the effects of land use change based on mean site conditions or land use history

Local vs regional factors as determinants of the invasibility of indigenous forest fragments by alien plant species

Both local and regional filters can determine the invasion of alien species into native plant communities. However, their relative importance is essentially unknown. We used plot data from fragments of indigenous forests in southeastern New Zealand to infer which factors are important in explaining invasibility, measured as alien species richness. Twenty-eight predictor variables comprising both local factors (stand structure and soil) and regional ones (climate and land cover) were assessed. Reduction or increase in deviance in linear models was assessed, both individually and with a forward and backward stepwise variable selection procedure using the Akaike information criterion (AIC). We found that higher alien species richness was mainly associated with forest fragments of small area in warm and dry climates and where there were only small areas of surrounding indigenous forest. Local soil and stand structure variables had considerably smaller effects on alien species richness than the regional land cover and climate variables. Alien species richness showed no relationship with native species richness. We conclude that in the forest fragments investigated here, of the variables included in the analyses, regional land cover and climate variables are potentially important drivers for alien species richness at plot level. This has implications for projections of alien species spread in the future under different climate change and land use scenarios

European map of alien plant invasions based on the quantitative assessment across habitats

Recent studies using vegetation plots have demonstrated that habitat type is a good predictor of the level of plant invasion, expressed as the proportion of alien to all species. At the scale of a few to hundreds of square meters, habitat types explain much more variation in the level of invasion than climate or alien propagule pressure. Moreover, it has been shown that patterns of habitat invasion are consistent among European regions with contrasting climates, biogeographical affinities, history and socio-economic background. These findings make a solid background for mapping the level of plant invasion, based on the projection of the habitat-specific levels of invasion onto land-cover maps. We used 52,480 vegetation plots from Catalonia (NE Spain), Czech Republic and Great Britain to quantify the levels of invasion by neophytes (alien plant species introduced after AD 1500) in 33 EUNIS habitat types. Then we estimated the proportion of each of these habitat types in CORINE land-cover classes and calculated the level of invasion for each class. The highest levels of invasion were predicted for agricultural, urban and industrial land-cover types, low levels for natural and semi-natural grasslands and most woodlands, and the lowest levels for sclerophyllous vegetation, heathlands and peatlands. We projected the levels of invasion on the European land-cover map, extrapolating Catalonian data to the Mediterranean bioregion, Czech data to the Continental bioregion, British data to the British Isles, and combined Czech-British data to the Atlantic and Boreal bioregions. The resulting map predicted high level of invasion in lowland areas of the temperate zone of western and central Europe and low level in the boreal zone and mountain regions across the continent. Low level of invasion was also predicted in the Mediterranean region except its coastline and areas with irrigated agricultural land