Separating Habitat Invasibility by Alien Plants From the Actual Level of Invasion

Abstract

Habitats vary considerably in the level of invasion (number or proportion of alien plant species they contain), which depends on local habitat properties, propagule pressure, and climate. To determine the invasibility (susceptibility to invasions) of different habitats, it is necessary to factor out the effects of any confounding variables such as propagule pressure and climate on the level of invasion. We used 20 468 vegetation plots from 32 habitats in the Czech Republic to compare the invasibility of different habitats. Using regression trees, the proportion of alien plants, including archaeophytes (prehistoric to medieval invaders) and neophytes (recent invaders), was related to variables representing habitat properties, propagule pressure, and climate. The propagule pressure was expressed as the proportion of surrounding urban and industrial or agricultural land, human population density, distance from a river, and history of human colonization in the region. Urban and industrial land use had a positive effect on the proportion of both archaeophytes and neophytes. Agricultural land use, higher population density, and longer history of human impact positively affected the proportion of archaeophytes. Disturbed human-made habitats with herbaceous vegetation were most invaded by both groups of aliens. Neophytes were also relatively common in disturbed woody vegetation, such as broad-leaved plantations, forest clearings, and riverine scrub. These habitats also had the highest proportion of aliens after removing the effect of propagule pressure and climate, indicating that they are not only the most invaded, but also most invasible. These habitats experience recurrent disturbances and are rich, at least temporarily, in available nutrients, which supports the hypothesis that fluctuating resources are the major cause of habitat invasibility. The least invaded habitats were mires and alpine-subalpine grasslands and scrub. After removing the effect of propagule pressure and climate, some habitats actually invaded at an intermediate level had very low proportions of aliens. This indicates that these habitats (e.g., dry, wet, and saline grasslands, base-rich fens, and broad-leaved deciduous woodlands) are resistant to invasion.

Plant invasions are context‐dependent: multiscale effects of climate, human activity and habitat

“…In our work, climate was used to estimate abiotic suitability (Thuiller et al, 2005), human activity at a landscape scale was used as a proxy for propagule availability (Chytrý et al, 2008a;González-Moreno et al, 2013b), and habitat type represented both characteristics of the native community and the human influence at a local scale (Chytrý et al, 2008a). Among these variables, we found habitat type to be the single most important factor associated with invasion.…”

“…Conceptual models to explain invasion success have pointed to the combination of having enough propagules and a suitable environment, biotic and abiotic (Catford et al, 2009;Chytrý et al, 2008a). In our work, climate was used to estimate abiotic suitability (Thuiller et al, 2005), human activity at a landscape scale was used as a proxy for propagule availability (Chytrý et al, 2008a;González-Moreno et al, 2013b), and habitat type represented both characteristics of the native community and the human influence at a local scale (Chytrý et al, 2008a).…”

The response of plant community diversity to alien invasion: evidence from a sand dune time series

“…As stated in several studies, the occurrence of many alien species has been found to be indicative of land-use change (Maskell et al 2006) and most habitats ranked as highly invasible are usually associated with human disturbance or alteration of the typical disturbance regime (Alpert et al 2000;Chytrý et al 2008a). Several proxy variables are normally used to infer the impact of human disturbance, for example the proportional area of urban and/or agricultural land in the surrounding areas, the density of buildings, or the human population density (Carboni et al 2010;Chytrý et al 2008a).…”

“…Several proxy variables are normally used to infer the impact of human disturbance, for example the proportional area of urban and/or agricultural land in the surrounding areas, the density of buildings, or the human population density (Carboni et al 2010;Chytrý et al 2008a). The lack of precise information on the geographic location of past phytosociological relevés prevented us from ascertaining the exact extent of past disturbance or its change over time.…”

Impact of urban factors and invasive species on white-footed mouse (Peromyscus leucopus) habitat use and foraging behavior in an urban forest park.

“…Urban parks and green spaces exist as fragments within a heterogeneous environment (Zipperer and Guntenspergen 2009), and are susceptible to invasion from the large number of introduced exotic species present in urban areas (Chytry et al 2008;Niggemann et al 2009). These invasive species work to colonize urban patches, where they often take advantage of increased edge habitat and a loss of specialist species (Fernandez-Juricic 2001;Bartuszevige et al 2006;McKinney 2006;McKinney 2008).…”