Shrub management is the principal driver of differing population sizes between native and invasive populations of Rosa rubiginosa L.

Abstract

An essential step in understanding biological invasions is the comparison of species' performance in the native and introduced ranges, especially for longlived woody exotics. We explored causes for the higher density and abundance of invasive Rosa rubiginosa L. populations by comparing plant performance and habitat attributes in both ranges. Native shrubs in Spain and Germany were, on average, taller than introduced shrubs in Central and Southern Argentina. Inside 100 m 2 plots rose-cover in Spain and Germany was significantly higher than in Central Argentina but comparable to that found in Southern Argentina. Growth rates of marked branches did not differ between ranges, but marked shrubs indicated that native R. rubiginosa stems are cut regularly, with the oldest rose stems being found in Argentina. Seeds from the introduced range did not have higher germination rates overall, and low seedling numbers in the field underline the general importance of vegetative growth for the species. Leaf damage did not differ between regions and soil analyses proved that R. rubiginosa tolerate a wide range of soil conditions without necessarily benefiting from any one in particular. No differences were observed in vegetation structure, pointing to favorable conditions in the introduced range, and greenhouse experiments showed that plants of invasive origin do not outgrow native roses. The smaller population sizes and lower abundance in the native range can therefore be attributed to management actions along with a lower level of viable habitat.

The Human Release Hypothesis for biological invasions: human activity as a determinant of the abundance of invasive plant species

“…The Ideal Weed and Disturbance Hypotheses ( Table 1) partly explain the invasion success of R. rubiginosa in Argentina 31, 35, 36 . However, the Enemy Release Hypothesis failed to explain abundance patterns – natural enemies appeared equally harmful to the species in the native and introduced ranges 31 ( Table 1).…”

“…First, we synthesize previous cross-continental case studies that compared plant performance between invasive populations in Central and Southern Argentina with native populations in Spain and Germany (for more details see Zimmermann et al , 2012) 31 . Second, we compare climatic conditions as well as land use and human population density between invasive and native R. rubiginosa populations at a global scale.…”

“…Low genetic diversity suggests that multiple introduction events constituting particularly high propagule pressure cannot explain the species' invasion success. Despite lower genetic diversity, populations of R. rubiginosa are considerably smaller in Spain and Germany than in Argentina ( Figure 3) – native populations consist of 5 to 20 individuals whereas invasive populations consist of hundreds of individuals 31 . In addition to propagule pressure, abiotic and biotic variables also cannot fully explain the invasion success of R. rubiginosa .…”

“…In addition to propagule pressure, abiotic and biotic variables also cannot fully explain the invasion success of R. rubiginosa . In Argentina, the species neither benefits from favourable soil conditions nor from reduced biotic resistance 31 .…”

“…In parts of Argentina, single disturbance events have offered windows of opportunity for the species to establish populations, some of which have remained undisturbed for 30 years or longer ( a ) 31, 36 . The low level of human landscape maintenance means that populations can expand over vast areas and consist of hundreds of individuals ( a , here along the whole visible lakeside in Patagonia).…”