ECOLOGY OF AN INTRODUCED SHRUB (ROSA-RUBIGINOSA-L = ROSA-EGLANTERIA L) - INVASION RISKS AND EFFECTS ON THE PLANT-COMMUNITIES OF THE ANDEAN-PATAGONIC REGION OF ARGENTINA

The relation between presence of Rosa eglanteria L. and environmental or antropic variables was studied in fifty nine plots, randomly established in ten areas representing different environments in or around the Nahuel Huapi National Park. Floristic differences between areas invaded by this shrub and areas without Rosa eglanteria were studied. The degree of disturbance, the openness of the shrub stratum and the average annual rainfall were the main factors influencing the invasion by Rosa eglanteria. Communities in early stages of invasion and with low disturbance, showed on the average, a higher species richness than those without Rosa. However, samples from communities dominated by Rosa eglanteria showed lower species richness. With the exception of two native species, neither the abundance of native species, nor that of other exotic invaders showed significant differences between early stage invaded sites or non invaded sites.