SPEZIALE Karina Lilian
Synergy between roads and disturbance favour Bromus tectorum L. invasion
SPEZIALE, KARINA L.; DI VIRGILIO, AGUSTINA; LESCANO, MARIA N.; PIRK, GABRIELA; FRANZESE, JORGELINA
Año: 2018 vol. 6
Background. Global changeproduces pervasive negative impacts on biodiversity worldwide. Land use changeand biological invasions are two of the major drivers of global change thatoften coexist; however, the effects of their interaction on natural habitats havebeen little investigated. In particular, we aimed to analyse whether theinvasion of an introduced grass (Bromustectorum; cheatgrass) along roads verges and the disturbance level in the naturalsurrounding habitat interact to influence the degree ofB. tectorum invasion in the latterhabitats in north-western Patagonia. Methods. Along 6 different roads, totalling approximately 370 km, we set two 50 m x 2 m sampling plotsevery 5 km (73 plots in total). One plot was placed parallel to the road (onthe roadside) and the other one perpendicular to it, towards the interior ofthe natural surrounding habitat. In each plot, we estimated the B. tectorum plant density in 1m2subplots placed every 5 m. In the natural habitat, we registered the vegetationtype (grassy steppe, shrub-steppe, shrubland, and wet-meadow) and the disturbancelevel (low, intermediate, and high). Disturbance level was visually categorizedaccording to different signs of habitat degradation by anthropogenic use. Results. B. tectorum density showedan exponential decay from roadsides towards the interior of natural habitats. Thedegree of B. tectorum invasion insidenatural habitats was positively related to B. tectorum density on roadsidesonly when the disturbance level was low. Shrub-steppes,grassy steppes and shrublands showed similar mean density of B. tectorum. Wet-meadows had the lowest densities of B. tectorum. Intermediate and highly disturbed environments presentedhigher B. tectorum density than thoseareas with low disturbance. Discussion. Our study highlights the importance of the interaction between roadverges and disturbance levels on B.tectorum invasion in natural habitats surrounding roads of north-western Patagonia,particularly evidencing its significance in the invasion onset. The importance of invasion in road verges depends on disturbancelevel, with better conserved environments being more resistant to invasion at low levels of B. tectorum density along road verges,but more susceptible to road verges invasion at higher levels of disturbance. Allthe habitats except wet-meadows were invaded at a similar degree by B. tectorum, which reflects itsadaptability to multiple habitat conditions. Overall, our work showed that synergiesamong global change drivers impact native environments favouring the invasionof B. tectorum.