Synergy between roads and disturbance favourBromus tectorumL. invasion

Abstract

BackgroundGlobal change produces pervasive negative impacts on biodiversity worldwide. Land use change and biological invasions are two of the major drivers of global change that often coexist; however, the effects of their interaction on natural habitats have been little investigated. In particular, we aimed to analyse whether the invasion of an introduced grass (Bromus tectorum; cheatgrass) along roads verges and the disturbance level in the natural surrounding habitat interact to influence the degree of B. tectorum invasion in the latter habitats in north-western Patagonia.MethodsAlong six different roads, totalling approximately 370 km, we set two 50 m × 2 m sampling plots every 5 km (73 plots in total). One plot was placed parallel to the road (on the roadside) and the other one perpendicular to it, towards the interior of the natural surrounding habitat. In each plot, we estimated the B. tectorum plant density in 1 m2 subplots placed every 5 m. In the natural habitat, we registered the vegetation type (grassy steppe, shrub-steppe, shrubland, and wet-meadow) and the disturbance level (low, intermediate, and high). Disturbance level was visually categorized according to different signs of habitat degradation by anthropogenic use.ResultsB. tectorum density showed an exponential decay from roadsides towards the interior of natural habitats. The degree of B. tectorum invasion inside natural habitats was positively related to B. tectorum density on roadsides only 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 presented higher B. tectorum density than those areas with low disturbance.DiscussionOur study highlights the importance of the interaction between road verges 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 disturbance level, 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. All the habitats except wet-meadows were invaded at a similar degree by B. tectorum, which reflects its adaptability to multiple habitat conditions. Overall, our work showed that synergies among global change drivers impact native environments favouring the invasion of B. tectorum.

Effect of Land Use History on Biodiversity of Pine Plantations

“…These plantations have been shown to generate significant changes in the physical environment in which they are established, including degradation and erosion of soils (Oyarzún and Peña, 1995;Turner and Lambert, 2000;Imaizumi et al, 2008;Soto et al, 2019) and an increase in water consumption (Licata et al, 2008;Scott and Prinsloo, 2008;Little et al, 2009), depending on the local environmental characteristics. In addition, management activities such as logging, weed control, fire or road construction, can have strong effects on biodiversity, for instance, facilitating the arrival of exotics or displacing organisms that are disturbances sensitive (Pauchard and Alaback, 2006;Tardif-Paradis et al, 2015;Cole et al, 2018;Speziale et al, 2018).…”

Alien plant species on roadsides of the northwestern Patagonian steppe (Argentina)

“…These families contribute a large number of exotic invasive species to the world's flora [62]. Many of these invader species have spreading strategies related to efficient long-distance wind or animals dispersal [14,40,63].…”

“…Both annual herb and grass appear to depend on intense disturbance (i.e., removal of soil, fire, grazing) to spread into less degraded sites. It is documented that B. tectorum spread from the roadsides to the interior of the natural ecosystem [40] and E. brachycarpum is frequently found in degraded environments [52], while in little-disturbed natural habitats it presents low cover [43]. The high germination potential, abundant seed production and high dispersal capacity by wind or animals of both species could favor their establishment in disturbed zones [74][75][76].…”

“…A large number of studies in the world have assessed the influence of roads on exotic plant dispersal and establishment in aboveground vegetation [9,11,13,37,38], but soil seed bank on roadsides have been less examined [27,39]. In particular these topics have been under-researched in Patagonian steppe roadsides [26,40].…”

Interaction of traffic intensity and habitat features shape invasion dynamics of an invasive alien species (Ambrosia artemisiifolia) in a regional road network

“…As a negative effect in this habitat, plants are stressed by pollutants from traffic exhausts and by de-icing salt that also affects soil pH (Forman and Alexander 1998;Seiler 2000;Hofman et al 2012;Gentili et al 2017). Habitat quality of roadsides is locally modulated by adjacent land-use patterns that may result in differences in shading or disturbance intensity (Christen and Matlack 2009;Speziale et al 2018). We expect that both shading and the availability of open habitats at road verges are critical for the establishment of roadside populations because most plant species growing on roadsides are commonly categorized as herbaceous generalists (Coffin 2007) or light, drought and disturbance tolerating ruderal specialists (Sera 2010;Gade 2013;Bochet and Garcia-Fayos 2015;Kalwij et al 2015).…”