Abstract
Road corridors are important conduits for plant invasions, and an understanding of the underlying mechanisms is necessary for efficient management of invasive alien species in road networks. Previous studies identified road type with different traffic volumes as a key driver of seed dispersal and abundance of alien plants along roads. However, how the intensity of traffic interacts with the habitat features of roadsides in shaping invasion processes is not sufficiently understood. To elucidate these interactions, we analyzed the population dynamics of common ragweed (Ambrosia artemisiifolia L.), a common non-indigenous annual species in Europe and other continents, in a regional road network in Germany. Over a period of five years, we recorded plant densities at roadsides along four types of road corridors, subject to different intensities of traffic, and with a total length of about 300 km. We also classified roadsides in regard to habitat features (disturbance, shade). This allowed us to determine corridor- and habitat-specific mean population growth rates and spatial-temporal shifts in roadside plant abundances at the regional scale. Our results show that both traffic intensity and roadside habitat features significantly affect the population dynamics of ragweed. The combination of high traffic intensity and high disturbance intensity led to the highest mean population growth whereas population growth in less suitable habitats (e.g. shaded roadsides) declined with decreasing traffic intensity. We conclude that high traffic facilitates ragweed invasion along roads, likely due to continued seed dispersal, and can compensate partly for less suitable habitat features (i.e. shade) that decrease population growth along less trafficked roads. As a practical implication, management efforts to decline ragweed invasions within road networks (e.g. by repeated mowing) should be prioritized along high trafficked roads, and roadside with disturbed, open habitats should be reduced as far as possible, e.g. by establishing grassland from the regional species pool.
Highlights
Plant invasions are a global phenomenon closely linked to human activities and related transportation network infrastructures (Bradley et al 2012; Seebens et al 2015; Chapman et al 2017)
Our results show that both traffic intensity and roadside habitat features significantly affect the population dynamics of ragweed
We address the population dynamics of common ragweed on a regional scale by performing a road-network analysis to reveal the spatial-temporal dynamics in roadside populations of common ragweed
Summary
Plant invasions are a global phenomenon closely linked to human activities and related transportation network infrastructures (Bradley et al 2012; Seebens et al 2015; Chapman et al 2017). A large number of studies revealed the importance of road corridors for the spread of invasive plant species (e.g. von der Lippe and Kowarik 2007; Brisson et al 2010; Joly et al 2011; Dar et al 2015; Manee et al 2015; Okimura et al 2016; Follak et al 2018a) and identified several important anthropogenic dispersal vectors as reviewed by Ansong and Pickering (2013) These vectors are commonly related to construction work, road maintenance and roadside management, agriculture, transportation industry and private vehicles. Traffic intensity is known to affect the diversity and composition of roadside vegetation (Truscott et al 2005; Jaźwa et al 2016), and distribution patterns of invasive alien species as well (Lemke et al 2019)
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