species in transportation corridors may have a lower impact in forested landscapes
than in open areas, such as grasslands.
The importance that verge areas represent for the spreading and fixation of
non-native species is therefore clear. In fact, despite their relatively narrow width,
verges can be long, creating continuous strips that may extend for many kilometers
and occupy considerable areas. Knowing that the global railway and road lengths
are, respectively, approximately 1.1 and 64.3 million km (CIA 2016), and using a
conservative value of mean verge width of two meters on each side, we realize that
more than 262,000 kilometers of the world are occupied by verges. For comparison, this is equivalent to approximately 33% of the terrestrial protected areas of
Natura 2000 Network (EU 2016). Therefore, the management of the vegetation of
verges is of utmost importance not only for traffic safety, but also for the control
of non-native species.
Management of Non-native Species
in Transportation Corridors
As discussed, transportation corridors can function as habitats and venues for the
dispersal of non-native species, hence they are an important element to consider
when managing and preventing the threats caused by biological invasions. On the
other hand, verges can also help maintain conservation values and the connectivity
among landscapes, particularly in areas that are heavily modified by human
activities (see Chap. 4). Because verges provide habitat areas and corridors for both
native and non-native species, it creates management challenges, such as how to
maintain or increase the conservation value of transportation verges, while preventing non-native animal and plant species from spreading throughout the network
and its surroundings. A delicate balance between restricting the arrival and dispersal
of non-native species and maintaining or restoring the conservation value of verges
is thus needed. This requires specific management actions, as we discuss below.
Identifying the factors that facilitate the arrival of propagules of non-native
species and their dispersal along the corridors may render it possible to manage
verges in ways that limit the expansion of an invasive species (Fagan et al. 2002;
With 2002). Despite the difficulties in identifying such key factors for all organisms, some general management practices are likely to prevent the dispersal of
non-native species in most circumstances.
Perhaps the best management option is to avoid setting up the conditions for
non-native species dispersal and establishment when a corridor is under construction, being upgraded or under maintenance. Such activities may imply baring soil,
clearing of natural vegetation, or drainage, resulting in considerable disturbance of
natural communities. In turn, these disturbances underlie ecological processes that
often facilitate the colonization by invasive species, as they “remove” any
pre-existing advantage of native over non-natives species that could be present in
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F. Ascensão and C. Capinha
than in open areas, such as grasslands.
The importance that verge areas represent for the spreading and fixation of
non-native species is therefore clear. In fact, despite their relatively narrow width,
verges can be long, creating continuous strips that may extend for many kilometers
and occupy considerable areas. Knowing that the global railway and road lengths
are, respectively, approximately 1.1 and 64.3 million km (CIA 2016), and using a
conservative value of mean verge width of two meters on each side, we realize that
more than 262,000 kilometers of the world are occupied by verges. For comparison, this is equivalent to approximately 33% of the terrestrial protected areas of
Natura 2000 Network (EU 2016). Therefore, the management of the vegetation of
verges is of utmost importance not only for traffic safety, but also for the control
of non-native species.
Management of Non-native Species
in Transportation Corridors
As discussed, transportation corridors can function as habitats and venues for the
dispersal of non-native species, hence they are an important element to consider
when managing and preventing the threats caused by biological invasions. On the
other hand, verges can also help maintain conservation values and the connectivity
among landscapes, particularly in areas that are heavily modified by human
activities (see Chap. 4). Because verges provide habitat areas and corridors for both
native and non-native species, it creates management challenges, such as how to
maintain or increase the conservation value of transportation verges, while preventing non-native animal and plant species from spreading throughout the network
and its surroundings. A delicate balance between restricting the arrival and dispersal
of non-native species and maintaining or restoring the conservation value of verges
is thus needed. This requires specific management actions, as we discuss below.
Identifying the factors that facilitate the arrival of propagules of non-native
species and their dispersal along the corridors may render it possible to manage
verges in ways that limit the expansion of an invasive species (Fagan et al. 2002;
With 2002). Despite the difficulties in identifying such key factors for all organisms, some general management practices are likely to prevent the dispersal of
non-native species in most circumstances.
Perhaps the best management option is to avoid setting up the conditions for
non-native species dispersal and establishment when a corridor is under construction, being upgraded or under maintenance. Such activities may imply baring soil,
clearing of natural vegetation, or drainage, resulting in considerable disturbance of
natural communities. In turn, these disturbances underlie ecological processes that
often facilitate the colonization by invasive species, as they “remove” any
pre-existing advantage of native over non-natives species that could be present in
72
F. Ascensão and C. Capinha