be the mechanism for the successional replacement of tamarisk by box elder.
The authors suggest that the preservation of box elder and other native tree
populations is probably a better and cheaper means of tamarisk control than
traditional control techniques.
As highlighted by Catford et al. (2012), however, there are several arguments
against the “do nothing” approach. Firstly, ecosystem functions may be significantly altered by early successional invasive plants colonizing soon after
disturbance (Peltzer et al. 2009). Secondly, some invasive species can outcompete functionally similar native species and therefore persist and dominate
over long periods after disturbance (Christian and Wilson 1999). Thirdly,
non-native species may establish themselves in highly disturbed areas first, and
subsequently adapt and colonize nearby areas with different environmental
conditions (Clark and Johnston 2011). Finally, most invasive species are not
early successional species that will be replaced over time, some of them are even
long-lived K-strategists that are highly competitive and able to invade even
undisturbed areas (Wilsey et al. 2009).
2. Manage the propagule supply. By reducing the propagule pressure of
non-native organisms and increasing that of native species, one can increase the
dominance of the former. For example, one control action against silver wattle is
the use of prescribed fire to favor the germination of the seed bank, therefore
reducing it by destroying part of the seeds or by stimulating the germination of
the remainders (http://invasoras.pt). Applying this or other measures to reduce
the seed bank soon after disturbance activities may strongly reduce the
propagule pressure and prevent or reduce the success of invasion. On the other
hand, native species suitable for direct sowing should also be selected based on
their traits and ability to establish and persist under the specific conditions of the
transportation verges. This active selection towards native colonists may benefit
not only local biodiversity but also regional agricultural areas. Blackmore and
Goulson (2014) found that sowing native wildflowers in road verges significantly increased the abundance of native flowering plants and that of pollinator
bumblebees (Bombus spp.) and hoverflies (Syrphidae), with benefits to agricultural crops. Furthermore, larvae of hoverflies prey on aphids, arthropod pest
species that are responsible for enormous crop damages worldwide, every year.
Hence, even easy to–implement interventions in verges may result in considerable environmental and economic gains.
3. Manage the environmental conditions. In some cases, it may be more effective
to target the causes that boost the disturbance and facilitate the spread of
non-native species than to attempt to manage their populations directly. For
example, some weeds are particularly adapted to severely eroded verges. Rather
than applying herbicide to control such weeds, it may be more effective to
stabilize the soil (Catford et al. 2012). This option requires excellent knowledge
of the ecological requirements of each invader and it may imply conducting
experimental ecological work in order to evaluate the effectiveness of distinct
management actions. Nevertheless, for some of the species the necessary
74
F. Ascensão and C. Capinha
The authors suggest that the preservation of box elder and other native tree
populations is probably a better and cheaper means of tamarisk control than
traditional control techniques.
As highlighted by Catford et al. (2012), however, there are several arguments
against the “do nothing” approach. Firstly, ecosystem functions may be significantly altered by early successional invasive plants colonizing soon after
disturbance (Peltzer et al. 2009). Secondly, some invasive species can outcompete functionally similar native species and therefore persist and dominate
over long periods after disturbance (Christian and Wilson 1999). Thirdly,
non-native species may establish themselves in highly disturbed areas first, and
subsequently adapt and colonize nearby areas with different environmental
conditions (Clark and Johnston 2011). Finally, most invasive species are not
early successional species that will be replaced over time, some of them are even
long-lived K-strategists that are highly competitive and able to invade even
undisturbed areas (Wilsey et al. 2009).
2. Manage the propagule supply. By reducing the propagule pressure of
non-native organisms and increasing that of native species, one can increase the
dominance of the former. For example, one control action against silver wattle is
the use of prescribed fire to favor the germination of the seed bank, therefore
reducing it by destroying part of the seeds or by stimulating the germination of
the remainders (http://invasoras.pt). Applying this or other measures to reduce
the seed bank soon after disturbance activities may strongly reduce the
propagule pressure and prevent or reduce the success of invasion. On the other
hand, native species suitable for direct sowing should also be selected based on
their traits and ability to establish and persist under the specific conditions of the
transportation verges. This active selection towards native colonists may benefit
not only local biodiversity but also regional agricultural areas. Blackmore and
Goulson (2014) found that sowing native wildflowers in road verges significantly increased the abundance of native flowering plants and that of pollinator
bumblebees (Bombus spp.) and hoverflies (Syrphidae), with benefits to agricultural crops. Furthermore, larvae of hoverflies prey on aphids, arthropod pest
species that are responsible for enormous crop damages worldwide, every year.
Hence, even easy to–implement interventions in verges may result in considerable environmental and economic gains.
3. Manage the environmental conditions. In some cases, it may be more effective
to target the causes that boost the disturbance and facilitate the spread of
non-native species than to attempt to manage their populations directly. For
example, some weeds are particularly adapted to severely eroded verges. Rather
than applying herbicide to control such weeds, it may be more effective to
stabilize the soil (Catford et al. 2012). This option requires excellent knowledge
of the ecological requirements of each invader and it may imply conducting
experimental ecological work in order to evaluate the effectiveness of distinct
management actions. Nevertheless, for some of the species the necessary
74
F. Ascensão and C. Capinha