Environmental Engineering Reference
In-Depth Information
forms of control (e.g. mechanical or chemical methods). A variety of hand imple-
ments, from primitive to very sophisticated, have been developed for the removal
of weedy vegetation. Hand pulling and using manual implements are most effect-
ive on annual or simple perennial plants that are not able to sprout from roots or
other vegetative organs. However, these methods are very labour intensive, and
over wide areas may be prohibitively expensive or unfeasible.
Even though manual methods of controlling unwanted vegetation have declined
in agroecosystems in favour of mechanized approaches, hand pulling and using
manual implements are still practised in certain high-value crops or habitats, or
when other types of plant suppression are not possible. For example, hand tools
are often used in wildland situations where selective herbicides are not available or
registered for use, where the area to be weeded is too small for most equipment,
or where the habitat contains species or other elements that are sensitive to dis-
turbance and may even be protected by law (Wittenberg and Cock 2005). h ese
methods are also widely used in areas where volunteer crews are available for weed
control but may not have the equipment, funds, or training to use mechanized
tools. Hand methods can also be eff ective and economical for removing the few
individual plants that escape other control measures. h ese few individual plants,
if left unattended, have the potential to expand and replenish the soil seed bank.
Similarly, the earliest stages of colonization by an invasive plant can sometimes be
eradicated by hand pulling in areas where fi nancial or environmental constraints
prohibit use of other methods (Wittenberg and Cock 2005).
9.4.2.2 Fire
Fire is another tool that has been available to humans for centuries for the manipu-
lation of vegetation. It is still used extensively to remove crop residues and other
unwanted vegetation in agriculture and to prepare forest lands for regeneration
after clearcut logging (Radosevich
et al
. 2007). Fire is also sometimes used to
remove weeds and other residue from along roadsides, canal banks, ditches, and
vacant areas. In addition, controlled burning has been used to manage fuel breaks
in shrublands that are prone to wildfi re. Broadcast burning is also an accepted
and effective method to periodically increase rangeland productivity by stimu-
lating growth of certain fi re-adapted grass species (DiTomaso and Johnson 2006;
DiTomaso
et al
. 2006).
Fire can be an eff ective weed management tool in certain wildland ecosystems
when applied carefully and selectively (Muyt 2001). Applying fi re for management
of unwanted vegetation can destroy mature plants, eliminate seedlings, exhaust weed
seed banks, improve access to a site for follow-up treatments, remove dried weed
material, and stimulate germination, growth, and spread of desirable vegetation.
However, fi re also favours some weeds and invasive plants and can have a detrimen-
tal eff ect on wildland ecosystems (Brown and Kapler-Smith 2000; Muyt 2001; Rice
2004). h erefore, it is critical to assess whether fi re is an appropriate invasive plant
management technique before conducting any controlled burning (Wittenberg
and Cock 2005; DiTomaso and Johnson 2006; DiTomaso
et al
. 2006).
