To begin with, new management regimes for birds should be introduced only
to a proportion of the existing habitat, to minimize the risk of extinction of inver-
tebrate species of conservation value, should the new management prove unsuit-
able for them. This is less of a problem for most plants, which can survive at least
short periods of unfavorable management as seed or spores. Most birds can move
elsewhere if conditions become unfavorable and re-colonize when suitable con-
ditions return. When introducing grazing to a previously ungrazed habitat, it is
prudent to start at low stocking levels to determine the effects of light grazing and
work up from there to find the optimal grazing level.
14.4.3Controlling unwanted plants
A frequent issue in habitat management is the control of unwanted plant species,
such as Bracken Pteridium aquilinumthat is invading dwarf-shrub heath or exotic
species that are outcompeting native vegetation. The first stage is to evaluate
whether the benefits of control will outweigh its costs. Issues to consider are whether
the unwanted plant species is spreading, what vegetation is likely to replace it
following removal, and the likelihood of the unwanted species re-colonizing from
elsewhere. It is also important to decide whether the aim of control is to simply con-
tain the species, or to eradicate it from the site, if indeed the latter is realistic.
There are two methods of reducing the competitive ability of the undesired
species relative to that of the surrounding vegetation. The first option to consider
is whether the abundance of the unwanted species can be reduced by modifying
the existing management. For example, changing the timing of cutting or inten-
sity of grazing might reduce the availability of suitable germination sites for the
unwanted species. The second option is to cut just the unwanted species to
reduce its vigor relative to that of the surrounding vegetation. Cutting is most
effective at reducing vigor if carried out at times of year when the plant has least
of its reserves stored underground, that is, when plants have produced leaves but
before they have replenished their underground reserves. Repeated cutting of
re-growth will further deplete the plant’s resources. Some emergent plants, for
example, Reed Phragmites australis, are most effectively controlled by cutting and
immediately flooding their stems, or cutting them underwater. This reduces the
plant’s strength by cutting off the supply of oxygen from the plant’s leaves above
the water to its roots in the anoxic mud.
If neither of these strategies proves successful, then the next options are to dig
up the unwanted species or use a herbicide. The former will only be feasible on a
small-scale, and may be followed by regeneration of the unwanted species from
seed in the freshly disturbed soil. Herbicides can be dangerous to people and
other nontarget groups, and in general should be used only as a last resort,
336 |Habitat management