46 NEBRASKAland • JULY 2015
An actively growing grass plant that is
abruptly chopped off by fire, grazing
or mowing suddenly loses its ability
to turn light into food. Severe drought
and flooding can have much the same
impact. When something like that
happens, a normally dominant grass
doesn't just lose its ability to shade
out competing plants aboveground, it
also has to abandon large portions of
its root system belowground because
it can no longer feed them. The result
is a sudden abundance of space, light
and nutrients in and around those
weakened plants. However, those
resources are only available for a short
time – until those occupiers recover
from whatever knocked them back. If
anything was going to take advantage
of that opportunity, it would have
to be nimble, adaptable, bold and
resourceful.
Welcome to the life of an
opportunistic (weedy) plant. Most of
the plants in the "colonizer" category
are annuals or biennials which
germinate from seed and produce
copious amounts of new seed within
a year or two. Others are perennial
plants that happen to be able to
establish quickly from seed or rapidly
expand their footprint via rhizomes
(underground stems). Colonizers,
however, don't tend to stick around
very long. As big dominant grasses
regain their strength, colonizers wither
(literally) under the competition from
those gorillas and vacate territory as
quickly as they took it.
Ah, but while they're around,
colonizers often live spectacular
lives. Because most rely on producing
lavish amounts of seed (which drops
to the ground and lies in wait until
the next opportunity arises) they
often produce lots of large, showy
flowers. In addition, since they can't
afford to be hindered during their
brief opportunity to grow, flower and
make seed, successful colonizing plant
species have developed strategies
to resist forces such as grazing or
drought that suppress their competition.
Many produce chemicals that make
Shell-leaf penstemon is a perennial plant, but a poor competitor. Because cattle
don't find it tasty, it often thrives in intensively grazed pasture, and can increase
in abundance quickly when given the opportunity. Here it is blooming in profusion
following a year of drought, fire and grazing.
Long-term intensive grazing removes the
tops of plants, but also shrinks the size
of roots beneath. As a result, temporary
space opens up for colonizing plants.
As long as it is paired with adequate
rest periods, intensive grazing can help
promote overall plant diversity – an
important factor in overall wildlife habitat
and grassland health.
