By James Cash, Texas A&M WFSC '17
Managing
vegetation is often the foundation of good wildlife management, and plant succession is a cornerstone of that foundation. Many wildlife biologists and managers will
tell you that knowing your plants and how to manipulate them is a vital skill. Plant succession is one of the most important
concepts to understand in order to manipulate the plant communities on your
property to benefit wildlife species. The
science of plant succession is a complicated one, and there is much variation
between regions and ecotypes. This
article is meant to serve as a primer for land managers who are interested in
learning how they can use plant succession to their advantage.
Prescribed
fire can be used to set back plant succession and promote plants that are beneficial
for wildlife.
Photo credit:
Texas A&M AgriLife Extension
Plant
succession is the progression of different plant communities (seres) over time
on a specific area (Ricklefs 2008). It
starts with a disturbance, which can be caused by events such as wildfires or
floods. These days natural disturbances
such as fires and floods are often limited by human interference. Land managers usually need to create smaller
scale, controlled disturbances in order to maintain plant communities in the
successional stage that they want. Examples
of manmade disturbances include prescribed fires, herbicide, disking, and
grazing.
After the initial disturbance, the site
progresses through several intermediate stages, or seres. The first
plants to colonize a site after soil disturbances such as disking are normally annual
forbs (weeds) and grasses. Over time,
perennial forbs and grasses invade and out-compete the annual species. Woody
shrubs and small trees often come next. These initial woody species are usually fast-growing,
shade-intolerant species. Finally, a
climax community typically composed of slow-growing shade-tolerant trees
develops. The climax community is the
final stage, and it only changes if subjected to considerable disturbances or
environmental changes. This is the
typical generalization that is used to describe succession in many areas of
North America.
The actual successional stages that
develop on a specific site do not always follow this pattern. Many variables including climate, soil types,
local seed bank, and others may cause a site to skip certain stages or reach a
climax community at an early stage. The
ecoregion in which a site is located usually determines the climax community,
but many sites differ from the climax community of the ecoregion due to slight
variations in the variables mentioned above. The time span over which different stages
develop is also highly dependent on local variables. On some sites it may only take a few decades
to reach a climax community (e.g. prairie); other sites may take centuries or
millennia to reach a climax community (e.g. old-growth hardwood).
The frequency and timing of
disturbances, both natural and man-made, plays a major role in the progression
of a site through successional stages. The time of year you disturb the landscape
will determine what species you suppress and what species you promote (Harper
and Gruchy 2009). This holds true for any type of disturbance –be it herbicide
treatment, prescribed fire, or mechanical.
The specific land management goals of the land owner will determine when
a disturbance should be conducted. The
frequency of the disturbance will determine at what successional stage the land
is maintained. High frequency
disturbances (usually 1-2 year interval) will maintain annual forbs and
grasses; moderate frequency will maintain perennial forbs, grasses, and woody
species (usually 3-5 year interval) (Harper and Gruchy 2009). The climate of a region will affect the
required disturbance frequency. In
eastern Texas, where rainfall is high, succession progresses rapidly and thus
disturbances need to be more frequent than in the arid western part of the
state.
Disking long, meandering strips into a
pasture promotes forb production while maintaining nesting cover in the
surrounding grassland. Alternating strips may be disked every 2-4 years
depending on your climate. Photo courtesy of Dale Rollins.
A common species reliant on early
successional habitat is the northern bobwhite (Colinus
virginianus). Bobwhites need a
combination of annual forbs for food, perennial grasses for nesting cover, and
woody shrubs for escape cover (James et al. 2015). This means that bobwhite habitat needs to be
managed simultaneously for several different stages of successional growth. The
best way to promote multiple successional stages is by disturbing alternating
strips or patches on a multi-year rotational basis (Burger, Harper and
Gruchy 2009). The disturbance can be achieved
with fire or disking. A recently disturbed site will have annual forbs as food
sources while adjacent sites that were disturbed 2-3 years ago will have
perennial plants such as bunch grasses that can provide nesting cover. When disturbing a site, make sure that you
protect an adequate amount of escape cover (i.e. shrubs). There should be
enough shrubs on the landscape that you can stand anywhere and be a softball
throw away from a shrub. How often one
rotates between burning or disking a site will depend on the climate of the
region you are in. In eastern Texas, a
site may require disturbance every couple of years, while western Texas
landowners should probably wait every 3-4 years to re-burn or disk a site.
The following videos provide more
information on using disturbances to manipulate plant succession:
Before implementing any intensive
wildlife management plan, it is a good idea to consult a local wildlife professional. A wildlife professional will be able to assess your property to determine when and how to create
disturbances to meet your specific wildlife management goals. To find a Texas
Parks and Wildlife Department biologist click here,
to find a Natural Resource Conservation Service office click here,
and to find your County Extension Agent click
here.
Funding support provided by the Reversing the Quail Decline Initiative and the Upland Game Bird Stamp Fund, based on a collaborative effort by Texas Parks and Wildlife Department and the Texas A&M AgriLife Extension Service.
Literature
Cited
Burger, W. Strip
disking and other valuable bobwhite quail management techniques. Mississippi
State University Extension Service. Publication 2032. Starkville, Mississippi,
USA.
Harper, C.A.,
J.P. Gruchy. 2009. Conservation practices to promote quality early successional
wildlife habitat. Natural Resources Conservation Service, United States
Department of Agriculture. Knoxville, Tennessee, USA.
James, A.S., M.
Marshall, B. Hayes, J. Hardin, R. Perez, J.C. Cathey. 2015. Habitat guide for
northern bobwhite. Texas A&M University AgriLife Extension Service.
Publication WF-020. College Station, Texas, USA.
Ricklefs, R.E. 2008.
The economy of nature. Sixth edition.
W. H. Freeman and Company, New York, New York, USA.