SPATIO TEMPORAL SUCCESSION AND WEED SUPPRESSION
April 17, 2002
Robert M. Dixon, Ph.D
Spatio temporal plant succession can be used to suppress weed patches along roadsides and elsewhere. Weeds tend to colonize areas along roadsides that suffer occasional disturbances such as grading; herbiciding; burning; sand, gravel and wind blasting; compacting; wet-weather rutting and icy-weather salting to name a few. These disturbances tend to stall and even reverse the natural succession of plant types. Weedy pioneer species find an empty niche to colonize in disturbed areas that are nearly or completely denuded-thus the roadside weed patches that characterize chronically disturbed land areas. Other chronically disturbed areas include croplands and grazing lands wherein weeds often flourish. Further disturbances are often used, unwittingly, to control weeds that are themselves a product of disturbances. A never ending cycle of weeds and more weeds is the result of such disturbance methods of weed control. One must recall Albert Einstein's statement: "A problem is never solved at the same level of awareness at which it was created." Thus a higher level of awareness is needed to solve weed problems.
This higher level is provided by the ecological theory known as natural plant succession in which a sequence of plant types replace one another beginning with short-lived, short-growing pioneer plants and ending with long-lived, tall-growing perennial plants. A number of stages in plant types occur between the early and late successional stages.
Application of this ecological theory usually involves accelerating the natural plant succession quickly past the weed stage to accomplish in just a few years a progression requiring nature decades or even centuries to accomplish.
Pushing the natural plant succession past the weed state, in turn, usually involves 3 main steps.
• Laying the weed top-growth down on the soil surface to form a beneficial mulch by cutting, rolling, or trampling.
• Seeding the weed-patch area and it's borders with early, mid and late successional species to suppress weeds through competition and replacement.
• Imprinting the weed patch area and it's borders to provide good seedbeds and seedling cradles for late successional species.
These 3 steps are accomplished in a single operation with seeding imprinter rollers.
In a weed patch, succession occurs in both time and space. Weed displacement occurs first in the center of the weed patch and last along it's borders. Thus mid to late successional species are ringed by early successional species or weeds. This ringed plant community expands in wet years and shrinks during dry years. Whereas, the ring of weeds widens during dry years and narrows during wet years.
Not only can succession be accelerated in the center of the weed patch, but on the edges as well by using a good seedmix and making good imprints. Pioneers in the seedmix should not only compete well with those in the soil seedbank, but also be easily displaced by later successional species. Good imprints improve deep soil moisture, thereby accelerating succession past the weed stage.
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