WEED PREVENTION: REVEGETATION
March 25, 2001
Robert M. Dixon, PhD
The most environmentally sound method for controlling weeds is to prevent them from occurring in the first place. The revegetation process can prevent weeds from colonizing disturbed or barren land areas. Light and fluffy weed seeds are forever blowing in the wind and settling out all over the landscape to become a part of the seed bank that resides in the surface soil. These seeds lie dormant in flourishing plant communities mainly because such communities consume the light and soil moisture resources needed for weed seed germination.
Weeds are usually pioneer plants in the natural plant succession; that is they come first in the sequence of plant types that colonize a barren soil area following a land disturbance. In revegetation, the barren area is seeded with a seed mix that includes fast germinating and fast establishing annual species such as annual ryegrass, oats and barley.
Land disturbances take many forms most of which are caused by a plethora of human activities including:
• Livestock grazing
• Cropland cultivation
• Forest logging
• Industrialization
• Military activities
• Transportation
• Recreation
• Land clearing
• Herbiciding
Natural causes of land disturbances include drought, fire, volcanic eruptions, tornadoes, hurricanes, wind erosion, water erosion, flooding, sedimentation, land slides and earth quakes.
Although there are nearly as many natural disturbances as those caused by humans, plant communities can better cope with the disturbances that they have coevolved with through eons of time. Many of the so-called natural disturbances are greatly intensified by human activities.
Finally there are three points in time at which weeds can be prevented or controlled. First, we can prevent or minimize the human activities that disturb land, leaving it vulnerable to weed colonization. Second, we can revegetate land just as soon as it becomes barren from a disturbance. And third, we can accelerate the natural plant succession past the weed stage where weeds have already occupied disturbed land. By the third point, it's high time for action against existing weed colonies, but there is still no reason to panic. After all, weeds are pioneers and thus the first stage in plant succession after a disturbance. Some weeds, however are quite persistent and thus harder to displace than a selected pioneer such as annual ryegrass.
In conclusion, it is good to remember Ralph Waldo Emerson's definition: A weed is a plant whose virtues have not yet been discovered. Most weeds do have virtues, if only to provide cover and erosion protection on a denuded landscape while filling the role of a pioneer in the succession of plant types and species that follow.
We also should remember Albert Einstein's statement: No problem was ever solved at the same level of awareness at which it was created. Applied to the weed problem land disturbances cause the problem that cannot be solved by even more disturbances. On the other hand, plant succession theory provides the new level of awareness required for a solution.
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