Southeast Exotic Pest Plant Council

THE LATEST TECHNOLOGY FOR MECHANICAL TREATMENTS AND PRECISION IVM Bob Rummer1 and Steve Taylor2, 1US Forest Service Forest Operations Research, Auburn, AL and 2Biosystems Engineering Department, Auburn University, AL, 36849. (


Increasingly vegetation management is focusing on treatments that restore native plant communities, address structural density, or address the spread of non-native invasives. The basic functional requirements of these prescriptions are to kill selected undesirable vegetation and to create favorable conditions for the continued growth and regeneration of desired plant associations. There are basically three types of tools that can be applied to achieve these goals: thermal, chemical, or mechanical. Each of these tools has its advantages and disadvantages and they may be applied singly or in combination. This paper provides an overview of these tools with a focus on new developments in mechanical and precision treatment technology.

Fire is often the natural process that establishes or maintains plant communities. Its effects can be varied by managing the timing (season), frequency and intensity of burning. Fire reduces competition, kills some vegetation, and initiates nutrient cycling. Fire can also have a "sanitizing" effect, reducing the incidence of pathogens and disease. Some of these beneficial effects are direct, others are very complex and difficult to emulate without burning. Fire, however, is also a significantly limited tool. Selectivity is difficult to manage, off-site effects of smoke may be unacceptable, opportunities to apply fire are limited to a range of ambient conditions, the risks of escaped fire may be significant, and existing fuel complexes may present unacceptable burning conditions. Consideration of these factors often leads to the selection of non-burning alternatives.

Precision chemical application

A variety of herbcides are available to target selected vegetation. Application methods can range from aerial and ground-based broadcast sprays to injection and stump treatments. While there are many concerns about the use of "chemicals" in the forest environment, there is a growing understanding that some invasive species treatments justify an aggressive approach. New precision technology for application can help address concerns about mis-application and over-treatment.

Manual backpack application can be effectively monitored using a GPS-equipped backpack sprayer. The patented Woodland Specialists (WS) SmartPack system collects spatial information about application rates and treated areas. The data serves as a work management tool to insure planned coverage and document labor resources. Field trials have demonstrated how the SmartPack data can improve chemical use. GPS technology can also be applied to ground-based mechanical application. The WS Site Prep Sprayer is a rubber-tired forest machine with direct-injection, variable-rate application, and GPS-control features. Like precision agriculture applications, this technology allows forestry herbicide treatment to be selectively targeted on a given site. Coupling spatial data with advanced control technology reduces active ingredient quantities, supports non-uniform boundary control, and minimizes drift and mis-application. Two sprayer designs have been developed-one specifically for application over planted stands and a second for pre-planting applications.

Mechanical reduction and removal

Mastication, or mulching, machines for forestry are becoming more common. There is a wide variety of equipment to cut and shred almost any type of vegetation. Windell and Bradshaw (2000) provide a comprehensive overview of this class of equipment, along with technical specifications and case studies. Recent advances in mastication machines include more robust prime movers and improved cutterheads. It is important to recognize that mastication treatment outcomes can be very different depending on the type of equipment and method of operation. Some cutters create lots of stump shatter, for example, while other cutters provide a cleaner sheared surface. The secondary effects of mastication are also important. Leaving significant amounts of shredded woody material on the soil surface affects soil moisture, temperature, and nutrient cycling. There are anecdotal reports that these micro-climate conditions may favor some invasives over native herbaceous species. Obviously re-sprouting is a concern with mastication treatments and this type of mechanical treatment will require follow-up chemical, fire or re-mulching.

Grubbing (removal of roots) has been a direct mechanical method to treat root-sprouting plants like alligator juniper (juniperus deppeana) and salt cedar (tamarix sp.). Older grubbing methods using tracked tractors resulted in significant soil disturbance and increased erosion risks. New grubbing attachments have been developed for excavators. These reduce soil disturbance and trafficking impacts. Grubbing may eliminate the need for follow-up chemical application, although fire may still be necessary to reduce the extracted vegetation.

Finally, there are new opportunities for mechanical treatment and removal of biomass. Developing bio-energy markets suggest that there may be future opportunities to treat vegetation of all types, recover the biomass and receive some product value for previously non-merchantable material. Unique equipment has been developed to collect and compact brush and slash into "composite residue logs." Currently biomass recovery is not self-supporting, but increasing energy prices and new developments in conversion processes may make this a feasible treatment in the future.


While fire is a relatively inexpensive and effective treatment to control vegetation, there are many places where it may not be used. The adverse impacts of mechanical and chemical treatments have often been cited as reasons to defer their application. New technological developments, however, are directly addressing many of these shortcomings. Precision application methods are being developed to reduce the scale of the vegetation management disturbance. Grubbing and mastication methods are being refined to better control sprouting vegetation with minimal additional treatment. Future developments will bring the opportunity to recover treated vegetation for utilization.


1. Windell, K and S. Bradshaw. 2000. Understory biomass reduction methods and equipment catalog. Tech Report 0051-2826-MTDC. Missoula, MT: USDA Forest Service, Missoula Technology Development Center. 156 p.

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