If you have fencing on your property, you will need to keep branches, trees and weeds from growing up on fence lines. Why worry about cleaning out brush and weeds from fence lines? Along an electric fence, weeds and brush can short out the fence and allow the livestock to walk through. Removing brush and weeds also helps prolong the life of the fencing and reduces breakage. As trees grow through the fence, the wire can be stretched or may break when limbs fall. In addition to gaps in the fence that allow livestock to roam, loose wire can pose a physical hazard for livestock and equipment. Clean fence lines can help prevent vehicle or equipment accidents by removing blind spots. Removing brush also reduces the fuel load along the fence line, thus limiting the amount of heat damage to the wire and posts during a fire. Cleaned out fence lines also serve as fireguards as wildfires move through. Your volunteer fire department will appreciate being able to easily drive around a property when putting out wildfires.
The challenge is to determine the best method for removing brush in your fence line. Options include mechanical, chemical and cultural practices, or a combination of these.
Two of the most common mechanical methods of controlling brush in the fence line are a chainsaw and bulldozer. Chainsaws are good for selectively removing large trees and saplings without damage to the fence. One of the drawbacks of the chainsaw is that most tree and brush species will resprout from cut stumps. One trick to reduce the chances of resprouting is to use glyphosate (the active ingredient in RoundUp™) or a mixture of triclopyr (the active ingredient in Remedy™) and diesel or mineral oil to "paint" the stumps immediately after you cut them. Depending on the amount of brush and trees, a bulldozer may be your best (and possibly your least expensive) option. Bulldozers or front-end loaders are usually used when you have decided to remove the section of fence and start over. One of the downsides of using large machinery is the amount of soil that is disturbed. You can unintentionally increase the chances of erosion on your property.
There are many chemical options available for brush and tree control. Glyphosate is a nonselective herbicide that may be used to kill a wide variety of weed and brush species during the growing season, but it has no soil residual and will require repeated applications. Glyphosate can be used to kill out weeds in the spring and summer, making it easier to return later to remove the trees and brush. Triclopyr mixed with mineral oil or diesel can also be used as basal bark treatment to selectively kill trees and brush. Apply this in a band around the base of the tree (up to a 6-inch trunk diameter). The downside of this option is that you will still need to remove the tree before it falls down on your fence. As with all chemicals, read and follow label directions.
There are fewer cultural practices for removing brush from fence lines. One that is often mentioned is the use of goats. This is usually not a good option as I have yet to see a truly "goat-proof" fence. Even with a sturdy enclosure, brush along the fence line will allow goats to climb and get over the fence. Prescribed fire is another option, but it can be very hard on wire, particularly galvanized wire, and it cannot be used with wooden fence posts.
Your fences didn't get overgrown in a day, and you definitely won't get them cleaned out in a day. Break the job into manageable sections and work on it a bit at a time.