Even before commercially thinning ~80 acres of the woods on our farm, I had come to appreciate the challenges of controlling the vegetative response to letting in more sunlight.
In open pastures, the grazier can readily mow, spray or even till and re-seed to deal with noxious weeds and invasive brush. But livestock impact is often the only practical tool for managing vegetation in tree-covered silvopastures. Consequently, silvopasturing relies on intensive rotation of higher livestock densities. When done correctly, the stock put enough pressure on plants in the silvopasture understory to avoid a blow-up of brush, brambles and other problematic plants. Animal impact is a combination of: duration; interval and frequency – as well as: density, stocking rate and stocking capacity. All are within the grazier’s control to be manipulated to achieve the necessary impact. Impact is also influenced by: vegetation quality and quantity; soil conditions; diet (e.g. animal craves woody plant fiber due to low fiber ration); accessibility (think of inside a brushy area vs. outside) and season (ground conditions, forage maturity, etc.).
After two and a half seasons now of trying to increase summer grazing densities to sufficient levels to beat back the bad brush that wants to "fill the void" we've created through harvesting trees and removing much of the undesirable understory plants in the early summer of 2015, I now have a better understanding of a few important considerations:
- If the bad plants are already present (even if in seedling or seed form), they quickly respond to the increased sunlight and become big, bad plants. Be prepared! It's usually most cost-effective to control the undesired understory vegetation in conjunction with a commercial harvest, but this has to be weighed against "dealing with a little problem before it becomes a big one". Chemical controls work especially well on little plants (and not so well on bigger ones where it's hard to get good foliar coverage or enough active ingredient in to the plant's system to kill a larger, more vigorous plant).
- It's tough enough to achieve really high livestock densities in open pastures, but even tougher in silvopastures with lots of trees, stumps, branches and other obstacles in the way. We've tried to increase densities to ~300,000 lbs/acre during the mid-summer rotation in silvopasture areas, but this is equivalent of putting 100 cow-calf pairs (weighing an average of 1,500 lbs each) on a half-acre at a time. Between the trees, the calves (which readily duck under the polytwine and make for an upset momma cow on the other side), and scares forage in these young silvopasture areas, it's just not possible to get much more than half of that density (~150,000 lbs/acre, or the whole herd on an acre at a time). But even at 300,000 lbs or more of density, I'm not convinced that it would be enough to control the really noxious stuff. In our case, this is primarily: privet, multiflora rose, and barberry - but you name it, we grow it. And it's all tough to kill just from trampling and defoliating.
- Consequently, we've shifted our focus to using our winter bale-grazing period to achieve high densities and impact. Last winter (2016-2017) was too mild and wet most of the time to get the bales in to the silvopasture areas nor graze them. But the cold came early this year, so we've spent the past six weeks feeding most of our hay in brushy spots. 20 hungry cows standing in a 15' radius around a round bale is the equivalent of ~1.5 million lbs of density/acre! Plus, unlike the grazing season, they pretty much stand in the same spot for hours, eating and trampling. And when they're done, there's a nice patch of fertility left behind the jump start new forage growth on the spot that will help to outcompete the invasive woodies. This probably will need to be repeated several times every other year or so until the bad plants fully succumb. We've been throwing bales in to brush patches for at least five years now, but this is the first year that we're able to start hitting the same spots twice - so it remains to be seen just how much it takes to get the job done. But even after a single bale is fed, there's a noticeable improvement by the following summer.