Slash: What Good Is It?

Posted: September 26, 2018

What to do with that mess? Pile it? Burn it? Or, tolerate it while it rots?

In my experience, people like to have their woods neat and tidy. Following a timber sale or nearly any work in the woods, folks want to remove the slash, which is generally the tree tops and unwanted larger branches and whatnot. Even after they take away the useful firewood, there is still tree “trash” left. What to do with that mess? Pile it? Burn it? Or, tolerate it while it rots?

Slash is important and contributes to site productivity and is for several reasons best left where it lies. Without going too deeply into nutrient cycling, slash contributes essential elements useful for tree and plant growth back to the site. The log, which is often taken from the site as the product, is mostly carbon and other micronutrients. The slash comprised of smaller branches, twigs, and leaves contain many of the micronutrients such as nitrogen, magnesium, phosphorous, and potassium. If these are removed, with time they will rebuild through soil building and precipitation, but slowly.

Slash contributes immensely to organic material cycling and, in that process, release those micronutrients. Organic matter is a principle component of the upper layers of the soil profile, which is known as the O-horizon, which helps protect the underlying soil (mineral components) from erosion. Think about rain – a timber harvest will open the canopy, leaving areas where there is little to reduce the impact of rain on the forest floor. While the removal of the slash may not always expose mineral soil, it does expose the existing organic layer to increased light and heat, which accelerates decomposition.

Slash, as it is left after a timber harvest, actually creates some shade, distributed across the site, and, over time, it continues to break down, adding to the site’s organic layer. This decaying organic matter acts as a “sponge,” absorbing water and allowing it infiltrate more slowly into the underlying soil structure. Then, too, all this organic matter supports a community of fungi, macro invertebrates, and amphibians, and reduces surface water flow.

From a forest renewal perspective, slash is known to help facilitate forest regeneration. One of the major challenges to establishing regeneration is white-tailed deer. Deer are known to be opportunistic feeders. Surprisingly, the residual slash is very important for deterring browsing on desirable, preferred browse species. So, a site with lots of slash is more likely to regenerate from the “fences” created by the residual detritus. The advantage afforded by the slash is relatively short lived (5 to 10 years), which can be especially critical to having the site revegetate.

Much of the micro-organism community (e.g., insects, fungi, reptiles, amphibians, small mammals) depend on the habitat created by the slash following harvesting. If you have had the opportunity to watch a log rot over many years, you might know something about all the species that use that log as part of their life cycle. As an example, back in 1975, we felled a large tree (sugar maple of about 28 inches diameter) in a Penn State woodlot and let it lie. Now, pushing 50 years later, that log has almost completely returned to the soil. Over the years, we saw fungi, small mammals, and insects using the log. Just last year, a black bear broke up the log to get at the grubs and whatnot it housed.

Various research literature documents the importance of slash as wildlife habitat. Studies suggest that at a minimum a woodlot should have 3 to 5 cords per acre of woody material on the forest floor. That would translate into 270 to 450 cubic feet of tree parts. A timber harvest might well leave more than that amount of slash; however, the more the better, as much of it is relatively short lived.

There might be some risks associated with leaving slash scattered about in a woodlot. It could become fuel and increase the risk of fire. Fortunately, in Pennsylvania and across most of the Northeast, our relatively even rainfall across the year keeps the moisture content of fine twigs and slash high enough that they do not easily support fire. Although, conifer slash and dried leaves, especially on south and west facing slopes, can dry and burn under the right (or wrong) conditions.

For the most part, having a messy woodlot with dead trees and tree parts scattered across the forest floor might not be as attractive as one swept clean; however, a watchful eye will find it more interesting.

For more information, check out the Penn State Extension publication, titled “Dead Wood for Wildlife.” 

Contact Information

James Finley, Ph.D.
  • Professor Emeritus of Forest Resources
Phone: 814-863-0402