Whether you're building on a new site or adding on to or renovating your existing home, you undoubtedly recognize the value of the existing trees on your property and want to keep them healthy and growing strong. But it's not always easy to do with the necessity of construction equipment crisscrossing the site. And it's not just a question of keeping the trees safe from the obvious dangers of contact with trucks and bulldozers. A tree's root system, which can extend out from the base of the tree for quite a distance, is vulnerable to damage from the soil compaction that results from heavy equipment moving across the site.
Recently Alabama Cooperative Extension System forestry agents Jack Rowe and Beau Brodbeck, working with Dr. Francisco Arriaga of the USDA's National Soil Dynamics Lab, carried out a study to assess not only how construction-related soil compaction affects trees, but to come up with inexpensive ways of lessening or preventing this problem and the damage to tree roots it causes. Advance planning is critical because, notes Rowe, it doesn't take a lot of passes of heavy equipment to create problems -- even three passes can cause enough compaction to have a large negative impact on a tree.
Fencing off the critical root zone -- the area around the tree where roots are most vulnerable to damage from soil compaction -- is key. But where constraints exist that make such fencing off impossible, the foresters discovered some simple ways to lessen the impact of heavy machinery. They found, for example, that simply spreading mulch 8 inches deep and covering it with 3/4 inch plywood distributed the weight of the equipment driving over enough to greatly reduce the amount of soil compaction below.
To read more about their project, go to Community Foresters Gaining a Clearer Picture of Building Construction Effects on Trees. The findings from their research, along with lots of helpful information on protection techniques, are detailed in the Alabama Cooperative Extension publication A Guide to Preventing Soil Compaction During Construction, available as a free downloadable PDF at ACES.