There are several facets of construction site tree protection that need to be covered. Most of the basics are pretty straight forward. Since all construction sites are different, the tricky part is understanding the impact to trees on your particular site. Some of the things you can do yourself, and some of the techniques will require you to hire a professional tree guy.
The most important part of construction site tree protection is fencing off root zone areas so construction workers don’t have access. The ideal situation would be to fence off the entire area within the tree’s drip line (the extremities of the branches reach). The tree roots definitely go out further. But, this would protect enough root zone to yield minimal damage to tree roots. In many cases, protecting this much tree root zone on a construction site is not possible, so fence off as much area as possible.
For areas that are likely to receive high traffic apply a 3-6” layer of mulch to reduce soil compaction. The thickness of the mulch will vary with the type of traffic. For foot traffic, a 3-4” layer will suffice. If heavy equipment will be driving across the root system, a thicker layer will be appropriate. If there is to be regular equipment activity, put plywood across the mulch to further distribute weight and reduce soil compaction.
Understanding that trees are going to suffer root damage during the construction process, it is important to engage a regimented fertilizer / treatment program to help the tree repair injuries. Ideally, this would start before construction begins, but it’s better late than never.
In addition to root injury, trees will typically require some pruning to allow room for the new structure and for traffic underneath. Over-pruning might be required to meet the goals of the construction project. All the more reason to fertilize the trees regularly.
The last construction site tree preservation technique I want to discuss is soil restructuring. The idea here is to till the areas of the construction site that received high traffic to un-compact the soil. Using and airspade to blow out the soil with air allow the earth to be tilled without destroying tree roots. Mixing in some finely ground mulch or other organic matter will further improve root growing conditions.