Dirt around live oak trees harmful?

[kingbee]

I have a lot on the river,and I am in the process of filling,and grading some areas so that the lot will be more level,and useable as a homesite,butI have four large live oak trees that will end up having anywhere from 3-4ft of dirt up on the trunk of the trees when done.I`ve been told that this could kill the trees from suffocating the roots.Is this true?If so could anybody give me some idea how I might level the lot,and preserve the trees?Possibly build a barrier around the root system before filling,or something like that...Thanks!KINGBEE...

 

[JesseJones]

Fill can suffocate roots of oaks.

Yes, burying live oak trees and their roots under fill during lot leveling can definitely harm or kill the trees. 4 feet is a lot of fill. Placing it against the trunk can put the trunk at risk of tissue death and infection.

As trees grow, they develop root systems in the soil. Many of these roots are in the upper foot of the soil because this is where water enters the soil, where nutrient availability is highest, and, importantly, where oxygen availability is highest. Roots breathe oxygen, and oxygen diffuses slowly through the soil, often travelling through voids in the soil created by burrowing organisms or left after decay of roots.

To bring heavy equipment into this root zone is to compact and destroy these air voids. To put fill onto this is to bury them. It may be the buildup of toxic gases, rather than the lack of oxygen, which then kills the roots. Significant root mortality is likely, possibly resulting in visible reduction in vigor and perhaps death. Larger, older trees are in an especially delicate balance with their environment, and are especially susceptible to decline and death due to environmental change.

To understand a tree, picture yourself standing waist deep in water. Only your upper half is visible. Now imagine a shark eating your invisible half. Your visible half looks great. How do you feel? How long will you remain standing? Trees can stand for centuries, but only if they have feet to stand on.

The root zone of a tree radiates out from the tree, often well beyond the extent of the overhead canopy of the tree. Without seeing your trees, I cannot tell you how large of an area you need to protect from this grading you intend to perform. I suggest you hire a competent arborist.

If your arborist recommends putting ventilated pipes on the ground and putting that 4 feet of fill on top of it in the root zone of the trees, you might consider hiring a different arborist. Such a system is no substitute for the air/soil interface, and soil void network your trees have grown in to date.

 

[treeclimber165]

You can look on this site to find all the consulting arborists in your area. http://www.asca-consultants.org/ I agree with everything Jesse said. I like the 'standing in water' analogy.

 

[Treeman14]

JesseJones,
I agree with all of your points except the final statement regarding ventilation pipes. I have installed several such systems with very satisfactory results. The first was a commercial property on which five feet of fill was used around two large live oaks. We installed a network of ventilated pipes covered by a 6 inch layer of gravel placed directly on the original grade. We also built a large well (20' x 20') around the tree before the fill was added. There is a building on one side of the trees and a pervious paved parking lot on the other three sides. These trees are still thriving sixteen years later.

Kingbee,

You've got a difficult situation which will require a lot of consulting and planning BEFORE you do any work. Before adding that much fill, I would look into other building options, such as a stilt house.