LIVING WITH OAKS

By Forrest Lockhart

UC Cooperative Extension, El Dorado County Master Gardener

The rural Sierra foothills lifestyle is changing rapidly, due to residential development and a shift in agricultural production. In many cases, this has resulted in destruction of thousands of our ancient heritage oaks. While future development and woodland destruction seems inevitable, there are things that you can do to protect the oaks living on your property. First you must understand a little about the tree itself.

Mature oaks thrive in a climate of cold, wet winters and hot dry summers. While they seem indestructible, they are sensitive to a balance of air, moisture, soil, temperature and nutrient levels at the root zones. Anything that changes these conditions may stress the tree and lead to early death.

Some of the major threats are:

· Changes in soil grade under the tree, either by mounding soil or excavating it, will adversely impact oaks either by limiting the air supply to the roots or destroying them. Mounded soil can also encourage fatal root rot.

· Changes in drainage around the tree, which may result in excess water to the roots during our hot summers, when the roots must be dry. Water applied during the summer months reduces air supply and encourages growth of frequently fatal soil-borne diseases that thrive in warm, damp conditions.

· Soil compaction under the tree that can be caused by auto traffic, the operation of heavy equipment, and even heavy foot traffic. In these circumstances, the spaces between soil particles become compressed and the tree may suffocate, resulting in eventual decline.

· Paving with a non-porous material such as asphalt or concrete under the oaks reduces air exchange, nutrients and rainwater to the roots. Better solutions are mulch, gravel, or bark. Regardless of what ground cover is used, do not disturb the soil within a minimum six-foot radius of the tree trunk, or if possible, out to the drip line.

· Planting grass or plants that require summer water near the trunk will increase the risk of fatal bacterial and fungal diseases. Preferably, mulch the area or install drought-resistant plants under your oak and make sure that sprinklers do not wet the base of the trunk. The local nursery or Master Gardener office can provide recommendations on attractive native plants that thrive beneath the oaks.

· Trenching within the drip zone is a major cause of early oak death. In general, over 70% of vital feeder roots are found within 30 inches of the soil surface. Utility trenches may sever major portions of the root system, resulting in stress and possibly early death. If trenching is required, route the trench as far from the trunk as possible and plan to have all utilities placed in the same trench. Better yet, arrange to have a conduit bored through the soil in lieu of trenching. This will minimize root damage.

While these are not the only things that threaten oaks, failure to address these issues may eventually result in premature tree death. So take a look at your property. Talk to a Master Gardener or a Certified Arborist to determine how well you are treating your oaks, then take any necessary steps to protect your investment. If we all treat our valuable oak trees with the respect they deserve, we will be preserving a piece of our Sierra foothills for the future. Our California oaks are magnificent and worth the effort.