As an arborist, I have been caring for trees in the Napa Valley for over 15 years. Because of my background, I look at trees as both an environmental resource, and an aesthetic resource. And I see a lot of trees in Napa Valley that have been preserved by vineyard owners and managers for the same reason - aesthetics. Much of Napa Valley's beauty is due to the trees that co-exist with the vineyards.
Site Planning
But as vineyard development continues up the hillsides, there have developed greater concerns about land clearing. Many of these concerns are justified, and the vineyardist must be sensitive to best management practices.
When considering a vineyard development, it is important that the tree resources be analyzed along with the rest of the resources. Wildlife depend on woodland areas food and shelter. They also use these areas to travel through areas. Try to identify the main corridors used by deer and other animals, and leave these corridors intact, or leave adjacent areas available for wildlife to travel through your property.
Also look for areas with fairly young, or small trees and try to preserve as many as possible. Young trees are more vigorous than older trees, and will be able to respond to injuries better than the older monarchs. They are easier to work around, and provide for the next generation of trees.
Once you have an idea of where to locate your vineyard, you need to take a closer look at the trees, and decide which ones should be preserved, and which are best removed due to concerned other than environmental. These concerns include:
- Potential hazards to those who work in the vineyards
- Disease and Insect Relationships
- Keeping trees healthy while farming
A Healthy Tree may be a Hazard!
While a tree may look and be healthy, with a full vigorous foliar crown, it may have significant defects that can cause the tree to become hazardous. Look for defects such as:
Decay - open cavities or large wounds. Not all decay is serious enough to warrant removing the tree. A tree can lose up to 70% of its interior wood and still have adequate wood strength to hold itself up. If you have a tree you want to preserve that has decay in it, have it looked at by a competent arborist, who can help you make the final decision about its care.
Cracks - Look for cracks in the bark of trees, these may indicate the tree is ready to fail. Cracks along the bottom of large heavy limbs may be associated with fluxing - sap oozing from the bark. Valley oaks commonly have such crack in their large horizontal limbs. Again, have an arborist look at the tree before you decide to keep it standing in the middle of your vineyard.
Old branch breakage - Trees that have a history of branch breakage are likely to continue breaking limbs. So if you have a large old tree with several old branch stubs, it should be analyzed for hazard.
Leaning trees - While not all leaning trees are hazardous, they tend to be more likely to break or fall over than upright trees.
Not Impacting Trees
Are you creating hazards?
Lack of good maintenance, or improper maintenance can create hazards, so having a maintenance plan for those trees you do preserve is very important. The basic element of a maintenance plan is to have the needed work analyzed and scheduled on a priority basis.
The types of things that can create hazards include:
Poor pruning cuts - Cuts should be made just outside the branch bark ridge and collar, so as to remove the branch and not cut into the trunk. Cutting too close can allow decay to enter the trunk. Leaving too much of a stub can allow decay organisms to become established in the limb.
Heavy limbs - Some vigorous limbs can actually become so heavy they cannot hold themselves up and subsequently break. Look for branches that are bending with the weight of foliage - these should be thinned near the end to reduce weight. Do not cut off the end, this will cause the branch to sprout back new foliage, and can become heavier than the original branch.
Removing too much inner foliage on limbs can displace weight to the end of the limb, actually making it more susceptible to breakage.
Elevating foliage too far up the trunk also displaces weight, and often leads to sprouting along the trunk, due to excessive foliage removal. Don't remove more than 25% of the foliage I any one season.
Either have a tree service do the pruning for you, or please take the time to train your workers if they are to do the pruning. Every cut stays with the tree for the rest of its life, so training workers can be very important to the longevity of the trees on your property.
Farming Practices
Farming practices can injure roots, and ultimately lead to either decline or instability of the tree.
A typical root system of an oak can be likened to a wine glass sitting on a dinner plate! The goblet portion of the glass would then be the foliar crown of the tree; the stem, its trunk; and the plate the root system. Characteristics of a typical root system include:
- The roots extend out 2 to 3 times the radius of the canopy - far beyond the "dripline".
- Most absorbing roots are in the upper foot of soil.
- Anchoring roots are generally found in the upper 3 feet of soil.
- Anchoring roots taper quickly as you get farther from the trunk.
Injuries to roots can therefore be caused by trenching, ripping, and disking. Soil compaction can also reduce the amount of oxygen available to tree roots. Excessive irrigation can favor disease organisms, while reducing the vigor of roots.
When working around trees:
- Stay out as far as possible from the tree, but at least a few feet outside the dripline.
- Where possible, work radially to the tree's trunk.
- Don't keep soils saturated, let the soil dry between irrigations, and move drip emitters away from the root collars of grape vines. Oak root fungus can become a problem in vineyards with dead trees near the edge, so keep trees healthy and vigorous through appropriate management practices.
- Herbicides can damage injured roots, so apply herbicides prior to disking. Herbicides, especially round up, can translocate to other trees of the same species through root grafts. So do not paint the stump of a tree to stop re-sprouting if another tree of the same species that you want to preserve is near by.
Tree Management
Have a plan:
- Identify hazards, prioritize work, and stick to the plan
- Remove dead limbs, thin heavy limbs
- Don't over-prune
- Keep trees healthy, so you don't have to remove them
Denice F. Britton
Britton Tree Services, Inc.
St.Helena, CA
phone (707) 963-7578