Selecting Trees

Desirable Tree Characteristics

Many tree characteristics are highly heritable, particularly growth, form, and resistance to insects and disease. Because we cannot easily distinguish genetic from environmental or phenotypic variations, we will assume that the physical characteristics of the selected trees indicate—at least partially—the seed’s genetic makeup. The selected trees shall be equal to or better than the average of the same species in the area and be healthy and vigorous. Although there will be variation among species, the desirable physical characteristics for selected trees include:

• Dominant or codominant crown position (tree crown extends above the general level of the canopy or forms the general level of the canopy) relative to the neighboring trees.
  
  
• Straight stem, free from crook, sweep, spiral grain, snow or wind breakage, or forking.
  
  
• Branch bases are small in relation to the stem and branches should project horizontally or angle slightly upward. Do not collect from wolfy trees.
  
  
• At least 30 percent live crown ratio.
  
  
• Tree crown is compact for the species, but has a large area of foliage.
  
  
• Crown is conical, indicating the tree growing and is vigorous.
  
  
• No damage from insects or disease.
  
  
• Trees are about 40 to 110 years old. Very old and very young trees have poor sound seed production even when they have many cones.

A history of past cone crops is desirable. Avoid trees that are isolated from trees of the same species by more than 100 feet. Such trees may not be pollinated adequately.

Select trees from stands in which the majority of the tress have above-average characteristics, evaluating both the desirable seed-bearing trees and their pollen parents. This rule applies regardless of the type of collection. Even with a bulk Tree Seed Zone collection, following this rule will improve the genetic value of the seed. Cones from above-average individuals scattered throughout a seed zone where the pollen parent (a tree nearby that pollinates the cone flower) is random or poor is less desirable. Be sure that you rotate collection areas, to ensure genetic diversity among seed lots.

The selected trees should have a cone crop that is expected to provide the quality and quantity of seed needed. Selected trees also must be appropriate for picking with the method you will use (suitable for climbing, accessible by cherry picker, or able to be felled safely).

Refer to your regional direction for establishing Seed Production Areas and Seed Collection Stands. Considerations are similar to those described here but may include additional considerations because Seed-Production Areas and Seed-Collection Stands may be used for more than one collection.

Distribution of Individual Trees

Trees where cones are collected must be well distributed to provide genetic diversity. A seed lot collection must include a minimum of 20 trees. Try not to have seed from a few trees dominate the seed lot. For example, do not have 5 trees comprising 80 percent of the seed lot and 15 trees comprising 20 percent of the seed lot. Doing so would skew the genetic variability of the seed lot. A good rule of thumb is that no single tree should comprise more than 10 percent of the collection.

Trees from which cones are collected should be widely separated to minimize the possibility of cross breeding and to provide more genetic variation in the seed lot. If trees are too widely spaced, they are more likely to be self-pollinated. For this reason, collecting from shelterwood stands is not desirable when trees of the same species are widely spaced. Consult your regional geneticist’s recommendations for the appropriate distance between trees for collections in your area.