Cone Crop History and Frequency

Local climatic effects, elevation, and stand and tree condition all influence the frequency of cone crops. The best information on seed crop frequency is a locally maintained historic record of cone crops by species. The Silvics of North America includes estimates of intervals between collectable crops. Although some trees will produce cones during most years, the number of cones must be sufficient to make the collection worthwhile. Good to bumper crops may occur on average just 1 in every 3 years. In some cases, the interval between good crops may be as long as 10 to 15 years.

The seed crop history for a specific site also can be reconstructed by examining and aging old cones in the litter and duff, aging cone scars on the tree, and by examining growth rings in the tree (narrow rings may indicate good cone crops). Refer to Region 6 Tree Improvement Paper Number 9 for procedures.

Factors Affecting Cone and Seed Production

Although plants produce an abundance of flowers, seed, and fruit, most of the seeds are destroyed by environmental conditions (mostly weather), predation, and insects. Monitoring cone and seed development is the only sure way to determine whether there is a crop that is worth collecting.

Flower formation starts when vegetative meristem tissue changes its pattern of division to produce floral tissue, also referred to as bud differentiation. A variety of controls, both internal and external, affect this change. Some of the internal biochemical controls can be affected by soil fertility, temperatures, light intensity, and hormone levels. External controls are primarily environmental effects.

For seeds to develop, pollen production and dispersal must be synchronized to allow fertilization. The pollen crop may be susceptible to many of the same controls as the cone crop.

Environmental controls are primarily related to weather and predation. A number of environmental conditions should be observed while predicting a cone crop:

• Freezing temperatures in the spring kill flowers and young fruit, but the whole crop may not be lost. The amount of sound seed may be reduced because of the fluctuations in local temperatures and the variability in seed development at the time of the frost.
  
  
• Extremely high temperatures can kill flowers and fruits, delay fruit development, or cause seed to abort.
  
  
• Continuous precipitation during flower development and pollen dispersal can reduce pollination and seed development.
  
  
• Extended periods of drought can cause seed to abort.
  
  
• Inadequate moisture may cause fruit to drop before seeds are mature.
  
  
• Strong winds or hail can destroy a crop or reduce the available crop in some areas