Time is a major constraint in the progress of tree improvement programs. Four ways in which time influences the tree improvement process are (i) evolutionary time, (ii) time to harvest, (iii) time to achieve phenotypic stability, and (iv) time to reach reproductive maturity. The ways in which each of these affect the three phases of a tree improvement program (conservation, selectin and breeding, and propagation) are identified and discussed. How biotechnological techniques, as well as other enabling technologies, address the time constraint problems is also discussed. The biotechnological approaches include tissue culture, molecular genetics, and genetic engineering; the enabling technologies include early testing and flower induction. Through tissue culture it is possible to increase genetic gain per unit time and increase total genetic gain by using more of the total genetic variation. Development of high-resolution linkage maps, through application of molecular genetics technology, will provide new approaches to early screening, testing, and selection. Additionally, molecular probes will be useful in improving methods that genetically fingerprint germ plasm. Genetic engineering has considerable potential to reduce time constraints. However, because of the diverse breeding and production populations typically employed, much basic work needs to be done to integrate genetically engineered materials into tree improvement programs. Early selection and flower induction address the time constraints imposed by age-stable performance and reproductive maturity. When used in combination with the previously described biotechnologies, a powerful system is created that can dramatically reduce the time required to integrate genetically improved material into forest regeneration programs. An example of integrating tree improvement, clonal forestry, and biotechnology is described for an existing black spruce regeneration program.
