The vegetative reproduction of genetically improved reforestation material in the form of cuttings or via tissue culture, instead of seed, creates new possibilities for increasing genetic gain. If any single genotype can be reproduced vegetatively in almost unlimited numbers, then the gain obtained through breeding is naturally much greater than that achievable through sexual reproduction. However, there are still many problems in applying vegetative reproduction and clone forestry in practice. The problems associated with the aging of the stock material are the greatest. Another important factor which has a wide-reaching effect on the implementation of clone forestry is how broad should the genetic variation be, i.e. the number of clones. Because the production of reforestation material by vegetative means is more expensive than that through seed, the breeding gain attainable must be significantly greater, and in fact must be verified, before it is worth while changing over to vegetative reproduction.