The Clonal Forestry Option

The industrial forestry sector has become aware of the risks involved, and there has been an encouraging change to more ecological thinking in the management of plantations. Where tree clones are used, their advantages are now weighted against increasing risks. There are several ways to avoid genetic narrowing in clonal forestry, the first being the use of clonal mixtures. But when planning to use cloned transgenic trees, one runs into problems. The transfer of a special gene to a certain location in the genome is still uncontrollable and therefore, if the same gene is to be transferred to several different genotypes, it ends up in different places in the genome, it functions differently, and it may influence adjacent genes differently. In annual crops this is not a particular problem, because the transgene can be backcrossed several times to different genotypes and thus the location is fixed and the gene duly integrated. Such backcrossing is prohibitive in trees simply due to their long generation interval but also due to their almost obligate cross-pollination with severe inbreeding depression. One is therefore forced to whole tree cloning when the desirable gene has been transferred.

Ultimately, one ends up having a single desirable transgenic clone that should go into plantation. There are, however, solutions to how such single clones could be used. First, they could be mixed in plantations with other nontransgenic clones according to regulations set for clonal forestry. The most valuable transgenic tree clone could thus be marked in the stand and left standing through stand thinnings until the harvesting of the most valuable end product at final stand rotation. Or a valuable transgenic clone could simply be planted among normal sexual tree seedlings, which would keep genetic variation at an acceptable "natural" level.

Whatever method is used in productive industrial forestry plantations, if the yield of the cloned trees is much superior to that of their wild relatives, there may be a possibility to grow industrial forests on a "plantation basis," leaving a larger share of natural forests as gene reservoirs. It is a fact that we are just now experiencing how forest trees are converted to cultivated plants. Simultaneously, the world is experiencing clear signs of global climatic change that may upset the adaptation of long-lived trees. Clonal forest stands have lost their ability to respond genetically to such change. Natural forests with high degrees of genetic variability have the capacity to respond dynamically to environmental change by genetic selection during natural regeneration. This is why natural forests must be managed and regenerated for a changing future environment.

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