| Forestry training manual Inter-America Region |
|Session XLVIII Forestry issues|
This issue concerns whether exotic species of trees should be planted in place of indigenous species. Foresters and people around the world are confronted with this question. The decisions made should be based on all available information because they carry long range consequences.
In many countries throughout the world, exotic species are favored over the indigenous species. In some countries, it is an issue over which environmentalists fight as they see the indigenous forests disappearing in favor of exotic species that are more commercially attractive (e.g. Pinus radiate in Australia). Initially, exotic species were transported around the world with the expansion and migration of human populations. Many species were unsuited to their new environments and failed to grow. Others expressed a different phenotype within their new environment. An interesting example of this is Pinus radiate - a species indigenous to Monterey, California. In its indigenous environment, it is a tree of poor form and quality and is considered a non-commercial species. Outside of its indigenous environment, it grows straight and fast in countries such as Australia, New Zealand, and South Africa, and in some countries in Latin America. In these countries, Pinus radiate is an important commercial species. Eucalyptus is another interesting example of the use of exotic trees. Eucalyptus is a genus of trees indigenous to Australia and contains over 500 different species. However, within a relatively short period of time, species of the genus have been planted in countries around the world. At the present, there are more Eucalyptus trees growing outside of Australia than within.
Exotic species are favored over indigenous species for a variety of reasons. Economics is probably the main one. Some exotic species simply grow faster and attain commercial value sooner than the local indigenous species. They may be of superior quality for certain products that the indigenous species are not adapted for ( i. e., pulp and paper ) . In some cases, exotic species are better suited to the site than the indigenous species. This can occur in areas where the indigenous trees have been cleared years ago through poor agricultural practices and over-grazing of the soil has altered it to the point that it will no longer support the indigenous species. Exotic species can be used in these areas for erosion control and for soil rehabilitation. An example of this is the use of ecualyptus for the control of desertification in some African countries. The scarcity of fuelwood is a major problem in some parts of the world, and it is getting worse each year with expanding populations. The slow growing indigenous species cannot keep up with the demand for fuelwood. The immediate answer may lie in the establishment of woodlots with fast growing exotic species. Also the establishment of exotic fruit and nut trees could improve the diets of the local people and can open up new markets for a cash crop. On an every-day level, throughout the world, exotic trees are used extensively as horticultural species. Many have a high aesthetic value and are found as shade trees around homes and within cities and parks.
On the negative side, when indigenous forests are cut and replaced with exotic species, the resulting forest is basically a desert with respect to the indigenous flora and fauna. The natural ecology of the area is drasticallly modified. Not only are the indigenous flora and fauna eliminated but the basic chemical composition of the soil is changed. Another point to consider is that most exotics are planted as monocultures and could fall prey to disease or insect attack.
The decision of whether to plant exotic species vs. indigenous species must be based on the specific site and the existing conditions. The pros and cons must be weighed. What are your objectives and what will the long range effects be?
In Summary - There is no easy answer when it comes to deciding whether to use exotic over indigenous species. The decision made must be based on each specific site. What are your objectives and what will the long range consequences be? The trade-offs associated with your decisions must be carefully weighed.