The main fast-growing, short-rotation species used in plantations are in the genera Eucalyptus and Acacia, and, to a lesser extent, Gmelina. Pines and other coniferous species are the main medium-rotation utility species, primarily in the temperate and boreal zones. All these species are generally exotics in the locations where they are planted. Use of native species is minimal. Exotic tree species predominate in both industrial and rural development plantations worldwide (Evans 1999). In some regions of the humid tropics, plantations using in-
digenous species are restricted for the most part to small and medium-sized farms practicing reforestation of degraded land in portions of their properties (Piotto et al. 2003 a; Fig. 6.3).
Native trees can be more appropriate than exotics because (1) they are better adapted to local environmental conditions, (2) seeds and other propagules are locally available, and (3) farmers are familiar with them and their uses. Besides, the use of indigenous trees in productive systems helps preserve genetic diversity and serves as habitat for the local fauna. Disadvantages of the use of native species can be (1) uncertainty of growth rates and adaptability to soil conditions other than those where naturally found; (2) general lack of guidelines for management; (3) large variability in performance and lack of genetic improvement for most species; (4) seeds of native tree species are not as often commercially available and have to be collected; (5) high incidence of pests and diseases (e.g., the attack of Hypsipyla grandella on species of mahoganies and cedars, as mentioned earlier); and (6) lack of established markets for many species.
As a consequence of the disadvantages of native species, exotic trees are often and more generally preferred for reforestation because (1) there is generally more silvicultural information; (2) often it is possible to obtain seed of known genetic makeup and certified origin, and (3) there are generally well-established markets for plantation products. In several known cases the exotic species, not having local enemies, initially grow free from pests. However, in some cases a local pest finds the species and causes serious problems, as has been the case with the yellowing of china berry trees (Melia azederach) and stem cankers in Australian cedar (Toona australis), both in northeast Argentina and Paraguay; and stem rottening of Acacia mangium in Costa Rica (Montagnini, pers. observ.).
One of the strongest arguments for the use of native tree species in plantations is the high value of the wood and its increasing scarcity in commercial forests. Many native tree species of valuable timber grow well in open plantations, with rates of growth comparable or superior to those of exotic species in the same sites. Such is the case of Vochysia guatemalensis in Costa Rica, whose growth rate and value are similar to those of Gmelina arborea, and of Terminalia amazonia in Costa Rica and Panama, with growth rates and value similar to those of teak (Piotto et al. 2003 a; Fig. 6.4).
Native species are often preferred for land restoration purposes, especially when the environmental services of plantations take precedence over their
Was this article helpful?