Mixed plantations of native and exotic species in the Brazilian Amazon

To compare the growth of monocultures with plantations of mixed species in the Amazon region of Brazil, Batmanian (1990) established replicated plots of Eucalyptus torelliana, Acacia mangium, and a mixture of six native species. For the first few years, the eucalyptus and acacia grew much faster than the native species. This may have been because the seeds were from parents selected to respond well to plantation conditions - direct sunlight and fertilization. Only one native species, Schizolobium amazonicum, an early succes-sional legume, grew well during the first few years. After about 4 years, however, the acacia stands were infected with a parasite from the misletoe family that severely damaged or killed all the trees within 1 year. The eucalyptus stands stagnated because they were not thinned. In contrast, as the stands of mixed native species began to get larger, their rate of growth increased. The increase was due partly to decreased competition from herbaceous weeds and grasses, and partly to an increasingly efficient use of light and nu trients. A similar result was found in a comparison of pine and native species in Puerto Rico (Jordan and Farnworth 1982). Initially the growth of pine was greater, but, eventually, the native species were more productive.

As seen from these examples, mixed plantations can have many productive and environmental advantages over conventional monocultures. However, their main disadvantage lies in their more complicated design and management. Thus mixed plantations are often restricted to relatively small areas or to situations where diversifying production is a great advantage, such as for small farmers of limited resources (Box 6.5).

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