Pham Duc Chien
Forest Science Institute of Vietnam
Eucalyptus (Eucalyptus spp) and Acacia (Acacia spp) are popular species for forest plantations in Vietnam to provide timber, firewood, materials for paper industry, manmade boards, and for construction. In order to combine the fast growing characteristics and large biomass of Eucalyptus with the capacity of Acacia to improve soil fertility and the environment, the study of rotation methodology between Acacia and Eucalyptus is necessary.
Forest plantations of Eucalyptus camandulensis, Eucalyptus urophylla, Acacia hybrid, Acacia mangium, and Acacia auriculiformic planted on soil that had been planted with one cycle of Eucalyptus or Acacia in three ecological regions (Dai Lai – Vinh Phuc, Phu Ninh – Phu Tho, and Bau Bang – Dong Nai) were studied. Data on growth, survival and quality of trees on temperate plots (20 x 25 m) with three replacements were collected and analyzed. The fall of branches and leaves and the speed of decomposition of those under the forest models were collected from two types of small plots (1 x 2 m). One type of plot collected branches and leaves and the other measures the speed of decomposition of branches and leaves. These data were collected monthly and analyzed. Dynamics of soil fertility and the humidity under the forest types were studied following common methods.
Eucalyptus camandulensis, Eucalyptus urophylla and Acacia hybrid planted on soil that had previously been planted with a cycle of Acacia grow faster (an increase of 10-25%) than those planted on soil previously occupied by a cycle of Eucalyptus. Acacia hybrid planted on bare hills also grows faster than when planted on soil previously occupied by a cycle of Eucalyptus. Acacia forests (particularly Acacia mangium and Acacia hybrid) annually return to land a great amount of branches and leaves, and this amount is from 1.3 to 2 times higher than that from Eucalyptus (PN2, U6, and E. camaldulensis). The speed of decomposition of branches and leaves under the acacia plantations is faster than that under the Eucalyptus plantations. The soil fertility under acacia forest is higher than that under the Eucalyptus forests. Soil porosity and humus content under Acacia forests increase overtime, but under Eucalyptus forest tend to decrease. Content of N, P, and K increases in soil under Acacia forest, increases slightly or decreases in soil under Eucalyptus forest, and dramatically decreases on bare land. Soil moisture increases under Acacia forest, and does not increase or decreases under the Eucalyptus soils or under bare land.
From the above results, we recommend that if a stand of Eucalyptus stops growing or decreases in growth, the land should be replanted by one or two cycles of Acacia allowing the soil fertility to improve before continuing with other Eucalyptus plantations.
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- Results from establishment of pilot plantation using approved planting varieties of Eucalyptus and Acacia
