THE TOTAL AREA of forest and forest land under management is about 20 million ha (General Statistical Office 1991) which occupies about 60% of the country's area. At the end of 1993, natural forest was estimated at 8630000 ha, forest plantation at 758 000 ha, and land without forest at 11 420000 ha. In the action plan for forest rehabilitation and reforestation, a total of 5 million ha is to be reforested by the year 2000. It is estimated that 1.5-1.6 million ha of plantation has to be established.Twenty species were selected as the main species for planting (Forest Science and Technology Department 1994) from a list of more than 50 tree species (including native and exotic species). Climatic conditions strongly affect the productivity of forests and plantations, so determining the climatic requirements of planting species is important work.Using Dr T.H. Booth's work on determining climatic requirements for many tree species (Booth 1991; Booth and Pryor 1991; Booth and Jovanovic 1994) as well as information on natural distribution and experience gained from many years of tree planting in Vietnam, this paper will present preliminary results of climatic requirements for 18 main planting species in Vietnam. These include nine native and nine exotic species. Climatic Requirements of Selected SpeciesThe following are the most important climatic requirements to be determined (Booth and Jovanovic 1994).
- Mean annual rainfall (mm)
- Rainfall regime
- Dry-season length (consecutive months, 40 mm precipitation)
- Mean maximum temperature of hottest month CC)
- Mean minimum temperature of coldest month (OC)
- Mean annual temperature (°C)
Acacia auriculiformis
A. auriculiformis A. Cunn ex Benth. is a nitrogenfixing fast-growing tree species in tropical lowland areas. It can grow in a variety of soils including very poor soil, clay, salt-affected and seasonally waterlogged soils. On favourable sites, the trees can reach a height of 25-30 m with a long bole, however, they are mostly 8-20 m high, multi-stemmed and crooked. The species is found from latitude 50S to I7°S, but mainly from latitude 80S to 16°S, with a maximum temperature of 32-34°C, and a minimum temperature of 17-22°c. In Vietnam, it is planted widely, even in the northern provinces and can tolerate low temperatures (8-1O0C). However, lower temperatures (4-8°C) occurred in 1987 and 1993, damaging seedlings in nurseries and tree plantations. At Tuy phong (Binh thuan province, central Vietnam) where the mean annual rainfall is only 800 mm, A. auriculiformis can grow well on sandy soil in plantations. On acid sulfate soil (pH KCl = 3.2-3.5) at Tan tao (Ho Chi Minh City) or other areas of southwestern Vietnam, A. auriculi{ormis is one of the few tree species which can be widely planted for fuel wood, construction wood and raw material for pulp production. Mean annual increment (MAl) on commercial plantations established in Dong nai (southern Vietnam) is 2.38-2.82 m/yr for height, and 2.52-2.82 cm/yr for diameter for trees 4-6 years old (Nghia and Kha 1993). Most of the seed used _n commercial plantations comes from local seed stands. Almost 20 provenances were obtained for trials in many areas of Vietnam, and preliminary results have shown that the most promising provenances are Coen River, Manton River, Kings Plains, Morehead River, Elizabeth River (Australia) and Mibinin (PNG). Acacia mangiumA. mangium Willd. (Mimosoidae, Leguminosae) is a nitrogen-fixing, fast-growing tree species. This is a medium to large sized tree (20-30 m in height and up to 60 cm in diameter). It is found in Northern Queensland, Papua New Guinea and Irian Jaya. It occurs naturally between latitude I°S and 18°S, at an elevation of 0-300 m. In natural distribution areas, the mean annual rainfall ranges from 1500 to 3000 mm. The species is widely planted in Southeast Asian countries such as Malaysia and Indonesia.
A. mangium requires more fertile soils, more rainfall and less variation of temperature than A. auriculiformis. In northern Vietnam, A. mangium plantations can attain a MAl of 2 m/yr in height and 2.5 cm/yr in diameter while in southern Vietnam, growth is better and MAl values are more than 2.5 m/yr for height and more than 3.0 cm/yr for diameter. On acid sulfate soil at Tan tao (Ho Chi Minh City) 4.3 year old trees grew 2.59 m/yr in height and 3.38 cm/yr in diameter (Nghia and Kha 1993).
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