The giant arboreal types of Leucaena are trees capable of growing to 20 min height. They are normally evergreen, but will shed their leaves during periods of prolonged drought or frost. They will tolerate partial shade, but grow best in full sun. Most cultivars tried grow best below 1000 m; at higher altitudes they may survive, but growth is likely to be poor.
Leucaena is sensitive to soil pH and where this is less than five growth is seriously reduced (Ahmad and Ng, 1979). It is also sensitive to relatively small differences in soil fertility, and within the same plantation very vigorous trees may be found growing within a few metres of poor stunted ones. In the constantly humid tropics, such as in the Philippines, it has been used successfully for reafforestation of denuded slopes, but in areas with a pronounced dry season it requires soils of at least moderate fertility. In Nepal it generally grows well on Bhabar Terai soils, but has failed on very gravelly and bouldery soils near rivers, though these soils are capable of growing good crops of Dalbergia sissoo and Acacia catechu. More needs to be learned about the tolerance of different Leucaena cultivars to different soils and altitudes in Nepal.
In the constantly humid tropics, such as in the Philippines, Leucaena will competc with and eventually dominate lmperata grass, but this is not the case in drier areas such as Ncpal, where thorough weeding is necessary if successful plantations are to be established. Young seedlings are killed by frost, and the trce should not be planted in frosty areas. They are very palatable to grazing animals including deer, and it is not practicable to plant Leucaena in areas where wild game is abundant, as the cost of erecting deer proof fences is prohibitive. Trees are fairly resistant to fire, but repeated fires will kill them.
Flowers and seed are often produced at a very early age, often less than a year. According to Hawkins (1986), at Adabhar in the Bhabar Terai varieties which flowered early also suffered from up to 1m shoot dieback during the dry season, while those which did not flower before 18 months avoided this.
The seedlings and older trees have very strong taproots. Rhizobial nodules which fix nitrogen are found on the roots, and if the appropriate strain of the Rhizobium bacterium is absent growth is considerably reduced. In some parts of Nepal inoculation by Rhizobium may occur naturally from bacteria within the soil, but this cannot be relied on and artificial inoculation in the nursery is a neeessary safeguard. Leucaena coppices very readily. Even if stems little over 1 cm in diameter are cut, the roots will frequently send out new shoot.