Damage by the mahogany shoot borer is the overriding global factor restricting the establishment of mahogany plantations.

Swietenia was introduced to Sri Lanka from Central America: plantations established in the 1920s were damaged by Hypsipyla robusta, which currently attacks regenerating seedlings in glades and along forest margins.

Establishment beneath natural forest canopy or a nurse crop are frequently recommended to avoid shoot borer damage. Degraded natural forests in Sri Lanka are routinely line planted with Swietenia after logging. However, growth is poor under the heavy shade of the canopy and scrub layer, weeding is expensive, and there is concern that mahogany may suppress regeneration of native species.

Plantations, however, are valued as sources of non-timber products, for amenity and as reserves for wildlife as well as for timber. Existing plantations are reaching maturity and may be heavily felled in the near future. Establishment of new plantations and production of silvicultural manuals are objectives of the DFID Forest Management and Plantation project (FORMP) and the Sri Lanka Forest Department.

As shade reduces mahogany growth it must be optimised to reduce shoot borer damage without suppressing tree growth. Given the high value of the timber and scarce land resource, even small scale losses will have significant impact. Available guidelines are inadequate and conflicting, frequently based on field observation not experimental analysis. Empirical data with which to explain and implement sound management are lacking. The work, if successful, would have global benefits to Swietenia plantation establishment.

To identify possible mechanisms controllable by silviculture whereby shade may reduce shoot borer attack on Mahogany.

• Effect of shade and nurse crops on growth and susceptibility to shoot borer of mahogany quantified.
• Silvicultural prescriptions for S.macrophylla nurse crop management produced.
• Experimental results disseminated.