I recently read a report that Laos is going to embark on a spate of tree-planting:

A report released by the Ministry of Agriculture and Forestry last week said that Laos plans to plant trees covering at least 25,000 hectares this year. This is a part of the bigger plan to reforest covering up to 53% of Laos by the year 2010 and at the same time Laos also plans to restore forests in the area of 2.5 million hectares damaged by heavy deforestation. Authorities have launched effort to reclaim the forests by urging cooperation from all sectors.

Commentators often assume that tree planting is a good thing. But considerable caution is warranted. There can be substantial social impacts as agricultural lands – or fallow plots in shifting cultivation systems – are taken over by enthusiastic tree planters. And extensive tree-planting can also have negative environmental impacts. As Tim Forsyth and I wrote in our recent book on environmental management in Thailand:

[S]ome caution is warranted in relation to extensive tree-planting programs, either in the form of plantations, orchards, or initiatives in watershed “rehabilitation.” Contrary to popular belief, increased tree cover is likely to reduce the annual water yield of upland catchments rather than increase water supply. If the objective is to secure larger supplies in major downstream hydroelectric and irrigation schemes, the initiatives are very likely to be counterproductive (Aylward 2000:18). There is also a good chance that extensive tree planting will reduce dry-season flow, because the medium- to long-term benefit in terms of enhanced infiltration on reforested soil may well be limited and strongly outweighed by short- to medium-term increases in the level of water “lost” due to the increased evapotranspiration. … Bruijnzeel’s (2004:208) finding should sound a warning note to those committed to upland reforestation: “the conclusion that already diminished dry season flows in degraded tropical areas may decrease even further upon reforestation with fast-growing tree species seems inescapable.” (Forest Guardians Forest Destroyers, page 115)

Tree-planting is a good and wholesome activity but there needs to be careful definition of the environmental objectives of such programs and some sober assessment of whether or not those objectives are likely to be met.