Direct seeding for forest restoration on abandoned agricultural land in northern Thailand

ABSTRACT: Seed predation and desiccation present major limitations to the use of direct seeding as an efficient forest restoration technique. The study presented here tested the hypotheses that scarifying seeds, before sowing them in fields cleared of weeds, would shorten seed dormancy, thus decreasing time available for seed predation,  and that burial conceals seeds from potential predators. Therefore, the effects of four treatments (scarification, burial, application of mulch and scarification with burial) were tested on seeds of four native forest tree species, sown in abandoned agricultural land, in an upper watershed in Doi Suthep-Pui National Park, northern Thailand. The four tree species studied were Sapindus rarak, Lithocarpus elegans, Spondias axillaris and Erythrina subumbrans. Instead of rodents, ants were the seed predators. Scarification without burial did not accelerate seed germination in the field, due to desiccation and severe predation by ants. Burial helped protect the seeds from predation, blocked direct sunlight and increased moisture-retention, thus preventing desiccation. Seeds that benefit from scarification, but which are susceptible to seed predation and desiccation, should be scarified and buried to a depth twice the diameter of the seed (3—5 cm). For certain suitable species, this technique could offer an effective, cost-efficient alternative to out-planting nursery-raised seedlings for forest restoration projects, particularly in montane areas.