Development of New Techniques of Seed Storage and Direct Seeding of Native Tree Species for Tropical Forest Restoration

ABSTRACT: Direct seeding (sowing seeds directly into ground) is a low cost method of forest restoration, which could potentially be applied to aerial seeding and replace conventional tree planting. This PhD study i) determined optimal seed storage conditions and behavior of native forest tree species, ii) compared direct seeding success between seeds sown at the time of seed collection and those stored from collection time to optimal seeding time, iii) compared direct seeding with conventional tree planting and iv) developed treatments to increase direct seeding success. Seeds were stored under various temperatures and moisture contents, to determine storage behaviour and identify optimal storage conditions. Seeds were sown into a deforested site, immediately after collection and after storage at the beginning of rainy season. Seeds were also sown with various proportions of hydrogel, to determine if it could increase germination. Growth performance was compared among seedlings under the different sowing conditions and with seedlings grown in a nursery.

In general, germination and median length of dormancy (MLD) did not differ significantly between seeds sown immediately after collection and those stored and sown at the beginning of rainy season. Furthermore, differences in seedling growth rates among the treatments were insignificant. Hydrogel also had no significant effects on seed germination, mortality and MLD. Most species could be sown, with good results, shortly after the seed collection date and recalcitrant seeds must be sown at that time. Alternatively orthodox species could be stored and sown all together at the start of the rainy season, for increased cost-effectiveness.