Crop, mulching and season effects on direct seeding for subtropical forest restoration and agroforestry systems

Abstract

Abstract Direct seeding is a cost-effective technique for forest restoration and a practical tool for establishing agroforestry systems, yet its performance in subtropical climates remains insufficiently documented. We tested the effects of season (winter vs. summer), mulching, and crop association on the emergence and establishment of 10 native tree species in southern Brazil. The experiment used randomized blocks with 8000 seeds per season, including pioneer and non-pioneer species, and treatments combining mulching and crop association to create favorable microsites. Seedling emergence and establishment were monitored for 12 months and analyzed with zero-inflated generalized linear mixed models. Summer sowing markedly increased both emergence and establishment compared with winter sowing. Mulching enhanced outcomes, especially when combined with crop association. Non-pioneer species showed higher establishment rates than pioneers, although responses varied among species. The best-performing treatments (summer + mulching, with or without crops) reached up to 14,500 individuals per hectare, exceeding densities typically achieved by seedling planting. Winter sowing resulted in poor establishment, emphasizing the importance of seasonal timing. These findings demonstrate that direct seeding in subtropical forests is most successful when implemented in summer with mulching. This approach improves restoration outcomes, reduces variability, and offers a cost-efficient alternative to conventional seedling planting, providing practical guidelines for ecological restoration programs in subtropical regions and for the design of agroforestry systems that integrate native species through direct seeding.