Assessing UAV direct-seeding for tropical forest restoration: early-stage growth and cost-effectiveness

Gregory Shteto , Leland K Werden, Manon Villa, James Tiburcio, Emira Cherif

 
Introduction: The high cost, labor intensity, and infrastructure needs of manual tree planting limit the scale of global forest restoration. UAV-assisted direct seeding is a promising alternative, but comparative empirical data are scarce.
Objectives: This study assesses UAV-assisted direct seeding as a cost-effective alternative to manual planting for tropical forest restoration by comparing early-stage above-ground biomass (AGB) accumulation, species diversity, and cost-effectiveness.
Methods: Over a 2.5-year period in the Amazon biome, we measured seedling growth and species diversity in UAV-direct-seeded sites. These measurements were compared to a benchmark from manual planting projects using descriptive metrics and statistical testing. Cost-effectiveness was analyzed across three adaptive management scenarios requiring one, two, or three seeding rounds.
Results: A descriptive comparison showed the median AGB of direct-seeded sites was nearly double that of a benchmark from manually planted projects at 1.5 years, increasing to over threefold at 2.5 years. However, outcomes across the sites were highly variable; estimated species richness (Chao1) ranged from 3 to 29, with natural regeneration comprising the majority of species at the youngest site. In a single-round scenario, direct seeding was 2- to 9-times more cost-effective (based on cost per kg AGB), but this advantage was lost when three rounds were required.
Conclusions: UAV-assisted direct seeding is a viable method for achieving key ecological outcomes, including rapid biomass accumulation and species diversity, in early-stage tropical forest restoration. However, its success and cost-efficiency are highly dependent on site conditions permitting establishment in a single seeding round.
Implications for Practice: This study provides evidence that, in suitable contexts, UAV direct seeding can more than double the area restored for the same cost as manual planting. This makes it a powerful addition to the practitioner's toolkit, especially for large or inaccessible areas where manual planting is logistically prohibitive. However, realizing this efficiency requires a holistic ecological approach, encompassing site assessment, species selection, and seeding density, to ensure high establishment success in a single intervention. By dramatically improving the cost-per-hectare, this technology can significantly increase the scale and impact of restoration programs.