Topsoil for restoration: Resprouting of root fragments and germination of pioneers trigger tropical dry forest regeneration

Topsoil translocation has been effective for the restoration of plant communities, but until recently this method had not been used for tropical dry forest restoration. We tested different methods of topsoil deposition for restoring a dry forest on an abandoned limestone quarry. We also tested the effects of irrigation during the first dry season after topsoil deposition. The study was conducted in the Federal District of Brazil. A 2.1-ha area was cleared of vegetation, and the topsoil from that site was deposited on an exotic pasture field 1.4 km away. First, a secondary forest was clear-cut, and the first 30 cm of topsoil were removed and translocated. The soil was transported in dump trucks to the deposition site, which had been scarified in advance, and deposited by either forming 1.25-m-tall mounds or by leveling the soil into a 40-cm or 20-cm deep layer using a hydraulic excavator. The seed bank and the availability of root and stem fragments in the soil were both surveyed. The origin of the regenerants was categorized as either from seed or resprouting. We estimated vegetation cover for each life form, and measured all trees and lianas. After six months, 74% of the tree individuals and 60% of the liana individuals came from resprouting. Ruderal herbs and shrubs germinated from seeds. After 28 months, there were 51 species of trees, 8 species of lianas, 12 species of shrubs, and 34 species of herbs in the deposition treatments. The three deposition treatments were thickly covered with herbaceous/shrubby species, and had nine times the number of species (44 vs. 5) and five times the tree density (1.17 ind./m2vs. 0.25 ind./m2) as the non-deposition control. Tree survival was relatively high in both the non-irrigated and irrigated treatments. The total cost of topsoil translocation was 9604 USD, and the output was 0.43 ha deposited/ha excavated when forming mounds of soil, 5951 USD and output of 0.75 when leveling to a 40-cm layer, and 3551 USD and 1.5 for a 20-cm layer of deposited material. However, deposition and transportation costs are fixed costs of establishing a new quarry that can be deducted from the total cost of restoration. Topsoil translocation was effective in kick-starting the succession process of a tropical dry forest.