Pit volume, soil cover and Eucalyptus forestry residues determine plant growth in restoring areas after gravel mining in eastern Amazon, Brazil

Gravel mining destroys the soil structures, with consequent losses in biodiversity and other ecosystem services, such as nutrient cycling, carbon sequestration and regulation of the hydrological cycle. In this context, planting with native species can be an effective method to restore the ecosystems functioning and structure after mining. A restoration study was conducted to evaluate the influence of different planting pit volumes and soil cover on the development of four Fabaceae tree species in an area degraded by gravel mining in the eastern Amazon, Brazil. Two types of ground cover and two pit sizes were assessed: soil covered with coconut fiber blanket and small pit (T1); soil covered with Eucalyptus forestry residues and small pit (T2); small pit filled with 160 dm(-3) with Eucalyptus forestry residues (T3) large pit filled with 320 dm(-3) of Eucalyptus forestry residues (T4). Periodic Annual Increment (PAI) was calculated 1.3 years after planting for total height (PAI(Ht)) and diameter (PAI(DBH)) as well as the survival percentage. All four evaluated species showed mean PAI(Ht) ranging from 160.75 to 279.26 cm year(-1), in which T2 and T4 provided the best performances. Clitoria fairchildiana showed the highest mean PAI(DBH) value at T2 and statistically differed from T1 and T4. On the other hand, there were no significant differences in the other tested species. Survival percentages were greater than 90% for C. fairchildiana, Inga edulis and Inga thibaidiana. Although there was not a clear pattern in relation to the applied treatments, the Eucalyptus forestry residues such as soil cover and large planting pits were more efficient in relation to the increments in growth, diameter and survival of the species used in the initial planting to restore ecosystems degraded by gravel mining. Such results can be applied in future forest restoration projects in the Amazon and other tropical regions.