Survival and growth of native Tachigali vulgaris and exotic Eucalyptus urophylla × Eucalyptus grandis trees in degraded soils with biochar amendment in southern Amazonia

Abstract

The impact of agricultural and livestock activities on tropical forests often results in long-lasting damage to soil and vegetation. In undisturbed tropical forests, nutrient stocks tend to be larger in the aboveground biomass than in the soil profile; therefore, deforested sites may remain bare for decades due to nutrient limitation. In such circumstance, amelioration of edaphic conditions and planting of tree species adapted to open canopy conditions (pioneers) could help restore ecosystem functions while providing a sustainable source of timber and prompting natural succession. The aim of this study was to evaluate the use of biochar as a soil amendment that could accelerate the reforestation of degraded lands. We used a randomized block design with five treatments and four replications, comparing the performance of exotic eucalyptus (Eucalyptus urophylla×Eucalyptus grandis) and native Tachigali vulgaris trees. We monitored reforested plots for 49months, evaluating tree survival and growth rates, litter production, canopy cover and density of invasive grasses. The addition of biochar in the soil did not result in significant differences in tree survival or productivity when compared to controls. Comparing the two species, native trees (T. vulgaris) performed better by all metrics, showing 52% survival and producing 241.7Mgha−1 of aboveground biomass after four years of growth. During that same period the survival rate of eucalyptus was 38% and the aboveground productivity was only 82.4Mgha−1. In contrast with eucalyptus plantations, T. vulgaris showed rapid canopy cover and completely suppressed invasive grasses, generating up to 11.7Mgha−1 more litter than eucalyptus trees. Although eucalyptus is one of the most commonly used species in reforestation for timber, charcoal, and pulp and paper production in Brazil, our results demonstrate that T. vulgaris has the potential to replace eucalyptus in commercial plantations with the added benefit of being a native species that can promote the establishment of a stable forest cover in degraded sites.