REVEGETATION OF DEGRADED CAATINGA SITES

The Caatinga vegetation covers approximately 0.8 × 10^6 km2 of Brazil’s north-east. It has 300 to 800 mm annual rainfall during the four to five months of wet season. Its vegetation (seasonal herbs, xerophilous cactus, shrubs and trees) has been grazed, cut or removed, resulting in environmental degradation and arrest of tree regeneration in sites where desertification processes are under way. This study examined the two-year survival and growth of native trees, and the effects of tree planting on soil cover in degraded Caatinga sites, Patos, Brazil. Seedlings were planted in a 2 m × 2 m grid, into 40 cm × 40 cm × 40 cm holes enriched with manure and fertilisers, according to randomised block design with five treatments (control, and planting of Poincianella pyramidalis, Mimosa tenuiflora and Cnidoscolus quercifolius in pure or mixed stands) and five replications. Survival of planted trees ranged from 72.5 to 95.0%. Mimosa tenuiflora was the most promising species. Its height, basal diameter and canopy cover averaged 250 cm, 41 mm and 77% respectively. Herb cover reached 53% under its canopy. In adjacent grazed plots in which no seedlings were planted, no tree regenerated and herbs covered 10% of the soil. The results showed that within two years, planted trees could thrive in degraded Caatinga sites and increase soil cover to 93%.