Context: Gold mining is the most destructive activity in the natural forests of the Madre de Dios region in the southeastern Peruvian Amazon. Understanding the natural regeneration process of these degraded areas is necessary to develop forest restoration projects in such conditions.Aims: We aimed to evaluate forest recovery and identify the successional and structure patterns of vegetation governing natural regeneration over time.Methods: Structure, composition, richness, diversity, and successional status were evaluated in abandoned artisanal gold mine areas in Madre de Dios, southeastern Peru. Vegetation data were recorded in 61 plots of 250 m2 established in five sites varying from 1 to 19 years of abandonment. Vegetation in abandoned areas was compared with six undisturbed forests evaluated in previous inventories.Results: In the mining lands, tree density and basal area recovered quickly, while species richness and composition were slow. Forest recovery is an initial stage of transition from pioneer to early secondary species until at least 19 years after abandonment. The most abundant and frequent species were the fast-growing species Ochroma pyramidale and Cecropia engleriana. These species could be considered potential candidates to promote restoration plans. Pioneer species represented 63% of the number of species in plots of 1–4 years, 57% in plots of 5–7 years, and 50% in plots of 8–19 years. Early and late secondary species represented 34 and 16%, respectively, of the number of species in plots of 8–19 years. Abandoned mining and reference plots present less than 5% of species in common.Conclusion: Our results highlight a slow natural regeneration process in areas for up to 19 years after gold mining. Species from different successional statuses were identified as potential candidates for recovering vegetation in such areas. Our findings may have important implications for further research focusing on the ecological restoration in tropical forests severely degraded by gold mining.
Knowledge of the effect of soil nutrients, such as K and Na and their interaction with water availability, on the growth and wood properties of the eucalypts, is needed to increase the productivity of commercial plantation forests in Brazil that generate employment and taxes. The present study evaluates the apparent wood density (at 12% wood moisture) of Eucalyptus grandis trees at 12, 24, 36 and 48 months old under ambient and lower than ambient (66%) rainfall conditions and K and Na nutrient enrichment. The treatments were two water availability (100 and 66% of the rainfall) and the three nutrient treatments were: K (4.5 kmol/ha), Na (4.5 kmol/ha) and a control (natural conditions). The apparent wood density of samples at breast height (1.3 m) was determined by X-ray densitometry and digital images. Increased nutrients at all four ages and water availability at 36 and 48 months reduced apparent wood density in E. grandis trees, however, effects of nutrients are lower under water availability reduction. The radial profile of wood density was higher in four-year-old trees, but there was radial variation in apparent wood density at all ages. These findings predict that, under water stress, apparent wood density will not decline in commercial E. grandis plantations fertilized with potassium. The use of sodium, as a substitute of potassium, should consider their negative impacts on wood density of Eucalyptus grandis trees. In Brazil, eucalyptus species are usually cultivated in soils with low fertility, potassium and other minerals scarcity and water deficit 1. The expansion of forest plantations in the country depends on the understanding of the interaction between minerals, such as sodium and potassium, and water availability, and their effect on the seasonality of tree growth and wood quality. The total or partial replacement of potassium by sodium in forest plantations has practical and scientific interest 2,3. Potassium sources, with sodium in their composition, require less energy in the fertilizer production and, therefore, reducing its final prices. These minerals affect the tree water balance and increase water use efficiency under water stress and improve drought resistance 1,4. Because wood is a product of tree growth, factors that affects the growth rate can also affect wood anatomy and therefore wood density and other physical properties. Thus, the application of silvicultural traits in a changing environmental conditions have consider the potential impacts on wood quality. As well as volume productivity, the wood properties are important factors in forest management, since its affects the transformation process and quality of wood products. In pulp and paper industry wood density is an important attribute for yield and quality of pulp and paper products 5,6. However, the effects of mineral fertilizers in wood density of young eucalyptus trees is poorly studied and with controversial results, indicating an increase 7 , decrease or no effect on apparent wood density with moisture content between 12 and 1...
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