Restauración del bosque nativo luego de la intervención minera

In the area of Minas de Corrales, in Rivera, northeastern Uruguay, in 2007 the expansion of a gold deposit called Arenal quarry was decided. This exploitation belonged to the company Orosur Mining and its objective was the extraction of gold. The Arenal quarry was located on the left bank of the Corrales stream, and its expansion involved the construction of a 1.3 km diversion channel on the right bank of the stream through which the intervened stream was channeled. Subsequently, several activities related to environmental restoration were carried out. Civil works began in March 2007 and were completed in June of the same year. The mining intervention project involved the removal of 10.5 ha of forest in the original channel of Arroyo Corrales and the preservation of 13.9 ha of forest patches, the recomposition of the banks of the new channel, soil shaping, revegetation with herbaceous plants and reforestation through the planting of native species extracted from the forest itself. Prior to the removal, all the natural regeneration was identified, marked and planted, 23,000 individuals were transplanted within the remaining forest patches, of which 17,000 were planted in two strata: the low 6.5 ha, adjacent to the watercourse, hygrophilous to mesic and the high: 6.1 ha xerophytic. From 2008 to 2016, permanent monitoring was implemented to characterize the dynamics of the initial restoration phase with planting and irrigation (2008-2009), analyze the growth in collar diameter (DAC, cm) and total height (ht, m), establish the dynamics of mortality and survival, with a quarterly seasonal frequency, in the summer, autumn and spring periods. Eleven species were selected from the most numerous families common to both strata: Phyllanthus sellowianus (Klotzsch) Müll.Arg, Sebastiania brasiliensis Spreng., Sebastiania commersoniana (Baill.) L.B.Sm. & Downs, Blepharocalyx salicifolius (Kunth) O. Berg, Eugenia uniflora O.Berg, Eugenia uruguayensis Cambess., Myrrhinium atropurpureum Schott, var. octandrum, Salix humboldtiana Willd., Scutia buxifolia Reissek, Vachellia caven (Molina) Seigler & Ebinger and Allophylus edulis (A.St.-Hil., A.Juss. & Cambess.) Radlk. We monitored 117 individual trees, 47 trees in the upper stratum and 70 trees in the lower stratum, where the same eleven species were analyzed: S. brasiliensis, S. commersoniana, B. salicifolius, E. uniflora, E. uruguayensis, M. atropurpureum var. octandrum, S. buxifolia, V. caven and A. edulis. Statistical analysis was performed using the GLM model (Generalized Linear Models) to find significant differences between the variables studied and the stratifications performed. Considering a minimum estimated age of 11 years (natural regeneration + afforestation), the following indicators were analyzed: the accumulated increment - IA, the annual periodic increment - IPA and the average annual growth - IMA. The species with the best performance for all variables in the high stratum were V. caven and S. buxifolia, while in the low stratum the two species with the best performance were S. humboldtiana and V. caven. It should be noted that for the survival indicator there were no significant differences between the 11 species and between strata. In the case of Myrtaceae and Euphorbiaceae species, all presented intermediate performance, with E. uruguayensis and S. commersoniana standing out as the best performers in both geomorphological conditions. As for the species A. edulis and B. salicifolius, they could be considered as very slow developing.