We studied the structure of a primary and a secondary forest in the driest portion of the South American Chaco (average annual precipitation 400 mm) and the forest evolution after exploitation. The work was conducted in Chancani Provincial Natural Park and Forest Reserve, Cordoba, Argentina, where the best preserved forests of the region are found. The secondary forest was subjected to moderate and selective exploitation of the most important forest species of the Dry Chaco region, Aspidosperma quebracho-blanco Schlecht., over 30 years ago. Density of trees and shrubs (>5 cm dbh) was similar in both forests, but total basal area and volume were markedly lower in the secondary forest. Also density of saplings and shrubs (<5 cm diameter) was similar in both forests. A. quebracho-blanco dominated in the primary forest, representing 85% of the total basal area (8 m(2)) and 92% of the total stand volume (54.03 m(3)). The secondary forest showed a relative increase of the second most important species, Prosopis flexuosa D.C., and significant differences (P < 0.05) in total basal area (4.72 m(2)) and total stand volume (24.77 m(3)) with respect to the primary forest. Furthermore, a tendency towards an increase of less abundant species of lower economic value as well as invasive shrub species was observed. Total basal area and stand volume of the primary, forest are indicators of the possible maximum values expected, and may be used as a reference to develop management plans to regenerate forests. (C) 2004 Elsevier B.V. All rights reserved.
