Plant richness and life form diversity along vegetation and forest use gradients in northwestern Patagonia of Argentina.
The imbalance between the increase in the demand and the decrease in the supply of products from natural forests, partly explains the on-going development of exotic tree plantations. In northwestern Patagonia of Argentina, Pinus ponderosa (Pinaceae) afforestation plays a key role in ameliorate degraded soils, but may also reduce biodiversity. The ecological sustainability of this activity was assessed in Aguas Frías (38°46′ W, 70°54′ S) and Litrán (38°54′ W, 71°01′ S) forest stations, where species richness and life form diversity of plants were compared in vegetation units, fenced and unfenced against livestock. Eleven vegetation units were identified, including natural herbaceous-shrubby steppes, xerophilous and hygrophilous meadows, pure and mixed forests of Nothofagus pumilio (Nothofagaceae) and Araucaria araucana (Araucariaceae), and P. ponderosa planted forests of dissimilar canopy cover. Xerophilous meadows on rocky outcrops held 1/3 of total richness in an extremely restricted area. Hygrophilous meadows exhibited the largest number of families and native and exotic species, and lower diversity of life forms. Dense pine stands exhibited low values of light in the undergrowth, water in the topsoil, cover of undergrowth plants, frequency of hemicriptophytes and richness and diversity of life forms. As canopy cover decreased, values for these indicators resembled those of the steppe of reference. Within a plantation, greater compatibility between conservation of diversity and wood production requires maintenance of fencing, reduced tree spacing over long rotations and the development of buffer zones and biological corridors. Although such a project may represent a decline in productivity, it will promote enhanced ecosystem and aesthetic values, increasing the likelihood of further economic support from society.