Experimental approaches to select tree species for forest restoration: effects of light, water availability and interspecific competition in degraded areas

Knowing what native trees can recruit on degraded areas allows selecting the best species to restore these sites. However, as this information is not often available, experimentation is required before large-scale planting. This study used ex situ experiments to make these decisions on recruitment. Competition with r-strategist plants, excessive solar radiation and water shortage commonly impair tree recruitment in open habitats. The experiments focused on the interactions among these factors and were conducted with three pioneer species from seasonally dry forests of northwest Argentina, Anadenanthera colubrina , Ceiba chodatii and Jacaranda mimosifolia . Seeds of each species were sown at two light levels (sunlight/shade), two rainfall levels (full/reduced) and two levels of interspecific competition (with/without competitor) in a tree nursery. Seedling emergence and survival were monitored over a year and the results indicate that species differentially respond to varying levels of light and water. Seedlings of A. colubrina tolerated water shortages under elevated solar radiation, which are desirable features for forest restoration. Seedlings of C. chodatii tolerated shade and drought, suggesting that they require shading for establishing in open areas. However, J. mimosifolia seedlings neither tolerated full sunlight nor water shortages, suggesting that this species requires shading and regular watering if used in reforestation. Regardless of the effects of light and water, the survival of all species was reduced by interspecific competition. These results highlight the importance of experimentation for selecting the best species for forest restoration and can enhance the cost/benefit ratios of these actions.