Weed control in forestations on abandoned agricultural lands in the Iberian Peninsula

Abstract

Afforestation on abandoned agricultural lands is spreading in many regions worldwide. Under a Mediterranean climate, successful rooting can be hindered by the weed competition characteristic of these ecosystems. Our objectives were to evaluate the colonizing potential of weeds in an old crop after 25 years of abandonment, and to study the effect of different control techniques on the survival and development of forest plants. The soil seed bank was sampled (direct and indirect methods) before afforestation the plot with Pinus halepensis, Quercus ilex subsp. ballota and Retama sphaerocarpa. After planting, different control techniques were applied: tillage, mowing and chemical treatment. Survival, diameter and height were measured for three years. The results showed an abundant weed community (67 taxa) with a persistent soil seed bank (almost 20 000 seeds/m²), causing high mortality mainly in pine. The first year tillage was the best technique for pine rooting, while holm oak and broom did not show differences between treatments. From the second year on, the chemical treatment was the one that most favored growth, being recommended with the necessary precautions for the use of herbicides. Regardless of whether  the response of each forest species to weed competition may be different, it is essential to analyze the need to control this vegetation. This will increase the success of afforestation in environments as demanding for plant life as the Mediterranean ones.