Pasture production under different tree species and densities in an Atlantic silvopastoral system

We studied the effect of six tree species planted at six different densities on pasture production seven years after establishment. Annual and seasonal pasture production was studied every six months, over three years. Pasture production was lower under conifer trees (Pseudotsuga menziesii (Mirb.) Franco, Pinus pinaster Aiton, Pinus radiata D. Don) than under broadleaved trees (Betula alba L., Quercus rubra L. and Castanea sativa Mill.). Annual pasture production under Pseudotsuga menziesii and Pinus pinaster decreased progressively starting from 952 trees ha-1, while decline in herbage production under Pinus radiata began to occur at 427 trees ha-1. Tree density effect on pasture production was detected at 2,000 trees ha-1 for all of the deciduous species studied. This effect on pasture production was more important in the first six months of the year (June sampling), while from June to December herbage production was less affected by tree density. The tree effect became more noticeable over time, with the last sampling showing the inverse relationship between tree density and herbage production most clearly. Seven years after tree establishment, pasture production was quite consistent under tree densities between 190 trees ha-1 and 556 trees ha-1 and declined remarkably from 556 trees ha-1 to 2,500 trees ha-1. The study also indicated that by the sixth growing season, annual pasture production under different tree species is inversely correlated with tree leaf area index.