A dendroecological study of a Epinotia subsequana Hw. (Lepidoptera: Tortricidae) attack on a fir (Abies alba Mill.) forest in the Aragón Pyrenees (Diazas, Torla)

Abstract

We found many narrow or missing annual tree-rings during the period from 1996 to 1998 in most of fir trees sampled in the Diazas forest (Torla; 42º 37’ 50’’ N, 0º 05’ 40’’ W, 1528 m a.s.l.). These tree-rings were synchronic with attacks in that area of the leaf miner Epinotia subsequana Hw. (Lepidoptera). This temporal coincidence motivated this dendroecological study. The radial growth in Diazas was compared with that observed in other 13 fir forests sampled across the Aragón Pyrenees and not affected by E. subsequana. During the 1996-98 period, the radial growth in Diazas was 12-22 % with respect to the mean growth in the rest of stands. The decrease of radial growth during these three years was the cause of the high frequency of missing rings. These were rarely found in others fir forests. This fact suggested that some local factor have caused the growth reduction. The lower radial growth was produced by the intense defoliations done by E. subsequana. The most pronounced reduction of growth was observed in 1997, one year after the maximum level of defoliation was reached (1996). This temporal lag may be due to the fact that the defoliation observed in 1996 reduced the reserves and growth potential to form the tree-ring in the next year. In fact, the radial growth did not increase notably until 3 years (1999) after the first intense growth reduction (1996) was observed