The Altitudinal Limit of Beech Woods in the Northern Apennines (Italy). Its Spatial Pattern and Some Thermal Inferences

The spatial pattern of the altitudinal limit of beech woods in the Northern Apennines and its correlation with the Fagus sylvatica thermal requirements were studied. The study area was the whole northern side of the Northern Apennines (latitude 44° N), including a timberline. The pattern was described on a scale of 1:25000, using digitized phytosociological vegetation maps. The timberline elevation ranges from 1200 to 1825 m a.s.l., with the highest range at 1525 to 1725 m and a peak (13%) at 1600–1625 m. As suggested by the known beech thermal requirements, the following thermal parameters were considered: mean annual temperature, mean of the coldest month (January), mean of the warmest month (July); days with maximum temperatures >10°C and summer mean (June to September). The values were calculated using data for 1951–2002 from six weather stations. The present upper timberline (1825 m) corresponds to the following: i) mean annual temperature of 4.5°C; ii) coldest month mean temperature of -2.3°C; iii) summer mean of 11.5°C; iv) warmest month mean temperature of 13°C; v) 139 days with maximum temperatures of 10°C or higher. The mean temperature of the warmest month corresponds to the July mean temperature in maritime mountains, such as the Appalachians and the New Zealand Alps (13°C). The geographical location of the Northern Apennines close to the Mediterranean Sea seems to indicate that such a conclusion is reliable. With reference to the elevation variability of the upper timberline, the multiple regression shows that the annual mean is the best explaining thermal parameter (P<0.05). Our thermal data do not take into account the atmospheric phenomena that can affect the temperature lapse rate with altitude, such as the cloudiness of the chain, and site factors, such as wind-exposed topography and snow cover duration, which play a crucial role in the Northern Apennine local climate.