The temporal pattern of the High Reggio Emilia Apennine upper timberline during the second half of the 19^th century has been studied at landscape level in the Prado-Cusna area since 1954. This part of the Northern Apennines is of outstanding biological value. Orthorectified aerial photographs (flights GAI 1954, RER 1978, IT 2000) were used to generate maps using an object-based method of classification. In the period studied the timberline was relatively stable despite the decline of local historical human impact based on agriculture and pastoralism on high mountain vegetation and the mean temperature in the northern Apennines has increased by about 1.3�C. Problems linked to the photogrammetric data processing of aerial photographs of the past and to the classification of images are briefly discussed.