Detailed characterization of plant formations using orthophotography

The detailed delineation of plant formations is superimposed over aerial orthorectified photographs of different dates (working scale 1:5,000-1:8,000). Certain zones within the distribution area of the formation are selected to make comparisons between dates, considering the availability of data as well as their quality. In these preselected areas, a series of 1-ha circular plots are randomly distributed. The individuals of the main species are counted and the coverage of this species estimated for the different dates.

In addition, a series of transects are laid out by photointerpretation according to an altitudinal gradient. Over each transect, tangential circles (the size is c. 30 m in radius) are drawn covering the distribution range of the oak forests and juniper thickets (1100 m to 2700 m). The working scale varies between 1:3,000 and 1:5,000. In these plots, the photointerpretation is made recording the variables of interest for each date.

At present, there are photos of Sierra Nevada of sufficient quality for the dates: 1956, 1977, 1984, 1998, 2001, 2004, 2007, and 2009.