Satellite-Based Monitoring of Ecosystem Functioning in Protected Areas: Recent Trends in the Oak Forests (Quercus pyrenaica Willd.) of Sierra Nevada (Spain)

The implementation of monitoring and early warning programs on the ecological status of natural areas is increasingly recognized as an environmental priority (Lovett et al., 2007). However, the development of such programs faces important challenges derived from the many requirements that ecological indicators should fulfill to achieve effective monitoring and alert systems (Oyonarte et al., 2010). Nowadays, ecosystem functioning characterization has become crucial for the monitoring and management of ecosystems due to several reasons (Cabello et al., 2008). First, the evaluation of functional features of ecosystems, such as the carbon gains dynamics, complements the traditional description of ecosystems based solely on vegetation structural features (like physiognomy, dominant species, or floristic composition) derived from few plot observations (Mueller-Dombois & Ellenberg, 1974; Stephenson, 1990; Alcaraz-Segura et al., 2009a). Second, ecosystem functional attributes show a much quicker response to environmental changes than structural ones (Milchunas & Lauenroth, 1995; Wiegand et al., 2004; Alcaraz-Segura et al., 2008a). Third, functional traits are related to key ecological processes that provide a direct measurement of key ecosystem services (Oyonarte et al., 2010; Paruelo et al., 2011; Volante et al., In press). Finally, remote sensing tools can be used to monitor ecosystem functional attributes over extensive areas, in different regions, and with a fast-revisiting frequency (Paruelo et al., 2005; Pettorelli et al., 2005; Baldi et al., 2008; Cabello et al., 2008; Alcaraz-Segura et al., 2009a). The use of satellitederived information allows for tracking the integrity of key ecological processes and their spatial and temporal variability with the advantage of using common protocols throughout the Earth (Dale & Beyeler, 2001). In this sense, several works have shown the ability of timeseries of satellite images to assess the existence of long-term ecosystem functional changes both at the regional (Baldi et al., 2008; Alcaraz-Segura et al., 2010b) and local (AlcarazSegura et al., 2008a; Alcaraz-Segura et al., 2008b; Alcaraz-Segura et al., 2009b; Cabello et al., Accepted) scales.