The Sky Oaks Old site is located near the Sky Oaks Field station, owned and operated by San Diego State University. Chaparral vegetation, associated with a Mediterranean climate, covers nearly half of the rough and rocky terrain. Precipitation is almost exclusively confined to the winter months. During the summer and early fall, hot and dry Santa Ana winds from the northeast bring desert heat to the site. A high intensity natural wildfire occurred in July of 2003. The stand age at the time of the wildfire was 80 years old, following an early wildfire poorly characterized. Following the 2003 wildfire, most native chaparral began to regrow from root stocks reaching a height of 1.0 m in 2008.

The research and science objectives of the Sky Oaks Old site are as follows: 1) Effects of elevated CO2 on belowground carbon dynamics in the chaparral ecosystem; 2) Investigate how elevated CO2 levels interact with a complex, patchy landscape in a natural ecosystem with strong water and nutrient limitations; 3) Investigate the effects of elevated CO2 levels on root growth and on microbial biomass, activity, and community structure in a chaparral ecosystem of southern California; 4) Understand how major soil energy channels, such as bacteria-protozoa/nematodes, fungi-mites/collembola, and mycorrhizal fungi, simultaneously respond to elevated CO2 and then to examine potential interactions among these components; 5) Determine if the 100-year-old chaparral stand senescent is in carbon exchange with the atmosphere; 6) Characterize the relationship between NEE and interannual variability in rainfall, the major limiting factor in most arid and semiarid ecosystems; 7) Examine the correlations between photosynthesis, light use efficiency, and various spectral reflectance indices over a range of timescales in a Southern California chaparral ecosystem as a basis for evaluating the light use efficiency model. (Treseder et al., 2003, Lipson et al., 2005, Allen et al., 2005, Sims et al., 2006, Luo et al., 2007)