## 2 Materials and Methods
### Measurement of Soil CO\({}_{2}\) Efflux  
Total soil CO\({}_{2}\) efflux (\(\mu\)mol CO\({}_{2}\) m\({}^{-2}\) s\({}^{-1}\)) was measured in situ on 17 sampling days, spread over the 4 seasons (2 sampling days in winter, 3 in summer and autumn, and 9 in spring, the most important growing season). Within each woodland area, six metallic collars (cylinder: 10.5 cm in diameter and 5 cm in height) were installed on the soil between the trunk and the projection limit of the crown in six juniper trees (Figure 3). Thus, a total of 12 metal cylinders were installed on the soil for the respiration measurement (6 juniper trees in each of the mature and young forests).  
Figure 2: Study area: young, more productive juniper woodland in abandoned farmland (**a**), and mature woodland in Leptosols (**b**). Below, the soil depth of each site is shown ((**c**) young woodland, 40 cm depth, and (**d**) mature woodland, 10 cm depth).  
The total soil CO\({}_{2}\) efflux was measured using LI-6400 CO\({}_{2}\) measurement equipment (LI-COR, Inc., Lincoln, NE, USA), to which an LI-6400-09 chamber was attached (closed system). For each CO\({}_{2}\) efflux measurement, three repeated measurements were performed, and the mean was the value used for data analysis. Thus, the total dataset included 204 measures. The measurements were conducted from 9:00 to 15:00 to minimize the effects of daytime soil temperature fluctuations and rainless days [10]. Measurements were performed by reducing the CO\({}_{2}\) concentration inside the chamber and then letting it increase to an upper concentration limit. Before starting each measurement, the ambient CO\({}_{2}\) concentration was used as the target. The air CO\({}_{2}\) concentration ranged between 370 and 421 p.p.m. during the research. The air flow (\(\mu\)mol air s\({}^{-1}\)) pumping down was fixed depending on the efflux level (200-700 for low and high efflux levels, respectively). The rate of change of CO\({}_{2}\) inside the chamber was calculated in three consecutive measurement cycles.  
Microclimatic Conditions and Organic Matter in Soils: Measurement of the Soil Temperature (Ts, \({}^{\circ}\)C), Soil Water Content (Sw, %), and Soil Organic C (%)  
The soil temperature (\({}^{\circ}\)C) was measured at a depth of 7 cm below the ground surface next to each collar using a temperature probe. Temperature measurements were recorded with HOBO sensors and data loggers (Onset Computers, Bourne, MA, USA). The soil water content (volumetric moisture, %) was measured with WatchDog sensors and data loggers (Spectrum Technologies, Aurora, IL, USA) close to the collars (at the depth of 7 cm). Finally, to determine the soil organic C, four samples of toposoil (0-10 cm) were collected in each woodland type in each season for the two years (in the middle of the season) using a soil core (5 cm inside diameter). To minimize the soil variability, each soil sample was made up of five random subsamples collected between the trunk and canopy edge. Soil samples were taken from the upper 10 cm layer after the litter had been removed (this layer presents the greatest microbial activity because of the shallowness of soils). In the laboratory, soil samples were sieved (<2 mm) and stored at 4 \({}^{\circ}\)C until analysis. The total soil organic carbon (%) content was determined by oxidation with K\({}_{2}\)CrO\({}_{7}\) in an acid medium and titration of the excess dichromate with (NH\({}_{4}\))\({}_{2}\)Fe(SO\({}_{4}\))\({}_{2}\)[39]. Samples were analyzed by assessing three replicates in the laboratory, and the mean value was used as the sampling data.  
Figure 3: Metallic collar to measure the total soil CO\({}_{2}\) efflux in juniper woodland soils.