## 2 Materials and Methods  
### Study Area  
This research was carried out in the Spanish juniper woodlands of the El Campo de Montiel Mountains (Southern Spain; Figure 1).  
Figure 1: Location of El Campo de Montiel juniper woodlands within the rest of the Spanish juniper formations (Spain). The delimitation of the study area was made with the Forest Map of Biodiversity Data Bank (Ministry of Agriculture and Environment of Spain) and the information published by [30]. UTM coordinates, ETRS89.  
These juniper woodlands are thermophilic according to [30]. The climate is semi-arid cold (BSk type, KOPPEN [36]) with extreme temperatures of between 43 and \(-21\)\({}^{\circ}\)C (data from \"El Bonillo\" station: 38\({}^{\circ}\)57\({}^{\prime}\) N, 01\({}^{\circ}\)09\({}^{\prime}\) W, 1068 m.a.s.l., period of 30 years, located within 7 km of the research area, and owned by the State Meteorological Agency of Spain). The average annual temperature is 12.8 \({}^{\circ}\)C, and annual rainfall corresponds to a dry ombroclimate (450 mm). Soils in which the total soil CO\({}_{2}\) efflux was measured were selected from the two types of thermophilic juniper woodland (Table 1, and Figure 2): (i) mature woodland with an average age of 170 years, growing in Leptosols (soil depth < 15 cm), and (ii) young woodland with a mean age of 66 years, growing in abandoned farmlands with deeper soils (Cambisols, with a mean depth of 42 cm).  
In each type of juniper woodland, a representative and homogenous experimental area (\"plots\", approximately 1 hectare) was selected. The areas were less than 1 km apart, ensuring that both woodlands are growing under the same climatology, as well as similar altitude (1050 m.a.s.l.), slope (gentle slopes, 5\({}^{\circ}\)), and exposure (paramo formation, flat surfaces). Referring to vegetation characteristics (Table 1, vegetation variables have been collected from the study of [PERSON] [33]), biomass stocks and productivity were scarce in both woodlands. However, the young site has higher productivity. Juniper trees in the young woodland area have slow growth, and trees in the mature woodland area represent very-slow-growing species. Litterfall and the LAI are also higher in young woodlands due to the superior productivity (joint effect of age and quality of soil). The two juniper woodlands contained lime-rich substrates (Jurassic dolomites) with a basic pH (Table 1, soil characteristics). The soils in the young woodland area had a greater clay content and water storage capacity (137.1 vs. 20.5 mm). The bulk density was slightly greater in the mature woodland.  
\begin{table}
\begin{tabular}{l l l} \hline \hline
**Characteristics** & **Young Woodland** & **Mature Woodland** \\ \hline Vegetation 1  & \\ \hline Mean age (years) & 66 \(\pm\) 4 & 170 \(\pm\) 5 \\ Woodland density (trees ha\({}^{-1}\)) & 308 \(\pm\) 40 & 95 \(\pm\) 12 \\ Juniper cover (\%) & 65 \(\pm\) 23 & 32 \(\pm\) 14 \\ Total biomass (t ha\({}^{-1}\)) & 30.8 \(\pm\) 2.6 & 7.6 \(\pm\) 0.6 \\ Net Primary Productivity (NPP, t ha\({}^{-1}\) year\({}^{-1}\)) & 1.91 \(\pm\) 0.14 & 0.44 \(\pm\) 0.01 \\ Litter fall (t ha\({}^{-1}\) year\({}^{-1}\)) & 0.98 \(\pm\) 0.13 & 0.24 \(\pm\) 0.05 \\ LAI (m\({}^{2}\) m\({}^{-2}\)) & 1.03 & 0.32 \\ \hline Soils 2  & \\ \hline Soil taxonomy (FAO [37]) & Calcaric cambisol & Lithic leptosol \\ Mean soil depth (m) & 0.42 \(\pm\) 0.04 & 0.10 \(\pm\) 0.02 \\ Soil pH & 8.3 \(\pm\) 0.1 & 8.6 \(\pm\) 0.1 \\ Soil texture (sand, \%) & 50 \(\pm\) 5 & 58 \(\pm\) 5 \\ Soil texture (clay, \%) & 28 \(\pm\) 1 & 12 \(\pm\) 1 \\ Bulk density (g cm\({}^{-3}\)) & 1.37 \(\pm\) 0.1 & 1.54 \(\pm\) 0.2 \\ Water storage capacity (mm) & 137.1 & 20.5 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Vegetation characteristics and graphic parameters in soils defining the site quality of the two thermophilic juniper woodlands. Errors: standard error.