## 1 Introduction
Forests in these areas, characterized by low precipitation and high evaporation rates, are exposed to a high level of climatic variability, and usually exhibit low soil fertility, affecting biomass production. These regions are of particular interest for the global C budget because their ecosystems are responsible for up to 20% of terrestrial Net Primary Productivity [25]. Semi-arid woodlands are widespread in regions with a Mediterranean climate where, in summer, long, dry periods are interrupted by heavy rainfall events. However, information about C dynamics in the soil in these environments remains scarce, and the effect of the interplay between soil temperature and soil moisture on soil respiration is not completely studied. More specifically, studies carried out in woodlands dominated by the _Juniperus_ genus in areas with a semi-arid climate are practically nonexistent. The _Juniperus_ genus is a major component of arid and semi-arid woodlands throughout the Northern Hemisphere [26], and comprises approximately 50 coniferous tree and shrub species [27]. _Juniperus_ originated in Eurasia and was part of the south Eurasian Tethyan vegetation from the Eocene to the Oligocene [28]. Therefore, it is a relic of Tertiary forests, containing slow-growing species that are well-adapted to climates with hot, dry summers typical of semi-arid climates [29]. The Spanish juniper (_Juniperus thurifera_ L., Cupressaceae) is an endemic diocious species of the Western Mediterranean. _J. thurifera_ var. hispanicaMill. is only found in Spain and the French Pyrenees [30], and due to its rarity and slow growth, it has been included in catalogs of endangered species in Spain. The phytoclimatic area of this evergreen conifer is correlated with severe climates [31], such as those predicted in climate change scenarios [32]. For this reason, this species is utilized for forest restoration in sites with low productivity, such as semi-arid areas [26]. Thermophilic juniper woodlands occupy the driest areas of the distribution of _juniperus thurifera_ in Spain [30]. The species here constitute relict forests [33] that can be classified into two levels of maturity and productivity [34]: (i) old or mature woodlands that generally contain trees that are over 150 years old that grow in stony soils with a low tree density (<100 trees ha\({}^{-1}\)), and (ii) young woodlands, with trees that are less than 100 years old growing in abandoned farmlands (i.e., better soils with a higher water storage capacity). These forests have higher growth rates, productivity, and tree density [34; 35]. After analyzing our study area, we hypothesized that total soil respiration would differ among the woodlands, and in addition to forest productivity, these differences would also be controlled by microclimatic factors. Consequently, the specific aims were the following: (i) to analyze the effects of the juniper woodland type (young and mature woodlands, effects of forest \"productivity\") on soil CO\({}_{2}\) efflux, (ii) to study the seasonal variation in soil CO\({}_{2}\) efflux in the two juniper woodlands under a semi-arid Mediterranean climate (\"seasonality\"), and (iii) to evaluate the effects of microclimatic conditions (soil temperature and soil water content) on soil CO\({}_{2}\) efflux for both juniper woodlands throughout the seasons.