## 2 The Montado Ecosystem
### The Components of the Montado  
#### 2.2.1 The Soil  
Soil fertility depends on the OM content, which results from the decomposition of organic residues such as leaves, branches, and dry grassland biomass and roots [9]. The predominant soils of the region where Montado occurs are soils with structural and fertility limitations, classified as Cambisoils, derived from granite [37]. They are thin, stony, acidic, and poor in phosphorus (P) and nitrogen (N), have imbalances at the micronutrient level (namely, the magnesium (Mg)/manganese (Mn) ratio), and are degraded as a result of erosion and nutrient loss, mainly due to their typical undulating topography, associated with intensive forms of land use [4; 38; 39]. Cambisoils are classified as Pg and Pg (non-humic lithidic soils of semi-humid and semi-arid climates) in the Portuguese soil classification. They are characterized by having a low cation exchange capacity, coarse texture, percentage of OM \(<\) 1%, pH \(<\) 5.5, and low water holding capacity [40; 41].  
[PERSON] et al. [30] experimented with the \"Dehesas\" of Extremadura, Spain, subdivided into three phases: (i) evaluate the effect of trees (holm oak) on soil, light, microclimate, soil moisture, roots, and the crop in 16 cultivated plots of hazel (_Avena sativa_ L.); (ii) evaluate the effects of different soil uses (forest, grazing, and abandonment) on trees; (iii) evaluate the response of trees to fertilization in four plots (oat only, oat and fertilization, grazing only, and grazing and fertilization). Regarding the radiation transmission through the canopy, for the herbaceous plants, the distance between these and the tree trunk (0.5; 1.0; 2.5; 5.0; 10.0; 20.0; and 30.0 m) and their orientation was taken in account, considering the four cardinal points (N, S, E, W). This study concluded that the radiation transmitted during the growth of herbaceous plants (pasture and oat) increased rapidly and significantly with the distance to the trunk. At 10.0 m from the trunk, the available radiation was greater than 95%, with non-significant differences between 10.0, 20.0, and 30.0 m, except in the north orientation, where the differences were significant between 10.0 and 20.0 m but not between 20.0 and 30.0 m. According to [PERSON] et al. [30], trees have a positive effect on most soil chemical parameters, mainly on OM, total N, nitrate (NO\({}^{3-}\)), P availability, cation exchange capacity, exchangeable potassium (K), and calcium (Ca). All these parameters were significantly higher under the canopy projection than outside the canopy. Values tended to decrease with an increasing distance to trees, with non-significant differences between 10.0, 20.0, and 30.0 m. Additionally, [PERSON] et al. [42] obtained an OM content under the canopy of Holm oak trees about twice as high as that found beyond the projection of those trees. A study carried out in Montado, in the region of Evora (Alentjeo), reports that the soil under the canopy showed significantly higher levels of OM, N, P, K, and Mg, with mean values of 3.1% vs. 1.7%, 0.2% vs. 0.3%, 117.7 vs. 68.2 mg/kg, 359.3 vs. 180.5 mg/kg, and 115 mg/kg vs. 76. 3 mg/kg, for each parameter, under and outside the canopy, respectively. No significant differences were found for texture, pH (values of 5.4 vs. 5.3, under and outside the canopy, respectively), and Mn (values of 16.2 mg/kg vs. 11.8 mg/kg, under and outside the canopy, respectively) [43]. The canopy is essential for protecting the soil from direct rainfall that can cause landslides and soil erosion, particularly on steep slopes. The soil under the canopy is often more permeable and has a higher water-holding capacity than bare soil [9]. On very acid soils (pH below 5.0), grazing can lead to higher acidification rates [44] compared to agricultural crops where no grazing occurs.