## 4 Discussion
### RS Ecological Variables Relationship with Field Integrity Values  
The relationship between remote sensing spectral indices (annual averages of BI\({}_{2}\), MCARI\({}_{\text{sent}}\), and NDWI\({}_{\text{Gao}}\)) and the structural alteration of forests (_SAI_) varied across sites in both plains and foothills landscapes. The Brightness Index (BI\({}_{2}\)) and the Modified Chlorophyll Absorption in Reflectance Index (MCARI\({}_{\text{sent}}\)) tend to increase in highly altered sites (e.g., with high _SAI_ values), while NDWI\({}_{\text{Gao}}\) exhibited the opposite trend (Figure 3). The Brightness Index (BI\({}_{2}\)) showed a significant response to an increasing Structural Alteration Index (_SAI_) in both annual averages (Figure 3A,B; Table 5) and monthly averages. The robustness of this response may stem from the sensitivity of both indices--one derived from remote sensing and the other from field data--to the presence and extent of bare soil. In the Chaco region, bare soil tends to cover larger areas in sites with low woody cover and high levels of silvopastoral and agricultural intervention (i.e., high _SAI_) [69; 99; 100]. This mosaic of woody vegetation patches intermingled with bare soil is characteristic of many dry forests worldwide, including the Chaco. In these ecosystems, degradation is often associated with an expansion of bare soil areas, and in severely degraded conditions, the landscape becomes dominated by bare soil [89; 101]. The observed behavior of BI\({}_{2}\) and field-measured _SAI_ across sites with different management pressures and conservation statuses effectively represents the forests of the Arid Chaco as highly heterogeneous, with woody vegetation distributed in a mosaic interspersed with bare soil and/or gaps [50; 102]. Increasing intervention in these ecosystems (e.g., to enhance forage biomass) [103] inevitably leads to a simplification of vegetation structure and an increase in bare soil. The higher average _BI\({}_{2}\)_ and _SAI_ values in some sites within the plains landscape may be attributed to specific land uses, including megathermal pastures and crops, which result in greater seasonal exposure of bare soil [50]. These results highlight the potential of BI\({}_{2}\) as a reliable remote sensing indicator for differentiating sites with distinct conservation statuses within the Arid Chaco, allowing for assessments based on both annual averages and monthly data (Figure 3A,B). The relationship between the Modified Chlorophyll Absorption in Reflectance Index (MCARI\({}_{\text{Sent}}\), annual average) and the Structural Alteration Index (_SAI_) showed moderate to weak correlations across sampled sites (Figure 3C,D; Table 5), likely due to phenological differences between the forest classes considered. The MCARI\({}_{\text{Sent}}\) index, a proxy for leaf chlorophyll concentration and canopy density, increased with _SAI_ values during the wettest months (February to May) but showed no significant relationship during the driest months (June to December). Sites dominated by herbaceous cover (e.g., savannas and grasslands with trees, CL 7-8) exhibited lower annual chlorophyll concentrations than woody communities (e.g., mature, closed forests where evergreen and deciduous species with diverse drought stress strategies coexist, CL 1-4). However, during periods of active growth (e.g., humid summers and autumns), the simplified structure of grasslands and savannas and the minimal interference from non-photosynthetic elements (e.g., trunks and branches) allowed them to exhibit higher MCARI\({}_{\text{Sent}}\) values. Moreover, most crops and pastures receive supplemental irrigation from spring through early autumn [104]. Sites with high structural alteration values (_SAI_ > 70%, CL 7-8), dominated by herbaceous species with shallow root systems highly dependent on monthly rainfall cycles, exhibited pronounced seasonal variability in MCARI\({}_{\text{Sent}}\) values [50; 98; 105].