## 3 Results and Discussion  
### Close Range Photogrammetry  
The CRP technique allowed a contactless non-invasive acquisition of morphological and geometric information from the investigated holm oak and faithfully reproduced the distribution of its shallow decay forms, highlighting the critical sectors. The CRP 3D models carried out in time (2018, 2019 and beginning 2020) allowed the high resolution 3D modelling of the stem, the computation of the reflectivity pattern, and the study of the kinematics of the holm oak. For example, Figure 7 shows the 3D model related to the CRP survey made in 2018. Thanks to the high resolution images, it was possible to create a realistic 3D model from which all the superficial characteristics of the bark as well as the relative forms of decay integrating the visual inspection results could be evaluated. By integrating the two above techniques we could better assess the spatial distribution of decay forms and the sectors most affected by pathologies. As can be seen in Figure 7, the external decay prevails on the south side of the stem and is concentrated mainly in its middle-apical part and in the branches. The most common decay form is bark darkening combined with other severe flaws such as fractures or splitting and bark detachments. Subsequently, we were able to detect the displacement of the holm oak. In particular, we performed another two CRP surveys in December 2019 and January 2020 using the same field geometry/strategy of the October 2018 relief. An inter-comparison of the three models calculated from the above surveys was performed in the same volume of the stem investigated by ultrasonic tomography. We used the inspection procedure of the JRC-3D Reconstructor(r) package by Gexcel, first computing the residuals of the three unified point clouds compared to cylindrical meshes suitably fitted and taken as references, following the methodology described in Section 2.3 in this study and in Fai  
Figure 7: CRP 3D model of the studied living holm oak and shallow decay forms (2018 survey). In a second step, we evaluated the displacement of the whole stem of the studied tree with the inspection procedure to compute the residuals (i.e., geometrical anomalies) of the 2020 relief 3D model, first taking as reference the mesh derived from the 2018 3D model, and then adopting as reference the mesh derived from the 2019 3D model. The results of the latter computation are represented in Figure 9a,b. In particular, the greatest differences were detected in the 2020-2018 time span, when the residuals varied in the \(\pm\) 0.05 m range. Conversely, the 2020-2019 residuals were negligible and varied in a range of a few mm. The external decay shown in Figure 7 is confirmed both by the geometrical anomalies represented in Figure 8 and by the deformation pattern represented in Figure 9. In the latter case the positive displacements (red anomalies in Figure 9b) were detected in the southern part of the holm oak. Conversely the negative trend (blue areas) is present in the northern side of the studied tree and varies over the \(\pm\) 0.05 m range. Moreover, a tilt st  
Figure 8: Evolution in time of the geometrical anomalies computed as residuals compared to meshed cylinders fitted to the unified clouds derived respectively from the October 2018, December 2019, and January 2020 CRP reliefs; (**a**) view from the southwest, (**b**) view from the northeast. Figure 9: (**a**) Displacement of the holm oak under study as detected by comparing the CRP 3D models of December 2019, taken as reference mesh, and January 2020; residuals are expressed in m.(**b**) Displacement in m obtained after the comparison of the October 2018 3D model, taken as reference mesh, and the January 2020 photogrammetric campaign 3D model. the south direction is evident both in the 2018 CRP 3D model (Figure 7) and in the geometrical anomalies and displacement maps represented respectively in Figures 8 and 9.