###### Abstract
CRP is a passive method that can also be applied as a stand-alone technique, because a priori information on the position of the cameras is generally not necessary, nor is camera orientation, calibration or the presence on the scene of geo-referred reference points [23; 24; 25]. The final 3D CRP models made available are useful for comparisons, animation, movies, measurements and conservation of the memory of the shape of trees in time as well as chronological evolution of the displacement of the tree. These models are given in digital form (easily computer manageable), are useful for future evaluations and can be sent all around the world for visual inspection. In addition, the evaluation of the possibility of preventing the instability and failure of standing trees is of great importance in forestry. This target can be achieved by ultrasonic methods, largely employed to detect the elastic characteristics of different materials (e.g., stone, concrete, wood), although the interpretation of the data is very complex because elastic wave propagation strictly depends on the heterogeneity, porosity, density and other material properties [19; 20; 25; 26; 27; 28; 29]. The presence of decay zones, small cavities and cracks or splits within the investigated materials are potential defects characterized by low ultrasonic velocity compared to the velocity in healthy materials. The ultrasonic techniques applied over time on the same trees in forestry or in an urban area can also deliver enhanced information about the possible evolution of tree disease and prevent their instability and failure. In this study, considering the nature and size of the investigated standing tree and the target of the study, an ultrasonic investigation by the 3D ultrasonic tomography technique was carried out at 24 kHz to obtain a three-dimensional representation of the distribution of the longitudinal wave velocity inside the stem. The 3D ultrasonic tomography was planned in an optimum way based on the CRP 3D model. This model also greatly contributed to the 3D ultrasonic tomography interpretation phase, as often external evidence reflects the presence of internal defects. The integration of the different types of complementary information aids the diagnostic process and adds value to the results. The integrated CRP and 3D ultrasonic tomography combined procedure was applied to a holm oak (_Quercus flex_ L.) living tree growth in a private garden in the town of Cagliarion the island of Sardinia, Italy. This tree was chosen due to the number of trees of this species in Sardinia. In fact, the natural distribution of holm oaks in Sardinia occurs from coastal zones up to an altitude of 1400 m in the upper part of the Gennargentu Mountains. Holm oak is a slow-growing shade-tolerant tree and is able to dominate in late successional stages. Sclerophyllous woods and maquis vegetation, where holm oak dominates, represent the most widespread evergreen woodland in the Mediterranean Region [30; 31]. Owing to recent human activity, holm oak trees are widespread in all Mediterranean coastal regions and are also intensively planted in public and private gardens, for example, in the town of Cagliari. At present, owing mainly to air pollution, many of these trees in urban environments suffer decay, especially from pathogenic fungi that can produce tail disease and bark cancer, thus increasing the risk failure [32]. Therefore, the specific objectives of this study were (1) to produce a 3D high resolution photogrammetric model of the investigated tree to store the memory of its shape and to check the chronological displacement evolution of the tree under observation, (2) to assess the tree health status by analyzing the elastic properties of the inner part of the stem using 3D ultrasonic tomography, planned based on the 3D high resolution photogrammetric model, and (3) to help prevent the instability and failure of the investigated tree by integrating the 3D CRP and ultrasonic tomographic models, obtained separately through independent processes.