This manuscript presents the results of a health assessment of a tree stand at the historic manor park in Rzeczyca (Łódź Voivodeship, Poland), carried out as part of its revitalization process. The study aimed to preserve the relics of the historic landed estate garden and adapt the park to contemporary public functions through the development of a tree management plan based on specialized arboricultural diagnostics. A dendrological inventory covered 370 trees within an area of approximately 3 ha, documenting their spatial distribution, species composition, morphology, and health condition. The dominant species were Tilia cordata (21.9%), Fraxinus excelsior (19.7%), and Prunus spinosa (9.4%). Advanced technical examinations were performed on 87 selected trees using sonic tomography with the ArborSonic 3D device and biomechanical assessment. These methods enabled the evaluation of internal wood degradation and the structural stability of mature trees, supporting decisions regarding their preservation. The findings emphasize the importance of cooperation between landscape architects and qualified arborists in the revitalization of historic parks with mature tree stands. The study also highlights the need for standardized diagnostic procedures and regular monitoring to improve public safety, support conservation efforts, and reduce unnecessary tree removal in response to increasing climate-related risks.