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Multibaseline 3D SAR Tomography (Tomo-SAR) is a promising evolution of SAR Interferometry, to sense complex scenarios with multiple scatterers mapped in the SAR cell. Recently, this concept has been integrated with multipass Differential Interferometry, producing the Differential Tomography (Diff-Tomo, “4D”) mode which furnishes “space-time” signatures of multiple scatterer dynamics. Diff-Tomo has been usefully applied to subsidence monitoring in garbled layover urban areas. Other emerging interferometric and tomographic remote sensing applications regard forest scenarios. However, these are characterized by a temporal decorrelating and volumetric canopy scatterer, are even more complex than the urban one, and a set of open problems exist, in particular for the Tomo-SAR techniques to be applied to biomass inventory and monitoring. In this paper, to deal with such issues, experimental advances are presented of the original extension of Diff-Tomo methods for analyzing vegetated scenarios, to extract both geometric and dynamic information of forest layers. In particular, the concept of space-time signatures of temporal decorrelation - a new vision in SAR Interferometry - is confirmed with non-parametric Diff-Tomo analysis of real P-band airborne forest data. Also, the first extensive P-band phenomenological analysis of height-varying temporal coherence is shown, obtained with the new semi-parametric unique Diff-Tomo functionality of separation of temporal decorrelation mechanisms of canopy and ground. Finally, a characterization is shown and recent real data results are reported of the related Diff-Tomo enabled developing functionalities of 3D forest Tomography robust to temporal decorrelation, and of possible sub-canopy subsidence monitoring.