Contrasting Sentinel-2 based biophysical constraints of growth, productivity, and stem water dynamics in thinning trials of two mediterranean pines

Thinning alters forest structure and functioning, yet its effects on canopy biochemistry, growth, carbon uptake and hydraulic dynamics remain poorly quantified across spatial and temporal scales. We combined Sentinel-2 PROSAIL inversion with explicit uncertainty propagation to derive monthly canopy traits in paired thinned and control stands of Pinus sylvestris and P. nigra, integrating these with high-frequency eddy-covariance GPP, maximum daily stem-shrinkage (MDS), and decadal basal area increment (BAI) from tree-ring records. Thinning reduced canopy density, pigment content, and albedo, indicating a shift in stand optical properties toward a more open but less reflective canopy structure. Functionally, thinning increased long-term basal-area increment by ~90% in P. sylvestris and ~35% in P. nigra, but reduced spring GPP by up to ~9 μmol CO₂ m−2 s−1 and intensified summer hydraulic drawdown (ΔMDS ≈ −60 μm). Trait–function models explained 61% of BAI, 85% of GPP, and 30% of MDS variance, indicating distinct biophysical controls across response variables: leaf structural traits (especially LMA) was the strongest predictor of long-term growth, canopy architecture primarily explained seasonal productivity, and pigment–structure interactions contributed most to stem-water dynamics. This multi-scale, uncertainty-aware framework shows how integrated satellite, flux-tower and dendrochronological measurements can robustly detect and interpret thinning impacts in Mediterranean pine forests.