The Droplet Lab Dropometer was used to quantify the wettability recovery of refoliated aspen leaves by measuring water contact angle (WCA) on the adaxial (upper) leaf surface during the regrowth period. Specifically:

• In Section 2.3 (“Wetting characteristics”), the study describes WCA measurements performed with the Droplet Lab Dropometer using 10 µL deionized water droplets, with ≥9 measurements per sampling date and reporting mean ± standard deviation.
• These WCA measurements provided the primary functional metric linking:
  (1) refoliation timing and leaf development, to
  (2) micro/nano surface morphology (SEM), and to
  (3) the onset and persistence of a superhydrophobic/non-wetting state.

Where contact angle is explicitly described in the paper:

• Methods: Section 2.3 (Droplet Lab Dropometer, 10 µL DI water, replicate counts)

Results: Section 3.2, plus Fig. 2–4 and Table 1 (WCA values/trends and correlation to surface structures)

• Same-season recovery is possible: Quaking aspen in the study could refoliate in the same year after complete LDD defoliation, though with smaller leaves than typical spring growth.
• High hydrophobicity appears quickly: Refoliated leaves were already strongly hydrophobic within ~2 days after budbreak, rather than requiring a long “ramp-up” period.
• Measured WCA range during refoliation: Reported average WCAs across the refoliation study window were approximately ~140° to ~150° (with date-to-date variation reported as mean ± SD). (See Section 3.2, Fig. 2–4, and Table 1.)
• Mechanism confirmed by structure + WCA: SEM showed a dual-scale hierarchy (microscale papillae + nanoscale ECW crystals) consistent with a Cassie–Baxter non-wetting state, aligning with the high WCA measurements.
• Ultra-low adhesion prevented roll-off testing: The team notes they could not accurately measure roll-off angle because droplets rolled off immediately with slight disturbance (stated in Section 2.3).
• Environmental conditions likely tune morphology: The refoliated leaves showed subtle morphology differences versus normal-season leaves, plausibly linked to temperature during growth after budbreak.

For forestry, tree health monitoring, and agriscience, this paper shows that contact angle can serve as a fast, quantitative “functional recovery” metric after insect-driven defoliation events. In practical terms, pairing WCA with microscopy allows researchers and land managers to distinguish between “leaf return” and return of critical surface function (water shedding/non-wetting), which can influence canopy water interception, surface cleanliness/pathogen interactions, and broader ecohydrology behaviors discussed by the authors.