Resin tapping of Atlantic pine forests: towards an optimized use of stimulant pastes over the season

Pine resin is a valuable non-wood forest product with an increasing interest in multiple industrial sectors. Resin-tapping activities also provide valuable ecosystem services in timber-oriented and highly productive pine forest of Atlantic regions, where little previous experience in resin-tapping is available. The objectives of this study were to determine the efficiency of different stimulant pastes and its variation with pine species, site conditions, seasonality and frequency of tapping interventions. We conducted parallel experiments using both conventional and micro-tapping techniques in mature pine stands in NW Spain. We tested four stimulants (control and Zeta, Cunningham and Salicylic pastes) and two groove frequencies (every 2 or 3 weeks). All stimulant pastes significantly increased resin yield compared to the control, being resin stimulation highly consistent across years, sites and species. In conventional resin tapping, resin yield was maximized with the Cunningham and Salicylic pastes while in micro-tapping Salicylic was the most outstanding stimulant treatment. According to the rapid decay of resin flow after wounding, total resin yield decreased with more spaced grooves. However, the reduction was low, and the global efficiency of the tapping operations are likely maximized with grooves applied every three weeks, which would allow increasing the number of tapped trees. Micro-tapping techniques were valuable for screening stimulant pastes and anticipating variation among sites in resin production. Altogether, the Salicylic paste is recommended, especially at the beginning of the resin campaign, when the effect of the pastes was maximized, and if tapping is conducted using closed atmospheres and containers.