Prescribed burning shows minor impacts on black pine needle terpenes and pine processionary moth larval survival

Prescribed burning treatments initially designed to mitigate wildfire risk may have broader ecological consequences and enhance forest resilience to various disturbances. Prescribed burning can alter tree defences both directly through thermal stress and indirectly through changes in forest structure. Such changes in defence investment may, in turn, affect defoliator species like the pine processionary moth (PPM). With the increasing severity of PPM defoliation associated with warmer winters, it is important to understand how treatments such as prescribed burning affect tree defences against PPM.

We quantified terpene composition and concentration in current year and mature needles of dominant black pines, sampled before and 1 year after prescribed burning, across burned and unburned sites in three sub‐Mediterranean forests. Additionally, we assessed needle N content, δ ¹³ C and δ ¹⁸ O composition, and fire severity parameters. A bioassay with first‐instar PPM larvae was also conducted to evaluate how needle terpene and N content influence the larval survival rate.

Prescribed burning had no effect on needle terpene content 1 year after treatments. Terpene concentration was neither explained by fire severity, N content, or isotope composition. Instead, drought conditions contributed to the increased terpene concentrations in current‐year needles of both burned and unburned pines 1 year after treatments.

Prescribed burning had a minor impact on PPM larvae. Larval survival is complex and shaped by multiple interacting factors including treatment, needle age, and terpene and N content. Notably, a higher survival rate was observed in mature needles of burned pines as terpene and N content increased.

Synthesis and applications. Our results highlight that prescribed burning in sub‐Mediterranean pine forests does not affect their resistance to PPM in the short term, either positively or negatively, indicating that it can be implemented to reduce wildfire hazard without influencing forest susceptibility to future PPM outbreaks.