Springtime ecosystem-scale monoterpene fluxes from Mediterranean pine forests across a precipitation gradient

•We quantified monoterpene (MT) fluxes in two pine forests across a rainfall gradient.•The drier site suffered a heat wave that lowered net daytime CO2 assimilation.•Both forests showed similar daytime standardized MT emission capacities.•Emission models overestimated MT fluxes under high temperatures of a heat wave.•Interaction of drought and high temperatures drives biogenic MT emissions.