Impact of drought-induced holm oak dieback on understory species composiBon and terpene emissions in a Mediterranean maquis

The occurrence of drought-induced holm oak dieback may alter the maquis species composi@on and volatile organic compounds (VOCs) emissions. Therefore, seasonal changes in holm oak canopy cover, herbaceous and shrub species richness and alpha biodiversity were investigated in two holm oak stands characterized by different degrees of crown dieback over four years (2019-2022) in Tuscany, while VOCs were monitored from 2019-2021. Holm oak canopy cover decreased by 50% in both stands, leading to increased radiation at the ground and a subsequent species richness increase in 2021. However, in 2022, the species richness was lower than the 2019 values in both stands, possibly because of the large amounts of dead wood on the ground. Although no changes in alpha biodiversity indices were observed, in 2021 a reduc@on in monoterpene emission was observed, thus reflec@ng the decline in holm oak canopy cover rather than the species richness modification. In conclusion, although the holm oak dieback did not have a significant impact on alpha biodiversity, it resulted in noticeable changes in the species composi@on of understory vegetation and terpene emissions. Our findings suggest that terpene emission in the Mediterranean maquis is more affected by holm oak dieback than species richness modifica@on.