Quantitative relationships between insect herbivory severity and BVOC emissions in a Subarctic mountain birch forest

Insect herbivory amplifies the biogenic volatile organic compound (BVOCs) emissions into the atmosphere, where BVOCs participate in atmospheric chemistry processes. In the high latitudes, herbivory induced BVOCs are considered as a major contribution to the total plant BVOC emissions during periods of active insect herbivore feeding. However, current BVOC models do not quantify BVOC emissions upon insect herbivory. Including effects of herbivory in models would be especially relevant in order to model BVOC emissions in the Arctic, where insect herbivore pressure is expected to increase with climate change.

We gathered data from enclosure-based field studies conducted in the Subarctic, that assessed the effects of outbreak-causing geometrid moth larvae (Operophtera brumata and Epirrita autumnata) feeding on the BVOC emissions of the dominant tree species, mountain birch (Betula pubescens var. pumila (L.)). The feeding damage ranged from background herbivory to up to 100% defoliation, thus mimicking local insect outbreak conditions.

The leaf area based BVOC emissions from mountain birch increased linearly with increasing feeding damage up to a maximum of 15 %, depending on the BVOC group. After this maximum, BVOC emissions declined as the leaf area decreased.

These results provide quantitative relationships between leaf area eaten and the emission rate of atmospherically important BVOC groups in the Subarctic mountain birch forest. Our results have practical implications for incorporating the modelling of herbivory induced BVOC emissions into the mainstream VOC models such as MEGAN (Model of Emissions of Gases and Aerosols from Nature) or LPJ-GUESS (Lund-Potsdam-Jena General Ecosystem Simulator).