Plants invest for VOC synthesis to protect their tissues against herbivore attacks, mainly feeding and other mechanical damages. Plants have a baseline of VOC emissions which means that plants emit regularity small amounts of thesVOC emissions but the amount of VOC synthesis and emissions increase when plants reach a signal from each other that the abundance of insects or pathogens has increased. This signal message moves also in the air through the VOC emissions. The same signaling happens also in soil by plant roots.
In the boreal forest the feeding pressure by insects, like bark beetles is lower than in the tropical forest, but the balance between herbivore and plants can change through the climate change and this is the possible mechanism which could increase VOC production by the plants. The insect abundance can increase through the climate change, although we cannot assume straight forward that the insect abundance will increase when average temperature increases. The most powerful affect is probably through the mild winters since this will increase survival of insects and young phase of insects.
Earlier we assumed that all the isoprenoids have the role in plant defense. At the moment, the results indicate that also monoterpenes can participate to the plant protection. Monoterpenes and sesquterpenes are stored into plant cells into trunk, shoots and roots and this emissions are released after a mechanical damage so this can form significant defense against herbivore and pathogens. Some VOCs are typically stored into plant cells but there are also significant amount of other compounds which are released usually straight away without any storage phase. Volatile isoprenoids can also increase mutualistic interactions between plant and insects by increasing the abundance of pollinators or ants and other insects which form a significant enemy for different herbivore insects. In the forest these interactions are present at the great balance but this can change through the climate change. On the hand, we can also claim that the nature will always return back into a balanced position.