Plants produce different volatile organic compounds (VOC) as secondary metabolites, although these emissions are not always related to the plants growth and development. However, these emissions have important role in plant defense and reproduction. There are three different mechanism which regulate VOC emissions. Plants emitted VOCs to limit the herbivore abundance since some VOCs are toxic to the certain herbivores. Plants can also emit these compounds to attempt parasites or secondary predators to avoid the feeding of secondary herbivores. It has been discovered that these compounds are travelling in the air from individual plant to other and this signaling is a message to the other plants that they need to prepare for a possible tread. On the other hand, monoterpenes are compounds which keep conifer resin as running. Resin with monoterpenes will form a protective layer on surface of the trunk. This layer will dry when VOCs, mainly monoterpenes will evaporate.
Different species produce different composition of VOCs and the genetic variation between individual trees and species is pretty high. Even pines growing right next to each other can produce different compound compositions. Tree age is the other factor that regulates quality and quantity of VOCs emitted by trees. VOC production consumes a lot of recently photosynthesized carbon and for this reason plants will store only small amounts of VOCs into tissues. During a physiological stress, the production of these compounds increases remarkable. Conifers traditionally hold large storages of these compounds and they release small amounts of monoterpenes, methanol and acetone continuously. Broadleaves usually produce isoprene emissions. The internal variation between individuals is also significant: pines growing next to each other usually produce different compositions of these compounds.