A new study revealed that trees have developed smart defense mechanisms to fight browsing animals that that eat or nibble their branch or bud.
The study, published in the journal Functional Ecology, showed that trees were able to determine if their branch or bud were purposely nibbled off by a roe deer, or just randomly torn off by a storm or strong wind.
For the study, the researchers simulated a roe deer feeding on young beeches (Fagus sylvatica) and maples (Acer pseudoplatanus) by cutting off buds or leaves of the trees and trickling real roe deer saliva on the cut surface from a pipette. The researchers will then measure and record the concentrations of the hormones and tannins in the samplings.
According to a press release, the saliva of the roe deer was able to trigger increase production of different hormones, including salicylic acid. Due to the increase production of salicylic acid, the trees will also increase the production of specific tannins, a substance known to influence the feeding behavior of roe deer, making them lose their appetite for the shoots and buds.
Additionally, the trees also increase its production of growth hormones. The increases in concentration of growth hormones allow the remaining buds to compensate for the lost ones. However, when the researchers cut the buds or leaves without trickling real roe doe saliva, the samplings did not increase its production of salicylic acid signal hormone nor the tannin substance.
Roe deer, like other browsing mammals, can cause great deal of damage and hinder the regeneration of many deciduous tree species. Young samplings gnawed by roe deer could take a few more years to grow when compared to non-bitten conspecifics. When the damaged caused by the browsing is severe, the tree could become stunted, or in the worst case, the trees would just gradually die after a number of years.