We know that trees, just as any living thing, have a limit to their stored energy reserves. With each action a tree takes – whether it be leaf and root production, lengthening of branches, flowering, etc – energy is used. Trees that experience sudden and unexpected stress do have some level of store energy to be used in case of emergency, but this has a limit as well.
A recently published Harvard research paper describes the results of repeated defoliation of trees and its impact on tree health. The study found trees that experience repeated defoliation, either due to insect infestation or drought stress, can directly lead to a ‘mortality spiral’. Non-structural carbohydrates (NSC’s) showed a clear decline with each defoliation event. The study also found that if a tree’s stored energy reserves go below a critical level, this leads to tree death.
This has a direct relation to Hong Kong’s current insect problem. Ficus trees account for approximately 10-20% of its +7 million trees. This insect has 4 active feeding cycles within 1 year which can mean up to four defoliation events for a tree, assuming the tree is able to produce leaves after each event. The infestation of Ficus trees by the Phauda flammans lepidoptera is a critical problem and must be addressed.
Read the full research paper here: Research 2021 – Defoliated trees die below a critical threshold of stored carbon.pdf