Plants in particular need to have a very efficient immune system for two important reasons. Firstly, they sit at the bottom of the food chain so there are a lot of opportunistic organisms out there, including insect herbivores and microbial pathogens who want to tap into that biochemical energy that is stored in plants. The other reason is plants are rooted to the ground – they cannot escape from the stressful conditions in their environment.
Rabbits eat grass and, in turn, are eaten by foxes.
caterpillars
Our hypothesis would be that, depending on the level of that stress – if it was a really long-lasting drought of a few years, then maybe the tree can remember it for a long time because it needs to adapt to that hostile environment. Now, maybe the hypothesis would be the other way around, maybe if it was a very dry July for instance, maybe the tree is not even that bothered and then it forgets within one year because that memory of stress is gonna be holding it back on its growth, for instance.
drought
They live even longer – over 5,000 years, in fact – all the way back to the Bronze Age.