Many trees first reproduce decades after germination. Many pests of trees reproduce in under a year. It would seem that the pests have an advantage in the evolutionary arms-race, as they can evolve a means of attack far faster than the tree can evolve a defense (cf. Does an increased reproduction/mortality rate provide an evolutionary advantage?).
I once read a speculation that trees might mitigate this by varying the genetics (or perhaps only epigenetics?) of different branches within an individual. The branches that do better produce more seeds. The seeds produced by a branch carry information specific to the branch. This means evolution (or the epigenetic equivalent) happens at the level of the organ, not the individual.
Is there any research supporting this speculation? If it has been refuted, how do trees compete effectively in the arms-race?