If that were generally true then tropical zones would be overridden with bark eating beetles. Vastly more biodiversity occurs in tropical zones than in Arctic and Temperate zones.
Apparently you dont understand how evolution works. Trees in colder climates dont have a resistance to certain pests because freezing weather keeps them in check. Changing the climate quickly allows these pests to overrun the tree populations. This isn't an issue in warmer climates because life evolved differently there.
