Most areas of switzerland have very warm climate. One of the warmest climate north of the alpes (except rhine dale in germany which is warmer based on the whole year). The whole countryside is full of "exots"... there. Trachy is growing in forrest... natural nucleation. Cupr. semp, Ficus carica and evergreen plants everywhere. Maybe in Gävle it´s also no problem...then try it.
But if i compare the vegetation in both areas (north-west switzerland and south geramny i see an enormeous difference. In Switzeland and south germany in end of february or march all trees and plants are green... in gavle not. They play football on green grass, in gävle not... maybe there is really a difference... ;)

Greets