Transport via Plants

Conjuration (Teleportation)
Level: Plant 6, Ranger 6, Travel 6
Components: V, S
Casting Time: 1 standard action
Range: Unlimited
Target: You and touched objects or other touched willing creatures
Duration: 1 round
Saving Throw: None
Spell Resistance: No
Spell Points: 11

And this is the real reason Druids plant those trees everywhere.

You can enter any normal plant (of a size category no smaller than your own) and pass any distance to a plant of the same kind in a single round, regardless of the distance separating the two. The entry plant must be alive. The destination plant need not be familiar to you, but it also must be alive. If you are uncertain of the location of a particular kind of destination plant, you need merely designate direction and distance and the transport via plants spell moves you as close as possible to the desired location. If a particular destination plant is desired but the plant is not living or otherwise impossible to travel to, the spell fails and you are ejected from the entry plant.

You can bring along objects as long as their weight doesn’t exceed your maximum load. You may also bring one additional willing creature (carrying gear or objects up to its maximum load) per three caster levels. All creatures to be transported must be in contact with one another, and at least one of those creatures must be in contact with you.

You can’t use this spell to travel through plant creatures.

The destruction of an occupied plant slays you and any creatures you have brought along, and ejects the bodies and all carried objects from the tree.

Augment: If you spend 2 additional spell points, you can travel through plant creatures with this spell, although most plant creatures find this gravely offensive.