The French entry at the 56th Vienna Biennial in 2015 featured an installation called transHumUs that used mobile robots to let trees move through their environment.
“The poetic ambition of the work is to free trees from their determinism by allowing them to explore the world by themselves.” 
The idea is “to reveal the invisible internal states of the trees.” The trees are mounted on robotic carts that allow them to move slowly along paths determined by their own physiology, measured by sensors that detect the flow of sap.
I’m not sure this is an especially exciting art work. As the video makes clear, things happen closer to the pace of the trees than to we hasty humans. And I, for one, don’t find giant root balls that decorative. (Don’t mistake me—I love healthy plants, and I know the value of a good root ball. But they aren’t all that much to look at, are they?)
More intriguing is the assertion that this project somehow offers “autonomy” to the trees, which are said to be “moving according to their metabolism”. It is true that the robots they are riding on are “autonomous” in the technical sense that they are guided by onboard logic. But, as in the case of the Purdue “Soybots”, the trees are more passengers than anything else.
The control signals from the trees (measures of sap flow) are certainly not voluntary directions from the tree in any sense. And the signals are used as input to the planning algorithm that was created by the humans, not the tree.
So there is no reasonable way to say that this is anything other than a robotic planter, guided by an arbitrary algorithm. Except for scale, this is pretty much the same idea as the Soybots, and they did it with robot vacuum cleaners!
As I always do, I will ask whether this system is beneficial to the non-human participants. Is this good for the trees? I don’t see that they benefit in any way, though they probably are not harmed as long as they were cared for and returned to the soil after the exhibition period. But really, this isn’t a good thing to do to a tree.
- Guilhem Saurel, Michel Taïx, and Jean-Paul Laumond, transHumUs: a poetic experience in mobile robotics. 2015. https://hal.archives-ouvertes.fr/hal-01206067