In this interview on sculpture.org, David Nash describes his work Divided Oaks, which we couldn't find.
David Nash: In contrast to Ash Dome, the trees for Divided Oaks, which is in a park at the Kröller-Müller Museum in Otterlo, the Netherlands, were already there. The soil there is very sandy, and it is quite tough for plants to grow. There was a quarter-acre of very scrubby oaks that weren’t growing. The site was offered to me because they were going to pull down all the trees. There were probably 600 trees. I thought that instead of pulling them all out and planting something new, I would work with the existing trees. I made a division through them, angling one side to the east and one side to the west. They began with an open space and at the end of this channel, the trees crossed over. I had been invited to come and make something apt, make some sort of interaction that signaled the presence of the human being.
JG: This kind of work admittedly demands some manipulation of nature. Do you prune the trees?
DN: It is called fletching. The very small trees, I simply pushed over and put a stake to hold them, while for the larger ones I cut out a series of V-shapes, bent them over, and then wrapped them so the cambium layer could heal over. This really woke the trees up. My intervention actually stimulated them, and they were obliged to grow. They are now growing and curving up.