Treeless saddles are often said to be more "natural," more comfortable for riders and/or horses, or more universally fitting for all equine back shapes and rider seats. But according to a leading equitation scientist, the tree still seems to serve a very important purpose: regulating pressure distribution.

"What you can see with the treeless saddle is a very definite concentration of pressure right underneath the rider’s seat bones," said Hilary Clayton, BVMS, PhD, Dipl. ACVSMR, MRCVS, Mary Anne McPhail Dressage Chair in Equine Sports Medicine at Michigan State University, during the presentation of her study at the 2011 International Society for Equitation Science (ISES) Conference, held Oct. 26-29 in Hooge Mierde, The Netherlands. However, that’s not the case with a well-fitted conventional saddle, which pressure mats reveal applies much more even pressure with lower peak forces across the horse’s back, she said.

"That suggests that the tree is indeed doing what it’s supposed to do, in terms of spreading the force over a larger area of the horse’s back," she said.

In her study Clayton fitted eight purebred Arabian horses with pressure mats under their saddles and had them ridden at a slow, sitting trot in a straight line by the same, experienced rider. The rider rode each horse once with a treeless saddle and once with a conventional English saddle custom-fitted to an Arabian horse. The saddles weighed exactly the same, and the rider rode without stirrups