A wooden tree with minor flexing provides more support and a proper distribution of weight over a large area without being too rigid. The common approach to building a seat on a non-flexible tree, influenced by mass manufacturing, is the metal strainer. We have found an all-leather seat to be ideal, as the leather will break in to the rider's shape, but maintain even support across the bars. The leather seat also allows just a bit more flexibility than the strainer, but not too much to cause injury to the horse.
Another alternative in saddle structure is what is referred to as a flex tree. This is when a saddle's bars are often made from recycled tire rubber, allowing the saddle to do exactly what it is named, flex. This flexing can cause hip pain for the rider and make a horse sore, as the pressure from the rider's weight is focused on a smaller area of the horse's back. This can cause pinching of a wide horse and rocking on a narrow horse. Also, due to their flexible nature, these saddles do not grip a horse well, which can make it difficult to mount and can cause slipping/sliding while riding. When building on a flex tree, the flexing of the bars can cause twisting during construction, resulting in a crooked saddle, which costs more and is less durable. The effects on a horse when riding in a flex tree resemble those of riding in a saddle with a broken tree. Pictured below is an image taken from placing a flex tree on a horse's back with a pressure sensor mat under it. Here you can see that the weight is not evenly distributed, creating pressure points on the horse's back, located just over the spine.
Treeless saddles produce very similiar complications to the flex tree as there is no support to evenly distribute the weight of the rider, resulting in too much pressure over the horse's spine and possible injury to the rider.
There is no "one size fits all", or even most, with saddles. A saddle that suggests it can fit a wide range of horses means it fits few VERY well. You need a saddle that fits YOUR horse and no amount of flexing in a tree guarantees a good fit.
For more information on the problems involved with a Flex Tree, please visit Saddle Tree Shop- From Shop and Desk
Wooden trees are usually covered in one of three materials; Bull-hide, Raw-hide, or Fiberglass. Of these choices, Bull-hide is considered the best option for saddles, as it is thicker than raw-hide, making a more durable saddle and it molds to the horse's shape quicker. Raw-hide, while not as durable, does hold up nicely and is a fairly good choice in tree covering. On the other hand, we do not recommend fiberglass covered trees as they are brittle and without any flex, the forks and cantles can become loose. Also, the fibeglass coating can break down causing delamination. While fiberglass is cheaper, the durability of a tree coated in it, makes it the more costly option, as the saddle is not likely to last very long.