Trees you depend on!
Trees are at the heart of nearly every saddle. Saddles started out as leather or cloth pads with a simple girth or surcingle. Many different people throughout history have improved upon that original design by adding more padding and stirrups. It wasn't until around 200 BC in China, that the first treed saddles where used. The first saddle trees were created to help reduce stress points on the horses back. By 477 AD the stirrup had been used in China then spread to Europe. Saddle trees have also evolved over time. Nowadays saddle trees can still be hand-made, but there are other methods of manufacturing and other materials for making saddle trees.
Traditional Wood Trees
Wooden trees are the traditional tree style. Wooden trees are made up of different types of wood either laminated together or glued and nailed. Western Trees can also be wrapped in rawhide for extra durability. This type of tree can be used for any discipline as it is very durable and slightly flexible for some shock absorption. They can withstand hard work well, although a disadvantage of a tree like this is that they can easily mildew or rot if moisture gets in, and they are very costly because of the labor involved.
Polyethylene Synthetic Trees
This type of tree is completely synthetic and is made from a form. Being that the manufacturing process does not require hours of work to sand down and shape the tree they are more economical to make. They can also come in a large range of sizes. They tend to be less flexible than a traditional wood tree. Disadvantages are that you need to make sure this saddle fits properly as it it is slower to mold to the horses back and is more rigid.
A fiberglass tree is a mix of wood and fiberglass. The fiberglass makes the saddle strong, durable and weigh less than a traditional wood tree. Fiberglass also has a very high tensile strength, more than steel the same thickness. These are used for many disciplines with exception to roping.
The flex tree saddle is a mix of synthetic materials and wood. With a rigid fork, cantle and wood laminated bars, the tree is allowed to move with the horse slightly. This was designed to eliminate some pressure points while still allowing for a more forgiving fit.
The modern treeless saddle is more developed than just a pad or leather cloth with a girth or surcingle. Now a days treeless saddles are gaining more popularity again due to the ease of fitting. The treeless saddle is nice as it will work on a variety of different horses with out changing anything, as well as being flexible. The treeless saddle also gives you a more close contact feeling when riding. One down side is that it can slip when getting on as there is no rigid form holding the saddle over the horses withers. Also make sure you are using a good supportive pad with a tree-less saddle, unless there is a spinal channel built in. Many treeless saddles place your seat bones as pressure points on the horse's back, as there is no tree to distribute the weight of a rider.
There are other variations of the types mentioned above. Some have wood as a base with polyurethane over it to provide the extra strength. As we continue to experiment with different materials there are even more types of trees to come. The bottom line is that modern saddle trees are a work in progress. The shape of the tree is essential when fitting a saddle to your horse, make sure you understand how it lays on your horse's back to provide the most comfortable ride for your horse.