There are two ways to create silvopasture, add pasture to woods or add trees to pasture. Adding pasture to woods involves manipulating the existing woods to allow enough sunlight to the forest floor to stimulate the growth of desired forage species. Always seek input from a forester when manipulating woody vegetation (either planting or cutting).
In the most general sense, the process of adding pasture to forest will remove some trees while leaving other trees. The goal is to increase sunlight to the forest floor to support desired forage species. The cutting and retention should also align with your woodlot management objectives. The questions you need to consider are: which trees to remove, which trees to retain, what methods are effective at removing trees, what will happen to the trees that are cut, and how can desired forage be best established. Two videos are available here to illustrate a couple steps in the multiple paths to adding pasture to woods.
Video 1 (http://youtu.be/YM0iEsegAZU) illustrates a FECON grinder head on a skid steer-typed machine that grinds low value conifers while creating a mulched forest floor. In this example, a winter yard is being created that will provide protection for livestock during winter storms. The FECON can also be used in hardwoods as illustrated in the picture.
Video 2 (http://youtu.be/zM2cm3UBHkU) is a brief discussion of the selection process being used to pick the retained and the cut trees as a forest is being developed into silvopasture. The same criteria would be used if the cutting was intended to improve the timber production of the woods. Eventually, this woodland area will have a second cut to further reduce the number of trees and add more sunlight to the forest floor, but no single cutting event should remove too many trees or the residual trees may suffer. A couple pictures are also included, plus in the "photos" tab above.
The process to select trees is best if completed with a forester. Not all foresters understand and appreciate the value of silvopasture as a land and forest management tool. If your forester is unfamiliar with silvopasture, suggest a review of the silvopasture guide, or some other resources available on the internet. Most concerns among foresters originate from the historical (and sometimes current) uncontrolled woodland grazing, a far cry from the management intensive process of silvopasture.
Your forester can also offer some guidance on the methods that best mesh with your circumstances for the removal of the trees and whether to utilize the trees. In small silvopasture operations, you might want to transition a couple acres of woods per year with utilization of the trees for firewood; or, disperse cutting across a larger area, but with less intense cutting. In larger silvopasture operations, you might want to have a cutting crew do the work and take the wood away. The logging crew might only pay a few dollars per ton of wood, but the work would be done for you. A forester can help find a competent logging crew in your area.