General:
* Horseback rider
* Equestrian
* Rider
* Horsewoman/Horseman
More specific:
* Trail rider (if they are on a designated trail)
* Woods rider (if they are riding off-trail)
* Hunter (if they are hunting while riding)
* Woodsman/Woodswoman (if they are skilled at navigating and surviving in the woods)
You could also use descriptive phrases like:
* Someone riding through the woods
* A person on horseback in the forest
The best term will depend on the specific situation and the level of detail you want to convey.