Scotland was once a largely forested country, but after centuries of human influence, only a tiny fraction of the original forest area remains. With one of the lowest forest covers of any European country and the majority consisting of non-native plantations, increasing the amount of native woodland is an urgent need. The natural expansion of native woodland is limited by three main factors in Scotland: browsing by wild deer, a shortage of regeneration niches, and a shortage of seed sources. In many areas, the process of natural regeneration is, therefore, very slow or entirely absent for some species. Cairngorms Connect is a land management partnership established to restore habitats and natural processes to 60,000 ha of the Scottish Highlands. Woodland expansion is a key goal—specifically, by departing from the recent norm of planting and aiming to enable expansion by natural processes. We have devised a Before-After-Control-Impact experimental trial to test methods of accelerating the natural expansion of native broadleaves via applied nucleation. The trial compares two methods of opening up regeneration niches by cutting the dense understorey vegetation, as well as two methods of seed source establishment by sowing or planting. Through detailed monitoring and thorough documentation of management methods, this Seed Source Establishment Trial will inform restoration efforts in Scotland and further afield.