It is often difficult to restore degraded lands within protected areas because of the high costs and because so little is known about the ecological requirements of the many species involved. Experience in Tam Dao National Park in northern Vietnam suggests the reforestation of degraded areas can be catalysed by simple monoculture plantations and that the cost of this may be modest. In this case, an existing Pinus massoniana Lambert plantation that was subsequently included within the national park was retained because native plant species were re-establishing in the understory. Within 20 years, a species-rich understory composed almost entirely of native species had established under the protective cover of the pines. This comprised 64 plant families, including 122 tree species, 46 shrubs, 33 vines, 2 herbs, 2 ferns, and 1 grass. Sixteen of these species were classified as threatened. Most of the colonists were most likely brought to the site from adjacent intact forest by wildlife over distances of up to 700 m. These plants were mostly small-seeded species, and many poorly-dispersed species remain absent from the site even after 70 years and will need assistance to colonize. The pines have persisted for 70 years, and some suggestions are made for managing the transition from a pine plantation with a native species understory to regrowth forest of solely native flora. This study suggests plantation monocultures may have a useful role in enhancing biodiversity in degraded areas within other protected areas - provided natural forest areas are close by.