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The loss of grassland due to anthropogenic activities has increased dramatically over the last 150 years. Originally the greatest threat to native grasslands was their conversion to row-crop agriculture. Today remnants of the grasslands that escaped the plow are threatened by the invasion and expansion of woody species. In eastern KS, establishment and expansion of Juniperus virginiana (one of the most common trees in North America) can completely displace native tallgrass prairies in < 40 years.  A similar replacement of grasslands by this and other Juniperus species is occurring in Texas and Oklahoma. In this presentation, we will provide a broad synthesis on the current understanding of Juniperus biology and ecology, which may provide a basis for the management of remaining grasslands threatened by Juniperus invasion and expansion. The ecological consequences of the replacement of C4 dominated grasslands by Juniperus have been well documented. These include shifts leaf-level physiology based on changes in photosynthetic pathway of the dominant species (from C4 grasses with high photosynthetic potential to C3 trees with much lower rates of C uptake), concurrent shifts in environmental controls over patterns of growth (from water availability in grassland to temperature in forest), large increases in aboveground productivity and biomass in forest, and reductions in plant species richness during the transition from grassland to forest. We need to understand how grasslands being invaded by Juniperus species can be managed to arrest this increase or even reduce woody plant abundance, (2) how the long-term stability of these forests compares to native grassland, particularly with regard to fire, extreme drought, climate change, and C storage, and (3) the degree to which closed-canopy Juniperus forest represents an alternative stable state, or one that can be readily restored to grassland.