Tallgrass prairie and oak savanna in Wisconsin, USA. We are standing atop a rise, overlooking a restored tallgrass prairie and oak savanna. Prairie restoration began in 1970. The bur oak (Quercus macrocarpa) trees that you see produce a corky, fire-resistant bark that allows them to tolerate the fire events that are needed to sustain the prairie ecosystem. The largest of the trees is over 200 years old. Prairie ecosystems are diversity hotspots, can exist in dry habitats, and are important carbon sinks. Prairie ecosystems are some of the most endangered in the world, with only about 1% of native prairie remaining in WI.