The tallgrass prairie that once expanded in a north-to-south band in the American Midwest developed deep, black loamy soils so productive for modern agriculture. This region transitioned the dry Great Plains to the wetter woodlands of the American East. The prairie usually lacked trees because of the frequent cleansing wildfires that rid the prairie of dead plant fuel from grasses that grew upwards of 6-to-10 feet tall. Barriers to the wind-driven wildfires, like lakes or rivers, created small areas for trees to prosper, called "prairie parklands."
Two oak species often found refuge in fire-less areas of the tallgrass prairies called "oak savannas." In the northern reaches of the area, burr oak (Quercus macrocarpa) grew tall and slowly. Further south, at the edge of the tallgrass prairie, in the transitional zone called the prairie brush land of Texas, live oak (Quercus virginiana and Quercus fusiformis) infiltrated into the grasslands.
Appreciating the deep soils on the tallgrass prairie were two species of hickory. Bitternut hickory (Carya cordiformis) and the shagbark hickory (Carya ovata) grew there; these trees develop deep root systems that resent disturbance.
Aspens grew in the northern reaches of the tallgrass prairie. The fast-growing aspens populated fire-ravaged land transitioning between the prairie and the northern conifer forests. Large-toothed aspen (Populus grandidentata) and the quaking or trembling aspen (Populus tremuloides) grew into expansive thickets where fire didn't naturally kill back sprouting, suckering root saplings. In addition, the eastern cottonwood (Populus deltoides) found niches along stream banks.
Also in the Texas prairie brush-land alongside live oaks grew many types of native juniper (Juniperus spp.), but only where fire could not ignite the oils of the needles. Fire killed young saplings but also destroyed lowest limbs of tall junipers, clearing the soil and allowing light to the ground for prairie grasses and wildflowers to become re-established.
While widespread across Texas, mesquite (Prosopis glandulosa) occasionally intermingled with the southernmost reaches of the tallgrass prairie, where grasses didn't grow too tall to out-compete it.
Rarely seen today, prairie crabapple (Malus ioensis) historically grew along fire-protected banks of streams, lake shores, wetlands called "prairie potholes" and on woodland edges across the Mississippi River basin, including the tallgrass prairie. Its fruits were sour and hard, but pioneers made them into jams and jellies.