Authors: Daniel L Hoff; Rodent E Will; Chris B Zou; Nathan D LillieThe Cross Timbers ecosystem lies between the eastern deciduous forest and Southern Great Plains and was historically dominated by Quercus stellata and Q. marilandica. It is currently threatened by encroachment of Juniperus virginiana and the proliferation of other more mesic species. This change mirrors the “mesophication” of the eastern deciduous forest as pyrophytic species are replaced by less fire-tolerant species due to fire exclusion. We measured 125 forest monitoring plots in the Cross Timbers of north-central Oklahoma on Bureau of Indian Affairs properties with various levels of J. virginiana encroachment. We measured tree characteristics, quantified recruitment, and aged a subsample of trees. Results indicate that while Q. stellata is still the dominant overstory tree species, the rate of J virginiana encroachment increased linearly since the 1950’s with a current density of 57 stems ha-1 that are greater than 10 cm dbh. Juniperus virginiana and species from the genus Celtis, Carya, and Ulmus currently compose 73% of sapling and 62% of the seedlings. Without implementation of prescribed burning, fire-intolerant species will continue to increase. These finding have important consequences for future fire regimes, forest composition, and resilience of the Cross Timbers ecosystem.