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Questions: (1) How have the composition and structure of undisturbed upland Quercus forests changed over 50 years across a large region and moisture gradient; (2) What factors are associated with long‐term and broad‐scale changes in these forests? Location: Oklahoma, USA. Methods: We re‐sampled 30 forest stands originally sampled in the 1950s across a large geographical area and compared basal area, tree density, and sapling density between the sampling periods using paired t‐tests, CCA, and DCA. We examined vegetation dynamics in the context of drought indices compiled for the sample period. Results: Total and Quercus stellata basal area and tree density increased, but Q. stellata and Q. marilandica sapling density decreased. Juniperus virginiana and woody species richness increased for all measures. DCA indicated that re‐sampled stands generally changed from Q. stellata–Q. marilandica‐dominated forests to forests with greater woody species richness and more J. virginiana. Q. stellata remained a dominant tree species; otherwise, composition shifted towards mesophytic and invasive woody species. Measurements taken in the 1950s immediately followed a major drought; whereas subsequent decades were significantly moister. Conclusions: Fire exclusion and drought may have played an important role in driving changes towards lower dominance by Quercus, increased importance of mesophytic and invasive species, and greater woody species richness. These phenomena are similar to those found in Quercus‐dominated forests throughout the northern hemisphere.

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The development of tap root anatomical features was investigated in seedlings of loblolly pine (Pinus taeda L.) under both pot and pouch growth regimes. The roots possessed the three anatomical zones previously observed in jack pine (Pinus banksiana Lamb) and Eucalyptus pilularis Sm. -white, condensed tannin (CT), and cork -suggesting that this developmental sequence is preserved over species and growth conditions. Xylem development was centripetal and similar to that found earlier in P. sylvestris. Tracheids with lignified, secondary walls were detected distal to the point of endodermal Casparian band deposition. However, tests for ability to conduct fluid indicated that the protoxylem was capable of transport only proximal to the Casparian bands. Detailed examination of suberin lamella deposition in the endodermis demonstrated that passage cells were present through the white and CT zones. Progressive, centripetal cortical death in the CT zone did not include the endodermis, which remained alive until the cork layer formed, at which point the endodermis was crushed. Therefore, passage cells remain as functional portals for nutrient and water uptake in the CT zone even though the central cortex is dead. Tracer tests indicated that the endodermis provides an apoplastic barrier to tracer diffusion into the stele and that this function was taken over by the young cork layers. Results of this study point to a strong role for the endodermis in the regulation of nutrient and water uptake until the maturation of the first cork layer.