The inception of terrestrial woody plant ecosystems on the Earth is thought to have caused decreases in atmospheric carbon dioxide and water vapor concentrations in the Middle Devonian. Decreased greenhouse gas concentrations enabled a series of long-term glacial-interglacial cycles from the Late Devonian through the Permian. Here we describe the environmental and ecological variability of the earliest known paleosols with evidence of in situ forests (stump casts and attached root systems) from the Appalachian basin. Four examples located in the Manorkill Formation in the Catskill Mountains of New York State, United States, are analyzed using macro- and micromorphological data. Woody plant stump casts and molds on exposed bedding surfaces were mapped at two of the sites and analyzed using nearest-neighbor analysis. This permitted quantification of spatial distribution and ecological conditions of these paleoforests. These fossilized forests exhibit both single and multi-generational growth and formed in both aquic and seasonally well-drained environments, thus indicating established populations and growth adaptations by the represented species. The occurrence of these diverse forested landscapes in the Givetian is concurrent with the onset of the prolonged decrease in atmospheric CO₂ concentrations that have been tied to a series of Paleozoic glaciations.