Effects of soil treatments and tree species on reforestation of well pads

Anthropogenically induced arrested succession is a global problem in forest ecosystems. In northern Michigan (U.S.A.), oil development has arrested succession in forest landscapes since the 1970s and oil well pads have not reforested up to 30 years after being vacated. To explore pathways for reforestation, we evaluated survivorship and growth of northern red oak (Quercus rubra), white oak (Q. alba), jack pine (Pinus banksiana), and red pine (P. resinosa) at monthly intervals during growing seasons from 2015 to 2019 on pads, which had been vacated 9–34 years prior to the initiation of our study. We planted trees in four soil surface treatments—experimental control (planting only, no treatment), disking, fertilization, and disking with fertilization. While monitoring survivorship and growth of planted trees, we concurrently examined natural reforestation in untreated control areas on each pad and differences between soil characteristics of pads and surrounding forests. Pinus resinosa displayed highest overall survivorship regardless of treatment, but maximum survivorship in disked soils and experimental control areas. Other species had highest survivorship in disked soils. There was no significant reforestation in untreated control areas during the 5‐year study period. Pads had higher levels of Bray P, Ca, and Mg, but lower levels of Fe, organic matter, and moisture than forest soils. Concentrations of toxic chemicals associated with drilling activities were not different between pad and forest soils or, if different, within acceptable levels for plant growth. In reforesting well pads, restorationists should plant P. resinosa in disked soil to achieve highest tree survivorship and density.