Legacy Effects of Oil Road Reclamation on Soil Biology and Plant Community Composition

Following the unprecedented oil drilling presently occurring in western North Dakota, thousands of kilometers of oil roads must be reclaimed to an acceptable post-extraction condition. This study assessed the soil biological and plant communities of nine decommissioned oil roads reclaimed during three periods between 1983 and 2002 in the Little Missouri National Grasslands of western North Dakota. We hypothesized that time-since-reclamation would positively affect soil biological and plant communities and, consequently, success of reclamation at older sites. To assess this hypothesis, we measured soil enzyme activity, soil microbial community composition, plant community composition, and soil physical and chemical properties along a gradient extending from road-center to adjacent native prairie for the nine roads. Time-since-reclamation did not affect soil and plant properties measured, indicating that older reclamations are not more similar to native prairie than reclamations occurring more recently. A strong gradient between samples from road-center and native prairie was identified with univariate and ordination analyses, indicating that soil and plant communities of reclaimed oil roads do not resemble those of the surrounding prairie. Soil organic matter (SOM) was identified as the most significantly affected soil property, being 30% lower on reclaimed roads than prairie. The relationship between SOM, microbial community, and plant community suggests that incorporating additional SOM could hasten reclamation as a result of improving the physical environment for plants and providing a labile carbon and energy source for the soil microbial community which, in turn, will enhance the nutrient and physical conditions for plant growth.