Road decommissioning is increasingly recognized as a critical first step in the restoration of terrestrial and aquatic habitats. However, crucial gaps in knowledge exist about the efficacy and ecological effects of road-removal practices. One particularly important issue is the effectiveness of post-road-removal revegetation practices. This study evaluated (1) the short-term effects of road decommissioning on plant community composition, (2) the effects of seed-mix origin, species diversity, and seeding density on vegetative establishment, and (3) the impact of overstory canopy cover and coarse woody debris (CWD) on revegetation success on recently decommissioned roads. One year after decommissioning, total vegetative cover (on the former roadbed) declined by 60%, with non-native plants showing the greatest magnitude of response (circa 90% decline). Although the use of non-native seed is often justified by the need for rapid vegetative establishment on disturbed sites, we did not find significant differences in percent cover of total vegetation between plots seeded with native versus non-native species. As expected, cover of native species was significantly higher in plots seeded with natives compared to those seeded with non-natives (12.3 vs. 7.8%, respectively). Furthermore, in plots seeded with native species, 43% of total vegetative cover was due to cover of seeded species; in comparison, non-native seeded species accounted for only 18% of total vegetative cover in non-native plots. Cover of seeded species was not significantly impacted by overstory canopy cover or CWD. These findings suggest that native seed mixes may outperform non-native seed mixes in terms of vegetative establishment after disturbance associated with road removal.
Seed transfer zones, which define the geographical relationship between adaptive traits and environmental factors, are increasingly used to determine the source populations that can be combined in restoration and revegetation. Climatic variables have been the most commonly used environmental data in transfer zone development, even though soils are also a primary selective force on plants. We assessed the importance of including soils in seed transfer zones using Bromus marginatus, a native grass used for restoration and revegetation in the western United States, as an example. Seeds were collected from 64 populations across Montana and Idaho and grown in a common garden for two years. We assessed among‐population variation based on 11 traits related to germination rate, plant size, vigor, inflorescence number, survival, and carbon isotope discrimination (∆13), and used this variation to develop seed transfer zone maps using two approaches: (1) a conventional approach, using only climatic variables (climate only) and (2) an expanded approach that included soils and climatic variables (soils + climate). The most influential drivers of trait variation were factors related to soil water availability: soil order, available water content (AWC), and organic carbon levels. Populations from areas with andic soils, which have high soil AWC and soil organic carbon, had low germination, limited first‐year survival, low ∆13, and small seeds. Growing season length and winter temperatures were also predictive of trait variation. In comparison to climate‐only models, soils + climate models explained 11% more variance (120% relative increase) for ∆13 and an average of 4.5% more (27% relative increase) for growth traits and survival. The transfer zone map developed using soils + climate differed from the climate‐only map in both spatial pattern of ecotypic variation and number of transfer zones; the soils + climate map had more zones and a higher proportion of small (<4 km2) transfer zone patches, while the climate‐only map had more large patches >37 km2. Including soils in transfer zone development may identify adaptive trait variation that is obscured by large‐scale differences in climate and could improve plant materials used for ecosystem management.
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