Rodents, beyond keystone species such as beaver (Castor canadensis), provide several important ecosystem functions that can impact restoration activities Rodent ecosystem functions include ecosystem engineering such as burrowing and mound building, trophic interactions like herbivory and seed dispersal, and serving as reservoirs for diseases. These functions will vary in importance over time and have mixed effects depending on the types of restoration employed and the level of desired control over outcomes. Specific outcomes may be highly contextual, but some generalizations can be made. In situations where active restoration or high levels of human control over the outcome are desired, ecosystem engineering and herbivory can negatively impact restoration activities and will need to be managed. In passive restoration, some functions, such as seed dispersal, will provide positive outcomes early in the process. Some functions, such as dam building by beaver, may never be viewed positively in highly controlled situations. Importantly, for any type of restoration activity, over time the disturbance caused by rodent foraging and burrowing appears to positively impact plant diversity and biomass. In highly managed systems, particular species of rodent could be managed to provide specific functions in lieu of other species.
Southern Appalachian spruce-fir sky islands are globally threatened, boreal-relict forests where Picea rubens (red spruce) and Abies fraseri (Fraser fir) are dominant. Stands are primarily composed of Fraser fir above 1,890 m with spruce-fir and spruce-dominated stands between 1,620 and 1,890 m and hardwood associates below 1,620 m. Hardwood encroachment and the reduction of spruce-fir forest cover are primary concerns as climate change increases droughts and raises temperatures, threatening high elevation-dependent systems. We compared growth rates (basal area increment; cm2 yr-1) of canopy red spruce, Fraser fir, and competing hardwoods among forest cover types and topographic aspects at six southern Appalachian sky islands in North Carolina, Tennessee and Virginia. We expected slower growth of red spruce and Fraser fir than hardwoods at ecotonal transitions, lower elevations, and on more xeric aspects. However, we observed that red spruce and Fraser fir growth rates were similar to or greater than those of hardwoods. Specifically, red spruce growth rates were greater than those of hardwoods on northern and southern aspects in the ecotonal transition whereas Fraser fir growth rates were often greatest in fir-dominated stands. Our findings could assist managers in prioritizing restoration treatment locations to expand the spruce-fir cover type downslope in the southern Appalachians.
Restoration efforts in North America targeting lands dominated by the non-native and persistent Agropyron cristatum (crested wheatgrass) have failed to sufficiently reduce the species in favor of native plant communities. Restoration efforts have largely focused on traditional vegetation control methods, but there is evidence crested wheatgrass alters soil properties and processes. This may contribute to its persistence and the poor success of native plant community reconstruction. We conducted a field trial in northeastern Montana, USA, to evaluate reconstruction methods that aim to condition the site for two years prior to native species seedings. We used combinations of herbicide, tillage, biological soil amendment, and cover crop, with the goals of reducing crested wheatgrass cover and improving soil nutrient content and microbial activity. We observed treatments including herbicide or tillage were effective at reducing crested wheatgrass cover from 20-35% in the control to less than 10% cover after two years of treatment. When tillage and herbicide were coupled with cover crops, we minimized soil exposure and reduced the risk for site degradation. Herbicide applications alone offered the cheapest method for effectively reducing crested wheatgrass, and cost increased as treatment complexity increased. Soil carbon and nitrogen pools and microbial abundance and composition were surprisingly uniform and stable across native, control, and treatment areas. At this location, which has been dominated by crested wheatgrass for over 80 years, we did not observe severe degradation of important soil health indicators, and we effectively reduced crested wheatgrass cover without degrading soil health.
Fire suppression in mesic grasslands has led to widespread woody plant encroachment (WPE)-the expansion of shrubs and trees into grasslands, often with negative effects on biodiversity and ecosystem services. Increasing woody cover reduces grass abundance and fine fuels, lowering fire intensity and facilitating further shrub expansion, making WPE difficult to reverse with prescribed fires. From 2021 to 2023, we applied annual prescribed burns to heavily encroached areas with and without bison access (paired exclosures) to test whether frequent fire and grazing by bison (Bison bison) begin to reverse WPE and restore grassland biodiversity and structure. Bison activity, measured by dung counts, nearly tripled during the first year of reintroducing fire. In the second and third year, bison usage was 50-70% higher than pre-fire values, though not statistically significant and slightly lower than areas burned annually for 30 years. Shrub area declined in both grazed and ungrazed plots, with the greatest reductions after the first year of burning and in grazed areas. Tree mortality was marginally higher without bison, and plant community composition shifted slightly, with grass cover increasing more in ungrazed plots. Shrub stem mortality was higher in exclosures but resprouting offset this effect. These results suggest that fire combined with bison grazing can help reduce WPE, but effects are modest in the short term. One immediate benefit is improved bison habitat. Restoration practitioners should recognize that even aggressive fire management and megafauna reintroduction may require decades to achieve meaningful woody reduction and should be paired with adaptive management.
Coastal development has negatively impacted estuarine ecosystems over the past two centuries. In southern California, USA, salt marshes are valued for their high animal and plant diversity and for providing foraging and nesting habitat for species of conservation concern. Given the ecological importance of this regionally rare habitat, coastal managers have prioritized salt marsh restoration, despite its many challenges. We review lessons learned on the effect of design and adjoining landscape on early vegetation development in a 60.7 ha tidal wetland restoration project in a southern California estuary where nearly one-third of 37.6 ha of planned salt marsh was excavated to high marsh elevations. Initial planting to facilitate vegetation development in large areas of the high marsh (> 1.7 m MLLW) was unsuccessful, likely due to hypersaline soils. In some areas, subsurface freshwater intrusion likely enhanced planted vegetation, which outperformed vegetation planted at comparable high elevations in other areas. In the mid-marsh (< 1.7 m MLLW), vegetation development from natural recruitment exceeded that of the planted high marsh. After five years, vegetation cover in the high marsh remained low. To address this issue, the marsh plain was re-graded lower in some areas and a planting program was established to hasten vegetation development. Lessons learned pertain to the critical importance of initial wetland design, which in this project led to sparse vegetation cover and the necessity of re-grading and largescale planting to facilitate vegetation establishment.
