Reestablishing native perennial plants and reducing invasive species are pivotal for many ecological restoration projects. The interactions among plant species, arbuscular mycorrhizal fungi, and soil P availability may be critical determinants of the success of native and non-native plants in restoration and species invasions. Here we assessed mycorrhizal responsiveness for three late-successional and three early-successional plant species native to Rocky Mountain National Park and for the non-native Downy brome, cheatgrass (Bromus tectorum L.) using field soil and commercial inoculum. Factorial greenhouse experiments were conducted to compare biomass of plant species with and without field soil and commercial inoculum treatments along a phosphorus (P) gradient, which ranged from ambient field levels to 12% of field levels, using dilutions of native soils. The two field soil inoculum treatments resulted in significant biomass differences for all species studied. Late-successional species responded positively to field inoculum, whereas early-successional species responded negatively. The two commercial inocula had low colonization rates (14 of 166 inoculated plants). The commercial inocula substrates had significant treatment effects on five of seven species included in the study in the apparent absence of mycorrhizal symbiosis. Soil P levels influenced mycorrhizal responsiveness in only one species, Smooth blue aster (Aster laevis L.). Our results show that, at least for the species studied here, locally collected field inoculum is the best choice for reestablishment of late-successional native plant species.

Invasive plants are a common problem in the management and restoration of degraded lands in the semiarid western United States, but are often not the primary focus of restoration ecologists. Likewise, restoring native vegetation has not been a major concern of weed scientists. But trends in the literature demonstrate increasing overlap of these fields, and greater collaboration between them can lead to improved efficacy of restoration efforts. Succession and ecosystem development are the products of complex interactions of abiotic and biotic factors. Our greatest restoration and invasive plant management successes should result when we take advantage of these natural processes. Recent shifts in management objectives have generated approaches to directing plant community development that utilize species that are strong competitors with invasive species as a bridge to the establishment of native perennial vegetation. Soil water and nutrient characteristics and their interactions can affect desired and undesired plant species differentially and may be manipulated to favor establishment and persistence of desired perennial plant communities. Selection of appropriate plant materials is also essential. Species assemblages that suppress or exclude invaders and competitive plant materials that are well adapted to restoration site conditions are important keys to success. We provide guidelines for restoration based on the fundamental ecological principles underlying succession. Knowledge of the complex interactions among the biotic and abiotic factors that affect successional processes and ecosystem development, and increased collaboration between weed scientists and restoration ecologists hold promise for improving restoration success and invasive species management.

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The low water-holding capacity and low nutrient levels of roadcuts in northern California cause many of these disturbed areas to remain chronically barren. Yard waste compost was incorporated into four nonvegetated substrates found along roadcuts (decomposed granite [DG], lahar, serpentine, and sandstone) in order to regenerate topsoil infiltration, water-holding capacity, and nutrient availability. Soil physical and chemical properties, as well as the vegetative response of a native perennial grass, were compared between treatments (non-tilled, tilled, and tilled with compost amendment). Tillage and compost addition decreased soil bulk density compared to the nontilled treatment, and the compost treatment increased the soil carbon and nitrogen contents compared to the nontilled and tilled treatments. Tillage alone resulted in an increase in saturated hydraulic conductivity in soils that did not contain a large amount of coarse fragments. Tillage also reduced sediment loss in all soils except the DG. Foliar C 13 content did not predict water stress consistently between treatments. The incorporation of yard waste compost increased plant available water in coarse but not in fine-textured soils, and aboveground plant biomass was significantly greater in the compost treatment than in either of the other treatments. Although the incorporation of yard waste compost generated the greatest revegetation success, tillage alone may be a sufficient treatment if residual soils have adequate nutrient levels.

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