Soil texture is associated with wide variation in forb communities in established nonnative perennial grass seedings

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We measured forb composition and other community characteristics at different scales in 17 sites across eastern Oregon with paired plots across seeding boundaries. We quantified differences associated with seeding overall. We also investigated the potential for seeding outcomes to relate to biotic interactions based on abundance of major functional groups, species traits related to competition, microsite features relating to competition, and soil texture. Finally, we tested the generality of our paired plot results across the study area by accounting for a broader range of management and environmental factors with a matching analysis using a large independent vegetation dataset. Paired plot comparisons suggested negative relationships between seeding and forb density. Biotic interactions with major functional groups were not strongly associated with forb community differences due to seeding, with the exception of a negative relationship between native annual forb abundance and increasing invasive annual grass cover. Few biotic interactions were related to seeding outcomes, though native annual forb abundance was negatively associated with higher invasive annual grass cover. Traits related to competition were not strongly related to species seeding response. Soil texture affected several forb community characteristics, including sometimes altering seeding outcomes. Increasing sand content was associated with lower perennial forb diversity and abundance, and annual forb richness decreased with higher sand content in seeded, but not unseeded, sites. The regional-level matching analysis, which controlled for the effects of management and environmental factors, generally supported the paired plot comparisons by showing that crested wheatgrass seeding was associated with lower invasive annual grass cover and lower total and perennial forb cover and richness.