We present a systematic literature review of exotic understory forest herbaceous invasions with a focus on the forests of East Asia (EAS) and Eastern North America (ENA), two dominant regions of the north temperate deciduous forest biome. We examined the biogeographic origins of herbaceous invaders in EAS and ENA forests, summarized their life histories and ecology, and compiled the relevant literature on the 10 leading mechanistic hypotheses proposed for these invasions. We asked whether invasions of EAS and ENA forests by herbs are shared between regions, and whether a common suite of ecological traits unite these invaders into a functionally distinct group. In a focused summary of the empirical literature, we investigated if leading hypothesized mechanisms for biological invasions at large are also invoked and supported for this ecologically important, but relatively understudied, group of species. In contrast to ENA, forest invaders in EAS are overwhelmingly herbaceous (78% of forest invasions vs. 34% for ENA) and originate from different regions. Plant families represented and species traits between regions differed. Within a single species, multiple invasion mechanisms were often supported, highlighting the need for future research that simultaneously investigates multiple mechanistic hypotheses. Further, because results for a single invader often differed across space and time, a shift in focus to incorporate the complex dynamics across temporal and spatial scales with the consideration of spatial heterogeneity and the interplays among natural and anthropogenic factors to study exotic invasions is needed.

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Urban ecosystems have great potential for urban biodiversity conservation, but achieving conservation goals relies on comprehensive ecological assessments to assist in active management practices; however, land use changes in urban ecosystems have led to unique abiotic and biotic inputs that have affected and altered below-ground soil composition, with potentially negative implications across trophic levels. We investigated the relationships between soil attributes and key indicators of forest health, specifically the composition and condition of vegetation and soils in an urban remnant forest area. The major findings revealed a dominance of native plant species, with some invasion by non-native plants, and acidic high-carbon soils sufficient in most plant available nutrients. Moreover, stepwise regression analysis showed significant relationships between soil attributes and native species diversity and abundance; prevalence of invasive plants (Lonicera maackii, Pueraria montana, Albizia julibrissin, Ligustrum sinense, Lonicera japonica, Ailanthus altissima, and Paulownia tomentosa); forest canopy gaps; and fine woody debris on the forest floor. These findings identified attributes of urban soils affecting forest health and biodiversity conservation, with broad implications for the long-term monitoring of urban forests.

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