Data from: Low recruitment of native trees in a deciduous forest associated with Japanese barberry (Berberis thunbergii) invasion

Invasive plants may dramatically impact forest ecosystems by establishing dense populations and suppressing the recruitment of native tree species. One invasive shrub currently spreading throughout eastern deciduous forests of North America, Japanese barberry (Berberis thunbergii DC), may be limiting tree recruitment in stands where it invades. Once established, B. thunbergii becomes densely populated within forest understories and suppresses native plants by competing for limited resources, altering soil conditions, and changing the understory microclimate. To quantify native seedling inhibition caused by B. thunbergii invasion, we conducted an observational study on seedling abundance within forest plots that were either invaded or not invaded by B. thunbergii and used survey data to generate Bayesian models of native seedling densities along gradients of increasing B. thunbergii stem counts and aboveground plant dry mass. Model outputs predicted that B. thunbergii–invaded plots had 82% lower seedling densities compared with uninvaded plots. Native tree seedling densities were very low even in areas with moderate B. thunbergii density, suggesting that reduced tree seedling densities are observed even at low densities of invasion. Our findings indicate that forests invaded with B. thunbergii harbor substantially lower densities of native tree seedlings, with potentially significant long-term consequences for forest ecological integrity, biodiversity, and ecosystem services.

外来入侵植物可通过形成密集种群、抑制本土乔木天然更新，对森林生态系统造成显著影响。目前正在北美东部落叶阔叶林中扩散的入侵灌木日本小檗（Japanese barberry, *Berberis thunbergii* DC），可能会在其入侵的林分中限制乔木更新。一旦定殖，日本小檗会在森林林下形成高密度种群，并通过争夺有限资源、改变土壤条件以及调控林下微气候来抑制本土植物生长。为量化日本小檗入侵对本土幼苗的抑制效应，本研究在受日本小檗入侵与未入侵的森林样地中开展了观测调查，统计幼苗丰度，并基于调查数据构建了本土幼苗密度随日本小檗茎秆数量、地上生物量梯度变化的贝叶斯（Bayesian）模型。模型结果显示，受日本小檗入侵的样地幼苗密度较未入侵样地降低82%。即便在日本小檗密度中等的区域，本土乔木幼苗密度也极低，这表明即使在较低入侵密度下，乔木幼苗密度也会出现下降。本研究结果表明，被日本小檗入侵的森林中本土乔木幼苗密度显著降低，这可能对森林生态系统完整性、生物多样性及生态系统服务功能造成长期的重大影响。