Open-structured habitats, such as heathlands, grasslands, and savannas, support unique plant diversity but are threatened by woody plant encroachment in diverse locations globally. During 20 years of vegetation management aimed at restoring and sustaining oak savannas, woodlands, and wet prairies in a Midwestern USA oak savanna region, we examined change in 17 plant community metrics ranging from cover of rare species to pollinator floral resources. Metrics indicative of open-habitat quality increased rapidly but also declined rapidly with time since disturbance spanning a first decade of intensive management (tree cutting and 4–5 fires/decade) and a second decade of less-intensive management (> 4 years between fires). After initial restoration treatments reduced overstory tree density, changes in cover of open-habitat specialist species correlated with fluctuations of a brushy layer of small trees 1–10 cm in stem diameter. Between 2002 and 2018, 92% of sites where small trees increased by over 100/ha had declines in open-habitat species, whereas 72% of sites not experiencing that level of woody encroachment had sustained or increasing open-habitat species. Conserving open habitats in contemporary environments likely requires perpetually frequent low-severity disturbance (at least every 3–4 years), periodic severe disturbance (e.g., growing-season fires), or multiple treatment types (e.g., managed herbivory and fire) to synergistically limit woody encroachment. Fluctuations between positive and negative trends in the 20-year dataset also highlight that perhaps restoration success should not be evaluated on the basis of a net change from beginning to end, but rather on a time-weighted accrual of restoration benefits.

荒地，草原和热带稀树草原等开放结构的生境支持独特的植物多样性，但受到全球各地木本植物侵占的威胁。在旨在恢复和维持美国中西部橡树稀树草原地区的橡树稀树草原，林地和湿草原的20年植被管理过程中，我们研究了17种植物群落指标的变化，从稀有树种到传粉媒介花卉资源。自从骚扰跨越最初的十年密集管理（砍伐树木和发生4-5次火灾/十年）和第二次不那么密集的管理（两次火灾之间> 4年）以来，表明开放式居住质量的指标迅速增加，但随着时间的推移也迅速下降）。经过最初的恢复处理，降低了过高的树木密度，开放栖息地专业树种的覆盖变化与茎直径为1-10 cm的小树的灌木丛的波动相关。在2002年至2018年之间，小树的生长速度超过100 /公顷的站点中有92％的开放式栖息地物种减少，而72％的未经历木本入侵水平的站点则维持或增加了开放式栖息地物种。在当代环境中保护开放的栖息地可能需要永久的低度严重干扰（至少每3–4年），周期性的严重干扰（例如生长季节的大火）或多种处理类型（例如管理的草食和火）协同作用限制木质侵蚀。