Floodplain hardwood forests that exist on islands and immediately adjacent to channels along the Upper Mississippi River System (UMRS) are ecologically important due to high floral and faunal biodiversity. The recent decline and regeneration failure of hard mast species—e.g. Quercus spp. and Carya spp.—along the UMRS has been well documented, but causes of these trends have not been widely examined and are thus poorly understood. To investigate the mechanisms of this decline, we installed three 0.20-ha plots within the floodplain forests of the UMRS amongst communities known to contain the northernmost documented individuals of Carya illinoinensis (Wangenh.) K. Koch, a regionally imperiled, yet ecologically, economically, and culturally important hard mast species. Tree density ($>$5 cm dbh) averaged 355 stems ha⁻¹ (n = 239, 12 representative species across 9 genera) and mean basal area was 77 m² ha⁻¹ across the three sites. Acer saccharinum L. was the most dominant species (49.0 m² ha⁻¹). The diameter distribution of trees demonstrated a negative exponential pattern, generally indicative of uneven-aged, regenerating forests. Over the past ca. 120 years, decadal-scale pulses of tree establishment across species show linkages with riparian engineering installments and flood and drought events. C. illinoinensis demonstrated a consistent establishment pattern since at least the 1860s through the 1950s, but experienced regeneration failure over the past ca. 50 years. Widespread ecological growth releases in C. illinoinensis are linked with known large-scale flood events along the UMRS (1965, 1993, 2001, 2011 CE). Correlation analysis revealed relationships between C. illinoinensis growth rings and drought, precipitation, maximum temperature, and river flow to be temporally unstable with an inflection point at the beginning of the lock and dam era (ca. 1930s–1940s). The coincidental decoupling of climate and flow variability with tree growth in the post-lock and dam era suggests that peripheral, disjunct populations of C. illinoinensis are sensitive to impacts from anthropogenic land and hydrologic modifications. Forest structure, disturbance history, and climate analyses demonstrate that without management intervention, C. illinoinensis will no longer have a significant presence within floodplain forests of the UMRS in the near future, contributing to loss in diversity. Direct forest restoration techniques, such as planting and creation of canopy gaps via regeneration-focused harvesting, are needed if C. illinoinensis is to return to historical abundance and distribution.

存在于岛屿上且紧邻密西西比河上游系统 (UMRS) 河道的漫滩阔叶林具有丰富的花卉和动物生物多样性，因此具有重要的生态意义。最近硬桅杆物种的衰退和再生失败 -例如 Quercus spp。和Carya spp.-沿 UMRS 已被充分记录，但这些趋势的原因尚未得到广泛研究，因此知之甚少。为了研究这种下降的机制，我们安装了正常市场需求量的漫滩森林中的三个0.20公顷的地块当中已知含有的最北端记录个人社区山核桃illinoinensis(Wangenh.) K. Koch，一种区域性危险，但在生态、经济和文化上具有重要意义的硬桅杆物种。树木密度 ($>$5 cm dbh) 平均 355 茎 ha ^-1（n  = 239，9 属 12 种代表性物种），三个地点的平均基底面积为 77 m ² ha ^-1。Acer saccharinum L. 是最主要的物种（49.0 m ² ha ^-1）。树木的直径分布显示出负指数模式，通常表明不均匀老化的再生森林。在过去约。120 年来，跨物种树木建立的十年级脉搏显示了与河岸工程分期付款和洪水和干旱事件的联系。伊利诺伊山竹至少从 1860 年代到 1950 年代表现出一致的建立模式，但在过去大约经历了再生失败。50 年。C. illinoinensis中广泛的生态增长释放与 UMRS 沿线已知的大规模洪水事件有关（1965、1993、2001、2011 CE）。相关性分析表明，伊利诺伊斯海棠年轮与干旱、降水、最高温度和河流流量之间的关系在时间上不稳定，拐点出现在水闸和大坝时代（约1930 年代至 1940 年代）之初。在后闸和大坝时代，气候和流量变异与树木生长的巧合脱钩表明，外围的、分离的种群C. illinoinensis对人为土地和水文变化的影响很敏感。森林结构、干扰历史和气候分析表明，如果没有管理干预，C. illinoinensis在不久的将来将不再在 UMRS 的漫滩森林中大量存在，从而导致多样性的丧失。如果C. illinoinensis要恢复到历史的丰度和分布，就需要直接的森林恢复技术，例如通过以再生为重点的采伐来种植和创造树冠间隙。