Long-term (1993-2019) dynamics of tree populations on a mapped 3-ha permanent plot in old-growth northern hardwood forest, Huron Mts., Marquette Co., MI, USA

This data-set includes multiple remeasurements, over 25 years, of all woody stems >2 cm diameter (total of 2125 stems) on a 2.72-ha stem-mapped plot in old-growth northern hardwood forest in the Huron Mountains region of northern Marquette County, MI. The plot and surrounding forest is dominated by sugar maple (Acer saccharum) and eastern hemlock (Tsuga canadensis). Among secondary species, yellow birch (Betula alleghaniensis) and basswood (Tilia americana) are most common. Soils (identified as Kalkaska series) are developed on deep sandy glacial outwash. The plot is within a much larger region of old-growth forest, protected since ca. 1880, with only minimal disturbance associated with access tracks and trails. Numerous other forest community and dendrochronological studies support the interpretation that the area around the study plot has not experienced stand-initiating disturbance for at least 400 years. Initial mapping and measurements (1993-1995 for 2.52 ha; an additional 0.2 ha added in 1999) used a 20x20 m grid established in a near-level area of uniform substrate. All stems were identified to species, mapped on polar coordinates from the center of each grid cell (including, at first measurement, identifiable dead trees, standing and down), and diameter at breast height (dbh) measured to nearest 0.1 cm. All stems were remeasured on a five-year cycle 1999-2019, and new mortality was recorded at each remeasurement. New recruits > 2 cm dbh were added at each remeasurement.

本数据集涵盖美国密歇根州马凯特县北部休伦山脉地区原始北方硬木林内一块2.72公顷茎干测绘样地中超过25年的多轮复测数据，该样地内所有直径大于2厘米的木质茎干总计2125株。该样地及周边森林以糖槭（Acer saccharum）和东部铁杉（Tsuga canadensis）为优势物种，次要伴生种中以黄桦（Betula alleghaniensis）与美洲椴（Tilia americana）最为常见。该样地土壤经鉴定为卡尔卡斯卡（Kalkaska）土系，发育于深厚的砂质冰川冰水冲积物之上。该样地隶属于一片更大范围的原始森林区域，该区域自约1880年起受到保护，仅存在与通行便道和步道相关的轻微人为干扰。多项森林群落学与树木年代学相关研究均证实，该研究样地周边区域至少400年来未发生过林分起源性干扰（stand-initiating disturbance）。初始测绘与测量工作于1993-1995年开展，初期覆盖2.52公顷样地，1999年新增0.2公顷样地；布设基准为基质均匀的近水平区域，采用20米×20米的网格系统。所有茎干均被鉴定至物种水平，以每个网格单元的中心为原点，通过极坐标完成定位（首次测量时还纳入了可识别的枯立木与倒木），并测定胸径（diameter at breast height, DBH），精度精确至0.1厘米。1999年至2019年间，所有茎干以5年为周期开展复测，每次复测均记录新出现的死亡个体；每次复测时均纳入新萌发且胸径大于2厘米的新增茎干。