Lyford Mapped Tree Plot at Harvard Forest since 1969

Permanent forest plots provide an empirical understanding of forest change over time, and are an invaluable part of forestry and ecological research. Walter Lyford began measurements of a 2.88 ha red oak-red maple forest on the Prospect Hill Tract of Harvard Forest in 1969. All trees over 2 inches (5 cm) were mapped on very large-scale (1 inch = 5 feet) hand-drawn maps, and included live and dead trees, stumps, windthrows and other features such as stone walls, boulders, soil moisture and a damage boundary from the 1938 hurricane. All living and dead trees have been re-located and measured (diameter at breast height, canopy class for live trees; condition, decay class, diameter, bole length and stem orientation for fallen dead trees) in 1969, 1975, 1987-1992, 2001, and 2011. In 2001, the original, hand-drawn maps were digitized using ArcView GIS. From 1969 to 2011, red oak (Quercus rubra) increased its dominance of the stand’s total basal area from 52% to 60%; however, red maple (Acer rubrum) has become relatively less abundant, decreasing from 30% to 23%. While red oak and red maple continue to account for the majority of the basal area in the stand, the secondary species experienced a dramatic increase in relative abundance of individuals in the stand; yellow birch (Betula alleghaniensis), black birch (Betula lenta), American chestnut (Castanea dentata), American beech (Fagus grandifolia), witch hazel (Hamamelis virginiana), eastern white pine (Pinus strobus), and eastern hemlock (Tsuga canadensis) have increased from comprising 25% of the individuals in the stand in 1969 to comprising 52% in 2011. The total biomass of living individuals is increasing linearly (R2=0.99, p=0.0002), which implies that the stand has not yet experienced an age-induced decrease in biomass accumulation.

永久森林样地（permanent forest plots）是解析森林随时间动态变化的实证基础，亦是林业与生态学研究中极为宝贵的核心资料。沃尔特·莱福德（Walter Lyford）于1969年启动了对哈佛大学森林（Harvard Forest）展望山地块（Prospect Hill Tract）内一块2.88公顷红栎-红枫林的监测工作。所有直径大于2英寸（5厘米）的林木均被标注于比例尺为1英寸=5英尺的手工绘图地图中，涵盖活立木、枯立木、伐桩、风倒木，以及石墙、砾石、土壤湿度和1938年飓风遗留的破坏边界等各类特征。研究团队分别于1969年、1975年、1987-1992年、2001年及2011年对所有活立木与枯立木完成重新定位与测量：活立木需记录胸径、冠层等级；倒伏枯木则需记录健康状况、腐朽等级、直径、树干长度与茎干朝向。2001年，原始手工绘图地图通过ArcView GIS完成数字化处理。1969年至2011年间，红栎（Quercus rubra）在林分总断面积中的占比从52%提升至60%，优势地位进一步巩固；而红枫（Acer rubrum）的相对丰度则有所回落，从30%降至23%。尽管红栎与红枫仍占据林分总断面积的绝大多数份额，但次要树种的个体相对丰度出现了显著增长：黄桦（Betula alleghaniensis）、黑桦（Betula lenta）、美洲栗（Castanea dentata）、美洲山毛榉（Fagus grandifolia）、金缕梅（Hamamelis virginiana）、东部白松（Pinus strobus）以及东部铁杉（Tsuga canadensis）的个体占比从1969年的25%升至2011年的52%。林分活立木总生物量呈线性增长趋势（R²=0.99，p=0.0002），这表明该林分尚未因林龄增长出现生物量积累的下降。