Vegetation - Permanent Plots - Saplings

Permanent plots are a powerful tool for understanding systems over the long term because of the rigorous quantification of patterns in a spatially refined way and because of the comparability of numerous variables measured in the same place. In 1998, 7 plots were surveyed into 3 forests in the study region of the Baltimore Ecosystem Study (BES): Oregon Ridge Park (4 plots), Hillsdale Park (1 plot), and Leakin Park (2 plots). Plots were surveyed in to correct for slope and to achieve an accuracy of plot side length to within 0.5 cm. Plots are 1600 m2 with the exception of the Hillsdale plot which is 900 m2. The Hillsdale plot is smaller to fit within the confines of the forest patch. Sites were selected 1) to represent urban and non-urban forests, 2) away from obvious habitat boundaries or edges, 3) with consistent drainage lines within the plot, and 4) with at least 80 % continuous tree canopy. All vegetation layers were sampled in order to characterize the structure and composition of the plant community. A variety of sampling methods were used for the different layers but all layers were quantified with a high level of detail to minimize variation and to best characterize the plot.永久样地（permanent plot）是开展生态系统长期研究的强有力工具，其核心优势在于能够以空间精细化的方式对生态格局开展严谨量化，且可对同一地点测得的各类变量进行跨时序比对。1998年，研究团队于巴尔的摩生态系统研究（Baltimore Ecosystem Study, BES）的研究区域内，在3处森林中布设了7块永久样地：俄勒冈岭公园（4块样地）、希尔斯代尔公园（1块样地）与利金公园（2块样地）。样地布设过程中完成了坡度校正，并确保样地边长的测量精度控制在0.5厘米以内。除希尔斯代尔公园样地面积为900平方米外，其余样地面积均为1600平方米。该样地面积较小，以适配其所在森林斑块的空间范围。样地的遴选遵循以下四项原则：1）能够代表城市与非城市森林类型；2）远离明显的生境边界或边缘区域；3）样地内部排水条件保持一致；4）树木冠层连续覆盖度不低于80%。为全面表征植物群落的结构特征与物种组成，研究人员对所有植被层开展了采样调查。针对不同植被层，研究采用了多样化的采样方法，但所有植被层均以高精细度开展量化工作，以尽可能降低采样误差，最优地表征样地的生态特征。