Long-term growth, mortality and regeneration of trees in permanent vegetation plots in the Pacific Northwest, 1910 to present

A network of more than 130 permanent vegetation plots provides long-term information on patterns and rates of forest succession in most of the major forest zones of the Pacific Northwest. The plot network extends from the coast to the Cascades in western Oregon and Washington and east to ponderosa pine forests in the Oregon Cascades. Most of the permanent plots were established during two intervals: from 1910 to 1948, and from 1970 to 1989. The earlier plots were established by U.S. Forest Service researchers to quantify timber growth in young stands of important commercial species and to help answer other applied forestry questions. The more recent period of plot establishment began under the Coniferous Forest Biome program of the International Biological Program during the 1970s, and continued under the Long-term Ecological Research program. A broader set of objectives motivated plot establishment since 1970, especially quantification of composition, structure, and population and ecosystem dynamics of natural forests. Plots have one of three spatial arrangements: (1) contiguous rectangles subjectively placed within an area of homogeneous forest; (2) circular plots subjectively placed within an area of homogeneous forest; and (3) circular plots systematically located on long transects to sample an entire watershed, ridge, or reserve. Rectangular study areas are mostly 1.0 ha or 0.4 ha (1.0 ac) in size (slope-corrected). Circular plots are 0.1 ha (0.247 ac), not corrected for slope. The tree stratum is the focus of work in closed-forest study areas. All trees larger than a minimum diameter (5 cm for most areas) are permanently tagged. Plots are censused every 5 or 6 years. Attributes measured or assessed at each census include tree diameter, tree vigor, and the condition of the crown and stem. The same attributes are recorded for trees (ingrowth) that have exceeded the minimum diameter since the previous census. In many plots tree locations are surveyed to provide a plot-specific x-y location. A mortality assessment is done for trees that have died since the previous census. The assessment characterizes rooting, stem, and crown condition, obvious signs of distress or disturbance, and the apparent predisposing and proximate causes of tree death.

由130余个永久性植被样地组成的样地网络，可为太平洋西北沿岸多数主要森林带的森林演替模式与演替速率提供长期观测数据。该样地网络覆盖范围从俄勒冈州西部、华盛顿州的海岸延伸至喀斯喀特山脉，东至俄勒冈州喀斯喀特山脉内的黄松（ponderosa pine）森林。绝大多数永久性样地的设立分为两个阶段：1910年至1948年，以及1970年至1989年。早期样地由美国林务局（U.S. Forest Service）的研究人员设立，旨在量化重要商用树种幼林的木材生长量，并解答其他应用林业相关问题。1970年代的样地设立工作始于国际生物计划（International Biological Program）下的针叶林生物群系项目，并在后续的长期生态研究计划（Long-term Ecological Research Program）中持续推进。1970年以来的样地设立基于更广泛的研究目标，尤其聚焦于天然林的群落组成、结构、种群动态与生态系统动态的量化研究。样地的空间布设方式分为三类：(1) 主观选取于同质森林区域内的连片矩形样地；(2) 主观选取于同质森林区域内的圆形样地；(3) 沿长样带系统布设的圆形样地，用于对完整流域、山脊或保护地进行抽样调查。矩形样地的面积多为1.0 ha（公顷）或0.4 ha（1.0 ac，英亩），已进行坡度校正；圆形样地面积为0.1 ha（0.247 ac），未进行坡度校正。在郁闭林分研究样地中，乔木层为核心研究对象。所有胸径超过最小阈值（多数区域为5 cm）的乔木均会被永久挂牌标记。样地每5至6年开展一次普查。每次普查中测量或评估的指标包括乔木胸径、树势、冠层与茎干健康状况。同时记录自上次普查以来胸径达到最小阈值的新增乔木（径阶补充木，ingrowth）的上述各项指标。多数样地会对乔木位置进行测量，以获取每个样地专属的平面x-y坐标。针对上次普查以来死亡的乔木开展死亡原因评估：评估内容涵盖根系、茎干与冠层的健康状况，明显的胁迫或干扰痕迹，以及导致树木死亡的潜在诱因与直接原因。