• Key message

Sampling needs differ by forest type for timber inventory and structural complexity metrics. We demonstrate in a typical mixed Eastern Hardwoods forest that optimal sampling of timber inventory metrics and spatially explicit structure indices may be achieved in one large plot plus a cruise for large diameter trees, but accurately capturing inventory metrics may not be possible with sparse large-scale sampling.

• Context

Managing forest stand structures for multiple objectives require accurate and precise estimates of structural features that may be best estimated at different scales.

• Aims

We document minimum necessary plot sizes for structural metrics and spatially explicit indices to characterize structure in a mature North American Eastern hardwoods forest.

• Methods

Metrics and indices (Index of Aggregation, Diameter Differentiation Index, Dissimilarity Coefficient, Structural Complexity Index) were calculated within 0.05–1.75-ha plots for 1000 iterations of random placement in two 2.0-ha macroplots. Estimation adequacy required (1) precision (varied < 10% among plots) and (2) accuracy (within 10% of the 2.0-ha value at 5th and 95th percentiles).

• Results

Minimum single plot sizes to achieve estimation adequacy were 0.25–0.75 ha for spatially explicit indices and 0.5–2 ha for stand metrics. A minimum of five 0.10-ha subplots would be needed for most indices and 6–25 for most metrics, but an untenable 375+ for the density of large diameter trees.

• Conclusion

Estimation adequacy for structural complexity requires no greater sampling intensity than for timber metrics, except for density of large trees. A single large plot may be most cost-effective. National inventories in Eastern hardwoods may not estimate structural complexity well due to inadequate sampling intensity.

中文翻译：

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东部硬木的结构面积曲线：最小样地尺寸的含义，以捕获空间明晰的结构指标

•关键信息

木材库存和结构复杂性指标的抽样需求因森林类型而异。我们在一个典型的东部硬木混交林中证明，在一个大地块中加上木材大直径树木的巡游中，可以实现木材库存量度指标和空间明晰的结构指标的最佳采样，但稀疏的大规模规模可能无法准确地捕获库存量度指标采样。

•上下文

为多个目标管理林分结构需要对结构特征进行准确而精确的估计，最好在不同规模下进行估计。

•目的

我们记录了用于结构度量和空间明确索引的最小必要样地大小，以表征成熟的北美东部硬木森林中的结构。

•方法

指标和指标（聚集指标，直径差异指标，相异系数，结构复杂性指标）是在0.05-1.75公顷的图中针对两个2.0公顷的宏图随机放置1000次迭代计算得出的。估算的适当性要求（1）精度（在地块之间变化<10％）和（2）精度（在第5个百分位数和第95个百分位数的2.0公顷值的10％以内）。

•结果

达到估计充分性的最小单样地面积，空间明确指标为0.25-0.75公顷，林分指标为0.5-2公顷。对于大多数指数，至少需要五个0.10公顷的子图，对于大多数度量标准，至少需要6至25个子图，但是对于大直径树木的密度，则至少需要375+。

•结论

除了大树的密度外，对结构复杂性的估计充分性不需要比木材度量标准更高的采样强度。单个大地块可能是最具成本效益的。由于采样强度不足，东部硬木的国家清单可能无法很好地估计结构的复杂性。