USE OF VISUAL COVER ASSESSMENTS AS QUANTITATIVE ESTIMATORS OF SOME BRITISH WOODLAND TAXA
USE OF VISUAL COVER ASSESSMENTS AS QUANTITATIVE ESTIMATORS OF SOME BRITISH WOODLAND TAXA
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DOI：
10.2307/2259726
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发表时间：
1983-07
影响因子：
5.5
通讯作者：
J. Sykes;A. D. Horrill;M. Mountford
中科院分区：
文献类型：
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作者：
J. Sykes;A. D. Horrill;M. Mountford
摘要(1)10名观察者对林地中4平方米、50平方米和200平方米的一系列样方的植被覆盖度进行了目测估计。(2)10个观测者的平均盖度值与4m2样方中大多数物种的样方估计值相当接近。(3)对于所有的分类群，不同观察者在所有样方大小的估计值之间存在显著差异。使用随机抽取的观察者，90%的可信区间在+10%-20%的范围内。在同一样本上重复估计的个体的相应范围是+5%-15%。(4)在估计阔叶树种时，观察者之间的变异性通常最小，而对于细叶树种和苔藓植物，观察者之间的变异性通常最高。(5)观察者在倾向于低估或高估与物种和样方大小有关的盖度的一致性上存在差异；这种一致性与经验无关。(6)不同观察者对特定物种和样方大小的偏差非常一致，使用平均偏差修正因子可以明显提高大多数物种盖度估计的精度。
SUMMARY (1) Ten observers made visual estimates of plant cover on a series of 4 m2, 50 m2 and 200 m2 quadrats in a woodland. (2) Mean cover values from the ten observers corresponded reasonably closely with point quadrat estimates of cover for most species in the 4 m2 quadrats. (3) For all taxa, significant differences occurred between the estimates of different observers at all quadrat sizes. Using an observer drawn at random, 90% confidence intervals were in the range + 10-20% cover. The corresponding range for an individual repeating an estimate on the same quadrat was + 5-15% cover. (4) Variability between observers was usually lowest when estimating broad-leaved species and highest with fine-leaved species and bryophytes. (5) Observers differed in the consistency with which they tended to under- or over-estimate cover in relation both to species and to quadrat size; this consistency was not correlated with experience. (6) The biases of different observers for a particular species and quadrat size were sufficiently consistent that the use of mean bias correction factors brought about clear gains in the precision of cover estimates for most species.