J Plant Ecol ›› 2020, Vol. 13 ›› Issue (5): 641-648.DOI: 10.1093/jpe/rtaa051

• Research Articles • Previous Articles     Next Articles

Interobserver error in grassland vegetation surveys: sources and implications

Lloyd W. Morrison1,2, *, Sherry A. Leis2 and Michael D. DeBacker2   

  1. 1 Department of Biology, Missouri State University, 901 S. National Avenue, Springfield, MO 65897, USA, 2 National Park Service, Heartland Inventory and Monitoring Program, Wilson’s Creek National Battlefield, 6424 W. Farm Road 182, Republic, MO 65738, USA

    *Corresponding author. E-mail: LloydMorrison@MissouriState.edu
  • Received:2020-01-07 Revised:2020-05-28 Accepted:2020-08-04 Online:2020-08-11 Published:2020-10-01

Abstract:

Aims

Observer error is an unavoidable aspect of vegetation surveys involving human observers. We quantified four components of interobserver error associated with long-term monitoring of prairie vegetation: overlooking error, misidentification error, cautious error and estimation error. We also evaluated the association of plot size with pseudoturnover due to observer error, and how documented pseudochanges in species composition and abundance compared with recorded changes in the vegetation over a 4-year interval.

Methods

This study was conducted at Tallgrass Prairie National Preserve, Kansas. Monitoring sites contained 10 plots; each plot consisted of a series of four nested frames (0.01, 0.1, 1 and 10 m2). The herbaceous species present were recorded in each of the nested frames, and foliar cover was visually estimated within seven cover categories at the 10 m2spatial scale only. Three hundred total plots (30 sites) were surveyed, and 28 plots selected at random were resurveyed to assess observer error. Four surveyors worked in teams of two.

Important Findings

At the 10 m2 spatial scale, pseudoturnover resulting from overlooking error averaged 18.6%, compared with 1.4% resulting from misidentification error and 0.6% resulting from cautious error. Pseudoturnover resulting from overlooking error increased as plot size decreased, although relocation error likely played a role. Recorded change in species composition over a 4-year interval (excluding potential misidentification error and cautious error) was 30.7%, which encompassed both pseudoturnover due to overlooking error and actual change. Given a documented overlooking error rate of 18.6%, this suggests the actual change for the 4-year period was only 12.1%. For estimation error, 26.2% of the time a different cover class was recorded. Over the 4-year interval, 46.9% of all records revealed different cover classes, suggesting that 56% of the records of change in cover between the two time periods were due to observer error.

Key words: cautious error, estimation error, misidentification error, observer error, overlooking error, pseudoturnover

摘要:

人类观测误差是植被测量中不可避免的一个问题。我们量化了与高草草原植被长期监测相关的观测者间误差的四个组成部分:忽略误 差、误识别误差、谨慎误差和估计误差。由于观察者会产生误差,我们还评估了地块大小与伪周转率的关系,以及对比了物种组成和丰度的伪变化与四年间植被变化之间的关系。这项研究是在美国堪萨斯州的高草草原国家保护区进行的。监测点包括10个地块,每个地块由一系列的四个嵌套框架(0.01, 0.1, 1和10 m2)组成。在每个嵌套框架中记录了所有的草本物种,并且在10 m2的空间尺度下,视觉估计了7个覆盖类别内的叶面覆盖。总共调查了300个地块(30个地点),并随机选择28个地块重新进行测量以评估观测者的误差。所有的调查由四名观测者分两组完成。研究结果表明,在10 m2空间尺度上,由忽略误差引起的伪周转率平均为18.6%,而由误识别误差和谨慎误差引起的伪周转率平均值分别为1.4%和0.6%。尽管由重新定位引起的误差可能也起一定的作用,由忽略误差导致的伪周转率随样地面积的减小而增 加。物种组成在四年期间的变化(排除潜在的误识别误差和谨慎误差)为30.7%,其中包括由忽略误差和实际变化引起的伪周转率。18.6%的忽略误差表明四年期间的实际变化只有12.1%。对于估计误差,26.2%会记录为不同的覆盖等级。在四年的时间内,46.9%的记录显示了不同的覆盖等级,这表明两个时间段间覆盖率变化的56%是由于观测者误差造成的。

关键词: 谨慎误差, 估计误差, 误识别误差, 观测者误差, 忽略误差, 伪周转率