Research NotePilot survey to assess sample size for herbaceous species composition assessments using a wheel-point apparatus on the Zululand coastal plain

Abstract

A pilot survey to determine sub-sample size (number of point observations per plot) for herbaceous species composition assessments, using a wheel-point apparatus applying the nearest-plant method, was conducted. Three plots differing in species composition on the Zululand coastal plain were selected, and on each plot 2 000 point observations were collected. Thirty sets of N point observations were produced, where N = 10, 20, 30, 40 to 300. For each 30 sets of N points, percentage replicate similarities were calculated. To the mean percentage replicate similarity, a Chapman-Richards function was fitted, and the asymptotic value (β⁰) was used to assess the increase in mean replicate similarity with increasing sample size. Efficient sample sizes were ≤ 200 pointobservations per plot, and in some situations, 𫏾 points might suffice. The sample size selected depends on the goals, species diversity and equitabilities (for species contributing >10% to sward composition), and the financial and time resources available.

Keywords: Coastal Forest and Thornveld, grassland, grass layer, Greater St Lucia Wetland Park, Monte Carlo simulation, point observations, species diversity

African Journal of Range & Forage Science 2006, 23(2): 153–157