Step-point sampling for broadleaved species’ ground cover estimation in pastures – an evaluation of Cockayne’s point on a boot toecap method

Abstract

ABSTRACT Step-point sampling, conceived by plant ecologist Dr Leonard Cockayne in ca. 1925 as a method for measuring the ground cover of species in New Zealand’s modified tussock grasslands utilises a point marked on the observer’s boot toecap. It is resource-efficient compared to other vegetation sampling methods and here we report on a unique evaluation of its accuracy and precision. The estimated cover of Taraxacum officinale in a grassy field (11%) was not significantly different from that obtained using line-point sampling (13%), but higher than that from line-intercept sampling (5.7%). It was unaffected across an order-of-magnitude range of sampling intensity (1600 to 160 observations/ha) and was acceptably precise with ≥ 400 observations/ha, although increased linearly with observation point size. These empirical results were supported by computer simulations enabling both accuracy and precision to be evaluated along with plant architecture. The simulations indicated that step-point sampling with ca. 400 observations per ha and an observation point diameter ≤ 1.1 cm (1.0 cm2), can provide ground cover estimates for a wide range of broadleaved species in pastures that are sufficiently accurate and precise for common pasture management applications. The method is deployed in the phone application, ‘Grassland Cover Estimator’ available at https://www.agresearch.co.nz/search?q = Grassland + cover + estimator.