Table 2.

Statistical outputs and performance parameters for segmented regression analysis modelling relationships between the accuracy of estimated means and sampling intensity (number of random samples/sampling grid). Response variables include Asiatic garden beetle, Maladera formosae Brenske, larvae/0.25 m² (larval density), plant height (cm), root rating (1–5 nominal scale), above-ground biomass (g), and below-ground biomass (g). Breakpoints estimates represent the sampling intensity where diminishing returns in accuracy accrue with additional sampling effort. Accuracy was calculated as the mean absolute difference (%) between estimates provided by 50 random draws at each level of sampling intensity (n = 1–63 or 1–47) and the mean estimated by sampling all cells in a 64- or 48-cell sampling grid (i.e., True Mean). Total area = 0.2 or 0.15 ha. N ≤ 20% = the number of samples required to fall within 20% of the true mean.

Field	Sampling Method	Response Variable	True Mean (± SE)	Accuracy Breakpoint (± SE)	df	t	P	R 2	N ≤ 20% True Mean
1	Cup-cutter	Larval Density	13.0 ± 2.7	6.7 ± 0.3	59	−11.8	<0.001	0.95	26.6
2	Cup-cutter	Larval Density	5.5 ± 1.8	7.2 ± 0.4	59	−12.4	<0.001	0.95	42.8
1	Cup-cutter	Plant Height	14.0 ± 0.5	7.2 ± 0.3	59	−14.2	<0.001	0.96	1.0
2	Cup-cutter	Plant Height	16.3 ± 0.4	9.8 ± 0.5	59	−14.0	<0.001	0.96	1.0
1	Cup-cutter	Root Rating	1.3 ± 0.1	7.0 ± 0.4	59	−11.7	<0.001	0.96	1.0
2	Cup-cutter	Root Rating	1.0 ± 0.0	27.9 ± 1.9	59	−16.6	<0.001	0.96	1.0
2	Quadrat	Larval Density	0.8 ± 0.2	16.6 ± 1.3	59	−10.7	<0.001	0.95	44.7
3	Quadrat	Larval Density	3.6 ± 0.3	5.5 ± 0.3	43	−10.2	<0.001	0.95	4.9
2	Quadrat	Above-ground Biomass	29.0 ± 2.7	6.7 ± 0.3	59	−13.7	<0.001	0.97	6.1
3	Quadrat	Above-ground Biomass	51.7 ± 3.4	4.5 ± 0.3	43	−8.4	<0.001	0.96	3.3
2	Quadrat	Below-ground Biomass	26.3 ± 3.0	5.3 ± 0.2	59	−12.2	<0.001	0.95	5.3
3	Quadrat	Below-ground Biomass	84.1 ± 7.6	5.4 ± 0.6	43	−9.3	<0.001	0.96	5.0