Two-stage sequential sampling for two rare species in western Inner Mongolia of China

Jingjing Shi,Tianzhong Zhao,Yuancai Lei

doi:10.1007/s11434-012-5308-7

Abstract

To evaluate the efficiencies of different sampling methods for a rare and clustered population, we investigated the sampling effects for the two species Tamarix chinensis (Salt cedar) and Elaeagnus angustifolia (Russian olive) in western Inner Mongolia with two-stage sequential sampling, which is a new sampling method, traditional simple random sampling and two-stage sampling. Based on two-stage sequential sampling and two-stage sampling, each population was partitioned into four primary sampling units, and then two of them were randomly selected. Sampling designs were simulated based on the conditions of five secondary sampling unit areas, two criterion values, five initial secondary sampling units and two sequential secondary sampling units in 1000 repetitions. To evaluate the performance of the sampling designs for each method, the variance and relative error of the density estimates were used. The relative sampling efficiencies of the three sampling methods were compared using the same final sampling sizes. We analyzed the sampling efficiency generated by two-stage sequential sampling and found that it yielded smaller variances than those of simple random sampling and two-stage sampling in all sampling designs, and that two-stage sampling was more efficient than simple random sampling. Density estimates from the two-stage sequential sampling were very close to the true values. We also determined the optimum secondary sampling unit areas for the two species in the two-stage sequential sampling. It was best for Tamarix chinensis and Elaeagnus angustifolia when the secondary sampling unit areas were 200 and 100 m2, respectively.

Highlights

To evaluate the efficiencies of different sampling methods for a rare and clustered population, we investigated the sampling effects for the two species Tamarix chinensis (Salt cedar) and Elaeagnus angustifolia (Russian olive) in western Inner Mongolia with two-stage sequential sampling, which is a new sampling method, traditional simple random sampling and two-stage sampling
The biggest relative errors of the density estimates were 3.714% for Tamarix chinensis and 2.567% for Elaeagnus angustifolia, and the results indicated that the differences between the estimated and true densities were small
The relative errors were smaller than 5%, showing that two-stage sequential sampling (TSSS) was suitable for the species studied

Summary

Data and methods

The study area is located in western Inner Mongolia along the Huanghe River Valley, which has an area of 1 km centered on 40°15′37.8′′N and 106°56′28.0′′E. The region is typical of areas with rare and clustered desert vegetation such as Elaeagnus angustifolia and Tamarix chinensis. The study area was divided into 100 plots, each of which was 100 m × 100 m. The starting points were always the southwest corners of the plots. The distance between points was measured by an electronic total station, and plot coordinates were recorded by a differential global position system. Each plot was further divided into 100 survey units, each of which was 10 m × 10 m. We measured and recorded the ground diameter and height of all desert vegetation (shrubs and trees) in all plots. The spatial distributions of the two investigated species in the survey region are displayed, and it can be seen that their distributions are spatially rare and clustered The spatial distributions of the two investigated species in the survey region are displayed in Figure 1, and it can be seen that their distributions are spatially rare and clustered

Two-stage sequential sampling

Simulation sampling designs

Evaluated indicators

Results and discussion

Conclusions