Sampling Strategies in Snyder-Middleswarth Natural Area

I used the distance-based method to compare between sampling strategies in the virtual Snyder-Middleswarth Natural Area. Distance-based methods takes much less time than area-based, as we are only noting the nearest tree in the four quadrants around each point surveyed. The sample size for all strategies is 25.

Table of percent error for common and rare tree density by sampling strategy.

1. Systematic

This took 4 hours and 15 minutes. It was extremely accurate for the most common eastern hemlock, with a percent error much smaller than 1%. However, the rare white pine was hugely overrepresented in this count.

2. Random

This method would take 4 hours and 55 minutes. It most accurately reflected the true density of the rare red maple; however, the numbers of the rarest species surveyed, the striped maple, was again overexaggerated.

3. Haphazard

This took 4 hours and 44 minutes to complete. The most common eastern hemlock had the smallest percent error for density again, while the count for the rarest species, white pine, was slightly exaggerated. The average percent error was lowest for this method.

Summary

Systematic sampling took the shortest duration of time; however, overall it had the least accurate results, mostly due to the huge inaccuracy with the count of the rare white pine. Haphazard sampling had the most accurate results altogether. This could be due to user bias in selecting areas of both low and high tree density for each of the 5 topographical categories. Common tree species did not consistently exhibit more accurate results, but the greatest disparities were observed in the counts for the rare species.

A curious phenomenon was that white pine was observed in the systematic and haphazard sampling strategies but was missing from the random strategy count. Instead, striped maple was the rarest surveyed species for this method. Perhaps this reflects one of the shortcomings of distance-based sampling, as some species in the survey area are completely missed out of counts, due to their rarity.