User: | Open Learning Faculty Member:
The Virtual Forests Tutorial revealed results that were surprising in varying degrees. I did the area based tutorial, and I think the most surprising aspect was that there wasn’t a single technique that produced the highest accuracy 100% of the time. While performing the tutorial, I thought that the random sampling method would produce the most accurate results because of the unbiased nature of the design: quadrats were scattered randomly throughout the entire study area as opposed to the single transect line of the systematic design. I assumed the haphazard design would produce the least accurate results (which it generally did), though I attempted to place the haphazard quadrats in spots that seemed “representative” or at least kind of random.
The systematic design had the fastest estimated time at 12 hours 4 minutes, which makes sense as it requires quadrats to be placed along a single line, or bearing. However it wasn’t faster by that much – all three sample designs were estimated to take between 12 and 13 hours.
As far as accuracy was concerned, the most common species encountered had the highest degree of accuracy in abundance estimates, and the accuracy of the estimates was relatively high in both systematic and random sampling placement strategies with random placement marginally the most accurate (except that it did not capture any data on the rarest species); the haphazard placements did not produce accurate abundance estimates for the common species. As a species abundance became scarcer, accuracy went down, except for the capturing of the rarest species (white pine) by the systematic placement of the quadrats, which (out of luck I presume) managed to pick up virtually all of the actual individuals in the sampling area.
Overall, it seemed like the number of samples was adequate to accurately quantify the most common species and would likely be sufficient in a relatively homogenous stand with uniform characteristics, but I would probably want more plots/quadrats if I was striving to capture rare species or a distribution pattern that was more clumped. If I could, I would attempt to use either random or systematic as my sampling placement strategy.
