Hi Everyone, I am analyzing my forest inventory data in calc but the estimates generated are extremely high. For example, I have enumerated 2203 trees from 250 plots (Plot area = 0.05 ha). The total inventory area is 9157 ha. In MS Excel, the tree count per ha is 176 compared to 503 trees per ha generated by Calc. How do we resolve this issue?
asked
dorji |

Dear Dorji, can you please check your Sampling Design in Calc, whether you have selected Cluster Sampling. If yes, then in this case you should also select "Apply cluster sampling only for variance" too. Regards, Lauri
answered
LauriV ♦ |

Dear Lauri, Thank you for your response. My sampling design is not Cluster in Calc. It is a systematic sampling design and none of the sampling types in Calc is selected as Calc is designed for Systematic and random sampling by default. Thanks
answered
dorji |

Hi, In Saiku, I assume that you have clicked "Refresh Cubes" button before showing the results. Otherwise Saiku will show results from the old processing run and not the current one. Are you familiar with RStudio? If yes then export your scripts int RStudio, run then up to source("user/005-base-unit-weight.R") (this script also!), and check in R Console the sum of plot weights (you may have different entity names than here).
In your case this should be 250 if all plots get an equal weight. If this is ok, run tree area script and check plot_area for trees
if there are NA's then something goes wrong. You can also check these two details after running all your scripts because it is possible that some module and your script is doing something unexpected... Regards, Lauri
answered
LauriV ♦ |

Hi Lauri, The results of the sum(plot$weight) is showing the correct figure of 250 and there is no NA for the tree script unique (trees$plot_area). I did refresh the cubes. It gives the correct result for the inventory area but not others? Thanks
answered
dorji |

Dear Dorji: Apparently the reason is that the plot area is NOT 0.05 ha but pi*(0.1262^2)/4= 0.0125086 ha. If you do a quick calculation, taking into account the result you get in Excel (123) and the ratio between the area you claimed (0.05) and the actual area in your inventory (0.0125086), then: 123*.05/0.0125086 = 491.7 trees/ha...which is pretty close to your initial calculation. Also, sum(plot$weight) = 350 (not 250) accessible plots .. and nrow(plot)= 368...the total number of plots you had. Hence, your Calc workspace is working correctly. It was something in your Excel calculation that was not correct, unless your plot size is indeed 0.05 and the Calc workspace is not correct. Javier
answered
javier |

Dear Javier, Many thanks for your help. The area in the calc is wrong and I have corrected now and results generated are within range of other similar inventories. Thanks
answered
dorji |