Sample design

Prior to inventory, a stratification needs to be done. This is valid also in a complete inventory (when all stands in the analysis area are included), since some general inventory parameters are set in this part. Considering cost-efficiency, the inventory is commonly based on a two-stage sampling procedure. Here, this starts with selecting the imported stand register of interest, i.e. the analysis area to be in-field inventoried by plotwise sampling in PPS-sampled stands.

NB: The following stand register parameters are (more or less) mandatory to enable stratification: stand area (productive forest land), volume, age, basal area, number of stems and tree species proportions.

• A stratum is defined usually based on volume and age from the stand register

The stands (their productive forest land areas) are related to one of the several user-defined strata. The stratum-matrix should first be arranged according to current forest state, and before that, you might want to separate the analysis area (imported as one stand register) into different sub-stand registers or "levels". A level could be a certain type of forest (e.g., stands with the dominating tree species Pinus contorta) where a certain inventory-scheme should be applied, e.g. securing a certain sample size in these forests.

• When a satisfying stratification of the analysis area has been obtained, the total number of sample stands are decided

First, a stratum will automatically obtain a number of sample stands (depending on the area in the stratum, or perhaps the average volume per hectare?). You should re-distribute the sample stands over the different strata, with a higher sampling intensity in strata with more valuable forests and where forest management decisions are supposed to be more difficult. This part is finished by actually sampling the sample stands in each stratum (done PPS where size is the stand area). Inspect the sampled sample stands regarding, e.g., the total number and each stands corresponding stratum.

NB: There should be at least three sample stands in each stratum. Moreover, aviod extreme differences in the (average) representative area of different strata.

• Next, the presupposed number of plots in a sample stand is set, depending on stand characteristics (chosen by the user)

The plot radius is set in a similar manner. Finally, some additional settings are made, necessary in the inventory (for the sample tree sampling). Inspect the sample stands. When values in corresponding columns (e.g. P1-P3, Stratum, Plots, and Radius) looks ok, check this "stratification" as finished.

NB: The number of plots per stand is set considering costs and assumed losses (caused by bad decisions made from erratic forest descriptions), less than three is only considered stupid. The plots are circular, however when acting as field-reference ("ground truth") to remotely sensed data with certain (quadratic) pixel size, you should adjust the plot radius hereof and define radii in meters with two decimals.