National Biomass Study, 2016-2019.

Systematic cluster grid of 5 km by 5 km, stratified by three population intensities of less than 50 people per km, between 50 and 100 people per km and above 100 people per km. Sampling included protected areas. Out of a cluster (PSU) of nine plots (SSU, their plot centers separated 300 m producing a cluster cross shape and 0.25 ha - 50 x 50 m - of area ) on each grid intersection a minimum of three plots are measured. A total of 439 square plots in a sampled area of 110 hectares. Given the unequal geographical representativity of the samples, it is difficult to assign a sampling intensity. The plot selection is made during the planning phase by the field Inventory Supervisor, the Field team leaders are allowed to make alternative selections only if a preselected plot(s) is inaccessible. Selection priority is given to the plot numbers 1, 2 and 3 at the centre although any other plot may be measured as replacement of any of the three key plots. Interest in getting information on certain vegetation types may influence plot selection. Each square plot is subdivided into five strips measuring 10 by 50 metres, running in the east-west direction. Tree measurements are done systematically from one strip to another, and tree numbering is based on the location of the tree in the strip. This is intended to make tree re-identification easier during subsequent visits. NBS has a nested plot approach whereby the minimum measurable DBH in the first strip is 3cm. In the rest of the plot, the DBH threshold is trees of 5cm and above.