Table 2 Sampling strategies used among NFIs based on systematic annual panels with respect to spatial alignment. Unalignment can be sought for at two different stages: (i) at a wide spatial scale in the spatial grid paneling design and (ii) at a local spatial scale in the sampling unit location strategy within grid cells. The deployment of plot clusters enabling the capture of local variability can also be seen as a third complementary degree in this approach. The table splits the reviewed NFIs according to the use of none, one, or both unalignment options. For the sake of comparison, some inventories were added to the review including the 9-year periodic Swiss NFI (Brändli et al. 2020; Vidal et al. 2016), the 10-year periodic Belgian NFI (Rondeux et Lecomte 2010; Tomppo et al 2010), and the 5-year periodic Finnish NFI (Tomppo and Tuomainen 2010). ^aPP = permanent plot, TP = temporary plot, PPC = permanent plot cluster, TPP = temporary plot cluster. ^bDepending on the NFI region, parallelograms of PPC can also be slightly unaligned (Fridman, pers. comm.)

From: Take five: about the beat and the bar of annual and 5-year periodic national forest inventories