Fig. 4

Example showing the procedure to develop a sequence of random arrangements for a 5-tree structural unit: Step 1), identify a reference tree as planting point 0; points 1 to 8 are nearest empty neighbors and the first 3 × 3 planting points. Step 2) The first random structural unit is developed and recorded based on planting points 0, 2, 3, 4, 8. In this example, we only show the first type of random structural unit in Fig. 4 (middle row). The code can also produce other types of random structural units. Thus, the remaining four planting points 1, 5, 6, and 7 are “destroyed”, and trees will not be planted. Step 3) Select a new reference tree that is not “destroyed” in step 2; we also call it planting point 0. This reference tree has its new 0 to 8 nearest planting points, including three “planted” (1, 2, 8), two “destroyed” (6, 7), and three empties (3, 4, 5). The R code will select 1, 2, 4, 8 to build the second random structural unit, and 3, 5, 6, 7 will be “destroyed”. The procedure is continued row by row