Mean number of trees per hectare by species (tree height above 10 cm)


Result of this task figures information about density of trees (total number of trees) per area unit (ha) by defined species groups.


Requirements:


For that task is necessary to run the stratification by forest development types (see Stratification), join trees from regeneration table to trees table (see Create virtual trees for regeneration action) and reclassify species  list into the species groups (see Re-classification).


Procedure:


    • Add new task and rename it.
    • Select “Trees” layer.
    • Select “Trees.Number of trees (TreeNumber)” attribute
    • Set “1” in the Units combo box and “0” decimal places.
    • Select “Forest development type (Forest development type)” in Stratifier section  and leave Use stratifier in output checkbox empty.
    • .Select “Trees.Species (SpeciesGroup)” as classifier (Note: Click Add classifier button, tag  “Trees.Species (SpeciesGroup)” check box and click OK)
    • Select Mean of plot sums per hectare and desired Alpha (e.g. 0,05) in Statistics section.
    • Tag Include trees of regeneration segment Check box
    • Run the task using Perform button


Comments:


Whole plot is assigned to particular forest development type while performing stratification. At the same time the total area of each forest development type is calculated based on existing vector map (shapefile).


Multiplier is not set since the calculated number of trees stay on the level of several tens upto several hundreds units.


Setting attribute ForestDevelopmentType as stratifier increases precision of the output since there is available  information about size of the stratums derived from the map offorest development types and variability within particular stratum is smaller than variabilitywithin whole population, but the stratifier is not shown in the result for this particular task.


Species groups are used for classification.


Since we are interested about average number of trees per area unit the mean of plotsums per hectare without any plot weight is used for calculation. Data is automatically normalized using representative area of particular tree (Normal. attribute is set as Area, ha (RepreArea_ha)). This is the procedure which recalculates volume to unit volume (i.e. m3/ha).


Since we are interested about all trees starting with 10 cm of height the check box Include trees of regeneration circle and consider segments in calculation have to be tagged.This ensures that trees of smaller dimensions (those from inner circles) are calculated inrelation to the size of the subcircle they belong to (for details see Using concentric circlesat inventory plots). In our case three separate calculations are performed. Trees between 7 and 15 cm of DBH are processed in relation to the circle of radius 3,5 m, trees between15 and 30 cm of DBH are processed in relation to the circle of radius 7 m and finally trees above 30 cm of DBH are processed in relation to the whole plot (radius of appr. 12,62 m).Error propagation procedure is used to combine those partial results to the final result.


Screenshots:



Results: