iLand includes a special output for assessing the development stage of forested cells on the landscape. The rule set to derive specific development stages is flexible (using a Javascript interface) in order to accomodate different ecosystems. Moreover, the base resolution of the grid is not fixed and can be 10m, 20m, 50m, or 100m.

Project file

The 'devstage' output is configured in the 'output' section of the project file. See also the outputs page.

 

Settingdescription
cellsize defines the cell size in meters. The value need to align with the 100m / 10m cells.  Possible values are therfore: 10, 20, 50, 100
handlerThe name of the Javascript object that is handling the calculation of development stages. See below.
filterfilter to limit output to specific years (variable: simulation year, e.g., 'in(year, 100, 200, 300)'
enabledboolean switch to turn output on / off (true / false)


 

Javascript

The 'devstage' mechanism expects a Javascript object in the global Javascript workspace (loaded e.g. via the `system.javascript` setting of the project file). The Javascsript object should have the the following properties / functions:

 

namedescription
typesAn object that describes the possible development stages with a numeric Id, name, a color.See below.
run()function with the signature "int run(cell)". This function calculates for each 'cell' a development stage and returns the numeric value. The function is only executed for cells that contain stockable area. See below for details.
onfinished()function that is called after completion of the development stage calculations. Can be used to save e.g. grids. Signature: "void onfinished(cell)". Note: onfinished with an upper-case "F", which is not saved correctly in the wiki.
grid()grid() returns the full development stage grid as a Javascript grid. Use in combination with the 'onfinished' callback.


 

The cell object

The cell object provides access to a fixed set of properties pertaining to a given cell. Extending this list of properties requires adding properties in C++ (see devstageout.h / devstageout.cpp).

The properties are either related to the trees on the cell (<4m, e.g., DBHMean), related to carbon pools (e.g., deadwoodShare), or special attributes (e.g., crown projection area CPA).

 

PropertyDescription
x x position of the current cell (cell index of the development stage grid)
y y position of the current cell (cell index)
DBHMin, DBHMean, DBHMedian, DBHMaxMinimum / mean / median / max DBH of all trees (>4m) on the cell (cm).
HMean, HMedian, HMaxMean / median / max tree height over all trees (>4m) on the cell (m).
NQDvariation in DBH expressed as 100 * interquartile distance / median. Interquartile distance: 75th - 25th percentile of DBH on the cell. (trees >4m).
N_hanumber of trees (>4m) per hectare (includes transformation from the cell size, but not stockable area within the cell)
CPAcrown projection area (0..1). Calculates the crown projection of all trees (>4m) on a 2m grid using the tree crown radii. See also http://iland-model.org/apidoc/classes/SpatialAnalysis.html. All 2m cells with more than 50% crown area are counted and the CPA is then calculated  as #total area of cells >50% crown cover / #stockable area.
deadwoodShare share of standing / lying (aboveground) deadwood relative to (aboveground) living biomass (Carbon). Values for standing / lying deadwood C are retrieved from the resource units (100m). Only the aboveground fraction of snags and coarse woody debris is counted. The deadwoodShare is calculated as: deadwood_carbon / living_aboveground_carbon(incl.regeneration). Note that deadwoodShare can become > 1.
Pct_PMugopercentage (0..100) of the (stockable) cell area, that is covered with trees of Pinus mugo with a height > 1.3m.

 

Output

The database output 'devstage' is described on the outputs page.

To save the development stages as a grid, you can use JavaScript (see in the example below).

 

Example

 
Below is an example of a classification (adapted after Zenner et al).

The code contains the definition of stages (including names and colors), the actual classifcation tree ('run()'), and some auxiliary code. The latter shows how cell variables can be logged to a csv file for testing (see (and uncomment) the 'dumpCell()' function), as well as a mechanism that fills an extra grid with custom values and writes that also to disk. 

// Example Object for ecological classification

function Logger(logfile) {
this.path=logfile;
this.text = "year;stand;text"; // the lines
this.save = function() {  Globals.saveTextFile(Globals.path(this.path), this.text);  }
this.log = function(txt) { //var line=Globals.year + ";" + stand.id + ";" + txt; 
this.text = this.text + "\n" + txt; }
}

var cell_acc;
var temp_grid;

const Stage_NonForest = 0;
const Stage_Krummholz = 1; 
const Stage_Gap = 2;
const Stage_Establishment = 3;
const Stage_Early_Optimum = 4;
const Stage_Mid_Optimum = 5;
const Stage_Late_Optimum = 6;
const Stage_Plenter = 7;
const Stage_Terminal = 8;
const Stage_Decay = 9;

var devStage =  {
   // define the available vegetation types
   // class 0 is reserved for non-forest!
   types:  { 0 : {name: "non forest", color: "#333333"},
 1: {name: "Krummholz", color: "#A0522D"}, 
                 2: {name: "Gap/Regeneration", color: "#FFFF99"}, 
 3: {name: "Establishment", color: "#FFCC00"},
 4: {name: "Early Optimum", color: "#99FF99"},
 5: {name: "Mid Optimum", color: "#00CC00"},
 6: {name: "Late Optimum", color: "#006600"},
 7: {name: "Plenter", color: "#3399FF"},
 8: {name: "Terminal", color: "#4169E1"},
 9: {name: "Decay", color: "#000080"}
 
   },  
   
   run: function(cell) {
   //this.dumpCell(cell); // write content to CSV
   //this.writeGrid(cell); // write variables to a grid
   
   // Krummholz: >=50% of the area covered with Pinus mugo
   if (cell.Pct_PMugo >= 50) 
  return Stage_Krummholz; 
  
   // Gap / Regeneration if crown projection area < 30%
   if (cell.CPA <= 0.3) 
  return Stage_Gap; 
  
   // "Establishment": max DBH < 20cm
   if (cell.DBHMax < 20) 
  return Stage_Establishment;
   
   // if there is a large amount of deadwood, we have decay, or establishment, or early optimum
   if (cell.deadwoodShare > 0.3) {
   // "Decay" if large trees are present
   if (cell.DBHMax >= 40)
     return Stage_Decay;
   
   // small mean dbh (<16) is "Establishment", "Early optimum" otherwise
   if (cell.DBHMean < 16)
     return Stage_Establishment;
   else
     return Stage_Early_Optimum;
   }
   
   // "Plenterforest" depends on DBH variation:
   if (cell.NQD > 150) 
     return Stage_Plenter;
 
   // Early / mid / late optimum depend on maximum DBH: 
   if (cell.DBHMax < 40)
      return Stage_Early_Optimum; // "Early optimum"
   if (cell.DBHMax < 60)
      return Stage_Mid_Optimum;
   if (cell.deadwoodShare <= 0.1)
      return Stage_Late_Optimum; // dead wood share < 5%
   else
      return Stage_Terminal; // dead wood share >=5% (and <30%)
  

   }, 
   onFinished: function(cell) {
   // called at the end of the year
   cell.grid().save('temp/devstage_' + Globals.year + '.asc');
   cell_acc = cell; // test access from outside...
   // only necessary if writeGrid() is active:
   if (temp_grid === undefined)
  temp_grid = cell.grid().copy();
   else
      temp_grid.save('temp/extra_' + Globals.year + '.asc');
   },
   lg: new Logger("temp/test.csv"),
   
   dumpCell: function(cell) {
   var line = "" + cell.x + "," + cell.y + "," + cell.DBHMax + "," + cell.DBHMean + "," + cell.NQD + "," + cell.CPA + "," + cell.deadwoodShare;
   this.lg.log(line);
   },
   writeGrid: function(cell) {
   if (temp_grid !== undefined)
       temp_grid.setValue( cell.x, cell.y, cell.NQD ); // fill the grid with the NQD variable
   }
};