ABE Example - setting target species composition

During tending phases, one of the major goals of forest management is to modify the species composition to better comply to the target species composition. In reality, this process is quite complex and includes many detailed decisions (which trees to keep and/or liberate, should extra trees be planted, and if so, where, …). An approach to mimic this in iLand is given in this example.

The target species composition can be set for the custom thinning activities. It works as follows:

-+{ piab: 0.3, fasy: 0.5, rest: 0.9}+-

The following code snipped illustrates the approach:

// add target species shares in the options of STPs
fmengine.addManagement({ … <other stuffs>,
        options: { plan: {piab: 0.5, fasy: 0.3, lade: 0.2}}}, 'stp04');

// use this in the activities of the STP: call a JS function with the plan
// defined for the STP and other parameters
var a_thinning2 = { … <other stuff>,
       thinning: 'custom',
       onEvaluate: function(){ var t=
                 calculateSpeciesProbabilities(stp.options.plan,
                                              this.targetValue, 5);
            if (stand.trace) { console.log("plan"); print(t);}
            return t; },
       targetValue: 30, …
    };

Below is this custom Javascript code, that acutally calculates the probabilties:

// the custom-javascript function:
// plan_rel: object with target species composition (fractions)
// pct_reduction: % of basal area to remove in the operation
// min_value_remaining: minimum basal area (m2/ha) that should remain
// Return: object with removal probabilities pers species
function calculateSpeciesProbabilities(plan_rel, pct_reduction, min_value_remaining)
{
    // collect basal areas (current state)
    var state_abs = {};
    var total = 0;
    for (var i=0;i<stand.nspecies;++i) {
        state_abs[stand.speciesId(i)] = stand.basalArea(i);
        total += stand.basalArea(i);
    }

    var target = Math.max(total * (100-pct_reduction)/100, min_value_remaining );
    if (target == min_value_remaining)
        return false; // in this case: cancel the thinning

  // call the ‘magic’ function that does the calculation
  var plan = alignTarget(state_abs, plan_rel, target);
  return plan;
}

function alignTarget(full_state_abs, plan_rel, target_abs)
{
    var plan = {}; // empty object
    var state_abs = {rest: 0}; //

    var plan_sum = 0;
    var state_sum = 0;
    var s;
    for (s in full_state_abs) {
        if (s in plan_rel)
            state_abs[s] = full_state_abs[s];
        else
            state_abs['rest'] += full_state_abs[s];
    }
    if (!('rest' in plan_rel))
        plan_rel['rest'] = 0;
    //print(state_abs);

    for (s in state_abs) {
        //fmengine.log(s + ": " + target_abs * plan_rel[s] + ": " + state_abs[s] );
        plan[s] = Math.min(target_abs * plan_rel[s], state_abs[s] );
        //fmengine.log(Math.min(target_abs * plan_rel[s], state_abs[s] ));
        plan_sum += plan[s];
        state_sum += state_abs[s];
    }
    //print(plan);
    //fmengine.log(plan_sum); fmengine.log(state_sum);
    if (plan_sum==0)
        return false;
    plan_sum = 0;
    for (s in state_abs) {
        plan[s] = state_abs[s]- plan[s];
        plan_sum += plan[s];
    }
    for (s in state_abs) {
        plan[s] = ( plan[s] * (state_sum-target_abs) / plan_sum);
        if (state_abs[s]>0)
            plan[s] /= state_abs[s];
        else
            plan[s] = 1; // do nothing when nothing is in state
    }
    return plan;
}