BiteImpact Class

BiteImpact

Description

Sequence of steps

The following steps are executed: * ask the impactFilter if an impact should happen * filter host trees (if provided) * run the impact (run either the onImpact handler, or the impact specified at the impact property)

Specifying the impact

BiteImpact supports different impact targets (i.e. which plants/part of plants to affect), and ways to further specify the impact (i.e. which fraction of the population to affect). The total impact is a combination of multiple impacts.

Impact targets (target):

  • tree: Trees (>4m height) are affected (mortality)
  • foliage: The foliage of trees (>4m) is reduced by the agent
  • roots: The root biomass is reduced (trees >4m) (not impl)
  • sapling: Sapling cohorts (trees <4m height) are affected (i.e. mortality)
  • browsing: The height growth of saplings (<4m) is set to 0 for the year of impact

Declaring impacts

The total impact is specified as an array of impacts:

...
impact: [ { impact 1}, {impact 2}, ... ],
...

An single impact is specified as a Javascript object with the following elements: * target: The impact target as a string (e.g. tree, see list above) * fractionOfTrees: a fraction specifiying which plants to affect (0..1). If omitted, all trees are affected. * fractionPerTree: the fraction of the respective biomass compartment to remove (0..1). Only applicable for biomass targets. * maxTrees: the maximum (absolute) number of plants to affect (optional) * maxBiomass: if provided, maxBiomass caps the removal at the given amount of biomass. * order: order specifies the order in which trees are processed. order is an Expression (provided as a string). For example, if order is ‘-dbh’, then the biggest trees would be first in the list, and thus affected first. If omitted, the trees are selected randomly. * treeFilter: an additional filter for trees / saplings (an expression). Applying a treeFilter within an item does not change the current tree / sapling list.

Notes: * if both specified, the smaller value of fractionOfTrees and maxTrees is effective; e.g. if the total number of trees is 100, fractionOfTrees 0.5, and maxTrees 80, then 50 trees are affected. If also a maxBiomass is provided, it acts as an additional limit (i.e. if in the above example maxBiomass is achieved after 20 trees, then execution stops there). * impact items are processed in the given sequence. * the properties fractionOfTrees, fractionPerTree, maxTrees, and maxBiomass are dynamic expressions (i.e. can be calculated dynamically). * if maxBiomass is provided, the model accounts for overshooting the threshold by scaling the impact of the last tree so that the total impact on the cell equals maxBiomass.

Example:

impact: [ {target: 'tree', fractionOfTrees: 0.1, maxTrees: 100}, // 10 % of all trees die, but not more than 100 (selected randomly)
          {target: 'browsing'}, // all saplings are browsed within the cell
          {target: 'foliage', fractionPerTree: 0.5, maxBiomass: 100, order: 'dbh' } ], // remove 50% of foliage (starting with the smallest) and stop when the cumulative removal reaches 100kg

Setup

  • hostTrees (expression)

    A filter expression to select those trees on the pixel which are considered as hosts. Note that BiteBiomass includes also this filter. If omitted or empty, no filtering will happen.

  • impactFilter (dynamic expression)

    A dynamic expression to determine whether an impact should occur on the cell (context is cell). The expression should return a boolean value.

Example:

impactFilter: 'agentImpact>0'  // impact only on cells where the biomass growth module indicates biomass loss

  • impact (array of Javascript objects)

    See the section about “Declaring impacts above”.

  • verbose (boolean)

    If true, the log contains more details. Mainly for testing purposes. Default: false.

  • simulate (boolean)

    If true no trees are harmed.

Properties

no properties

Variables

no variables

Events

  • onImpact(cell)

    The onImpact event is responsible to implement the agents impact on a cell and should return the number of killed trees during the calculation.