Generalized Harvest Regime

This behavior can perform harvest very flexibly, depending on the parameters used. The behavior itself decides when harvests will occur and how much to cut, then chooses trees to cut with the help of a preference algorithm.

Trees removed by this behavior will have a mortality reason code of "harvest".

Parameters for this behavior

Parameter nameDescription
Gen Harvest Regime Cut Preference "A" "A" in the function that calculates cut preference of individual trees.
Gen Harvest Regime Cut Preference "B" "B" in the function that calculates cut preference of individual trees.
Gen Harvest Regime Cut Preference "C" "C" in the function that calculates cut preference of individual trees.
Gen Harvest Regime Cut Preference "Alpha" Alpha in the function that calculates cut preference of individual trees.
Gen Harvest Regime Cut Preference "Beta" Beta in the function that calculates cut preference of individual trees.
Gen Harvest Regime Cut Preference "Beta" Beta in the function that calculates cut preference of individual trees.
Gen Harvest Regime Cut Preference "Gamma" Gamma in the function that calculates cut preference of individual trees.
Gen Harvest Regime Cut Preference "Mu" Mu in the function that calculates cut preference of individual trees.
Gen Harvest Regime Gamma Scale Parameter Scale parameter for the gamma probability distribution function.
Gen Harvest Regime Harvest Probability "A" "A" term in the function that determines the probability that the plot will be harvested this time step.
Gen Harvest Regime Harvest Probability "B" "B" term in the function that determines the probability that the plot will be harvested this time step.
Gen Harvest Regime Harvest Probability "M" "M" term in the function that determines the probability that the plot will be harvested this time step.
Gen Harvest Regime Remove Amount "Alpha""Alpha" term in the function that determines percentage of adult basal area to be removed from the plot.
Gen Harvest Regime Remove Amount "Beta""Beta" term in the function that determines percentage of adult basal area to be removed from the plot.
Gen Harvest Regime Remove Amount "Mu""Mu" term in the function that determines percentage of adult basal area to be removed from the plot.
What should calculations be based on?Flag for whether calculations should be based on total adult biomass or total adult basal area.

How it works

The behavior calculates many probabilities to decide whether and what to cut. These calculations can be based on either total adult biomass in the plot (Mg/ha), or total adult basal area in the plot (m2/ha). The parameter What should calculations be based on? indicates which to use. If biomass is chosen, biomass is calculated using the Dimension analysis behavior.

The behavior begins the time step by deciding whether or not a harvest will occur. The probability of harvest is calculated as follows:

P equals a exp(-mAmt^b)

where:

A random number is compared to this probability to decide whether or not harvest will occur. The frequency of harvest in previous time steps is not take into account.

If harvest is to occur, the percentage of adult basal area to remove is calculated as follows:

BAR equals alpha*exp(-mu*Amt^beta)

where:

Note that the BAR is the mean removal rate. This value is used, along with the Gen Harvest Regime Gamma Scale Parameter, in a draw on the gamma distribution in order to get the actual target removal rate.

The adult plot biomass or basal area in the equations above is the total for all species. All species must participate in harvest, and only adults are counted and cut.

Once a basal area removal target has been established, the individuals to cut must be selected. A preference function determines the probability that an individual will be cut, as follows:

P equals (1 - gamma * exp(-beta * BAR ^ alpha)) * (exp(-0.5*((DBH - mu)/sigma)^2))

where:

The term σ is:

σ = a + b * BAR c

where:

An individual's probability of removal is compared with a random number to determine if that individual is cut.

The preference function takes into account the target basal area removal rate of the plot. However, the function shape does not necessarily produce a mean removal probability equal to that of the target removal rate, particularly near 0 and 100. If you wish, the behavior can refine the probabilities on a second pass to get closer to the target. You can set a tolerance using the Gen Harvest Acceptable Deviation From Cut Target parameter. This is expressed as a proportion of the removal rate, between 0 and 1. So a value of 0.1 allows first-pass acceptable deviation of 10 percent from the target. If the actual removal rate falls outside this limit, the function adjusts all preferences by a correction factor and re-evaluates individual cut decisions. No more than two passes will be made, even if the second pass does not achieve a removal rate within the tolerance. Setting a high tolerance such that a second pass is not often needed eliminates a lot of calculations and will allow a run to be faster.

How to apply it

Apply this behavior to the adults of all species. If you choose to make calculations based on biomass, you must also apply the Dimension analysis behavior to the same trees.