Management rules and external factors - INRA Montpellier

Rule n°3a. Pruning decision rule

Title

Time step for examining the rule

Limits of time step for applying the

rule

Options

To prune or not to prune next year to get a high quality bottom log

Year

Year 1 to year n when the expected bole height is obtained. If bole height

is expressed as a % of the tree height, year 1 to year f (f is the final harvest

year for the trees)

Y/N

State variables required for the rule Actual pruned height (Bole actual )

Tree height (Height)

Annual tree height increment (Ht increment )

Parameters of the rule

Desired length of bole of tree crop (Bole desired ) calculated as a fixed value or

a % of tree height or a % of tree height at a given age.

Minimum ratio of canopy height to total height (Ratio)

Tree shelter height

Minimum height of the tree to start pruning (or minimum diameter of lateral

branches)

Calculations required for applying the

rule

Likely consequences known by the

manager

Decision criterion

Net present value of the plot with pruning (NPV prune )

Net present value of the plot without pruning (NPV notprune )

Increased profitability of the agroforestry system if pruning benefits crop

growth **and** results in higher quality timber at the end of the tree rotation.

However, this must be evaluated against the cost of pruning. The cost of

not pruning would include the lost revenue of the crop component if not

pruning results in agricultural equipment not being able to access the site

for crop operations due to interference of tree branches.

Biophysical **Management** Rule: IF Bole actual < Ratio (Height) AND Bole actual

< Bole desired , AND Tree Height > minimum tree height THEN Prune ELSE

Not Prune.

Economic management rule: IF NPV prune > NPV notprune THEN Prune, ELSE

Not Prune.

Questions **and** comments

Are NPV values the right decision criteria for an economic management

rule At the time of pruning, NPV are not influenced by the pruning

operation. They will be influenced during the following years. The right

criterion should be the “Valeur d’avenir” (the sum of all discounted cost **and**

revenues expected after the current date until the tree harvest). But the

calculation of this criterion is impossible at the current year, as it would

require two full runs of the model (**and** many more as new choices will

occur later for the same rule). I am afraid an economic management rule

is therefore not possible at the year time step for any operation. But

may be I don’t underst**and** clearly the process. Christian Dupraz