# RECRUIT

During any cycle, the Recruit command can schedule new trees to be created and added to a temporary recruit tree list managed by OSM. At the end of each cycle, OSM will sort through the recruit tree list and add these new recruits to either the main tree list (trees >= breast height) or to the seedling list (trees < breast height). Depending on the OSM Variant model you are using, there may be restrictions on the size of trees that can be recruited.

Recruit commands provide a way to:

1) Specify regeneration response following certain harvest or natural disturbance events.

2) Transition a stand from a bare ground (clearcut) state.

3) Override or augment regeneration predicted by the Variant model.

4) Easily create test stands for model benchmarking and error testing.

Actions

def MyExampleAction

Recruit {cycle delay}

{Recruitment statements…}

See Actions for information about cycle delay arguments and changing default unit systems

See Operable to schedule recruitment under certain stand conditions.

## Recruitment statements

Species, density (tree factor), age, DBH, and height can be assigned to new recruits. It is also possible to recruit a number of new trees across a range of DBH or height sizes with a single command. The lower and upper bounds of these tree size ranges, as well as the mean and standard deviation of tree sizes within these specified ranges, can be stated.

Each statement under the RECRUIT signifies that a new tree is to be generated and the command line must start with one of four origin command keywords:

1) UNKNOWN

2) SEED Tree originated from seed

3) COPPICE Tree originated from a stump

4) PLANT Tree was planted

Depending on the Variant, tree growth, form, and / or mortality may depend on tree origin.

Arguments following the origin statement include:

1) Species Code Variant or USDA plant codes can be used for species. Species group variables are not permitted.

2) Density Tree Factor; #/hectare (DEFAULT) or #/acre (if USA units are used).

3) DBH DBH keyword followed by value or range (may be optional if HT stated)

Must be >0. Some Variants may constrain DBH further.

4) HT HT (height) keyword followed by value or range (optional)

5) MEAN Mean keyword followed by value (optional)

6) SD SD (standard deviation) keyword followed by value (optional)

7) AGE AGE keyword followed by whole number >= 1 (optional)

DBH and/or Height (HT) must be defined. If the Variant model cannot handle seedlings or cannot predict DBH from tree height, DBH may always need to be stated. If the HT argument is not stated it will be predicted by the Variant model. AGE is optional and if not stated, OSM will assume the recruit was born at the beginning of the cycle. Mean and standard deviation (SD) are used to adjust the shape of the diameter or height distribution of recruits.

The following commands will add 2000 planted WS trees with a DBH of 5 cm and Age of 10, 10 years post clearcut. In this case HT is predicted for all 2000 recruits.

ACTIONS

def ClearcutPlant

OPERABLE.GMV >= 150

CUT

RECRUIT 10

PLANT WS 2000 DBH 5 Age 10

Important: if using multi-year cycles, remember that DBH, HT, and AGE values must be set so that they represent end of cycle conditions because OSM will insert these new trees then. In other words, no growth, mortality, or aging is applied to these trees in the cycle they are added.

### Recruiting a distribution of tree sizes

In the example above, all 2000 trees had DBHs exactly equal to 5 cm. It is possible to equally or normally distribute trees within a size (DBH or HT) range.

For the same example, to simulate an equal distribution of DBHs between 1 and 10 cm use:

PLANT WS 2000 DBH 1 10 Age 10

For each recruit command line, when using diameter or height distributions, OSM will generate 10 tree records. In the case above, each of the ten record will contain 200 trees (equally diameter distribution among the ten records summing to desired density) and would be equivalent to writing out the 10 commands below.

PLANT WS 200 DBH 1 Age 10

PLANT WS 200 DBH 2 Age 10

PLANT WS 200 DBH 3 Age 10

PLANT WS 200 DBH 4 Age 10

PLANT WS 200 DBH 5 Age 10

PLANT WS 200 DBH 6 Age 10

PLANT WS 200 DBH 7 Age 10

PLANT WS 200 DBH 8 Age 10

PLANT WS 200 DBH 9 Age 10

PLANT WS 200 DBH 10 Age 10

To normally distribute with a standard deviation of two use:

PLANT WS 2000 DBH 1 10 SD 2 Age 10

Note that the mean DBH of these distributions will be 5.5 cm within a constrained DBH range of 1 and 10 cm. Proportion of trees falling outside this DBH range will be redistributed back into this range respecting the shape of the desired distribution shape.

To shift the mean DBH for the distribution:

PLANT WS 2000 DBH 1 10 Mean 3 SD 2 Age 10

Shifting the distribution left or right by adjusting the mean, as well as increasing or reducing the standard deviation, can provide a wide range of DBH or height distributions (Examples A & B).

### Short-hand command structure for mixed species regeneration

Where overall stand regeneration density and % species composition is known, the following short-hand command structure is possible.

RECRUIT

SEED 10000 Age 5

BF 25% DBH 2

WP 0.1% DBH 30 Age 50

BS 49.9% DBH 1 5

RM 10% DBH 2 10 SD 2

WB 15% DBH 2 10 Mean 2 SD 2

Unlimited recruit commands can be stated in subsequent lines.

PLANT WS 2000 DBH 5 Age 10

COPPICE RM 1000 DBH 5 HT 5 Age 10

Any tree attribute (DBH, HT, AGE) stated in the main statement will be inherited by species percentage sub-statements, unless overridden by restating a different value.