INTRODUCTION
GENR is an interactive computer program that is designed to generate
a one acre representation of a pure or mixed-species, natural young growth
even-aged stand typical of the north coast region of California. The primary
purpose of this program is to convert some general broad stand descriptors
(input) into a plausible representative tree-by-tree inventory record for
direct use by the Cooperative Redwood Yield Project Timber Output Simulator
(CRYPTOS) program (Wensel, Krumland, and Landrum 1986). As a secondary
feature, GENR has some display capabilities which can be used to generate
frequency diagrams of trees by species and two-inch DBH classes, thus allow-
ing the user to get a visual picture of the population of trees being generated.
Only combinations of the following four species can be generated: redwood,
Douglas-fir, tanoak, and red alder.
The mathematical models documented in GENR are summarized in Appendix
A. Appendix B contains a sample runstream to illustrate the operation of the
program.
GENR is coded in standard FORTRAN 77 and executable code is available
for use on a number of computers including the VAX, IBM PC-compatible (with
math coprocessor), and the Apple MacIntosh.
OPERATION
The interactive nature of GENR makes it easy to use. However, there
are a few codes you will need to know. You will initially be asked to enter
a code designating the control species : to be used as a base for estimating
missing site index and age values for other species (See Appendix A ),
responding with a "1" for redwood or "2" for Douglas-fir.
You will then be asked to input the following values for each of the
previously mentioned species groups:
(a) stems/acre (TPA)
(b) site index (SI )
(c) average breast high age of dominants (Age)
(d) quadratic mean DBH (optional )
(e) number of tree records (NR ) to be generated (optional)
Further notes:
(1) Items (b) and (c) listed above are both required for the control
species selected. If you fail to enter them, the program will mercifully give
you another chance.
(2) For any other species you want to have as part of your stand (e.g.,
you have entered a stem/acre value of 25 or greater for the species) you may
enter site index and age. If either or both of these are not entered, they
will be estimated using the control species as a basis.
(3) It is not necessary for the control species stems/acre value to be
nonzero.
(4) If quadratic mean DBH values are supplied for any species, model II
will be used in estimating diameter distributions. Otherwise, model I will
be used (Krumland and Wensel, 1979a).
(5) The number of tree records (NR) by species is defaulted to 15 if the
stems per acre for any species is greater than 25. This value may be over-
riden on input with any value greater than or equal to 10. The following
conventions are used:
(a) If a species record number is entered in the range 1-9, it is changed
to 10.
(b) If the total number of records for all species is greater than 500,
the program will start all over. So 500 is a maximum.
(c) If the total number of records is greater than 65, a warning to the
effect that your output file is unusable for CRYPTOS will be issued.
Preliminary Output
The program will next print two tables. The first one displays the
input information (or program-generated estimates if they were not entered)
plus the estimated dominant height for each of the four species.
The second table is the result of the diameter distribution estimation
process by species. The Yi's are DBH's at approximately the .89, .61, and
.33 percentage points. 'The coefficients a, b, and c are the Weibull dia-
meter distribution parameters. If '(mod )' is printed, some adjustments were
made in the parameters (Krumland and Wensel, 1979a App. IV). The original
values are given in the column labelled "originals." E(D) is the estimated
quadratic mean DBH on the Weibull estimates. It is approximately (exactly,
if Model II is used) the same as listed under "First Stage Estimation."
Display
Next, you may look at DBH frequency diagrams by species. These are
the species codes in this program:
0 - all trees
1 - Redwood
2 - Douglas-fir
3 - Tanoak
4 - Alder
Entering a species code of '9' will allow you to exit from the display sub-
routine.Storing your stand for future use
Upon exiting the display routine, you have the option of (1) starting
all over, (2) stopping, or (3) preserving your stand record for future use
(in CRYPTOS most likely). If option 3 is chosen you will be asked to enter
a file name for the generated-stand description file. The appropriate in-
formation will be stored in CRYPTOS-compatible format on this file. You
will also have an opportunity to examine this tree file before storage pro-
cedures are completed.
In order to screen for estimated tree diameters less than 1.0 inches,
if the original estimated value for the Weibull parameter 'a' (the minimum
DBH) for any species is less than1.0 inches, the program will issue a warning
to the effect that you may wish to reconsider your decision to save this
stand for future use. These stands represent an extrapolation far beyond the
reasonable limits of the data used to construct the component models.
Limitations
The data used to develop the diameter distribution equations used by
GENR were somewhat deficient in the younger age classes and lower stocking
levels. Thus, if the quadratic mean DBH is not supplied by the user, the
resulting diameter estimates may be too large for young sparsely stocked stands.
This may then cause overestimates of future yields in CRYPTOS if GENR is used
to create an input file.
If you are supplying the quadratic mean DBH by species based on what-
ever local experience you have, a proper model I distribution can be estimated
directly. Otherwise, the following procedure can be used to obtain a work-
able quadratic mean DBH for stands with younger age classes. First, find the
age and site index of your stand in Table 1. If the total number of stems
per acre of all species combined is less than the amount listed, use the
corresponding mean quadratic DBH as model input. Otherwise, the program can
be used without specifying a quadratic mean DBH and use model II for the pro-
jection.
Table 1 was prepared by iteratively generating stands and finding a
stem count that corresponded to approximately 100 percent canopy cover at
ground level. This is the stem count listed in the table along with the es-
timated mean quadratic DBH for this stocking level. Stands with lower stock-
ing levels were presumed to have the same average size.
TABLE 1. Minimal stocking levels for which program estimated quadratic
mean DBH's are acceptable.
REDWOOD
SITE Breast High Age
INDEX 10 15 20 25 30
(STEMS PER ACRE/QUADRATIC MEAN DBH )
90 450/4.32 160/7.01 100/9.68 75/11.73 65/13.33
100 360/4.90 135/7.60 85/10.35 65/12.47 55/14.18
110 300/5.44 115/8.17 75/10.98 59/13.13 50/14.19
120 250/5.97 100/8.37 67/11.59 53/13.81 45/15.66
130 210/6.51 87/9.28 61/12.17 48/14.49 41/16.41
140 185/7.03 80/9.76 56/12.75 44/15.15 38/17.12
DOUGLAS-FIR
SITE Breast High Age
INDEX 10 15 20 25 30
(STEMS PER ACRE/QUADRATIC MEAN DBH )
90 430/2.82 150/6.05 95/8.31 72/10.07 59/11.54
100 310/3.19 120/6.65 80/8.49 62/10.76 52/12.28
110 228/3.82 105/7.13 70/9.51 55/11.40 46/13.01
120 190/4.26 93/7.58 63/10.03 50/12.01 42/13.70
130 165/4.63 83/8.01 57/10.54 45/12.61 38/14.40
140 145/4.97 75/8.40 53/11.00 42/13.17 35/15.06
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