Vegetation Resources Inventory
Forest Inventory Statistical Rigor (Biometrics) Support
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Growth Relationships and Model Components |
Biometrics Overview of VDYP 7 Components
This document provides an overview of the VDYP7 system from a
functional biometrics perspective. From that perspective there are a
number of major components to VDYP7; some are empirical and others
are algorithmic. All the major components are described here. The
purpose of the document is to provide the user with an understanding
of what the major components of VDYP7 do, and how they interact.
This will be useful in understanding how system outputs relate to
the inputs, and why the system behavior for VDYP7 may sometimes be
quite different from that of VDYP6. [download]
A Comparison of the Interfaces that uses VDYP 7 Core Modules
The VDYP7 Core Modules are utilized within four different
User Interfaces: WinVDYP, VDYP7 Console, VDYP7 Growth Projection
within VRIMS, and VDYP7 Attribute Adjustment (VDYP7_ADJUST). It
should be noted that there are differences in how the modules
operate within each of these interfaces, particularly within
WinVDYP7. To download document [download]
Advantages and Limitation
VDYP 7 addresses the weaknesses of its predecessor and
provides many advantages:
- It is a true
growth model. Yields are
projected by incrementing density attributes
including basal area (BA) and quadratic mean
diameter (QMD), rather than only incrementing age
and growing height.
- More accurate
measurement of stand density. VDYP 7 uses BA as
a direct measure of stand density. Therefore the
model is more sensitive to changes in stand density
and can be used to model catastrophic mortality
(e.g. stands affected by mountain pine beetle), or
selectively harvested stands.
- Estimation of
average stand diameter. VDYP 7 can produce quadratic
mean diameters (QMD) for all stands in a management
unit. In the future, this will facilitate the
estimation of stand-level stand structure
attributes, such as piece size, for industry.
- More flexible
yield reporting.
VDYP 7 generates a wider variety of outputs than
VDYP 6. Five different volume types (whole stem
volume; close utilization; close utilization net
decay; close utilization net decay and waste; and
close utilization net decay, waste and breakage) are
generated at five different diameter limits (4.0
cm+, 7.5 cm+, 12.5 cm+, 17.5 cm+, and 22.5 cm+). The
4.0 cm+ diameter limit allows for more accurate
estimation of forest biomass.
- Ecologically-based growth and yield functions. VDYP 7 growth and
yield functions are fitted based on Biogeoclimatic
Ecosystem Classification (BEC) zones. This is
consistent with the ecologically-based taper
equations and loss factors that predict more
accurate volumes. VDYP 6 was based on forest
inventory zone (FIZ).
- More accurate
predictions due to additional attribute inputs.
When there are no errors in attributes, VDYP 7
predicts more accurate volume yields. Figures 1a and
1b show ground-compiled volumes plotted against VDYP
6 and VDYP 7 predicted volumes. VDYP 6 inputs
include: height, age, crown closure and stocking
class, whereas VDYP 7 inputs include: site height,
age, Lorey height, basal area, and trees per
hectare. From these figures, it is evident that VDYP
7 is a better predictor of volume than VDYP 6.
Although there are distinct advantages to using VDYP 7 relative to
VDYP 6, users should be aware of the following challenges with VDYP
7. Efforts are being made to address these challenges:
- VDYP7 Console
requires eight .csv input attribute tables; more
than required in VDYP6.
Attributes describing vegetation and non-vegetation
layers, history, etc. are required. Users need to
establish specific table structures that will store
the inputs. If these tables are not established
accurately, the model will not run.
- VDYP7 Attribute
Adjustment requires a working knowledge of MS Access
computer programming language.
This language has limitations in processing a large
number of records.
- Short, young
stands may not return any yields.
This is largely
dependent on a stand’s QMD. Stands that are less
than 6-8 m in height and that do not meet the 7.5 cm
QMD criteria, will not be assigned volumes.
- Very low SI
polygons that were assigned volumes in VDYP6 may not
necessarily be assigned volumes in VDYP7 until they
become older than approximately 100 years.
Sometimes, VDYP 7 returns null values, i.e., no
volumes for these stands.
- VDYP7 Attribute
Adjustment requires a very specific database format
for load into the VRIMS environment.
The format of the
personal geo-database (PGDB) is specified in the
document, VDYP7 Attribute Adjustment Procedures
Manual (currently not available)
