Likewise, there is no one "best" modelling approach. A model’s
architecture stems from the modelling approach (philosophy) chosen by
the modeller based on the intended application and available data. Limited
databases along with our limited knowledge of tree and stand growth necessarily
lead to different approaches for different needs and applications. For
instance, a primary emphasis on supporting silviculture prescriptions
is likely to lead to a different model than an emphasis on inventory or
planning. Similarly, an emphasis on single-rotation yields will produce
a different model than an emphasis on long-term sustainability. We are
already seeing a merging of modelling approaches (e.g., trends toward
individual-tree, spatially explicit models) but it will be years before
our understanding and data enable us to create one model for all situations
and applications. For the immediate future we must expect to deal with
more models, not fewer.
Growth and yield prediction models are abstract or simplified representations
of some aspect of reality used primarily to estimate the future growth
and yield of forest stands. A stand growth model
represents an abstraction of the natural dynamics of a forest stand,
and depicts growth, mortality and other changes in stand composition
and structure. It also mathematically describes the growth and yield
of trees and stands. Some models are developed to predict Yield,
which is the final accumulated growth at the end of a certain period
(e.g., total volume growth in cubic meters per hectare); while others
predict Growth, which is the total increase in dimensions
of one or more individuals in a forest stand over a given period of
time (e.g., total volume growth in cubic meters per hectare and per
year), as well as Yield.
Traditional growth and yield models are classified into two major
groups. The models which require stand summary information (e.g.,
volume per hectare and stand average diameter) are called Whole
Stand Models. The models which require a sum of individual tree
information (e.g., tree heights, diameters and crown lengths) to produce
estimates of yield are called Individual Tree Models.
These models are further subdivided according to how the stand density
is modelled. For instance, variable density whole stand models can assess
the effects of yield on variation in stand density (e.g., crown cover,
basal area). Of the individual tree models, only distance-dependent
models maintain a spatial record of the point density around individual
trees.
|
Year
|
Event
|
|
1913
|
- H.R. MacMillan made the first estimates of quality and growth
of British Columbia’s timber resource
|
|
1920
|
- First "normal" yield tables were developed for fully stocked
stands of hemlock, balsam, cedar and spruce. First growth plots
were established in coastal Douglas-fir stands.
|
|
1928
|
- Preliminary yield tables, based on permanent plot data, were
prepared for hemlock, balsam, spruce, coastal Douglas-fir, lodgepole
pine and ponderosa pine.
|
|
1936
|
- First volume, yield and stand tables were developed for the
principal commercial species.
|
|
1947
|
- First normal yield tables, based on the periodic remeasurement
of permanent sample plots became available.
|
|
1961
|
- First empirical yield tables, based on continuous forest inventory
data, became available.
|
|
1963
|
- First volume- and diameter-age curves were produced using
forest inventory plot data and harmonized hand-drawn curve techniques.
|
|
1976
|
- All forest inventory plot data were compiled to new size limits
and utilization standards, and stratify by site class, species
composition, and geographic location. Began the process of fitting
non-linear Chapman-Richards regression function to volume- and
diameter-over-age data in each stratum.
|
|
1981
|
- A Site Index System (i.e. formerly called the Ek_Payandeh/Volume
Ratio System) was first used in TSA plans and MOF inventory
file updates. Began the development of a Variable Density Yield
Prediction system (VDYP) for pure species stands.
|
|
1985
|
- First managed stand yield tables for coastal Douglas-fir were
generated using the Tree And Stand Simulator (TASS) growth and
yield model.
|
|
1989
|
- SYLVER was completed to evaluate the impact of silvicultural
practices on wood quality, product value and economic return
of second-growth Douglas-fir stands.
|
|
1991
|
- TIPSY, a program that interpolates managed stand yield tables
generated by TASS, was first distributed to forest managers
across de province. This program included four coastal and three
interior BC commercial tree species.
|
|
1993
|
- VDYP was released to replace all earlier versions of natural
stand yield prediction systems.
|
|
1994
|
- The Stand and Tree Integrator Model (STIM) version 2.0 for
western hemlock was first released by the Canadian Forest Service
(Pacific Forestry Centre, Victoria). .
|
|
1996
|
- The Stand Density Management Diagrams (SDMDs) for lodgepole
pine, white spruce and interior Douglas-fir were published by
Craig Farnden from the Canadian Forest Service.
- STIM version 3.0 for trembling aspen was first released by
the Canadian Forest Service (Pacific Forestry Centre, Victoria).
- The B.C. Ministry of Forests assumed the custodianship of
STIM for western hemlock and trembling aspen.
|
|
1997
|
- The Stand Density Management Diagrams (SDMDs) for coastal
Douglas-fir, western hemlock, Sitka spruce, and western redcedar
were published by Craig Farnden from the Canadian Forest Service.
|
|
1998
|
- Prognosis BC Beta version 1.0b was released for use in South
Eastern BC to simulate the development of complex stands (ie.
mixed, uneven-aged). This model was calibrated for eleven conifers
species from the ICH, IDF, and southern ESSF biogeoclimatic
zones.
- TIPSY version 2.1e was released to replace earlier versions
of TIPSY. It included improved functionality, as well as many
new tables and features
|
|
