Tree & Stand Simulator (TASS)
The Tree and Stand Simulator (TASS) is a biologically based, spatially explicit, individual tree model. The TASS brochure (PDF, 1.3 MB) provides a brief overview. TASS currently exists in 3 main forms:
- TASS III is the all-new public-release Windows™ version, which begins to extend TASS into more complex stand structures with multiple-species and -age cohorts. The initial release is limited to lodgepole pine (Pinus contorta var. latifolia) and white spruce (Picea glauca).
- TASS II (commonly referred to as TASS) is the well-established, in-house version described below. Although, the concepts largely apply to TASS III, as well.
- TIPSY (Table Interpolation for Stand Yields provides direct operational access to yield tables generated by TASS II. For scenarios outside the limited range of TIPSY, a custom TASS run service is available by contacting the Growth and Yield Application Specialist.
TASS predicts the potential growth and yield of even-aged, single-species managed stands for 10 commercial tree species:
B.C. Coastal Tree Species
- Douglas-fir, Pseudotsuga menziesii
- Western hemlock, Tsuga heterophylla
- Western redcedar, Thuja plicata
- Sitka spruce, Picea sitchensis
- Red alder, Alnus rubra
B.C. Interior Tree Species
- Douglas-fir, Pseudotsuga menziesii var. glauca
- Western hemlock, Tsuga heterophylla
- Lodgepole pine, Pinus contorta var. latifolia
- White spruce, Picea glauca
- Trembling aspen, Populus tremuloides
The core purpose of TASS is to predict silvicultural treatment response by modelling individual tree crown dynamics and their relationship to bole growth and wood quality. This focus on crown dynamics makes TASS particularly well suited for predicting response to treatments such as:
- Pre-commercial and commercial thinning
TASS enables a suite of programs developed and maintained by the Stand Development Modelling Group. TASS is linked to models in Silviculture on Yield, Lumber Value, and Economic Return (SYLVER) that predict log and lumber yields.
TASS and SYLVER generate the large database of yield tables stored and reported by TIPSY. TIPSY is the user-friendly table interpolation program responsible for most TASS operational applications.
Financial Analysis of $ilviculture Investment and Economic Return (FAN$IER) adds economic silvicultural investment analysis capability to both TIPSY and SYLVER. The Stand Development Modelling Group offers custom TASS runs to users needing more flexibility than TIPSY provides. Examples include spatial distributions and pruning.
TASS has many potential applications:
- Analyzing managed stand yield curves at the forest level to support allowable annual cut (AAC) determinations and forest management planning. Examples include:
- Timber Supply Review (Forest Analysis and Inventory Branch)
- Forest Development Plans (licensees)
- Planning and analysis of silviculture investment. Examples include:
- The Ministry’s Forests for Tomorrow and Land Based Investment programs
- Silviculture Strategy development
- Stocking Standards development under the B.C. Forest and Range Practices Act
- Stand-level prescriptions
- Exploring questions involving tree growth and stand dynamics. For example:
- Evaluating proposed silvicultural treatments and policies in the absence of conclusive field data
- Assessing impacts on wood quality and value
- Projecting carbon sequestration and biomass production
- Analyzing pest and disease yield impacts
- Teaching and demonstrating the principles of growth, yield and stand dynamics
Many of TASS’s component growth relationships were derived from detailed stem analyses of tree boles, branches and foliage. The resulting model was then calibrated to data from approximately 15,000 permanent sample and research plots in B.C., Alberta, the U.S. Pacific Northwest, Europe and New Zealand.
Goudie (1998) compared pre-commercial and commercial thinning response predictions from TASS against data from many long-term research installations in B.C., Alberta and Washington State. He concluded that “while growth and yield models cannot be proved valid, models must be evaluated or tested against available data to identify potential biases. The [TASS] system generally performs very well but may moderately overestimate the response to thinning in some cases."
Goudie (1996) also compared lodgepole pine managed stand yield tables generated by TASS against data and a yield model from Sweden (Elfving, 1990). He concluded that the appearance of higher productivity in Sweden, relative to B.C., is due largely to the absence of natural, unmanaged stands in Sweden, where lodgepole pine is an introduced exotic. Comparing managed stands, he found similar upper productivity limits and similar standing volumes at common stages of stand development. Thinning yields produced by two very different models (TASS and Elfving, 1990) are quite similar for standing volume, the culmination of mean annual increment and total production.
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Elfving, B. 1990. Nya produktionsdata och prognosfunktioner förcontortatall. (New yield data and functions for contorta pine). Sveriges Lantbruksuniversitet Institutionen för kogsskötsel Arbetsrapporter Nr 34. (Swedish Royal College of Forestry Department of Silviculture Working Report No. 34). 19 pp + Appendix.
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Goudie, J.W. 1996. A comparison between managed-stand yields of lodgepole pine in British Columbia and Sweden. p. 51–63. January 24 and,25, 1996, Smithers, BC, Tollestrup, P. (ed.). Northern Interior Vegetation Management Association, Prince George, BC.
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