Tree & Stand Simulator (TASS)

Last updated on January 22, 2024

The Tree and Stand Simulator (TASS) is a biologically based, spatially explicit, individual tree model. The TASS brochure (PDF, 1MB) provides a brief overview.

The Tree and Stand Simulator currently exists in three main forms:

  1. TASS III is the 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). An Introduction to TASS III Video Tutorial is available to provide a brief demonstration of the program functionality
  2. 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
  3. Table Interpolation for Stand Yields (TIPSY) provides direct operational access to yield tables generated by TASS II.

Use of Tree and Stand Simulator to predict potential growth and yield

TASS predicts the potential growth and yield of even-aged, single-species managed stands for ten 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:

  • Espacement
  • Fertilization
  • Pruning
  • 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.


Potential applications of Tree and Stand Simulator

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

Tree and Stand Simulator calibration and validation

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.


Tree and Stand Simulator references:

  • Alfaro, R.I., G. Brown, K.J. Mitchell, K.R. Polsson and R.N. Macdonald. 1996. SWAT: A decision support system for spruce weevil management. pp. 31–44. In: T.L. Shore and D.L. MacLean (Eds.). Decision support systems for forest pest management. FRDA No. 260
  • Bloomberg, W.J. 1990. Modeling control strategies for laminated root rot in managed Douglas-fir stands: model development. Phytopathology, Vol. 78, pp. 4903–4909
  • British Columbia Ministry of Forests. 1999. Guidelines for Developing Stand Density Management Regimes. B.C. Ministry of Forests, Victoria, ISBN 07726-3746-6. 94 pp
  • Brunner, A. 1988. A light model for spatially explicit forest stand models. For. Ecol. Manage. 107:29–46
  • Di Lucca, C.M. 2019. Using the Tree and Stand Simulator (TASS) model to predict the effect of stand management on quantity and value of carbon and biomass in British Columbia, Canada. Poster prepared for IUFRO 2019, Curitiba, Brazil. Sept. 29 – October 5, 2019 (PDF, 600KB)
  • Di Lucca, C.M. 1999. TASS/SYLVER/TIPSY: systems for predicting the impact of silvicultural practices on yield, lumber value, economic return and other benefits. In: Stand Density Management Conference: Using the Planning Tools. November 23–24, 1998, Colin R. Bamsey [Ed.] Clear Lake Ltd., Edmonton, AB. pp. 7–16
  • 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
  • Goudie, J.W. 1980. Yield tables for managed stands of lodgepole pine in northern Idaho and southeastern British Columbia. University of Idaho, Moscow, Idaho. 111 pp
  • 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, B.C, Tollestrup, P. (ed.). Northern Interior Vegetation Management Association, Prince George, B.C.
  • Goudie, J.W. 1998. Model validation: A search for the magic grove or the magic model. In: Stand density management conference: Planning and implementation, November 6–7, 1997, Edmonton, AB, Bamsey, C. pp. 45-58
  • Greenough, J.A. and W.A. Kurz. 1996. Stand tending impacts on environmental indicators. B.C. Min. For. Silviculture Practices Branch. FRDA II- ISBN 0-7726-2943-9. 58 pp
  • McWilliams, E.G. and R.E. Carter. 1998. Silviculture investment opportunities: A Methodology for identifying key decision variables. Forest Renewal B.C., No. HQ96463-RE. 102 pp
  • Mitchell, K.J. 1969. Simulation of the growth of even-aged stands of white spruce. In: Yale Univ. School of Forestry Bull. No 75, Yale University, New Haven, CN. 48 pp
  • Mitchell, K.J. 1975. Dynamics and simulated yield of Douglas-fir. For. Sci. Monogr. 17, 39 pp
  • Mitchell, K.J. 1978. Impact of planting density and juvenile spacing on the yield of Douglas-fir. pp. 143–158. In Joran Fries, Harold E. Burkhart and Timothy A. Max (editors). Proceedings of the Conference on Growth Models for Long Term Forecasting of Timber Yields and Forest Resources Management; Mensurations, Growth and Yield Section of IUFRO, Virginia Polytech. Inst and SU, Blacksburg, Virginia
  • Mitchell, K.J. 1986. Comparison of Mcardle, DFSIM, and TASS growth and yield models. pp. 350–359. In Proc. Symp. Douglas-fir: Stand management for the future, June 18–20, 1985, Seattle, Wash., C.D Oliver, D.P. Hanley, and J.A. Johnson (Editors). Inst. For. Res., Univ. Wash., Contrib. No. 55, Seattle, Washington
  • Mitchell, K.J. 1987. Predicting the impact of silvicultural treatments on yield, products and value. pp. 44–60. In H.N. Chappell and Douglas A. Maguire (Editors). Predicting Forest Growth and Yield: Current Issues, Future Prospects. College of Forest Resources, Univ. Wash., Seattle, Wash. Inst. For. Resources Contribution No. 58
  • Mitchell, K.J. 1988. SYLVER: modelling the impact of Silviculture on Yield, Lumber Value and Economic Return. For. Chron. 64(2):127–131
  • Mitchell, K.J. 1995. Simulate the Treatment Before Pruning the Stand. In D.P. Hanley, C.D. Oliver, D.A. Maguire, D.G. Briggs, and R.D. Fight (Editors). Forest Prunning and Wood Quality of Western North American Conifers. Coll. For. Res., Univ. Wash., Seattle, Washington
  • Mitchell, K.J. and I.R. Cameron. 1985. Managed stand yield tables for coastal Douglas-fir: initial density and precommercial thinning. B.C. Min. For., Res. Branch, Victoria, B.C. Land Manage. Rep. 31
  • Mitchell, K.J. and W.J. Bloomberg. 1986. Expanding concepts of growth and yield modelling to disease impacts and forest products. In Second Can. For. Serv. Modelling Workshop, 1986, Can. For. Serv., Victoria, B.C.
  • Mitchell, K.J., R.M. Kellogg, and K.R. Polsson. 1989. Silvicultural treatments and end-product value. pp. 130–167. In Second growth Douglas-fir: Its management and conversion for value. A report of the Douglas-fir Task Force, Kellogg, R.M. (editors). Forintek Canada Corp. Spec. Publ. No. SP-32, Vancouver, B.C. 173 p. B.C. Min. For., Res. Branch, Unpubl. Rep. 31 pp
  • Stone, M.S. 1993. An economic evaluation of commercial thinning Douglas-fir in the coastal region of British Columbia. FRDA Working Paper WP-6-002. Canadian Forest Service/B.C. Ministry of Forests, Pacific Forestry Centre, Victoria, B.C. 146 p
  • Stone, M.S. 1996. Commercial thinning lodgepole pine: An economic analysis. FRDA Working Paper WP-6-017. Canadian Forest Service/B.C. Ministry of Forests, Pacific Forestry Centre, Victoria, B.C. 153 p
  • Stone, M.S. 1998. Economics of Pre-commercial and Commercial Thinning. In Stand density management conference: Planning and implementation, November 6–7, 1997, Edmonton, AB, Bamsey, C. pp. 61–71



Contact Information

For more information on TASS contact:

Growth and Yield Application Specialist