Bringing biology into growth and yield: An overview of the ecologically based forest growth model, FORECAST

Clive Welham, PhD
Brad Seely, PhD
Hamish Kimmins, PhD

Forest Ecosystem Management Simulation Group
Department of Forest Sciences, University of British Columbia
Vancouver, BC, V6T 1Z4

The pervasive trend towards ecosystem-based management associated with the national sustainable forest management (SFM) initiative has significantly changed growth and yield modelling needs in British Columbia and across Canada.  The traditional empirically based growth and yield models currently supported by the Ministry of Forests were not designed to address the broad range stand types associated with the diversity of alternative management practices being developed across the province.  Practices such as variable retention, uneven-age and mixedwood management create complex stands whose characteristics are not represented in these models.  To project the developmental dynamics and subsequent yield of such stands and to project the impacts on associated indicators of non-timber values, stand-level planning models must have the capability to represent a suite of key biological processes.  Here we present a brief overview of the ecologically based model FORECAST including a synopsis of its application in BC and elsewhere.

FORECAST is an ecosystem-based, stand-level, forest growth simulator. The model was designed to accommodate a wide variety of harvesting and silvicultural systems in order to compare and contrast their effect upon forest productivity, stand dynamics, and various biophysical indicators of non-timber values. The model uses a hybrid approach whereby local growth and yield data (often from TASS/TIPSY) are combined with other data to derive estimates of the rates of key ecosystem processes related to the productivity and resource requirements of selected species. FORECAST uses relatively simple measures of decomposition, nutrient cycling, light competition, and other ecosystem properties to simulate forest growth and ecosystem dynamics under changing management conditions (Fig. 1). Growth occurs in annual time steps. Depending upon the species, plant populations within the model can be initiated from seed and/or vegetatively, and stand development can occur with or without competition from non-target tree species and understory populations. Details of FORECAST calibration and its application are provided in Kimmins et al. (1999), and Seely et al. (1999).

Figure 1. Schematic of basic ecosystem processes represented in FORECAST.

As a management model, FORECAST can simulate a wide variety of activities such as fertilizer application, brushing, partial harvesting, and mixedwood management.  Disturbances such as fire and insect defoliation can also be represented. Timber volume projections generated by FORECAST are ultimately constrained by the potential yields of single species stands as specified in the calibration data for a range of site qualities.   Growth and yield in complex stands is based on a simulated partitioning of limited resources (light and nutrients) among species and age cohorts.  The biological properties of individual species, as defined by the input data, determine their relative competitiveness for limited resources.

To date, the FORECAST model has been calibrated and used in variety of forest ecosystems, both in Canada and elsewhere (Table 1). In B.C. it has been used in conjunction with various landscape level models for projecting the spatial and temporal dynamics of a wide range of stand attributes in forests subjected to alternative management strategies.  The output of such analyses is being used to support the development of sustainable forest management plans.

Table 1. Current applications of the FORECAST model.





British Columbia


Arrow TSA

Arrow IFPA Project

G&Y projection in complex stands, long-term site productivity, indicators of non-timber values


Canfor TFL 48

Development of SFM plan, Certification

G&Y projection in complex stands, long-term site productivity, indicators of non-timber values, carbon sequestration



Oil sands reclamation

Ecosystem recovery, long-term site productivity



Boreal mixedwood management

G&Y projection in aspen / spruce mixedwoods, economic analyses, decision support tool



Plantation forestry

Projection of treatment response in sitka spruce stands, long-term site productivity



Plantation forestry

Projection of treatment response in Norway spruce stands, long-term site productivity



Plantation forestry

Projection of treatment response in Chinese fir stands, long-term site productivity


  1. Kimmins, J.P., D. Mailly, and B. Seely (1999). Modelling forest ecosystem net primary production: the hybrid simulation approach used in FORECAST. Ecological Modelling 122: 195-224.
  2. Seely, B., J.P. Kimmins, C. Welham, and K.A. Scoullar (1999). Defining stand-level sustainability, exploring stand-level stewardship. Journal of Forestry 97: 4-10.