Newfoundland and Labrador Variant Calibration

This Variant calibration has not been reviewed by the NL government for use in forest planning, and only limited validation of growth forecasts have been conducted by FORUS Research to date.

This Variant calibration is not recommended for use in management planning or decision making at this time by FORUS Research or the NL government.

This Variant is being distributed for testing only.

Calibration of core growth and height models for the two main species in Newfoundland (black spruce and balsam fir) has been mostly completed using a little over 1,150 permanent sample plots (PSP) across forested regions in both Newfoundland and Labrador, including over 101,000 individual tree observations measured repeatedly on average about 5 times each over about 25 years. Some plots date back as early as 1985 and are still being measured to monitor growth as of 2023. Tree and stand-level models outlined below provide some insight into the variables used, when the models were developed, and who developed them. Tree height, diameter growth, and mortality models were developed for black spruce and balsam fir from these data. Data was limited for plantations, so models combined both planting or pre-commercial thinning as a single intensive management term in the model.

About 90% of trees measured were either black spruce or balsam fir. There were insufficient samples from the PSP data to fit reliable models for species other than black spruce and fir; so, for now, Nova Scotia (NS) models are used from the Acadian Variant to predict tree dynamics for other species in NL. Future efforts could leverage the larger NL temporary sample plot (TSP) network to fit height models for other species like white birch, poplar, white spruces, etc. The NS height imputation and diameter increment models require Biomass Growth Index (BGI) as a predictor, which is not an available in NL. Where NS models were leveraged, the BGI default value used by the NL variant was lowered to 3,000 kg/ha/year from a default value of 3,500 kg/ha/year in the Acadian model. This value reduced average mean bias across most species tree height models during testing. Where necessary, accuracy of these models was further corrected using the self-calibration features of OSM with available observations from the TSP or PSP plot networks. Tables below provide additional information about modeling approaches used for each tree model and species.

Tree crown width and recession models, stand ingrowth, and stand self-thinning line models were also borrowed from the Acadian Variant. It is anticipated that these will be updated or adjusted over time to better reflect NL forest dynamics, along with improvements to other models. Little testing was conducted on the ingrowth model, and it should be prioritized for update as it has been shown to underpredict ingrowth in the Acadian region, and we would expect different rates of ingrowth in NL compared to the Acadian Forest region. Tree crown models are not used by the NL variant in any downstream predictions, so they are not high priority for revision, as they do not influence stand dynamics currently. The self-thinning line (STL) maximum stand density is calculated as a function of species composition in the stand and was developed from data in New Brunswick. Initial testing of the STL in NL showed relatively good agreement with self-thinning dynamics in the NL PSPs. The STL can be adjusted using the OSM.Simulation.Model.Aline command if stands are found to be self-thinning to early or too late in NL.

Distribution of tree data used during calibration:

As this model was calibrated for the entire province, users should test this calibration against local data. Where local bias is evident, consider using OSM’s auto-calibration routines and/or prediction amendments via OSM commands.

Model revision will continue for the foreseeable future, so expect updates over time.

Models

Table 1. Overview of Newfoundland and Labrador (NL) tree and stand models used in the NL Variant.

Model	Description and Discussion
Background Mortality March 2024	Non-linear logistic regression model as a function of Stand Age, Management (PCT or Planted – yes/no), IsLabrador (1= Labrador, 0=Newfoundland), DBH, basal area, QMD, and basal area of larger trees. Each species model was fit independently and not all variables were used in each model depending on available data. Fit for fir and black spruce by C.R. Hennigar, FORUS Research, March 2024. See Acadian Variant calibration for details on other species mortality models from Nova Scotia. These models can run stochastically if Simulation.Model.IsRandom is set to TRUE (Default = FALSE). Updated in June 2019 to always operate stochastically when trees/ha are < 0.5 (kills individual trees randomly according to mortality probability), rather than deterministically (proportion of tree record stems/hectare killed equal to mortality probability). This hybrid approach is used even when Simulation.Model.IsRandom = FALSE. When Simulation.Model.IsRandom = TRUE, mortality of individual trees in every tree record will be set stochastically. To ensure results are repeatable from run to run, for testing, benchmarking, and validation work. Use command Simulation.Model.SetRandomSeed #, where # is a fixed positive integer. Do this for each stand simulation to force the random number generator to provide the same series of random numbers during simulation. For example, the Seed value could be the plot number.
Self-Thinning Mortality March 2013	See Acadian Variant calibration – replicated model here. The maximum stocking relationship was developed with a wealth of NB forest development surveys collected since the 1980s. The relationship was formulated as a function of basal area weighted species specific-gravity. This relationship was fit at the stand-level (>= 3 plots per stand), rather than plot-level, so it may over-estimate mortality for some plot-level comparisons. Fit by C.R. Hennigar, NB DNR 2013, following methods from Chris Woodall et al. (2005, For. Ecol. Manage. 216: 367-377). In April 2018, the specific gravity for red pine was reduced from 0.46 to 0.36 when used in this maximum stocking equation because self-thinning was occurring too early in red pine plantations (C.R. Hennigar, NB ERD 2018). Default A-Line set to 0.85 in this Variant. In some regenerating types, especially for single plantation plots, this default A-Line (0.85) has been observed to cause competition induced mortality too early during stand development. Increasing the Simulation.Model.ALine to 0.95-1.00 may be required for some of these intensively managed types.
DBH growth January 2024	See links below for details. Fit for fir and black spruce using NL data. Other species leverage the Nova Scotia models in the Acadian Variant with some large bias adjustments. Fit by C.R. Hennigar, FORUS Research 2024. See NL Diameter Growth Model See also Acadian Variant calibration.
Height model February 2024	See links below for details. Fit for fir and black spruce using NL data. Other species leverage the Nova Scotia models in the Acadian Variant with some minor bias adjustments. Fit by C.R. Hennigar, FORUS Research 2024. See NL Height Model See also Acadian Variant calibration.
Height increment	Currently deduced from DBH growth and height predictions. A formal height increment model by site and management type would be recommended if development of the Variant continues. See also NL Height Model See also NL Diameter Growth Model
Crown models 2014	Same as Acadian Variant. Maximum and largest crown width models for Maine (Russell and Weiskittel 2011. Nor. J. Appl. For. 28: 84-91). Height to crown base models for 13 species in the Acadian region (Rijal et al. 2012. For. Chron. 88: 60-73). Height-to-crown base increment in the Acadian region (Russell et al. 2014. Eur J. For. Res. 133:1121–1135).
Taper & Volume 1974, 1986	Total and merchantable bole volumes based on Newfoundland total and merchantable volume reports. · For fir and black spruce, District level equations are used from G.R. Warren and J.P. Meades 1986. Wood defect and density studies: Total and net volume equations for Newfoundland forest management units. Info. Rep. N-X-242. Newfoundland Forestry Centre, NL. · For all other species, taper equations from M.F. Ker 1974. Metric tree volume tables for Newfoundland. Info. Rep. N-X-122. Newfoundland For. Res. Centre, St. John’s, NL. were used. Default merchantable bole stump height in the NL Variant is set to 0.1524 meters and top height set to 7.62 cm inside bark for all species; adjust these defaults using Simulation.Species. Total and gross merchantable volume (GMV) is reported by default in TreeList Report. Users can also choose to report net merchantable volume (NMV) in place of GMV by setting command property Simulation.Model.Volume.NetDownGrossVolumeIfPossible to TRUE (default = FALSE). The reason NMV is not the default is because only fir and black spruce have NMV equations (gross with decay deductions, Table 4 in N-X-242); all other species will report GMV from N-X-122. In addition, users should be aware that some NL District parameters for the NMV equations result in very high reductions to GMV (30-50% in some cases; more than what one would consider believable in practice), suggesting some issue with some parameters for some districts. To avoid large GMV deductions, and sometimes higher NMV than GMV predictions, the NL Variant caps gross deductions to between 0% and 5%. No net volume equations exist for other species, so gross is used for those always even if this property is set to true. Volume does not influence stand development. These estimates are only calculated if desired during reporting. See also Acadian Variant calibration, as Honer et al. 1983 (Metric timber tables for commercial tree species of central and eastern Canada. Maritime For. Res. Centre. Info, Rep. M-X-140) equations were also included in the NL variant source code, though these are not currently used in NL simulations.
Ingrowth 2011	See Acadian Variant calibration – replicated model here. Estimates ingrowth probability, density, and composition at the 1 cm DBH boundary in each simulation cycle based on pre-cut stand conditions according to Li et al. (2011; CJFR 41: 2077-2089). This model can run stochastically if Simulation.Model.IsRandom is set to TRUE (Default = FALSE). A number of conditional adjustments to the base Li et al. (2011) ingrowth model were introduced by C.R. Hennigar, NB DNR in 2013 to improve realism in the context of harvest, current overstory species composition, and pre-existing stand ingrowth expected from small trees and seedlings in survey records or inserted in a previous cycle via OSM commands. In April 2018, C.R. Hennigar made further adjustments to reduce ingrowth in well managed plantations and PCTs and increase in growth in recently clearcut conditions.
Snag model	There is no snag model currently developed for NL. The Acadian snag model could possibly be used or adapted for NL.
Grade model	There is no tree quality grade model currently developed for NL.
Spruce Budworm Disturbance Model	Spruce Budworm Disturbance model uses the disturbance model directly from the Acadian Variant. See OSM.Simulation.Model.SBW.