Y Technical Report (Part 2) April Submitted to Forest Science Program Vancouver, BC

Transcription

1 Simulation of Fire Dynamics and the Range of Natural Variability of Forest Stand Structure in the Cranbrook Timber Supply Area, Southeastern British Columbia Y93167 Technical Report (Part 2) April 29 Submitted to Forest Science Program Vancouver, BC Submitted by Dr. Lori D. Daniels and Dr. Kari Stuart-Smith Prepared by Reg Davis, RPF, Forsite Consultants Ltd Tree-Ring Lab at UBC Department of Geography University of British Columbia, Vancouver

2 Simulation of Fire Dynamics and the Range of Natural Variability of Forest Stand Structure in the Cranbrook Timber Supply Area, southeastern British Columbia April 1 29 Photo courtesy of Kari Stuart-Smith, Tembec Completed by Reg Davis, RPF Forsite Consultants Ltd th Ave S. Cranbrook, B.C. For Lori Daniels University of British Columbia Vancouver, B.C. and Kari Stuart-Smith, Tembec, Western Canada Division Cranbrook, B.C.

3 EXECUTIVE SUMMARY In 26 Tembec completed a stand structure classification system and a simulation model to project these structure classes into the past and the future. They successfully modeled the historic range of variability in stand structure classes within the Invermere TSA, and compared this to the current and future distributions under current management, as required by the FSC-BC standards. Since then, new data has became available on the fire regimes in the East Kootenay. This data was incorporated into the model and the model run for the Cranbrook TSA. This modeling suggests Forests of today appear to be quite different than historic forests in terms of age class and structural classes. In general, the trends in the future show a transition to conditions found in historic forests. While the trends are positive, in many cases the forest of the future will not attain the same conditions found in historic forests. ii

4 Table of Contents EXECUTIVE SUMMARY...ii Table of Contents... iii List of Tables... iii List of Figures...iv Introduction... 1 Objectives... 1 Methods... 2 Study Area Cranbrook TSA Portion... 3 Overview of the Modeling... 4 Fire regime parameters... 6 Logging module Pattern and amount of logging Type of logging Results Conclusions References List of Tables Table 1 Historic Natural Fire Regimes... 7 Table Version of Historic Natural Fire Regimes - FRI and burn proportions... 7 Table Version of Current Fire Regimes - FRI and burn proportions... 8 Table 4 Fire area in each zone in historic fire regime - 26 vs Table 5 Variable Retention Stand Types Table 6 Structural stage classes (as per Prczecek et al, 24) Table 7 Tree size class limits Table 8 Crown closure limits Table 9 Biogeoclimatic subzone variants within each BEC group Table 1 Abbreviations used in the figures Table 11 Relative area of structure groups found in historic vs. current forests in the Cranbrook TSA Table 12 Trends in structural groups trend in future forest compared to historic conditions Table 13 Relative area of age groups found in historic vs. current forests in the Cranbrook TSA 34 Table 14 Trends in age groups trend in future forest compared to historic conditions Table 15 Cranbrook TSA Historic, Current and Future Structural Group area (min/max/avg).. 38 Table 16 Cranbrook TSA Historic, Current and Future Age Group area (min/max/avg) iii

5 List of Figures Figure 1 Location maps of the Cranbrook TSA... 3 Figure 2 Map of Cranbrook TSA - THLB and Non-THLB (NHLB) forested landbase... 4 Figure 3 Fire multiplier curve for determining amount burned per year Figure 4 Sample of the total area burned each year during one 5 year period Figure 5 Historic fire regime fire area and severity class (26 versus 29)... 9 Figure 6 Current fire regime fire area and severity class (26 versus 29)... 9 Figure 7 Historic versus current fire regime simulated fire area (29)... 1 Figure 8 LFASS model algorithm Figure 9 NROV of structural groups within the Cranbrook grassland BEC group Figure 1 NROV of structural groups within the Cranbrook IDF BEC group Figure 11 RONV of structural groups within the Cranbrook MS BEC group Figure 12 RONV of structural groups within the Cranbrook Dry ICH BEC group Figure 13 RONV of structural groups within the Cranbrook Wet ICH BEC group... 2 Figure 14 RONV of structural groups within the Cranbrook Dry ESSF BEC group... 2 Figure 15 RONV of structural groups within the Cranbrook Wet ESSF BEC group Figure 16 RONV of structural groups within the Cranbrook Parkland BEC group Figure 17 RONV of age groups within the Cranbrook Grassland BEC group Figure 18 Future trend of age groups within the Cranbrook Grassland BEC group Figure 19 RONV of age groups within the Cranbrook IDF BEC group Figure 2 Future trend of age groups within the Cranbrook Grassland BEC group Figure 21 RONV of age groups within the Cranbrook MS BEC group Figure 22 Future trend of age groups within the Cranbrook MS BEC group Figure 23 RONV of age groups within the Cranbrook Dry ICH BEC group Figure 24 Future trend of age groups within the Cranbrook Dry ICH BEC group Figure 25 RONV of age groups within the Cranbrook Wet ICH BEC group Figure 26 Future Trend of age groups within the Cranbrook Wet ICH BEC group Figure 27 RONV of age groups within the Cranbrook Dry ESSF BEC group Figure 28 Future trend of age groups within the Cranbrook Dry ESSF BEC group Figure 29 RONV of age groups within the Cranbrook Wet ESSF BEC group Figure 3 Future trend of age groups within the Cranbrook Wet ESSF BEC group Figure 31 RONV of age groups within the Cranbrook Parkland BEC group Figure 32 Future trend of age groups within the Cranbrook Parkland BEC group Figure 33 Aging of Canadian forests over the period 192 to Figure 34 Age class structure of Canadian forests from 192 to iv

6 Introduction In 26, Tembec completed a project entitled Stand Structure and Seral Stage Projections for the Invermere TSA (Davis 26). The Invermere Timber Supply Area (TSA) project was the culmination of several years work developing a stand structure classification system and a simulation model to project these new stand structure classes into the past and the future. The ultimate goal of the project was to model the historic range of variability in stand structure classes, and compare this to the current and future distributions under current management, as required by the Forest Stewardship Council BC standards. The input data for the historic projections were based on the best available data for wildfire return intervals, combined with expert knowledge from a group of fire scientists. Several new studies on fire regimes have been completed since 26, including one specifically in the East Kootenay (Daniels et al 26, Cochrane 27). These data suggested improvements could be made in the fire return intervals used in the 26 model. This project entailed using this data to update the model and run it for the Cranbrook TSA under FSP project title: Coarse Woody Debris in the East Kootenays: Understanding Sources and Dynamics to Guide Target For Sustainable Forest Management. Objectives This project has two main objectives: run the model for the Cranbrook TSA with the new fire regime data, report on key BEC groupings and seral/structural classes for this TSA. In addition, this project will provide the data (and summaries) to allow future re-analysis or reporting. 1

7 Methods This work is an expansion of the two previous projects (Davis 25, 26) that studied the Invermere TSA. A summary of the modeling process follows, however the reader should refer to the 25 and 26 reports for details of the modeling assumptions, data inputs, model functions, and the model outputs. The landscape fire model is called the Landscape Fire And Stand Structure Simulator (LFASS). The major components of the LFASS model are a fire generator, which produces fires of variable size and locations, a fire regime module which controls the total area of fire burned over the simulation run and the proportion of the landscape assigned to each of three burn severity classes, a stand dynamics module, which simulates the regeneration, growth, and mortality within each stand, and a reporting module, which saves the model status at pre-selected times during a model run. Post-processing is performed on the output files to generate summary statistics. The LFASS model has been used in the past to predict stand structure classes, and structural elements such as coarse woody debris and snags over the planning horizon under current forest management practices, compare current amounts of each structural class to the range of natural variability (RONV) associated with each structural class, and to predict changes in habitat abundance and stand structure elements through time under various management scenarios. The "landscape" specifically modeled in this project was the Cranbrook TSA (Error! Reference source not found.). 2

8 Study Area Cranbrook TSA Portion The study area is the Cranbrook Timber Supply Area (TSA), an area of 1.24 million hectares in south-eastern British Columbia (Figure ). The Invermere TSA is adjacent to, and nestles within the bite in the northern boundary of the Cranbrook TSA. Figure 1 Location maps of the Cranbrook TSA The Cranbrook Timber Supply Area (TSA) is within the boundaries of the Rocky Mountain Forest District and is administered by the district office in Cranbrook. It is situated in the southeastern corner of British Columbia (Figure ). The Cranbrook TSA is bounded by the Skookumchuck Valley to the north, the Canada-U.S. border to the south, the Alberta border to the east, and the southern Purcell Mountains height-of-land to the west. Three major physiographic regions characterize the varied terrain of the Cranbrook TSA: the Rocky Mountains in the east, the Purcell Mountains in the west, and the Rocky Mountain Trench in the middle (Forsite, 23). The productive, crown forested landbase (CFLB) within the TSA totals 762, hectares. The CFLB is divided into the timber harvesting land base (THLB), which is the working forest where logging occurs, and the non-timber harvest land base (NHLB) where logging does not occur due to legal restrictions, e.g. private land or Parks, environmental restrictions such as sensitive sites or special habitats, or due to economic factors such as low growing sites (Figure 2). 3

9 Figure 2 Map of Cranbrook TSA - THLB and Non-THLB (NHLB) forested landbase Reference: Forsite (23) The Tembec operating area is a portion of both of these timber supply areas. Overview of the Modeling The Cranbrook TSA is represented in the LFASS model by 2,+ polygons. These polygons represent the productive forest, or crown forest land-base (CFLB) of the TSA. The nonproductive stands, such as rock are not included within the fire model. The polygons in the model are, on average, smaller than the forest cover polygons. Each fire regime is referred to as a "zone" in the LFASS model. A spatial hierarchy exists: one or more cohorts (i.e. tree layers) may occupy one polygon, multiple polygons are nested within a zone, and multiple zones are nested within the landscape (in this case, a TSA). Each LFASS zone is characterized by a co-dependent set of parameters, the most important being: 1) a fire return interval (FRI), 2) the proportion of high, moderate and low severity burn, and 3) the mortality curve associated with the high, moderate and low severity burns. 4

10 The LFASS model uses one-year time steps that are strung together into model runs of userdefined length. In each year, the model applies stochastic fire disturbances across the landscape. Fire is applied, by the model, in a two step process: 1. Randomly choose, for each year, the total area to be burned that year. The area burned is the product of a random multiplier, ranging from to 1, chosen from the distribution curve in Figure (a random number between and 1 is chosen, used for the X value on the Figure, and the corresponding value of Y is the multiplier), times the average area burned over the long term. An example of the area burned each year for one 5-year time span is provided in Figure Randomly assign the burn area to fire locations (one or more polygons) Area Burned in One Year (relative to long term average) Multiplier Random Value ( to 1) Figure 3 Fire multiplier curve for determining amount burned per year. A fire location is chosen with replacement between years. It is possible if a polygon burns in year 1, it might also be chosen to burn again in year 11. Conversely, it is possible for a polygon to never burn during the whole simulation period. On average, however, the model forces the total area burned within each zone, over a long time period, to equal the fire return interval for each zone. 5

11 4 3 Area Burned Years Figure 4 Sample of the total area burned each year during one 5 year period. Each polygon that is burned is assigned to a burn severity class. Each cohort in a burned polygon will sustain some level of mortality that depends upon its species composition, its age, and the fire severity class. These data were developed by fire experts; for details see Appendix 4 in Davis 26. The difference between the 26 model runs and this year s runs were modifications to both the historic and current fire regime parameters (as per input provided by Dr. Lori Daniels, UBC). Fire regime parameters Two fire regimes are modeled: the historic natural fire regime (HNFR) and the current fire regime. The historic natural fire regimes (HNFR) were originally mapped by Gray et al. (23). Each regime is divided into eight fire zones characterized by its location (a map), and by the amount of fire within that zone. The amount of fire is divided into the proportion that is burned by three fire severity classes (high, moderate and low). Over the course of successive projects (Davis et al 25, Davis 26, this project) the burn proportions were modified, and a fire skip proportion (or no burn ) was added. Seven of the eight fire zones on the HNFR map (Gray et al., 23) occur within the Cranbrook TSA (Table 1). The location of the fire zones is the same in both fire regimes. Fire zone 4, for example, is assumed to occur in the same locations in both the historic natural fire regime (HNFR) and the current fire regime (fires as-of-today). 6

12 Table 1 Historic Natural Fire Regimes Zone # HNFR # Description 1 I -35 year Frequency, Low Severity 2 II -35 year Frequency, Mixed Severity 3 III -35 year Frequency, Stand Replacement Severity 4 IV 35-1 year Frequency, Mixed Severity 5 V 35-1 year Frequency, Stand Replacement Severity 6 VI 1-2 year Frequency, Mixed Severity -- VII 1-2 year Frequency, Stand Replacement Severity 7 VIII 2+ year Frequency, Stand Replacement Severity The parameters that describe each of the seven fire zones are provided in Table 2 and Table 3. Changes made to the 26 values are based on the new studies of fire regimes in the East Kootenay by Daniels et al (26) and Cochrane (27). Most of the changes in the historic natural fire regime (HNFR) were made in the fire zones numbered 4 through 6, which are the zones with a mix of high and low severity fires. In general, if a change was made, the fire skip (or no burn ) percentage was increased, and/or the fire return interval was increased. In Zones 4 through 7 the percentage of high severity burns was decreased, otherwise it remained the same. Almost uniform changes were made to all fire zones in the current fire regime. In general, the fire skip (or no burn ) percentage was increased, the fire return interval was decreased (amount burned per year increased), and the proportion of high severity fire was decreased and, conversely, the low severity proportion was increased. The percentage of high severity burns was increased in Zones 1, 3, and 6 and decreased in Zones 4, 5, and 7. Table Version of Historic Natural Fire Regimes - FRI and burn proportions Zone FRI Percent high severity Percent moderate Percent low severity Percent Skips Fire Return Interval (min, max) 1 17 (17) (*) 5 (*) 95 (*) (7) 1 to 3 (*) 2 28 (28) 37 (*) n/a 56 (*) 7 (*) 3 to 7 (*) 3 17 (17) 95 (*) n/a 5 (*) (*) 1 to 3 (*) 4 71 (65) 37 (74) n/a 48 (19) 15 (7) 4 to 14 (35-1) 5 14 (1) 44 (84) n/a 41 (9) 15 (7) 4 to 14 (35-15) 6 15 (13) 68 (75) n/a 17 (19) 15 (7) 1 to 2 (*) 7 25 (*) 81 (94) n/a 4 () 15 (6) 2 to 5 (*) Notes: Figures in brackets are values used in 26; (*) = no change from 26 Percent high, moderate, low fire, plus fire skips add to 1 percent. 7

13 Table Version of Current Fire Regimes - FRI and burn proportions Zone FRI Percent High severity Percent moderate Percent low severity Skips Fire Return Interval (min, max) 1 15 (2) 8 (74) (*) 2 (19) (7) (**) 2 15 (2) 74 (74) (*) 19 (19) 7 (7) (**) 3 15 (2) 95 (84) (*) 5 (9) (7) (**) 4 15 (2) 68 (74) (*) 17 (19) 15 (7) (**) 5 15 (2) 68 (84) (*) 17 (9) 15 (7) (**) (2) 77 (75) (*) 8 (19) 15 (6) (**) 7 25 (3) 81 (94) (*) 4 () 15 (6) (**) Notes: Figures in brackets are the values used in 26; (*) = no change from 26. Percent high, moderate, plus low severity fire, plus fire skips add to 1 percent. (**) = not estimated by the UBC researchers The changes made to the fire parameters translate, in the model, to an area of each fire severity class that is burned within each fire zone, on average, each year. The average area burned each year (over a long term) is indirectly proportional to the fire return interval (FRI). Conversely, the proportion burned is equal to 1/FRI. For example, in Zone 4 in the current fire regime, the proportion burned each year, on average, is 1/15 or.667 (.67%) of the total zone area. If Zone 4 s total area was 1 hectares, then (1 x.67) or 6.7 ha would be expected to burn each year. The actual area burned in Zone 4 in each year, however, is usually more or less than this average (Figure 4). The area burned in each severity class is then a proportion of the total area burned, as per the tables. The proportions of each severity class within each year was not stochastically varied, only the amount burned each year. Higher burn severity causes increased tree mortality. For example, high severity burns result in 95 to 1% tree mortality for small-sized trees. Fire skips are treated as not burned areas and therefore cause no mortality. They are included in the model to allow simulations of fire shapes and sizes. Figure 5 and Figure 6 depict the expected (average) area burned each zone, assuming each zone was 1 hectares in size, for both the previous (26) study and after changes made this year (29). The fire in each zone in the historic natural fire regime is shown in Figure. In general, small changes between 26 and 29 are discernible in Zones 4 to 6, all of which have slightly less fire area, and a lower proportion of high severity fire. Little change is visible in Zones 1 to 3, and Zone 7. 8

14 Low Moderate Severe Fire (ha) Zone 1 29 Zone 1 26 Zone 2 29 Zone 2 26 Zone 3 29 Zone 3 26 Zone 4 29 Zone 4 26 Zone 5 29 Zone 5 26 Zone 6 29 Zone 6 26 Zone 7 29 Zone 7 Figure 5 Historic fire regime fire area and severity class (26 versus 29) The area of fire in each zone in the current fire regime is depicted in Figure 6. Large changes are discernible between 26 and 29 in all the fire zones. The total area of fire is significantly increased in 29, as is the area and proportion of high severity fires Severe Moderate Low 5. Fire (ha) Zone 1 29 Zone 1 26 Zone 2 29 Zone 2 26 Zone 3 29 Zone 3 26 Zone 4 29 Zone 4 26 Zone 5 29 Zone 5 26 Zone 6 29 Zone 6 26 Zone 7 29 Zone 7 Figure 6 Current fire regime fire area and severity class (26 versus 29) 9

15 Table 4 Fire area in each zone in historic fire regime - 26 vs. 29 Zone 26 Severe 29 Severe 26 Moderate 29 Moderate 26 Low 29 Low Total 26 Total Figure 7 shows the differences between the 29 version of the historic natural fire regimes and the 29 current fire regimes. The changes between the historic fire regime and current fire regime are largely attributed to fire suppression. In general, the historic fire regime has much more fire in each fire zone, although the proportion of high severity fire is lower. As well, the large, between-zone differences in the historic regime are dampened, and each fire zone is very similar to the others in the current fire regime Severe Mod Low Zone 1 - Historic Zone 1 - Current Zone 2 - Historic Zone 2 - Current Zone 3 - Historic Zone 3 - Current Zone 4 - Historic Zone 4 - Current Zone 5 - Historic Zone 5 - Current Zone 6 - Historic Zone 6 - Current Zone 7 - Historic Zone 7 - Current Figure 7 Historic versus current fire regime simulated fire area (29) Logging module The pattern of logging (amount and location) and type of logging (clear-cut or retention) determines the stand structures within the THLB. Pattern and amount of logging Logging is controlled by a fixed harvest schedule that was generated by a forest estate model prior to the fire modeling, and then input to the fire model at the start of the simulation. The fixed schedule imposed a pre-determined harvest pattern (location and timing) within the THLB, for a set period of time. The fire model, therefore, closely simulates the complexity of the TSR harvest rules such as: 1

16 Prioritizes the harvest of certain stand types or within certain geographic areas, such as pine-leading types (to simulate efforts at controlling the mountain pine beetle) or within NDT4 types (to reflect fire maintained ecosystem restoration priorities). Limits harvesting within resource emphasis areas, such as within ungulate winter range types or visual quality objective zones, to maintain certain percentage old or maximum percentage young seral, and Limits harvesting in different biodiversity emphasis option zones, to maintain greater or lesser amounts of old-growth. Two distinctly different fire regime populations are the result (see previous reports): 1. The non harvest landbase (NHLB) portion of the landscape is impacted by the current fire regime parameters, and 2. The timber harvest land base (THLB) portion is impacted by logging. An important assumption, which is taken from TSR, is that fire suppression effectively limits fires within the THLB, and if any stands burn they are promptly salvaged (logged). In essence, no fires occur within the THLB. Type of logging The timber supply review assumed that virtually all logging is clear-cut. A very small amount is partial-cut, or is conversion of stands to rangeland. Fire regime modeling within the Invermere TSA varied from that assumption. Logging was modeled as mostly clear-cut, which reflects TSR assumptions, along with a portion that is short- or long-term retention of the over-story, which deviates from TSR. The details of short- and long-term retention were described previously (Davis, 25). In simple terms, the retention of the overstory, both the amount (%) retained and the period of retention (years) is primarily based on stand type, which is primarily based on leading species. These percentages were determined by silviculturists at a stand-retention workshop (Table 6) (Davis, 23). Previous reports (Davis 25, 26) provide details of the logging regimes and the differences that resulted in the THLB (timber harvest land base) and NHLB (non timber harvest land base). In general, logging resulted in a forest with simpler stand structures, and a higher proportion of the closed stand structure types. Fire zones overlap both THLB and NHLB, so the impact of the THLB fire regime on a particular zone is related to the proportion of the zone falling within the THLB. In summary: Historic stand structures in both the THLB and NHLB will be determined by the fire regime in Table 2 (the HNFR, or historic natural fire regime) as well as the natural stand dynamics of regeneration, growth and mortality; Future stand structures in the NHLB will be determined by the fire disturbances described in the Table 3 (current fire regime Table 2), and Future stand structures in the THLB will be largely determined by the type of logging, either clearcut, short-term, or long-term retention. 11

17 Table 5 Variable Retention Stand Types (A) Stand Type Number Stand Type : Species mixes ; in / not in NDT 4 (C) Short term retention (%) (D) Long term retention (%) (E) Tree class retained 12 Pl-pure XX 14 Pl-pure 2.5 SP 16 Pl-pure 2.5 MT 18 Pl-pure 15 MT 11 Pl-pure 2.5 LT 112 Pl-pure 15 LT 114 Pl-pure 2.5 GT 22 Pl with F/L/Py XX 24 Pl with F/L/Py 4.5 SP 25 Pl with F/L/Py MT 28 Pl with F/L/Py 4.5 MT 21 Pl with F/L/Py 2 MT 212 Pl with F/L/Py 4.5 LT 214 Pl with F/L/Py 4.5 LT 216 Pl with F/L/Py 2.5 GT 32 Pl with S/B/C/H XX 34 Pl with S/B/C/H 4.5 SP 41 Fir or Larch with Pl ST 43 For L with Pl MT 46 For L with Pl 7 MT 48 For L with Pl 7 LT 52 F/L with any conifers, not in NDT 4 XX 54 F/L with any conifers, not in NDT LT 62 Within NDT 4: F/L with other conifers XX 64 Within NDT 4: F/L with other conifers 7 ST 66 Within NDT 4: F/L with other conifers 12 ST 68 Within NDT 4: F/L with other conifers 7 MT 61 Within NDT 4: F/L with other conifers 12 MT 72 Conifers with deciduous 3 ST 82 S/B/C/H XX 84 S/B/C/H 2.5 SP 86 S/B/C/H 2.5 MT 92 Deciduous stands XX 999 Stands in the non-timber harvesting land base (n/a) (n/a) (n/a) Notes: (A) = number assigned in the model (not at the workshop) (C) = initial retention, for an assumed period of 2 years until another stand entry (D) = retention of overstory over the whole rotation, until regeneration is harvested (E) XX=none; SP=sapling pole; ST=small tree; MT=medium tree; LT=large tree; GT=giant tree 12

18 The LFASS algorithm is summarized in Figure 8. Descriptions of the model functionality, its inputs and the methods used to classify the output into age class and stand structure class (Table 6) are described in detail in the previous reports (Davis, 25, 26). Modeling, in simplified form, was performed as follows. Two simulations, or model runs were completed for each TSA. One model run represented historic conditions and used the historic natural fire regime (HNFR) parameters. The second run represented future conditions and used the current fire regime parameters. The simulation period was sampled at 1 year intervals. Each sample is a copy of all the stand data in the model at that year, i.e. each forest cohort (layer) within each polygon (stand) within the landscape (TSA). During the simulation a large volume of raw data is produced and saved. Over 148, stands (and each cohort within each stand) are tracked in the Invermere TSA. Over 2, polygons are tracked in the Cranbrook TSA. After the simulation is completed, the raw data (samples) are post-processed. For example, each stand is assigned an age class value and a stand structure class (Table 6) based on the cohorts in that stand. The post-processed datasets are also saved. The raw data or the post-processed datasets are then examined according to one s interest, and statistics generated. The post-processed datasets are probably the most useful products from this project. They represent a happy medium between the huge volume of raw data and the simple data summaries as presented in reports. The post-processed data contains variables of interest such as stand number, sample year, fire zone, biogeoclimatic subzone variant (BEC), BEC group, stand structure class, stand structure class group, age class, age class group, ecoregion, forest licensee operating area, etc. 13

19 The LFASS model uses the following procedure to simulate stochastic fire disturbances and stand succession across a multi-zone landscape with multiple runs and multiple years within a run. 1. Initialize PROGRAM and assign memory variables such as: number of runs in this series; number of years in one run; set flags to start run 1 from a new forest, or utilize a previous forest; set flag to start each run from year= or chain multiple runs end-to-end; set number of zones to model; set Fire Return Interval for each ZONE; set proportion of high, moderate and low burns for each ZONE; assign curve values, such as the proportion of mortality according to cohort age and burn severity class 2. For each RUN in a SERIES of runs 3. For each ZONE in this RUN. Read the polygon table and store total hectares for zones to be modeled. Calculate amount of burn as the gross fire area for each ZONE area and Fire Return Interval (FRI), as Gross Fire Area in this RUN in this ZONE = [1/FRI] x [ZONE area] x [YEARS in RUN]. Create a new burn table with cells for each ZONE and YEAR. Fill in the table with a stochastic estimate of the area burned in that ZONE & YEAR. Redo the table, and for each ZONE prorate the YEAR values so the total area burned equals the expected area for the whole run. 4. For each YEAR in the RUN 5. For each ZONE. 6. For each POLYGON in this ZONE. 6a. Allocate harvesting according to harvest queue. Schedule level of removal, and level and years of long and short term retention of the overstory. 6b. For each POLYGON in this ZONE. Allocate burns to polygons by either: a) randomly draw polygons to meet ZONE hectares for that year; or b) randomly draw individual fires from fire size classes, according to the desired proportion of sizes. For each burned polygon, assign the required proportion of high, moderate and low severity burn based on a ranked list of time-since-fire. 7. For all COHORTs in all the POLYGONs. Increment cohort age. If logged, assign new cohort ages and stocking value. If this polygon is burned, assign fire mortality based on cohort's age. If not burned, assign mortality due to senescence. Transfer all cohort mortality to stand vacancy table. 8. If last ZONE go to step 9, else go to step If reports are due this YEAR within a RUN, do the REPORTS. 1. If last YEAR in the RUN, go to step 11, else return to step If reports are due at the end of a RUN, do the REPORTS. 12. If last RUN in a SERIES, go to step 13, else return to step END Figure 8 LFASS model algorithm 14

20 Table 6 Structural stage classes (as per Prczecek et al, 24) No Structural class Structural Group 1 1 GRASS / FORB A 2 2 SHRUB-OPEN A 3 3 SHRUB-CLOSED A 4 4 SAPLING-OPEN A 5 5 SAPLING-MODERATE A 6 6 SAPLING-CLOSED B 7 7 SMALL-SINGLE OPEN B 8 8 SMALL-SINGLE MOD B 9 9 SMALL-SINGLE CLOS B 1 1 MEDIUM-SINGL OPEN C MEDIUM-SINGLE MOD C MEDIUM-SINGL CLOS D LARGE SINGLE OPEN E LARGE-SINGLE MOD E LARGE-SINGLE CLOS F SMALL-MULTI OPEN B SMALL-MULTI MOD B SMALL-MULTI CLOS B MEDIUM-MULTI OPEN C 2 2 MEDIUM-MULTI MOD C MEDIUM-MULTI CLOS D LARGE MULTI OPEN E LARGE-MULTI MOD E LARGE-MULTI CLOS F GIANT MULTI E The details of the classification criterion (crown closure, tree size, etc.) are provided in Davis et al (25). This system was modified slightly from the stand structure classification system developed for the Columbia Basin by Johnson and O Neill (21), to account for tree diameters and crown closure in East Kootenay forests. In general, SMALL, MEDIUM, LARGE, GIANT = tree size of dominant layer; OPEN, MOD(erate), CLOS(ed) = relative crown closure of that layer, as in Table 7 and Table 8. For example, a recent clear-cut with 1 % residual mature trees would be classified as grass/forb or shrub/open, depending on the size of the regenerating trees, but a heavy seed tree cut with 21 % residual mature trees (medium size diameter class) retained would be classified as medium tree single open, until the regenerating trees reached sapling size, upon which it would be classified as medium tree multi-open. Structural Groups (Table 6) are used in the figures, where A = Shrub Sapling; B = Small tree; C = Medium tree open; D = Medium tree closed; E = Large tree open; F = Large tree closed Table 7 Tree size class limits. Diameter refers to the quadratic mean diameter of the stand. Tree size grass sapling small tree medium tree large tree Height or Diameter Class Less than 1.3 m 1.3 m height to 12.5 cm dbh 12.5 to 24. cm dbh 24. to 33. cm dbh over 33. cm dbh Table 8 Crown closure limits Crown Closure Class Open Moderate Closed Range in Crown Closure -2 % cc 2-4 % cc > 4 % cc 15

21 Results The previous project (Davis, 26) summarized the range of natural variation (RONV) of structural groups for various strata, such as biogeoclimatic variant with one ecoregion. RONV was defined as the mean, minimum and maximum values of an attribute, as determined from samples taken over a long time period. Historic fire regime For the historic fire regime, a 5 year period was modelled. That period was divided into two periods: 1) Years=1 to 25, and 2) Years = 251 to 5. During years 1 to 25 the model equilibrated from its present state to a "dynamic equilibrium". During the second time span the forest (in terms of its stand ages, stand structures etc) fluctuated around the dynamic equilibrium. The second time span was sampled in each decade, yielding 25 samples that were used to estimate the range of variation, i.e. the min/max/mean values. The range was then compared to current conditions (i.e. the current forest state at Years=). The condition of forests prior to non-first nations influencing them is considered natural, and hence the term Range of Natural Variation (RONV) has been adopted to refer to the variation seen, over time, within these natural forests. In the past, this was referred to as Natural Range of Variation (NROV). To separate RONV from the range of variation seen in future conditions, the term ROFV (Range of Future Variation) is used in this report. Future fire regime For the future fire regime, a 25 year period was modeled, starting in year 24 (the date of forest inventory data). That time span was sampled in each decade, yielding 26 samples (one at time=, and then 25 decades) and these were used to estimate the ROFV (range of future variation), i.e. the min/max/mean values. Summary statistics The following figures-of-interest were chosen by Tembec staff out of the myriad of possible combinations. The charts depict both the RONV and ROFV of structural groups, or of age groups (early, mid, mature or old) for particular biogeoclimatic subzone variant groupings, or BEC groups. These groupings were used rather than the smaller BEC variant by Ecosection groupings that were used in the 26 report, because the latter proved too small (often < 5 ha) to generate meaningful summaries of the range of natural variation. See Error! Reference source not found. to Error! Reference source not found. for Invermere structural groups and Error! Reference source not found. to Error! Reference source not found. for the Invermere age groups. In the case of the Cranbrook age group charts, two charts are provided - a RONV summary chart, as well as a chart of the future age group trends that is used to produce the RONV summary chart. The latter charts show the variation, over time, within the range of future variation (ROFV) itself. The grouping of biogeoclimatic variants for each BEC group is defined in Table 9. Abbreviations that are used in the figures are provided in Table 1. Appendix A contains tables with the values correspond to the figures. Table 9 Biogeoclimatic subzone variants within each BEC group Bec Group Grasslands IDF MS Dry ICH Wet ICH Dry ESSF Wet ESSF Parkland and upper variants Biogeoclimatic subzone variant PPdh, IDFxk, ICHxk IDFdm2, IDFdm2n, IDFun all MS variants ICHdm/dk1/dw/dw1 ICHmk1/mw1/mw2 ESSFdm/dm1/dmw/dk/dk1/dk2 ESSFwm ESSFdku/dkp, ESSFwmu, wmp 16

22 Table 1 Abbreviations used in the figures. Code Description A. Shrb/Sap Shrub Sapling Stand Structural Group B. Sm tree Small Tree Structural Group C. Med OM Medium Tree, Open or Moderate Crown Closure D. Med Clo Medium Tree, Closed Crown Closure E. Lg Open Large Tree, Open or Moderate Crown Closure F. Lg Clos Large Tree, Closed Crown Closure Early Mid Mature Early seral, as per Biodiversity Guidebook (-4 yrs in all BEC zones) Mid seral, as per Biodiversity Guidebook (4-1 yrs in IDF, MS and dry ICH and dry ESSF, 4-12 yrs in wet ICH and ESSF) Mature seral, as per Biodiversity Guidebook (1-14 yrs in IDF, MS, and dry ICH and ESSF; yrs in wet ICH and wet ESSF) Old Old seral, as per Biodiversity Guidebook (> 14 yrs in MS and dry ICH and dry ESSF; > 25 in IDF and wet ICH and ESSF Hist F Current Historic natural fire regime (historic conditions) Current fire regime (future conditions) Current state (years=) Examples: Hist Sh/Sapl = historic natural fire regime, shrub sapling structural group F Sh/Sapl = current fire regime, shrub sapling structural group Hist Mid = Historic natural fire regime, mid seral age group F Mid = Historic natural fire regime, mid seral age group 17

23 2 Cranbrook - Grassland BEC Group Current Future 15 Historic 1 5 Sh/Sapl Sm Tr Med Tr/OM Med Tr/C Lg Tr/OM Lg Tr/C Figure 9 NROV of structural groups within the Cranbrook grassland BEC group 4 Cranbrook - IDF BEC Group 35 3 Current Future Historic Sh/Sapl Sm Tr Med Tr/OM Med Tr/C Lg Tr/OM Lg Tr/C Figure 1 NROV of structural groups within the Cranbrook IDF BEC group 18

24 Cranbrook - MS BEC Group Current Future Historic Sh/Sapl Sm Tr Med Tr/OM Med Tr/C Lg Tr/OM Lg Tr/C Figure 1 RONV of structural groups within the Cranbrook MS BEC group 4 Cranbrook - Dry ICH BEC Group Current Future 3 Historic 2 1 Sh/Sapl Sm Tr Med Tr/OM Med Tr/C Lg Tr/OM Lg Tr/C Figure 2 RONV of structural groups within the Cranbrook Dry ICH BEC group 19

25 3 Cranbrook - Wet ICH BEC Group Current Future Historic 2 1 Sh/Sapl Sm Tr Med Tr/OM Med Tr/C Lg Tr/OM Lg Tr/C Figure 3 RONV of structural groups within the Cranbrook Wet ICH BEC group Cranbrook - Dry ESSF BEC Group Current Future Historic Sh/Sapl Sm Tr Med Tr/OM Med Tr/C Lg Tr/OM Lg Tr/C Figure 4 RONV of structural groups within the Cranbrook Dry ESSF BEC group 2

26 Cranbrook - Wet ESSF BEC Group Current Future Historic Sh/Sapl Sm Tr Med Tr/OM Med Tr/C Lg Tr/OM Lg Tr/C Figure 5 RONV of structural groups within the Cranbrook Wet ESSF BEC group 16 Cranbrook - Parkland BEC Group Current Future Historic Sh/Sapl Sm Tr Med Tr/OM Med Tr/C Lg Tr/OM Lg Tr/C Figure 6 RONV of structural groups within the Cranbrook Parkland BEC group 21

27 Cranbrook - Grassland BEC Group 2 Current Future 15 Historic 1 5 Early Mid Mature Old Figure 17 RONV of age groups within the Cranbrook Grassland BEC group 25, 2, Cranbrook Grassland Early Mid Mature Old 15, 1, 5, Year Figure 18 Future trend of age groups within the Cranbrook Grassland BEC group 22

28 45 Cranbrook - IDF BEC Group 4 35 Current Future Historic Early Mid Mature Old Figure 19 RONV of age groups within the Cranbrook IDF BEC group 5, 45, 4, 35, Cranbrook IDF Early Mid Mature Old 3, 25, 2, 15, 1, 5, Year Figure 2 Future trend of age groups within the Cranbrook Grassland BEC group 23

29 14 Cranbrook - MS BEC Group 12 1 Current Future Historic Early Mid Mature Old Figure 21 RONV of age groups within the Cranbrook MS BEC group 12, 1, 8, Cranbrook MS Early Mid Mature Old 6, 4, 2, Year Figure 22 Future trend of age groups within the Cranbrook MS BEC group 24

30 4 Cranbrook - Dry ICH BEC Group 35 3 Current Future Historic Early Mid Mature Old Figure 23 RONV of age groups within the Cranbrook Dry ICH BEC group 35, Cranbrook Dry ICH 3, 25, 2, 15, 1, 5, Early Mid Mature Old Year Figure 24 Future trend of age groups within the Cranbrook Dry ICH BEC group 25

31 3 Cranbrook - Wet ICH BEC Group Current 25 Future Historic Early Mid Mature Old Figure 7 RONV of age groups within the Cranbrook Wet ICH BEC group 3, 25, 2, Cranbrook Wet ICH Early Mid Mature Old 15, 1, 5, Year Figure 26 Future Trend of age groups within the Cranbrook Wet ICH BEC group 26

32 16 Cranbrook - Dry ESSF BEC Group Current Future Historic Early Mid Mature Old Figure 8 RONV of age groups within the Cranbrook Dry ESSF BEC group 16, 14, 12, Cranbrook Dry ESSF Early Mid Mature Old 1, 8, 6, 4, 2, Year Figure 28 Future trend of age groups within the Cranbrook Dry ESSF BEC group 27

33 3 Cranbrook - Wet ESSF BEC Group Current 25 Future Historic Early Mid Mature Old Figure 29 RONV of age groups within the Cranbrook Wet ESSF BEC group 3, Cranbrook Wet ICH 25, 2, 15, 1, 5, Early Mid Mature Old Year Figure 9Future trend of age groups within the Cranbrook Wet ESSF BEC group 28

34 Cranbrook - Parkland BEC Group 15 Current Future Historic 1 5 Early Mid Mature Old Figure 31 RONV of age groups within the Cranbrook Parkland BEC group 18, Cranbrook Parkland 13, 8, 3, Early Mid Mature Old -2, Year Figure 32 Future trend of age groups within the Cranbrook Parkland BEC group 29

35 Observed trends in the structural groups (summarized by BEC group) differ in some aspects from the previous results of 26 (although they were summarized by BEC variant-ecoregion in that report). A quick review of the dynamics in the modeling, and their impact on forest ages and structures: Amount and severity of fires Historic fire regimes had more fire with a higher proportion of low severity fires. More fires results in increased mortality within stands, and hence a higher proportion of younger (and smaller) stands. A higher proportion of low severity fires results in more cohorts in the stand, on average, which arise from (a) remnants of cohorts that existed prior to the disturbance, and (b) cohorts that regenerated following the disturbance. Stands that have more cohorts and remnants of older cohorts will result (due to the classification system) in a higher proportion of more open-type stands and more multiple layer-type stands. One expects, therefore, stands in the past to have more young stands and more open stands compared to today. Recent aging of forests Kurz and Apps (1999) examined Canadian forests during the period of 192 to 199. They document the general aging of the forests (Figure 33) and the resulting age class profile (Figure 1). They attribute this as partially due to fire suppression associated with settlement by Europeans. However, they noted that researchers have found this same trend in forests where Europeans did not settle, hence the aging of forest is likely due in some part to a change in the fire regime, perhaps related to a change in climate. Assuming that the Cranbrook TSA forests fit this pattern, one would expect that the starting inventory would have less young forests and more old forests than the historic forests. One would also expect to see more closed forests as stands aged and closed their canopies (or filled in ). Figure 33 Aging of Canadian forests over the period 192 to

36 Figure 1 Age class structure of Canadian forests from 192 to 199. Logging Logging has been introduced into the landscapes over the last 1 years, and the amount of harvesting has generally increased over that period. Clearcut-type logging will cause simpler stand structures than those caused by fires in the areas (fire zones) where the historic, partial disturbance type fires occur. Logging concentrates on the older stands, and tends to cause an even-aged age class distribution up to the minimum harvest age, and then few old forests above that age (see the charts of such trends in Forsite, 24). Logging will only occur within the timber harvesting landbase (THLB) which is generally in the lower elevations of the Cranbrook TSA. One expects, therefore, within the THLB portion of future forests, to see more young stands and less old stands, and more closed stands than were found in historic forests. One would also expect these trends to have more effect in forests (or portions of forests) that have a higher proportion of THLB. These factors act together in various combinations, and they result in the forests depicted in the stand structure and age group charts. It is difficult to immediately see the trends in the charts. Simplifications of the trends in the structural groups within the Cranbrook TSA are shown in Table 11 and Table 12. Table 11 shows whether present-day forests have more or less of a particular structural group than historic conditions. Table 12 shows whether the future trend is towards or away from historic conditions. 31

37 Corresponding tables are provided for the Cranbrook age class groups in Table 13 and Table 14. Stand structure Groups Table 11 Relative area of structure groups found in historic vs. current forests in the Cranbrook TSA BEC Group Sh/Sapl Sm Tr Med Tr/OM Med Tr/C Lg Tr/OM Lg Tr/C Grassland IDF MS Dry ICH Wet ICH Dry ESSF Wet ESSF Parkland Shading Description - - Less area found in forests of today than found in historic forests Present forests have approximately the same area as historic forests. + More area found in forests of today than found in historic forests. The trends in stand structure groups are A. Current versus historic conditions 1) Current forests are generally different than historic forests (all shaded cells in Table 11 denote differences). 2) The current shrub/sapling structural group is always less than historic conditions (pink shading). This fits with the expectation that historic fire regimes had more fire, and that forests have generally aged for the recent past. 3) The small tree structural group is either within RONV, or above RONV, which fits the general aging of forests in the recent past. 4) The total amount of medium tree or large tree (i.e. open and closed together) cannot be ascertained from the charts. 5) The amount of closed canopy, for both medium tree and large tree classes, is higher than historic forests. Conversely the amount of open/moderate, for both medium tree and large tree classes, is lower than historic forests. This fits the expectation that forests closed their canopies as they aged during the recent past. B. Trend in future forests towards or away from historic conditions 1) In most cases future forests trend back towards conditions found in historic forests (blue shading, Table 12). In a few cases they trend away from historic conditions. 2) While the trends are mostly positive, in many cases future conditions do not reach historic conditions. It will be decided later, by forest managers, whether or not these generally positive trends are acceptable. 32

38 Table 12 Trends in structural groups trend in future forest compared to historic conditions. BEC Group Sh/Sapl Sm Tr Med Tr/OM Med Tr/C Lg Tr/OM Lg Tr/C Grassland + (*) + + IDF + (*) MS (*) Dry ICH Wet ICH Dry ESSF Wet ESSF Parkland (*) = In these cases the current conditions move out of RONV or further away from RONV. Shading Description + Trend is positive, future forests trend towards historic forests. No significant change. Trend is negative, future forests trend away from historic forests. The trends in age groups are as follows: A. Current versus historic conditions 1) Current forests are generally different than historic forests (all shaded cells in Table 13). 2) The proportion of early age group in current forests is always less than historic conditions (pink shading, Table 13). This fits with the expectation that historic fire regimes had more fire and caused more young forests, similar to the shrub/sapling results. 3) In general, more mid seral stands are found in current forests than in historic forests. That also matches expectations based on the general aging of the forests over the recent past. 4) Some forests have mature seral proportions that are within (or close to) historic RONV levels, but most are less than historic levels. The converse is generally seen for old seral there is often more old seral in current forests than found in historic forests. Given that the proportion of mature is less than expected, and old is more than expected, and given that logging during the recent past has concentrated on older forests (both mature and old) the proportions of older forests are as expected. 33

39 Table 13 Relative area of age groups found in historic vs. current forests in the Cranbrook TSA BEC Group Early Mid Mature Old Grassland IDF MS Dry ICH Wet ICH Dry ESSF Wet ESSF Parkland Shading Description - - Less area found in forests of today than found in historic forests Present forests have approximately the same area as historic forests. + More area found in forests of today than found in historic forests. B. Trend in future forests towards or away from historic conditions 1) In most cases future forests trend back towards conditions found in historic forests (blue shading, Table 12). 2) An interesting question arises in the case of old seral, where the trends are away from historic forests (orange shading, Table 14). In these cases, the amount of mature or old forest is forecast to increase, but that trend is towards a level that is greater than that found in historic forests, hence it is negative. Conversely, the trend for old seral in the Parkland BEC group is positive as it moves toward historic conditions, but the amount of old is predicted to actually decrease. These ratings seem opposite to what would commonly be consider positive, which is more old seral is better. Table 14 Trends in age groups trend in future forest compared to historic conditions Early Mid Mature Old Grassland + + IDF + + MS (1) Dry ICH (1) Wet ICH + + (2) (2) Dry ESSF (1) Wet ESSF + + (1) Parkland (3) (1) In these cases the negative trend (away from historic conditions) is associated with less old. (2) In theses cases the negative trend is associated with more mature and old. (3) In this case, the positive trend (toward historic conditions) is associated with less old. Shading Description + Trend is positive, future forests trend towards historic forests. No significant change. Trend is negative, future forests trend away from historic forests. In summary 1) Forests of today appear to be different than historic forests. 2) In general, the trends are back towards conditions found in historic forests. 3) While the trends are positive, in many cases the forest of the future will not attain the same conditions found in historic forests. 34