MERRITT TIMBER SUPPLY AREA

Transcription

1 SMALLWOOD POPULATION SITE INDEX AUDIT MERRITT TIMBER SUPPLY AREA Prepared for: Nicola-Similkameen Innovative Forestry Society Merritt, BC Glenn Thiem, RFT Forsite Forest Consultants Salmon Arm, BC Prepared by: Stephanie Ewen, BSF Timberline Natural Resource Group Ltd. Kamloops, BC Project Number: BC March 2008

2 i

3 Merritt Smallwood PSI Audit EXECUTIVE SUMMARY In 2003, the Regional Manager (Southern Interior Forest Region) granted an allowable annual cut (AAC) uplift within the Merritt Timber Supply Area (TSA) to members of the Nicola- Similkameen Innovative Forestry Society (NSIFS). This uplift was granted under several conditions, including that the NSIFS update their Forestry Plan to include a growth and yield monitoring program that will identify deviations from expected overall average site productivity estimates, including low elevation, high elevation, and smallwood stands. 1 The objective of the smallwood project was to audit the potential site index (PSI) estimates used in the smallwood population for the 2003 AAC uplift analysis and report on differences between the estimates used in the uplift application and those observed on the ground. The smallwood PSI estimates could not be directly audited using ground-sampled site indices (SIs), as potential site index cannot be observed in repressed stands. In order to gain more confidence in the estimates used for this population, a comparison was made between ground-sampled SIs derived from polygons that were formerly classified as smallwood but are regenerating following harvest and PSI estimates used in the AAC Uplift Application. The results found in this analysis reflect the results expected in the smallwood population. Overall, there is no evidence that the field SIs from the sample are different from the PSIs used in the 2003 AAC Uplift Application. As such, we recommend that: 1. The PSIs used in the smallwood population portion of the 2003 AAC Uplift Application be used in future base case analyses; and 2. The productivity of post-harvest smallwood stands continues to be monitored through Change Monitoring Inventory (CMI). This will maintain confidence in the PSI estimates and act as an early warning in the event that these estimates need to be revised. The typical re-measurement cycle for CMI is five years. 1 1 British Columbia Ministry of Forests Rationale for Increase in Annual Allowable Cut (AAC) Determination of Merritt Timber Supply Area Innovative Forestry Practices Agreements. Effective January 1, Southern Interior Forest Region. 50 pp. ii

4 iii

5 Merritt Smallwood PSI Audit TABLE OF CONTENTS 1.0 INTRODUCTION BACKGROUND OBJECTIVES LAND BASE TERMS OF REFERENCE METHODS OVERVIEW SOURCE DATA TARGET POPULATION AND SAMPLE SITE TREE DATA ANALYSIS RESULTS TARGET POPULATION VERSUS SAMPLE PSI T-TEST RESULTS RECOMMENDATIONS... 9 APPENDIX I: DESCRIPTION OF MERRITT TSA APPENDIX II: SITE INDEX DATA FOR EACH SITE TREE APPENDIX III: PLOT AND TREE DATA COLLECTION LIST OF TABLES Table 1: Source data used in smallwood analysis... 3 Table 2: Land class distribution... 1 Table 3: Area and percent of population and sample by productivity class... 4 Table 4: Number of plots by number of site trees observed... 6 Table 5: Number of plots by average plot breast-height age... 6 Table 6: Summary statistics of site tree characteristics... 6 Table 7: Summary of observed versus PSIs... 8 Table 8: BEC subzones found in the smallwood population Table 9: Site index plot data iv

6 Merritt Smallwood PSI Audit LIST OF FIGURES Figure 1: Proportion of population and sample in each productivity class... 5 Figure 2: Smallwood plot layout... 1 Figure 3: Distribution of the smallwood population within the Merritt TSA v

7 - Merritt Smallwood PSI Audit 1.0 INTRODUCTION 1.1 Background In 2003, the Regional Manager (Southern Interior Forest Region) granted an allowable annual cut (AAC) uplift within the Merritt Timber Supply Area (TSA) to members of the Nicola- Similkameen Innovative Forestry Society (NSIFS). This uplift was granted under several conditions, including that the NSIFS update their Forestry Plan to include a growth and yield monitoring program that will identify deviations from expected overall average site productivity estimates, including low elevation, high elevation, and smallwood stands. 2 In response, the NSIFS contracted Timberline Natural Resource Group Ltd. 3 to develop a sample plan that outlined a Change Monitoring Inventory (CMI) strategy for the low elevation stands and site productivity programs for each of the high elevation and smallwood populations. This sample plan was reviewed and approved by staff from the Ministry of Forests and Range (MoFR) South Interior Forest Region and Forest Analysis and Inventory Branch. Due to the difficulty associated with sampling smallwood lodgepole pine (Pl), two iterations were made to the smallwood program methods, with the most recent version being approved by the MoFR in April Objectives The objective of this project is to audit the potential site indices (PSIs) used in the smallwood population for the AAC uplift and report on differences between the estimates used in the uplift application and those observed on the ground. 1.3 Land Base The Merritt TSA is located in the BC southern interior within the Cascades Forest District. The TSA is located between the US border, the Cascades Range, Kamloops TSA, and the Okanagan TSA (Appendix 1). The TSA covers 1.1 million ha, of which 0.6 million ha (53%) 4 are in the timber harvesting land base (THLB) and Vegetated Treed (VT) land base. The majority of the TSA is located in interior biogeoclimatic (BGC) zones and contains the following commercial tree species Pl, interior Douglas-fir (Fdi), interior spruce (Sx), and interior balsam (Bl). 2 British Columbia Ministry of Forests Rationale for Increase in Annual Allowable Cut (AAC) Determination of Merritt Timber Supply Area Innovative Forestry Practices Agreements. Effective January 1, Southern Interior Forest Region. 50 pp. 3 The project was started under J.S. Thrower & Associates Ltd. (JST) until the company was acquired by Timberline in June The statistics identified in this report vary slightly from the sample plan to reflect more recent data since the start of the project. 1

8 - Merritt Smallwood PSI Audit 1.4 Terms of Reference This project was completed for members of the NSIFS. The Forest Investment Account (FIA) administrator and project contact was Glenn Thiem, RFT of Forsite Consultants. The Timberline project manager was Hamish Robertson, RPF and the field program and analysis was completed by Stephanie Ewen, BSF, with technical support from Guillaume Thérien, PhD. 2

9 - Merritt Smallwood PSI Audit 2.0 METHODS 2.1 Overview PSIs derived from the smallwood stands in the 2003 AAC uplift were compared to field site indices for 30 forest-cover polygons. The forest conditions within these 30 polygons were previously considered to be smallwood before being harvested between 1989 and 1996 and were selected for this study because they were both smallwood (pre-harvest) and old enough to provide reliable site index estimates (post harvest). While the sampled stands are no longer considered smallwood stands because they were harvested and have grown free of suppression, they provide a cohort for which to investigate the potential productivity of smallwood stands. 2.2 Source Data The Vegetation Resources Inventory (VRI) Phase I data used in the analysis was downloaded from the MoFR website on December 18, 2007 and is slightly different than that used in the sample plan. To maintain as much consistency with the sample plan as possible, only the forest cover layer was updated. The other layers included in the resultant (THLB, ownership, and Predictive Ecosystem Mapping [PEM]) were the same as those used during sample plan preparation (Table 1). Table 1: Source data used in smallwood analysis Layer Status Note Forest Cover Updated Downloaded from MoFR data warehouse on December 18, PEM Unchanged Ownership Unchanged THLB Unchanged A resultant was created by overlaying all four data layers. The smallwood population was identified using the definition used for Timber Supply Review (TSR) 2 and the 2007 VRI attributes backdated to Corrected GPS locations of the sample plots were used to link inventory and ground sample data. 3

10 - Merritt Smallwood PSI Audit 2.3 Target Population and Sample Target Population The target population comprised the areas in the THLB component of the VT land base that were: Pl-leading stands where inventory site index is less than 14 m and height is less than 19.5 m. 5 The target (smallwood) population covered 83,790 ha (7% of TSA or 14% of the VT THLB) (Table 2). Table 2: Land class distribution Land Class Area (ha) % of % VT- TSA THLB Total TSA 1,131, Non-THLB 447, THLB 683, Non-VT 82,337 7 VT 601, Non-Smallwood 517, Smallwood 83, Sample The sample population consisted of 30 Pl-leading VRI polygons harvested between 1989 and 1996 from the smallwood population (561 ha). 6 These polygons were selected because they were known to exist in a previous smallwood definition, had since been harvested, and whose growth reflected the potential productivity of the site (i.e., free of repression) Stratification The target population and the sample were stratified by productivity class as defined using the Site Index Biogeoclimatic Ecosystem Classification (SIBEC) estimates. The limits of the productivity classes were arbitrarily selected with the objective of choosing round numbers that would split the population in three equal strata as much as possible. The stratification was used to ensure that the sample was representative of the population in terms of potential productivity. The sample over-represented the Medium class and under-represented the High class. A weighting procedure (described in Section 2.4.1) was used to correct this imbalance. Table 3: Area and percent of population and sample by productivity class Productivity SIBEC Population Area Sample Class SI Class (m) (ha) (%) n (%) Area (ha) (%) Low < , Medium , High > , Total 83, British Columbia Ministry of Forests Merritt TSA Timber Supply Area Rationale for Allowable Annual Cut (AAC) Determination Effective January 1, pp. + app. 6 J.S. Thrower & Associates Ltd Merritt Timber Supply Area Smallwood Population Site Index Audit. Unpublished Report, Project No. MTI-802, April 15, pp. 4

11 - Merritt Smallwood PSI Audit Figure 1: Proportion of population and sample in each productivity class Sample Selection The plot location within each sampled polygon was determined by selecting a random point on a 5 m grid. Only one sample point was selected in each polygon Plot Layout The plot structure was a nine-point cluster of 5.64 m radius sub-plots (Figure 2). A plot was considered valid if it contained a site index estimate from at least one of the sub-plots. Only Pl site trees 7 were considered in this project. Height and lab-counted breast-height (BH) age observations were used to derive a SI estimate for each site-tree, using growth intercept models within Sitetools (BatchTools Version 3.3) (Appendix 2). SiteTools SI estimates were averaged to create a single plot SI observation for each plot cluster. 2.4 Site Tree Data One hundred and ten (110) site-trees were observed in 30 plots. The number of site trees/plot varied between 1 and 8, with most plots having between 2 and 4 site trees (Table 4). The average Figure 2: Smallwood plot layout 7 Site trees were defined using SIBEC standards (largest diameter tree of the leading species in a 100 m 2 plot, with less than 5% height loss). 5

12 - Merritt Smallwood PSI Audit plot BH age varied between 6 and 11 years, with most plots having an average of 8 years (Table 5). Unweighted average site index was 19.1 m with a mean BH age of 8 years (Table 6). Appendix III lists all of the attributes collected. Table 4: Number of plots by number of site trees observed No. Site Trees No. Plots (%) Table 5: Number of plots by average plot breastheight age Mean BH No. Plots Age (yrs) (%) Table 6: Summary statistics of site tree characteristics Variable n Avg Min Max SD Site Index (m) BH Age (yrs) Weighting The sample did not represent the same proportion of each productivity class as the target population. To ensure the sample was representative of the population, each observation was weighted using a factor proportional to the area of the sampled polygon and the area ratio between the target population and the sample of the productivity class from which the observation was selected (Equation [1]). Equation [1] w ij = a ij N i j= 1 n i j= 1 where w ij = Observation weight A a ij ij a ij = Area of the sampled polygon j in productivity class i A ij = Area of the target polygon j in productivity class i n i = Number of sampled polygons in productivity class i N i = Number of target polygons in productivity class i 6

13 - Merritt Smallwood PSI Audit 2.5 Analysis The average PSI and field site index estimates were calculated for each productivity class and for the overall sample. These values were compared using a weighted t-test. 7

14 - Merritt Smallwood PSI Audit 3.0 RESULTS 3.1 Target Population versus Sample PSI The average sample and target PSI were similar for both the Medium and High site productivity classes; however, the average sample PSI in the Low class was significantly higher than the PSI in the same class in the target population. This indicated that the target population included more very low sites than the sample, likely due to the fact that very poor sites are rarely harvested and therefore not included in the sample. 3.2 t-test Results Overall, the average difference between sample PSI and field site index estimates was 0.2 m (95% confidence interval [-0.2, 0.6]) (Table 7) and was not significantly different from zero. This indicates that the PSIs are most likely reasonable site productivity estimates for the smallwood population. The Medium class was the only strata with sufficient observations to make a subpopulation conclusion and showed that the PSI and field site index estimates were similar (18.8 m versus 19.0 m). The sample sizes were too small in the other strata to infer conclusive results at the stratum level. The results of the t-tests confirmed that there were no statistical differences at the 95% confidence level. Table 7: Summary of observed versus PSIs Productivity Smallwood Population 30 Polygon n Class PSI (m) Area (ha) PSI (m) Ground SI (m) Low , Med , High , Total , These results reflect the most appropriate site index estimates for the sample, however, they should be viewed with some caution due to the relatively low average BH age of the sample trees (8 years BHA). 8

15 - Merritt Smallwood PSI Audit 4.0 RECOMMENDATIONS As a result of the analysis of the smallwood program, we recommend that: 1. The observed site indices provide strong evidence that the PSIs used in the smallwood population part of the 2003 AAC uplift are reasonable and should be used in future base case analyses; and 2. The productivity of post-harvest smallwood stands continues to be monitored through CMI and be incorporated into the CMI population. This will maintain confidence in the PSI estimates and act as an early warning in the event that these estimates need to be revised. The typical re-measurement cycle for CMI is five years. 9

16 Merritt Smallwood PSI Audit Appendix I TSA Description APPENDIX I: DESCRIPTION OF MERRITT TSA Figure 3: Distribution of the smallwood population within the Merritt TSA Table 8: BEC subzones found in the smallwood population BEC Label Area (ha) % of total MSxk 32, MSdm2 17, IDFdk2 12, IDFdk1 10, ESSFdc2 4,383 5 ESSFxc 4,250 5 ESSFmw 1,243 2 MSmw IDFxh IDFxh ESSFxcp 21 0 ESSFdcp IDFdk1a 3 0 CWHms IDFxh2a Total 83,

17 Merritt Smallwood PSI Audit Appendix II Tree Data APPENDIX II: SITE INDEX DATA FOR EACH SITE TREE Table 9: Site index plot data Subplot Lab Age Field SI (Growth- Sub- Lab Age Field Height SI (Growth- Plot (yrs) Height (m) Intercept) (m) Plot plot (yrs) (m) Intercept) (m) 101 SE I E NE I NW N S NE W NW N SE NE SW S W SE E SW NE E SE NE E S I SW NE W W E E N I NW N SW NW E SE I W N E W I NE N N NW NE S W SW E W SE E I N NW NE S W E E I N N SE S SW SE

18 Merritt Smallwood PSI Audit Appendix II Tree Data Subplot Lab Age Field Height Plot (yrs) (m) 119 SW I SI (Growth- Intercept) (m) N NE N NW I NE SE E I N NW SW W N NW S SW E SW E NE S SE SW NW E NW S W S SW

19 Merritt Smallwood PSI Audit Appendix III Data Collected APPENDIX III: PLOT AND TREE DATA COLLECTION Plot data collected: Access Notes GPS location and elevation Slope & Aspect Slope Position and Shape BGC Subzone and Site Series Moisture and Nutrient Classes Indicator Vegetation Tree data collected: Species Crown Class Breast-Height diameter & age Site Series Field estimate of site index Notes on tree conditions Vertex height 13