Oregon Department of Forestry Harvest Scheduling Model Yield Table Creation Project

Transcription

1 Oregon Department of Forestry Harvest Scheduling Model Yield Table Creation Project Recommendation of Growth Model and Tree Volume Estimation System To the H&H Core Team for the Tillamook, Forest Grove, Astoria, West Oregon, And Western Lane Districts Stephen E. Fairweather, Ph.D. Mason, Bruce and Girard, Inc. 707 SW Washington Street, Suite 1300 Portland, Oregon 97205

2 Recommendation of Growth Model and Tree Volume Estimation System to the H&H Core Team for the Tillamook, Forest Grove, Astoria, West Oregon, And Western Lane Districts Table of Contents Topic Page Abstract 3 Introduction 3 Methods 3 Results 4 Applicable Models 4 The Short List of Models to Evaluate 5 Anecdotal Data 12 Comparing ORGANON and FVS 12 Draft Recommendation to the H&H Core Team 15 Final Growth Model Recommendation 15 Recommendation of a Volume Determination Method 16 Appendix A Letter Soliciting Growth and Yield Data from the District Foresters 17 Appendix B Matrix of Comparative Information About the Growth Models 21 2

3 Recommendation of Growth Model and Tree Volume Estimation System to the H&H Core Team for the Tillamook, Forest Grove, Astoria, West Oregon, And Western Lane Districts Abstract We recommend using the Pacific Northwest Coast variant of the Forest Vegetation Simulator (PN-FVS) for developing yield tables for the current round of forest planning on the northwest state forests. Of the growth models evaluated for this particular project, PN-FVS appears to be the best choice by virtue of its user support, documentation, and flexibility. We recommend using the Flewelling taper system for estimating tree volume. Introduction Mason, Bruce and Girard, Inc., (MB&G) was hired by the Oregon Department of Forestry to help create yield tables for the current round of forest planning. The first task in the project was to evaluate and recommend a growth and yield model for this purpose. A related task was to recommend a tree volume estimation system to use for the project. In this particular report we present our recommendations for the northwest districts, which include Tillamook, Forest Grove, Astoria, West Oregon, and Western Lane. Methods Our approach to recommending a growth model was organized into discrete steps: 1. Collect all applicable models and review their documentation. Given the need to simulate the development of mixed species stands, both even and uneven-aged, and given the emphasis on structure-based management, we felt applicable models would include only the individual-tree models. 2. Develop a short list of models to evaluate. Some of the models could be eliminated easily after a quick review based on their geographic applicability and/or other obvious weaknesses. We could also draw on our experience evaluating growth models for the Elliott District in late

4 3. Solicit hard and anecdotal growth and yield data from the ODF. Early in the project we asked the ODF foresters for data that might be useful for judging the validity of the growth model predictions. We were particularly interested in documented observations, and in the forester s opinion of whether the observation was typical, or particularly high or low for the given site and age. See Appendix A for more information. 4. Conduct a subjective evaluation of the models. We have conducted several growth model evaluation projects making use of permanent plot data and an array of objective measures for selecting a best model. But in the current project, we were restricted to conducting a more subjective evaluation due to (1) the tight timeframe for completing the project, and (2) the lack of permanent plot data that spanned the long time horizons (150 years) of interest to the ODF. Much of our evaluation was based on past experience, a review of the model documentation (captured in the matrix in Appendix B), and some simple projections to test the biological integrity of the models. 5. Make a draft recommendation to the H&H Core Team. We attended a meeting with several representatives of the H&H Core Team in Salem on February 25, 2004, and made our recommendation. 6. Finalize the recommendation after getting some feedback. Our recommendation of the PN variant of the FVS model is finalized in this report. Results Applicable Models Our list of applicable models for the Yield Table Creation Project included the following: FVS (Forest Vegetation Simulator) Pacific Northwest Coast (PN) and West Cascades (WC) variants. FVS is maintained by the USFS. ORGANON Southwest Oregon, Northwest Oregon, and the SMC variants. ORGANON was developed by Oregon State University. FPS (Forest Projection System), developed by Dr. James Arney. SPS (Stand Projection System), developed by MB&G. Conifers USFS, Pacific Southwest Station. 4

5 RVMM (Regional Vegetation Management Model) developed by USFS/OSU. TreeLab developed by the Stand Management Cooperative, University of Washington. Conifers, RVMM, and TreeLab are growth models specifically designed to grow very young stands. These were selected for inclusion in the study because the other individual tree models often have trouble growing young stands. If a distinct advantage in simulation accuracy could be seen with the young-stand models, then we would find a way to use them in conjunction with the other models. We realized that TreeLab was not an individual-tree growth model, but as a new model we thought it would be worthwhile to take a look. If the model looked promising, we would consider finding a way to take the stand-level attributes it projected and form a tree list as input to the older-tree models. The Short List of Models to Evaluate Based on our work in growth model selection for the Elliott District, we eliminated the three regeneration models (TreeLab, Conifers, and RVMM) from further consideration for the northwest districts. TreeLab was limited to pure Doug-fir plantations, so it was eliminated from further consideration. Conifers was eliminated based on geography, since it is applicable to southern Oregon. Our tests (for the Elliott) of RVMM showed an insensitivity to site index, and the lack of a mortality model for western hemlock, so it was eliminated. We also removed the West Cascades variant of FVS and the SW and SMC variants of ORGANON from the longer list of models to look at for the northwest forests. SW ORGANON and the WC variant of FVS could be eliminated based on geography. Based on the documentation, it appeared the SMC variant of ORGANON was only applicable to young-growth, even-aged stands of western hemlock and/or Doug-fir, so it was eliminated from further consideration. 5

6 The short list of models to evaluate for the northwest forests therefore included the following: FVS (Forest Vegetation Simulator) Pacific Northwest Coast (PN) ORGANON Northwest Oregon SPS (Stand Projection System) FPS (Forest Projection System) Our growth model recommendation for the Elliott in late 2003 was the PN variant of FVS. In that study the choice came down to SPS, PN-FVS, or NWO-ORGANON, as FPS was not available to us at that time. In the end FVS was chosen for its good documentation, availability of user support, access to source code, reasonable projections for both young and old stands, and lack of dependence on stand age. Given the subsequent success with which FVS was being used in the development of yield tables for the Elliott, we framed the current question as whether or not PN-FVS was also a logical choice for the northwest forests. We began our comparison by using SPS, FVS, ORGANON, and FPS to grow a very young stand of 600 trees per acre. The stand consisted of 300 Doug-fir and 300 western hemlock, all 4.5 tall, at a site index of 110 (King 50-year base). Our experience with SPS in the Elliott study was that it had trouble growing seedling stands, and we wanted to revisit that question. Figures 1 and 2 show the results of growing the seedling stand for 20 years. Each tree was assumed to be 1/10 th inch in diameter at breast height at the start of the projection. 6

7 Figure 1. Projected trees per acre in seedling stand. 700 Projection of Seedling Stand SI = TPA FPS Organon 200 SPS 100 FVS Projection Year Figure 2. Projections of quadratic mean dbh in seedling stand. 10 Projection of Seedling Stand SI=110 9 QDBH FPS Organon SPS FVS Projection Year 7

8 The SPS model exhibited almost zero mortality during the 20-year projection, and very little diameter growth. Mortality rates appeared reasonable for both Organon and FVS, but excessive for FPS. These results for SPS were in line with our observations during the Elliott project. In the current project we also pursued the question of how sensitive SPS was to stand age. The following figures illustrate the results of a simple experiment where a stand was grown at two different ages; otherwise the starting stand was identical in both projections. In this experiment the starting stand had 104 trees per acre, 206 square feet of basal area, and a quadratic mean dbh of Figure 3. Effect of stand age on SPS prediction of QMD. SPS - Effect of Age on QMD QMD Years 50 Years Projection Year 8

9 Figure 4. Effect of stand age on SPS prediction of trees per acre. SPS - Effect of Age on TPA TPA Years Years Projection Year The fact that stand age will impact projections in SPS is significant, in that the ODF will need to be able to grow stands with indeterminate ages. For this reason, and for the apparent problems with growing seedling stands, the SPS growth model was eliminated from the list of models to consider further. The FPS results for growing the seedling stand were also troubling. As noted earlier, the results in Figure 1 suggest an excessive rate of mortality in FPS. Figure 2 shows that the seedlings that survived in the FPS projection did not grow in diameter at all. Figures 5 and 6 show the results of growing a mature stand in the 1D3H type with all four models. This particular stand began with 127 trees per acre, a qmd of 17.7, and 217 square feet of basal area. The site index was 112, and the stand was 94% Doug-fir with small amounts of western hemlock, red cedar, and red alder. This stand was listed as being 113 years of age in the SLI database. 9

10 In both Figures 5 and 6 the shape of the FPS projection is unexpected, in that the increase in neither basal area or volume tends to slow down over time. The other models exhibit behavior more in line with our expectations. Figure 5. Projection of BA/a in a mature stand with SPS, FPS, FVS, and Organon. 500 Projection of Mature Stand BA/acre BA/Acre FPS Organon SPS FVS Projection Year Figure 6. Projection of net board feet/a in a mature stand with SPS, FPS, FVS, and Organon Projection of Mature Stand Net BF/acre FPS Organon Net Boardfoot Volume SPS FVS Projection Year 10

11 In Figure 6 the beginning volumes per acre for each model are not the same because each model was using different volume equations. However, in this case we are examining the relative shapes of the yield curves, not their magnitudes. For whatever reason the FPS model is growing the stand along a linear trajectory which seems unreasonable given the stand characteristics and the length of the projection. Given the results in Figures 5 and 6, and the apparent problems with growing the seedling stand, we decided to eliminate FPS from further consideration. With the elimination of FPS and SPS, our list of candidate growth models for developing yield tables for the northwest forests included only the northwest Oregon variant of ORGANON, and the PN variant of FVS. The rate of diameter growth in FVS for the seedling stand (Figure 2) might appear to be unrealistic at first glance. Upon closer inspection, in year 2013, when the stand is 10 years old at breast height, the FVS tree will have a dbh of 5.7 inches. This translates to 3.5 rings per inch at breast height, which may be higher than expected, but is not unreasonably high. The magnitudes of the FVS projections in Figures 5 and 6 appear overly optimistic, at least in relation to the other model projections. In Figure 6 this may be at least partly a function of the volume equations being used. In Figure 5, however, the model is clearly growing trees faster, or killing fewer trees, than the other models. At this point we will point out that the model predictions can be toned down by adjusting the maximum SDI in effect for the projection. For these particular runs FVS was using a maximum SDI of 950, while Organon was using 520. In our work on the Elliott, we arrived at a maximum SDI of 720 for FVS to produce projections in line with the foresters experience and expectations. 11

12 Anecdotal Data We received cruise data from Astoria that showed volume per acre figures for 32 stands cruised between 1989 and All of the stands were natural (not plantations), and were purposefully picked to represent higher than average yields. Figure 7 shows that volumes as high as 90 mbf/acre, and mean annual increments of 900 to 1,000 board feet per acre are certainly plausible. Figure 7. Growth and volume observations from the Astoria District MBF/acre MAI (bf/a/yr) Stand Age Site Index These observations suggest that yields predicted by the growth model of more than about 105 mbf/acre at a stand age of 100 years would be questionable. This number is only a guess, but represents the observed maximum of about 92 mbf, plus reasonable increases due to genetics and stand density management. Comparing ORGANON and FVS Both models use the same set of predictor variables to model diameter growth site index, current dbh, crown ratio, basal area in the stand, and basal area in the stand in trees larger than the subject tree. The FVS model also makes use of elevation, slope, and aspect, but these variables will have little value in an application that is building yield tables for the average stand representing an analysis area. FVS also makes use of 12

13 nearest National Forest, but in the case of the PN variant the only choices relevant to the northwest forests would be the Olympic National Forest or the Siuslaw National Forest, neither one of which exhibits a clear advantage in terms of proximity. How do projections compare between the two models? The projections of the seedling stand (Figures 1 and 2) showed little difference between the two models with regard to mortality. While the FVS projection of average qmd may have appeared overly optimistic, the ORGANON projection appeared too low, with a dbh of only 3 at a breast height age of 10 years (about 6 rings per inch). The FVS projection could probably be toned down by decreasing the SDI max value to something less than 950. Figures 5 and 6 showed ORGANON and FVS to exhibit similar basal area and volume curves for a mature stand over time, and also showed that both models were probably overly optimistic given the anecdotal evidence from Astoria. Figure 8 displays the drop in trees per acre for the mature stand projections. The sharp decline in trees per acre early in the projection for the ORGANON model seems unreasonable. Figure 8. Predicted trees per acre for the 1D3H stand; site 112, 127 tpa, 17.7 qmd, 217 sq. ft. / acre. 140 Projection of Mature Stand TPA Trees/Acre FPS Organon 40 SPS 20 FVS Projection Year 13

14 At the meeting in Salem on February 25 th, we experimented with different values of maximum SDI in PN-FVS after agreeing that yields under a maximum SDI value of 950 were obviously too high. Figure 9 shows the FVS projections of the mature stand after setting the maximum SDI value for Doug-fir to 600. Figure 9. FVS projections of the mature stand (refer to Figures 5 and 6) under maximum SDI values of 950 and 600 for Douglas-fir BA/Acre FVS 150 FVS Projection Year Net Boardfoot Volume FVS FVS Projection Year 14

15 One more consideration in the question of whether to use NWO-ORGANON or PN-FVS is the ease with which problems can be diagnosed and remedied. The FVS source code is in the public domain, while the ORGANON code is not. FVS is also supported by a staff of USFS personnel in Fort Collins, Colorado, and we have found them to be very helpful and responsive when we ve had past questions about the program. The Oregon State University staff has also been very helpful with our questions about ORGANON, but the FVS group in Fort Collins is dedicated to helping the FVS user community. Draft Recommendation to the H&H Core Team We attended a meeting with several members of the H&H Core Team in Salem on February 25, and recommended using the PN-FVS model for developing the yield tables. We presented the same evidence and reasoning presented in this report. Final Growth Model Recommendation We recommend using the PN-FVS model for developing the yield table for the northwest districts. This recommendation is not based on a direct, objective evaluation of the model using remeasurement data, but on the following observations: The model is well documented, and the source code is available to the public, so we can know exactly how the model works; The FVS support center in Fort Collins is a good resource if we need technical help in using the model; The basal area, trees per acre, and volume per acre projections made by the model appear biologically sound for both seedling stands and mature stands, and their magnitude can be calibrated to observed values by adjusting the value of maximum SDI. Our experience with using PN-FVS in building yield tables for the Elliott district has been positive. 15

16 Recommendation of a Volume Determination Method We recommend using a taper-based tree volume determination method, so the ODF can look at the impact of changing merchantability specifications if those questions arise. Good candidates for the taper system include the Flewelling taper routines, and the SIS taper routines. The SIS routines require species, dbh, total tree height, and either the SIS taper class or the observed height above ground where diameter is 80% of the diameter at breast height. If SIS taper class is not supplied, the routines will predict taper class based on species and regional averages. For the northwest state forests, the region would be the Pacific Northwest, which includes most of Oregon and Washington. The Flewelling routine requires species, dbh, and total height, and will make use of up to two more upper stem height/diameter pairs if they are available. Otherwise the routine uses only dbh and total height, and equations for several geographic variants. For the northwest districts, the Flewelling Oregon Coast variant would be most appropriate. We have had good experiences with both systems for estimating tree volumes. Based on its slightly less demanding data requirements, and greater geographic specificity, we recommend using the Flewelling taper system for estimating tree volumes for the northwest forests yield tables. 16

17 Appendix A Letter Soliciting Growth and Yield Data from the District Foresters 17

18 Dear : Mark Rasmussen and I are very excited about getting to work on the project to develop yield tables to support forest planning and harvest scheduling for the Oregon Department of Forestry. We are looking forward to working with you and bringing our expertise and experience to the table. One of the first tasks in the project is to recommend and select a growth model, or growth models, to use to develop the yield tables. In our original project proposal we explained that given the need to project both even and uneven-aged stands with a variety of species mixes, we believe it will be most appropriate to evaluate individual-tree growth models. These would include ORGANON, FPS, FVS, and SPS, and for young stands, Conifers, RVMM, and TreeLab. We have a list of 19 criteria we plan to use to evaluate the models. These are listed in Figure 1. We will be reviewing each model, filling out a "score card" with regard to the criteria, and eventually making a recommendation based on the model rankings. We think this is the best way to proceed with this phase of the project given time and cost constraints. Figure 1. Criteria for Evaluation of Growth and Yield Models 1. How well does the original data used to build the growth model coincide with the stands to be grown? How well does the original data match the stands to be grown in terms of geography, age class, range of stocking, species mix, treatment history, and site quality? 2. How long ago was the growth model calibrated? 3. How long were the growth intervals used to calibrate the model? 4. Were there any peculiarities in the weather during the growth intervals used to calibrate the model? 5. Will the SLI data provide all the site and tree attributes necessary to run the growth model? 6. Does the growth model provide all the attributes necessary for input to the planning model? 7. Does the growth model require data items that limit its usefulness for ODF forest planning? 8. Does the growth model rely on assumptions with regard to tree and stand development that undermine its usefulness for ODF forest planning? 9. How well documented was the model development? 10. How well documented was the model validation? 11. Has the growth model been peer-reviewed? 12. How does the growth model behave in long projections (100 years +)? 13. Does the model maintain biological integrity at extremes of stand density? 14. What have other growth and yield experts written about the validity of the model? (Is there a consensus?) 15. How well does the model project the development of very young stands? 16. Does the model grow a patchy stand any differently than a uniform stand? 17. Does the model have a provision for reflecting the impact of pathogens on tree growth? If not, does the model lend itself to being modified to do that? 18. Does the model have a provision for reflecting the impact of fertilization on tree growth? If not, could it be modified to do that? 19. Are the underlying equations in the growth 18 model biologically sound? Was the methodology used to fit them statistically sound?

19 We have conducted several growth model evaluation exercises in the past using permanent plot data. That kind of approach allows us to compare predicted (modeled) and observed plot attributes, and provide some objective measures of how well the growth models perform. In some ways this kind of approach may be preferable to the "score card" approach we intend to use, but the permanent plot approach requires a lot of time, and more importantly, data which are relevant to the questions of interest. In the current project we would ideally work with permanent plot data that (1) reflect the types of structure-based management prescriptions planned by the ODF, and (2) represent measurement intervals on par with the long planning horizons required for the planning model. Unfortunately these kind of data do not exist, so we feel that a subjective approach based on the 19 criteria is a good alternative. And now we'd like to ask for your help. First, if you are aware of permanent plot data sets which might be useful for this project, please let us know. We will of course try to make use of any good data we can. Secondly, if you are aware of an individual-tree growth model not listed above that may be a good candidate for evaluation, please let us know. And finally, we are very interested in soliciting from you any hard data or anecdotal data you have from your forests with regard to stand growth and yield. Our feeling is that if these data are substantiated, they can be valuable for evaluating candidate growth models. Of course, we have to be careful not to put too much weight on "vague recollections" of volume per acre figures; instead, we need observations that can be backed up with ancillary information such as site index, stand age, stand structure, species mix, location, method of origin, and treatment history. Also, your opinion as to whether the observation was typical, exceptionally high, or exceptionally low, will be very important. To help out with this request we've put together a form (Figure 2) to help you report your observations. We realize that you may not be able to fill out every entry on the form, but the more information you can provide the more substantiated the observation will be. If you have any questions about using the form, please let us know. If you have some data to offer we hope to hear from you by October 31. Thanks very much for your help. Sincerely, Stephen E. Fairweather, Ph.D. Biometrician Mason, Bruce, and Girard, Inc. Mark L. Rasmussen Forest Economist Mason, Bruce, and Girard, Inc. 19

20 Figure 2. Growth and Yield Observation Reporting Form ODF Yield Table Creation Project, Oct Phase 1 - Growth Model Evaluation ODF Yield Table Creation Project Growth and Yield Observation Reporting Form Please use this form to report your observations on growth per acre, volume per acre, average tree size, etc., as experienced on your forest. Fill in as much of the supporting information as you can. We may use this information to help evaluate growth models to be used to create yield tables for forest planning. Please submit your form to: Dr. Steve Fairweather Phone Appendix B Mason, Bruce, and Girard, Inc. FAX SW Washington Street sfairweather@masonbruce.com Suite 1300 Portland, Oregon Contact Information Your Name Your Phone Number Forest/District Address Growth and Yield Information Describe the data source (e.g., CFI plot; cruise; cut out analysis; timber sale; casual observation) When was the observation made? (approximate year) Geographic location (e.g., watershed, TRS) Method of stand origin and treatment history (e.g., planted 1925, thinned from below 1955) Species mix at time of observation (e.g., 60% DF, 40% RA) Site index/site quality (e.g., 120 for DF at 50 yrs) Observed volume per acre (e.g., 50,000 bf in 10" dbh and larger; long log scale) Observed growth per acre per year - either current annual growth or mean annual growth (e.g., 500 bf/ac/yr cai) Observed average tree size - or range of tree sizes - in terms of dbh and/or total height - Observed number of trees per acre (e.g., 200 tpa 10" and larger) Observed stand age or age structure (e.g., 45 years, or "uneven-aged") Was this observation typical, or exceptionally high or low? (e.g., growth seemed typical for the area) 20

21 Appendix B Matrix of Comparative Information About the Growth Models 21

22 Criterion Organon-N.W.O. FVS - PN 1. How well does the original data used to build the growth model coincide with the stands to be grown? How well does the original data match the stands to be grown in terms of geography, age class, range of stocking, species mix, treatment history, and site quality? 2. How long ago was the growth model calibrated? 3. How long were the growth intervals used to calibrate the model? Young growth DF and WH stands in NW Oregon; 20 to 120 years BH age; primarily even aged; Spp: GF,DF,PY,RC,WH, BM,RA,MA,PD,WO,WI. Submodels fitted with data from Coastal Range foothills west of Corvallis. Siuslaw NF to Olympic NF, approx growth sample trees, 39 spp modeled. Data source is NF, BLM, and BIA inventory. Data from 1973 to Model predictions can be affected by specifying closest National Forest (e.g., Siuslaw) or by referring to coastal BLM data years for large tree diameter and height, 5 years for small tree height. 4. Were there any peculiarities in the weather during the growth intervals used to calibrate the model? Not known Not known 5. Will the SLI data provide all the site and tree attributes necessary to run the growth model? min input data:plot, sp, dbh, tpa optional: height, crnratio, past 5 yr radial growth good. "Pre-translators" exist to allow for data from databases to be read into model-compatible data files. 6. Does the growth model provide all the attributes necessary for input to the planning model? 7. Does the growth model require data items that limit its usefulness for ODF forest planning? 8. Does the growth model rely on assumptions with regard to tree and stand development that undermine its usefulness for ODF forest planning? 9. How well documented was the model development? 10. How well documented was the model validation? 11. Has the growth model been peerreviewed? 12. How does the growth model behave in long projections (100 years +)? treelist. Separate program converts Organon output file to comma delimited file of yield data (BA/acre, TPA, CUFt and BdFt) through the projection cycle. program issues warning if stand age is less than year minimum projection interval. individual sub-model documentation in several separate pubs Publications describing component models were refereed using a double blind review process. Model issues warning that "results are extrapolations" when projection is beyond 120 years from initial stand. The warning reads that the stand age is in excess of 120 years even if there are no stand trees of that age. Model ceases to calculate age after 1000 years of projection. Maximum DBH class is >50". Projection behaves well through at least 250 years; resultant stand is reasonable. treelist No. good, standard fvs variant documentation Forest Service internal review. FVS may need growth modification keywords to constrain long projections 22

23 Criterion Organon-N.W.O. FVS - PN 13. Does the model maintain biological integrity at extremes of stand density? 14. What have other growth and yield experts written about the validity of the model? (Is there consensus?) 15. How well does the model project the development of very young stands? 16. Does the model grow a patchy stand any differently than a uniform stand? Setup option allows for no limit on SDI. Default is to only allow stands to reach a predetermined maximum. Model issues warning that BH age should be >= 10 during initialization. No tree heights <= 4.5 are accepted. No. No options for inputting spatial distribution of trees in a stand. Prone to catastrophic mortality if initial stand is high density, can adjust via keywords point crown competition factor, pccf, is a diam increment predictor variable for some species 17. Does growth model have a provision for reflecting the impact of pathogens on tree growth? If not, does the model lend itself to being modified to do that? 18. Does model have a provision for reflecting the impact of fertilization on tree growth? If not, could it be modified to do that? 19. Are the underlying equations in the growth model biologically sound? Was the methodology used to fit them statistically sound? None. Could use calibration data to affect change in tree growth due to SNC. Limited to 400 lbs. N fertilizer that can be applied to even aged stands < 70 years old with 80% BA in DF. Yes. Yes -- root disease or mistletoe. Could use modifiers on height growth, basal area growth, or tree mortality to reflect impact of SNC. not directly can proxy via site index or growth multipliers Yes Summary Age limit is a problem. DOS-based user interface is unwieldy, especially with regard to entering full path names for saved files. Required input file is column delimited, making data entry potentially painful. Stochastic feature is opportunity and curse. FVS is the FS national standard and as a result is wellsupported and documented, probably moreso than most other models. 23