FR 3218/5218 Spring 2008

Due May 9, 2008

1. The purpose of this question is to give you practice conducting a stand table projection. There will be a stand table projection question on the fourth exam.

A northern hardwoods stand was cruised to get a current stand table estimate. The results for sugar maple were as follows:

DBH     Sugar Maple
---     -----------
 2          35.3      
 4          69.7      
 6          52.5         
 8          21.2        
10          11.4

Basswood was also present in the stand. Your stand table entries for basswood are on the data slip given to you in class. They are the first five numbers following your name. For example the numbers might be:

40 30 40 30 20

That would mean 40, 2-inch basswood per acre, 30, 4-inch basswood per acre, ..., 20, 10-inch basswood per acre. If you lost your slip, ask for a duplicate copy. Do not use someone else's numbers.

To conduct the stand table projection, first combine the values for the two species (e.g. here there would be 75.3 trees per acre in the 2-inch class) - that is ignore species for the stand table projection. The following information should then be used to estimate basal area and volume by DBH class for the two species combined for this stand, 10 years hence. Assume merchantability begins at DBH=6 and ignore "stand ingrowth".

10-year mortality: 10% for all trees 6-inches DBH and less
tree volume: 0.021 * DBH^2.59
10-year DBH increment: 0.987 + DBH^0.418 * (0.28 - 0.000002 * DBH^2.97)

(To clarify, a tree of DBH 8-inches would be predicted to grow by 1.65 inches in 10 years according to the last equation)

COMPLETE THE NEXT TWO QUESTIONS USING COMPUTERS IN THE CNR COMPUTER LAB. UNDER NO CIRCUMSTANCES TRY TO PRINT ANYTHING FROM EITHER OF THE TWO PROGRAMS YOU'LL BE USING. YOU MAY LOCK UP THE COMPUTER AND LOSE YOUR WORK.

2. The purpose of this question is to give you experience running an individual tree growth model. You will be using the TWIGS model. Both the TREEGEN and LSTWIGS components of the model implementation are accessible from the Programs menu (Natural Resources Apps) on the CNR Computer Lab machines (the TWIGS-Lake States model can also be downloaded from here). Files created in TreegenW and TWIGS will, by default, be placed in C:\Program Files\TWIGS_TREEGEN (you have the option to put the file created by TreegenW elsewhere - DO NOT). You will want to refer to the "Using TWIGS" material that is on reserve in the Forestry Library to complete this question (ignore what those materials might say concerning the location of the program files).

Use TWIGS to project __your__ stand table ahead 10 years (__DO__ ENTER SPECIES SEPARATELY HERE). Use 1 year in the projection interval, 5 years in the growth cycle, and 2 cycles. Be sure to set option G to 0. Use a site index of 64 feet (basswood) and an age (in 2008) of 58 years (let TWIGS calculate sugar maple site index on its own). Enter 0 for crown ratio (TWIGS will predict it). Assume all trees are "acceptable" and "live." Do not add in ingrowth. Write down the TWIGS projected basal area value (total for both species) at the end of each cycle. At the end of the TWIGS run, save the projected tree list into a new file.

How does the TWIGS projected basal area compare to that from your stand table projection? Are the tree DBH growths for the two methods (stand table projection and TWIGS) comparable? In addition to the two basal areas and answers to the two questions just given, e-mail the TA, ccing yourself, the two tree list files (initial and projected; each identified properly).

3. The purpose of this question is to give you experience applying a stand-level growth and yield model to evaluate options for reaching an objective for managing a particular stand. The model is PCWTHIN, developed for old-field loblolly pine plantations. PCWTHIN can be run from the Programs menu (Natural Resources Apps) on the machines in the CNR Computer Lab. There is a manual for PCWTHIN on reserve in the Forestry Library that you will want to refer to while completing this question.

Your stand is 20 years old (previously unthinned) and is on site index XX land and was __PLANTED__ at YYYY stems per acre, where XX and YYYY are the last two numbers on the data slip given to you in class. HINTS: be sure to enter __TREES PLANTED__ properly and let the model initially estimate basal area (just press <Enter> when prompted for initial basal area).

The objective for your stand is simple (and somewhat unrealistic): maximize diversity (as measured by Shannon's index) in terms of DBH at age 35. You may thin the stand once (__AT MOST__) between ages 21 and 34. You may select the age, the amount, and the type of thinning.

Hand in the initial condition of your stand (site index, trees planted, trees surviving at age 20, basal area at age 20) and a table showing:

thinning age
thinning type
thinning amount
Shannon's index at age 35

for each alternative you try. You should attempt at least four alternatives. An Excel spreadsheet to calculate Shannon's index is available.

(Clarification: Due to a shortcoming of the PCWTHIN program you must reinitialize your stand for each alternative you try)

4. The purpose of this question is to give you experience using an ecosystem process model. The model is 3-PG, a generalized forest growth model designed for stand- to regional-scale analysis. A version of the model is embedded in a PC-compatible Excel workbook (an MS Word document containing the current 3PG user-guide is also available). NOTE: the 3-PG Excel workbook contains macros - it does not contain viruses - if Excel gives a warning, you will need to select "Enable Macros" to run 3-PG. NOTE 2: computers in the CFANS computer labs are running Office (Excel) 2007 and are set to NOT allow macros. When you load the 3-PG workbook you will get a warning message "Macros have been disabled" under the ribbons near the top of the Excel window. Click the Options button next to the warning and enable macros. The 3-PG menu will be available in the Add-Ins ribbon.

Read the "Instructions" worksheet and look over the "3PGpjs_Keywords," "3PGpjs_Outputs," and "3PG_Parameters" worksheets. Note that all units are metric.

The worksheet "aspen1" contains stand and climate conditions for an aspen stand in Cloquet, Minnesota. Worksheet "aspen2" contains the same stand, except average climate variables (minimum and maximum temperature, solar radiation, and precipitation) have been increased each month. Your objective is to calculate the biological rotation age and compare stand growth under the two climatic conditions. For each scenario, run the model from year 0 to year 75. For each year, calculate the mean annual increment (MAI) and periodic annual increment (PAI) using a 6-year period length (e.g. PAI at 10 years of age would be computed as volume at age 13 minus volume at age 7 divided by 6); you will be able to compute PAI from age 4 to age 72 in this manner. The quantity of interest is stand volume (m³/ha). Plot MAI and PAI on a graph to determine biological rotation age.

1. What is the biological rotation age of the stand assuming current average climate? (include a graph and a description of the stand at biological rotation age - Mean DBH, Basal Area and Stand Volume).
2. What is the biological rotation age under the assumed climate change? (include the same information as in a.)
3. Briefly describe (and explain) the differences in stand growth (pattern and magnitude) between the two scenarios.
4. Under increased temperatures the PAI curve takes a notable dip towards the end of the model run. What is the cause of the dip?