REN R 431/728. Assignment 2. Yield curves
Yield Curve Development Demo
The RMarkdown file src\yc_demo.Rmd in the YieldCurveDevelopment folder in the data pro- vided for REN R 431/728 is the code I demonstrated on video. It contains and documents the steps I took to estimate conifer, deciduous, and total yield curves for what I defined as a mixedwood stratum and for a lodgepole pine/black spruce stratum. These yield curves were estimated using non-linear regression to fit a Chapman-Richards equation to the strata. The Chapman-Richards model has the form.
U(t) = b0 (1 — e∞p(—b1t))b2
where U(t) represents yield (m³/ha) at age t (years), and b0 , b1 , and b2 are coefficients.
The curve estimated for the deciduous yields did not show the decrease in yield for older plots. I used the estimated curve for total and coniferous volumes, and calculated deciduous volumes as the difference.
Your tasks
1) Explain, at least in general terms, what each chunk of code is doing in data/yc_demo.Rmd
2) Fit alternative yield tables to the same PSP data. Use the functional form below.
U(t) = b0tb1 e∞p(—b2t)
where the variables are the same as defined for the Chapman-Richards model. Only do this for the mixedwood yield stratum.
Regressing this function will require new starting variables. Use b0 = 0.00877, b1 = 2.28851, and b2 = 0.00877.
You can use src/yc_newfunction.Rmd as a starting point. It uses an .RData file created by yc_demo.Rmd so you do not have to do all of the preliminary data manipulation.
Change the file so that all the calculations are done with the alternative functional form. Present the yield curves and tables created for the alternative function.
3) Which set of curves do you feel best captures the development of aspen/white spruce stands in the boreal mixedwood forest? Why?
4) Your instructor has expressed some doubt about the appropriateness of these estimated curves for use in FMU G14. Examine the cover type and age class structure of G14. Why is your instructor doubtful.