Thomas J. Brandeis, Olaf Kuegler, and María del Rocío Suárez Rozo

1. Estimating merchantable wood volume in two Puerto Rican watersheds, the San Juan Bay Estuary and Río Grande de Arecibo Thomas J. Brandeis, Olaf Kuegler, and María del Rocío Suárez Rozo

2. Why estimate volume? • Estimating wood volume allows the placement of a monetary value on one of the many commodities and services forested watersheds provides to society. • FIA produces resource bulletins, which include volume estimates. CUFC 06/15/04

3. How is volume estimated? • Volume tables • Geometric formulas • Regression equations Few examples of regression equations that predict tree volume for Puerto Rican forests CUFC 06/15/04

4. DOB pole top DOB pole top Bole length Bole length DOB sawlog top Sawlog length DBH DBH DBH height (1.37 cm) DBH height (1.37 cm) DOB stump DOB stump Stump height (30 cm) Stump height (30 cm) Pole timber (min DBH = 12.5 cm, min to DOB = 10.0 cm) Saw timber (min DBH = 27.5 cm, min top DOB = 22.5 cm) Figure 1a. Figure 1b. How was it done in the past? CUFC 06/15/04

5. How was it done in the past? • Inner bark diameters calculated • Section volume: VSEC = [HSEC * {(DIB12) + (DIB1* DIB2) + DIB22)}* 0.00007854] / 3 • Each section summed for total stem volume • Excludes 30 cm stump and branches CUFC 06/15/04

6. How can we make it easier? • Derive regression equations • Based on previous inventory data’s multiple stem measurements • Uses only DBH and total height measurements CUFC 06/15/04

7. Regression equations • Equations fitted to the 1990 inventory data, all species combined. • Mallow’s Cp, PRESS, Variance Inflation Factor (VIF), and R2 statistics • Equations with DBH and HT, log transformed, produced the best fit to the data. CUFC 06/15/04

8. Regression equations • DBH and total height Vstem = exp (-12.00089+ 2.75276 (ln DBH) + 0.88961 (ln HT) – 0.02072 (DBH) MSE = 0.041395, RMSE = 0.20346, R2 = 0.90827, N = 1,247 • DBH only Vstem = exp(-11.37782+ 3.3595 (ln DBH) – 0.0273 (DBH) MSE = 0.083472, RMSE = 0.28891, R2 = 0.81503, N = 1,247 CUFC 06/15/04

9. Applications • San Juan Bay Estuary watershed • Inventoried in 2001 • 108 plots • Upper reaches of the Río Grande de Arecibo watershed • Inventoried in 2003 • 91 plots CUFC 06/15/04

10. Assumptions • Palms, tree ferns, bamboo, some fruit trees, and some other species excluded from volume estimates. • Assumes log lengths similar to those of the 1990 Puerto Rico forest inventory. • Unsound cull trees not removed from data sets, so merchantable volume is over-estimated. • Estimates do not take into account smaller dimension material such as branch wood. CUFC 06/15/04

11. Example 1: San Juan Bay Estuary Watershed CUFC 06/15/04

12. SJBE watershed volume estimate CUFC 06/15/04

13. Example 2: Río Grande de Arecibo watershed CUFC 06/15/04

14. RGA watershed volume CUFC 06/15/04

15. Conclusions • These equations could be applied to other forests in Puerto Rico, and other Caribbean islands with similar structures and species compositions. • Note: no attempt made to place monetary value on this wood. CUFC 06/15/04

16. Future work • Species-specific equations • Taper equations; volume to a variable upper diameter merchantability limit • Biomass studies CUFC 06/15/04

17. Acknowledgements • Andy Hartsell, Raymond Sheffield, James Rosson and Larry Royer of the USDA Forest Service Southern Research Station. • Prof. Luis R. Pérez Alegría of the Department of Agricultural and Biosystems Engineering, University of Puerto Rico at Mayagüez, PI of the Atmospheric Carbon Sequestration Project of the UPRM-NASA-URC. CUFC 06/15/04