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

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

CUFC 06/15/04 How was it done in the past? Inner bark diameters calculated Section volume: V SEC = [H SEC * {(D IB1 2 ) + (D IB1 * D IB2 ) + D IB2 2 )}* ] / 3 Each section summed for total stem volume Excludes 30 cm stump and branches

CUFC 06/15/04 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 Regression equations Equations fitted to the 1990 inventory data, all species combined. Mallow’s Cp, PRESS, Variance Inflation Factor (VIF), and R 2 statistics Equations with D BH and H T, log transformed, produced the best fit to the data.

CUFC 06/15/04 Regression equations DBH and total height V stem = exp ( (ln D BH ) (ln H T ) – (D BH ) MSE = , RMSE = , R 2 = , N = 1,247 DBH only V stem = exp( (ln D BH ) – (D BH ) MSE = , RMSE = , R 2 = , N = 1,247

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

CUFC 06/15/04 SJBE watershed volume estimate Land useArea (ha) Mean Vol/ha (m 3 /ha) SE Total Vol (m 3 ) Urban11, , Forest4, , Totals15, ,704 m 3

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

CUFC 06/15/04 RGA watershed volume StrataArea (ha) Mean Vol/ha (m 3 /ha) SE Total Vol (m 3 ) mf-S-Kt , mf-S-Tkp2, , mf-S-Ts , wf-Lm-Kt1, , wf-Lm-Tkp , wf-S-Kt7, , wf-S-Ti , wf-S-Tkp5, , wf-S-Tks2, , wf-S-Ts4, , Totals27, ,239,559 m 3

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

CUFC 06/15/04 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.