Estimating merchantable wood volume in two Puerto Rican watersheds,

the San Juan Bay Estuary and Río Grande de Arecibo

Thomas J. Brandeis, Olaf Kuegler, andMaría del Rocío Suárez Rozo

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.

How is volume estimated?

Volume tables Geometric formulas Regression equations

Few examples of regression equations that predict tree volume for Puerto Rican forests

How was it done in the past?

DOB pole top

DBH

DOB stump

Pole timber (min DBH = 12.5 cm, min to DOB = 10.0 cm)

Stump height (30 cm)

DBH height (1.37 cm)

Bole length

Saw timber (min DBH = 27.5 cm, min top DOB = 22.5 cm)

DOB pole top

DOB sawlog top

DBH

DOB stump

Stump height (30 cm)

DBH height (1.37 cm)

Bole length

Sawlog length

Figure 1a. Figure 1b.

How was it done in the past?

Inner bark diameters calculated

Section volume:

VSEC = [HSEC * {(DIB12) + (DIB1* DIB2) + DIB2

2)}* 0.00007854] / 3

Each section summed for total stem volume Excludes 30 cm stump and branches

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

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.

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

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

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.

20 0 20 40 60 80 100 120 Kilometers

N

San Juan Bay Watershed

Example 1: San Juan Bay Estuary Watershed

SJBE watershed volume estimate

Land use Area (ha)Mean Vol/ha

(m3/ha)SE

Total Vol (m3)

Urban 11,430 19.98 4.49 228,384.33

Forest 4,032 53.65 25.52 216,319.69

Totals 15,462 444,704 m3

Example 2: Río Grande de Arecibo watershed

RGA watershed volume

Strata Area (ha)Mean Vol/ha

(m3/ha)SE

Total Vol (m3)

mf-S-Kt 617.10 67.47 25.00 41,635.29

mf-S-Tkp 2,341.59 59.08 8.04 138,350.93

mf-S-Ts 704.55 116.70 45.78 82,224.52

wf-Lm-Kt 1,725.61 57.70 16.27 99,560.10

wf-Lm-Tkp 471.46 108.34 107.03 51,075.95

wf-S-Kt 7,930.23 83.03 5.88 658,472.05

wf-S-Ti 478.77 71.89 49.33 34,416.30

wf-S-Tkp 5,929.00 85.25 1.65 505,426.21

wf-S-Tks 2,972.25 88.72 1.92 263,690.91

wf-S-Ts 4,129.21 88.32 1.97 364,707.24

Totals 27,299.76 2,239,559 m3

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.

Future work

Species-specific equations

Taper equations; volume to a variable upper diameter merchantability limit

Biomass studies

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.