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Response: Letter to the Editor by David South
EC O L O G IC A L E C O N O M IC S 6 4 ( 2 0 07 ) 46 3 –4 64
a v a i l a b l e a t w w w. s c i e n c e d i r e c t . c o m
w w w. e l s e v i e r. c o m / l o c a t e / e c o l e c o n
Response: Letter to the Editor by David South
old unthinned oak/hickory stand contains more C than a thinned 16-year-old pine plantation. However, this says nothing about the relative productivity of the two stands. In Table 1, we used the Carbon On Line Estimator (ncasi. uml.edu/COLE) to illustrate the relative importance of stand age and type on standing aboveground carbon. With a 15-year harvest rotation, three rotations of oak–hickory stands might produce 108 (i.e. 36 × 3) MTC/H in LA. In contrast, three 15-year rotations of pine plantations might produce 159 MTC/H (47% more C). The COLE model does suggest a 45-year oak/hickory stand would contain more C than a 45-year pine plantation in LA (but not in AR). Although wood harvested from thinning were not included in these comparisons, these results illustrate the greater importance of rotation age over that of species or establishment method. It seems curious that Sohngen and Brown's projection shows C for PP to be fairly constant throughout the projection (at about 36.5 MTC/H), while the per hectare biomass for NP and UHW decline, by 21% and 16% respectively. In the case of NP, in the first decade this forest type area did not change but the standing C fell by 20%. This loss of biomass is likely a result of the fixed harvest rate assumption in the model. That is, there was likely a concentration of age 40+ NP stands in the starting inventory that, due to the model assumption, 11% were projected to be harvested in the first decade. A similar case could be made for UHW. Although the authors attribute the loss of aboveground C
Dear Editor: Sohngen and Brown (EE 57:698–708) developed a model of forest type conversion for the South Central U.S., and conclude that conversion of natural pine (NP) and upland hardwood forests (UHW) to pine plantations (PP) “…could reduce overall carbon storage in aboveground carbon stocks” (p.706). Their assertion that “…hardwood forests have higher annual wood production and higher carbon stocks than softwood forests” (p.699) is critical to their conclusions. This assertion is based on analysis of U.S. Forest Service Forest Inventory and Analysis (FIA) data that indicate current inventories, but that do not reveal the stand histories that were responsible for current inventories. Current inventory divided by stand age is not a complete measure of forest production rate. When forests are thinned (more common in PP than in natural stands), the harvested and carbon (C) (which is subsequently fixed in products) should be credited towards total C production (but is not included in the FIA data). If total production was properly accounted for, PP wood production rates would certainly be higher than those in natural stands. Wood production rates are influenced more by stand age and management intensity than to species per se. For example in USDA (1988), Table 5.5 indicates that 55-year-old PP's produce about 67% more wood volume than UHW's of equal age and site. FIA plot data from AR might reveal that a 50-year-
Table 1 – Standing aboveground carbon (metric tons of C per ha: MTC/H) by age-class and stand type State
Stand type
Average age
0–10 years
11–20 years
21–30 years
Year AR
LA
MS
Oak/hickory Natural pine Planted Pine Oak/hickory Natural pine Planted Pine Oak/hickory Natural pine Planted Pine
50 40 16 34 30 14 7 16 11
31–40 years
41–50 years
66 73 79 71 77 83 n.a. 87 90
76 81 82 87 88 82 n.a. 74 63
MTC/H 21 33 26 25 25 22 16 26 25
38 59 57 36 54 53 21 51 51
61 66 65 49 66 67 64 92 68
Data for pine represent only the loblolly/shortleaf group and were generated using COLE–Lite and do not include biomass removed during thinning. Bold numbers derived from less than 5 plots.
0921-8009/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.ecolecon.2007.09.014
464
EC O LO GIC A L E CO N O M ICS 6 4 ( 2 00 7 ) 4 6 3 –4 64
(2000 vs. 2010) in NP to the establishment of PP, it in fact appears to be due largely to a change in management practices in NP stands. In summary, we believe: (a) C removed during thinning was not included in the model; (b) the harvest rate assumptions in the model implicitly represent a change in management practices that reduces standing C in natural stands, and; (c) total wood and C production for thinned, 20-year-old PP (in 2030) is higher than for 20-year-old UHW stands, therefore the projections underestimate future carbon stocks; Both the survey data used to support faster C accumulation in natural stands and the model itself seem to be confounded by unstated attributes of stand age, thinning intensity, and site productivity. To draw such sweeping policy conclusions from this study might result in a significant expenditure of subsidy dollars with little hope of achieving the desired outcome.
REFERENCE USDA, 1988. The South's fourth forest: alternatives for the future. U.S. Forest Service. Forest Resource Report 24. 512 p.
FURTHER READING Sohngen, Brent, Brown, Sandra, 2006. The influence of conversion of forest types on carbon sequestration and other ecosystem services in the South Central United States. Ecological Economics 57 (4), 698–708. 1 June.
David B. South Auburn University, Alabama 36849-5418, School of Forestry and Wildlife Sciences, United States Corresponding author. Tel.: +1 334 844 1022; fax: +1 334 844 1084. E-mail address: [email protected]. Samuel J. Radcliffe Prentiss & Carlisle, Milwaukee, WI, United States
a v a i l a b l e a t w w w. s c i e n c e d i r e c t . c o m
w w w. e l s e v i e r. c o m / l o c a t e / e c o l e c o n
Response: Letter to the Editor by David South
old unthinned oak/hickory stand contains more C than a thinned 16-year-old pine plantation. However, this says nothing about the relative productivity of the two stands. In Table 1, we used the Carbon On Line Estimator (ncasi. uml.edu/COLE) to illustrate the relative importance of stand age and type on standing aboveground carbon. With a 15-year harvest rotation, three rotations of oak–hickory stands might produce 108 (i.e. 36 × 3) MTC/H in LA. In contrast, three 15-year rotations of pine plantations might produce 159 MTC/H (47% more C). The COLE model does suggest a 45-year oak/hickory stand would contain more C than a 45-year pine plantation in LA (but not in AR). Although wood harvested from thinning were not included in these comparisons, these results illustrate the greater importance of rotation age over that of species or establishment method. It seems curious that Sohngen and Brown's projection shows C for PP to be fairly constant throughout the projection (at about 36.5 MTC/H), while the per hectare biomass for NP and UHW decline, by 21% and 16% respectively. In the case of NP, in the first decade this forest type area did not change but the standing C fell by 20%. This loss of biomass is likely a result of the fixed harvest rate assumption in the model. That is, there was likely a concentration of age 40+ NP stands in the starting inventory that, due to the model assumption, 11% were projected to be harvested in the first decade. A similar case could be made for UHW. Although the authors attribute the loss of aboveground C
Dear Editor: Sohngen and Brown (EE 57:698–708) developed a model of forest type conversion for the South Central U.S., and conclude that conversion of natural pine (NP) and upland hardwood forests (UHW) to pine plantations (PP) “…could reduce overall carbon storage in aboveground carbon stocks” (p.706). Their assertion that “…hardwood forests have higher annual wood production and higher carbon stocks than softwood forests” (p.699) is critical to their conclusions. This assertion is based on analysis of U.S. Forest Service Forest Inventory and Analysis (FIA) data that indicate current inventories, but that do not reveal the stand histories that were responsible for current inventories. Current inventory divided by stand age is not a complete measure of forest production rate. When forests are thinned (more common in PP than in natural stands), the harvested and carbon (C) (which is subsequently fixed in products) should be credited towards total C production (but is not included in the FIA data). If total production was properly accounted for, PP wood production rates would certainly be higher than those in natural stands. Wood production rates are influenced more by stand age and management intensity than to species per se. For example in USDA (1988), Table 5.5 indicates that 55-year-old PP's produce about 67% more wood volume than UHW's of equal age and site. FIA plot data from AR might reveal that a 50-year-
Table 1 – Standing aboveground carbon (metric tons of C per ha: MTC/H) by age-class and stand type State
Stand type
Average age
0–10 years
11–20 years
21–30 years
Year AR
LA
MS
Oak/hickory Natural pine Planted Pine Oak/hickory Natural pine Planted Pine Oak/hickory Natural pine Planted Pine
50 40 16 34 30 14 7 16 11
31–40 years
41–50 years
66 73 79 71 77 83 n.a. 87 90
76 81 82 87 88 82 n.a. 74 63
MTC/H 21 33 26 25 25 22 16 26 25
38 59 57 36 54 53 21 51 51
61 66 65 49 66 67 64 92 68
Data for pine represent only the loblolly/shortleaf group and were generated using COLE–Lite and do not include biomass removed during thinning. Bold numbers derived from less than 5 plots.
0921-8009/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.ecolecon.2007.09.014
464
EC O LO GIC A L E CO N O M ICS 6 4 ( 2 00 7 ) 4 6 3 –4 64
(2000 vs. 2010) in NP to the establishment of PP, it in fact appears to be due largely to a change in management practices in NP stands. In summary, we believe: (a) C removed during thinning was not included in the model; (b) the harvest rate assumptions in the model implicitly represent a change in management practices that reduces standing C in natural stands, and; (c) total wood and C production for thinned, 20-year-old PP (in 2030) is higher than for 20-year-old UHW stands, therefore the projections underestimate future carbon stocks; Both the survey data used to support faster C accumulation in natural stands and the model itself seem to be confounded by unstated attributes of stand age, thinning intensity, and site productivity. To draw such sweeping policy conclusions from this study might result in a significant expenditure of subsidy dollars with little hope of achieving the desired outcome.
REFERENCE USDA, 1988. The South's fourth forest: alternatives for the future. U.S. Forest Service. Forest Resource Report 24. 512 p.
FURTHER READING Sohngen, Brent, Brown, Sandra, 2006. The influence of conversion of forest types on carbon sequestration and other ecosystem services in the South Central United States. Ecological Economics 57 (4), 698–708. 1 June.
David B. South Auburn University, Alabama 36849-5418, School of Forestry and Wildlife Sciences, United States Corresponding author. Tel.: +1 334 844 1022; fax: +1 334 844 1084. E-mail address: [email protected]. Samuel J. Radcliffe Prentiss & Carlisle, Milwaukee, WI, United States