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Biological and economic potentials of Eucalyptus grandis and slash pine as biomass energy crops
Biomass 20 (1989) 155-165
Biological and Economic Potentials of Eucalyptus grandis and Slash Pine as Biomass Energy Crops D. L. Rockwood & D. R. Dippon Department of Forestry, University of Florida, Gainesville, Florida 32611-0303, USA
ABSTRACT Various cultural factors influence the biological and economic potentials of Eucalyptus grandis and slash pine as biomass energy crops for southern and northern Florida, respectively. On muck soil, superior E. grandis progenies may produce up to 70 dry Mg ha-I in 24 months. However, coppicing success on muck soil has been inconsistent. Clones superior in frost-resilience and vigor and propagated as rooted cuttings have increased productivity potential on sandy soils. Break-even costs GJ- 1 range from just under US$2 for E. grandis short-rotation intensive culture (SRIC) on muck soils (10000 trees ha-i with a 6-year rotation, i.e. seedling~coppice~coppice cycles of 2 years each) to USS4.00 GJ i on sandy soils. Planting density, but not coppice rotation, is sensitive to the discount factor. Through 8 years, slash pine yields responded well to soil amendments on typical sites and to high planting densities. Fertilization and vegetation control increased productivity some seven times over conventional culture through 5 years. For slash pine SRIC, higher discount rates increased initial stocking levels and shortened rotations. Break-even costs for slash pine are within the range of values estimated for E. grandis. Key words: Eucalyptus grandis, Pinus elliottii, biomass, energy crops, short-rotation intensive culture.
INTRODUCTION This paper compiles past and present data on biomass production of Eucalyptus grandis Hill ex Maid. and slash pine (Pinus elliottii var. elliottii Engelm.) in Florida to update estimates of their economic potentials. Previous short-rotation intensive culture (SRIC) research suggested that the two species were suitable biomass energy crops for Florida. ~ Recent research has further defined their biological responses to cultural a m e n d m e n t , planting density and genetic options. 155 Biomass 0144-4565/89/S03.50 - © 1989 Elsevier Science Publishers Ltd, England. Printed in Great Britain
D. l.. Rockwood, D. R. Dippon
156
MATERIALS A N D M E T H O D S
E. grandis To extend results from earlier E. grandis studies I (ORNL-16 on muck soil and ORNL-7 on sandy 'palmetto prairie' soil), studies ORNL-35 and ORNL-362 were established on adjacent muck and sandy soils, respectively, with additional progeny and planting density components (Table 1) using randomized complete block designs with three replications. In ORNL-35, coppicing following harvests in December 1986 and March 1987 was evaluated. Initial field evaluation of rooted cuttings of cloning candidates for frost-resilience and vigor on 'palmetto prairie' was conducted in study O R N L - 3 7 ) Three top clones in 16-tree square blocks replicated four times were remeasured at 5"3 years to estimate the maximum productivity that could be expected under extreme freezes. Additional cloning candidates were outplanted in ORNL-40 (Table 1) to test new clones in comparison to the top three from ORNL-37 and to evaluate site/site preparation effects. SRIC E. grandis systems tested densities ranging between 1600 and 20 000 trees ha-~ on both muck and sandy soils. Three harvests cornTABLE 1 Description of Eucal)ptus grandis and Slash Pine Studies Contributing to Updated Biological and Economic Assessments E. grandis study
(bmponent
ORNL-35 Location Latitude (N) Longitude(W) Ahitude (m) Date planted
Slash pine study
ORNL-36 ORNL-40 ORNL-IO ORNL-II
Belle Glade
LaBellc
Trenton
Gainesville
26°41' 80°39 ' 4 7/1985
26°46 ' 81°26 ' 10 7/1986
26°46 ' 81°26 ' 10 8/1987
29°46 ' 82013 , 29 1/1980
29o47 ' 82°47 ' 26 1/1980
29o46 ' 85°52 ' 28 1/1983
Muck
Sand
Sand
Sand
Sand
Sand
0 3 27 0 2
1 3 27 0 2
1 1 33 235 2
5 6 33 0 2
3 6 25 0 2
Soil
Treatments:" Fertilizers Planting densities Progenies Clone s Reference
"Number of treatment levels.
Palmdale Gainesville
0-85
1 1 4 0 5
Eucalyptus grandis and slash pine as biomass energy crops
157
prised each complete planting to replanting cycle. SRIC on muck soils consisted of 2-year seedling growth before the first harvest with two coppice harvests following at 2-year intervals, resulting in a 2/2/2 system with seedlings planted only once every 6 years. SRIC on 'palmetto prairie' involved a 3/3/3 system. Economic analyses assumed that coppice growth would be 20% greater than seedling growth. Yield data for economic analysis were primarily taken from ORNL-35. Derived growth functions updated preliminary production functions developed from ORNL-16. Coppicing production functions were extrapolated from ORNL-7, ~ ORNL-16, ~ and ORNL-35 data. Pertinent data were also derived from studies ORNL-36 and ORNL-37. SRIC break-even costs Mg-~ and GJ-L assumed that 1000 ha were placed under management for 35 years. The cost of such an operation was assumed to be divided into several components: regeneration activities at the start of each plantation and at coppices, initial and annual costs incurred, and the harvest/transportation cost incurred at the completion of each cycle. Tax effects were not considered. Costs were assumed to increase at the overall inflation rate. The costs for seedlings, planting, harvesting, processing and transportation (Table 2) were based TABLE 2 Cost Assumptions for E. grandis and Slash Pine SRiC Scenarios Input
Lease (USS ha-I) Infrastructure (USS ha i) Site preparation (USS ha -L ) Management expenses (USS ha +~) Fertilization (USS ha -~ ) Harvesting and chipping (USS Mg- ~) Transportation (USS Mg -~ ) Cost of seedlings (USS tree ~) Planting cost (USS tree ~)
E. grandis
Slash pine
247 5O 123 30 93
75 50 177 30 100
24 4
24 4
0' 15 O'O55
0"07 0"05
on data from ORNL-35 and ORNL-36. The annual rental price for land in southern Florida varied from USS247 ha -~ for muck soil to USS128.50 for sandy soil. These data were input values for the program BIOCUT ~ to derive the break-even analysis for the SRIC scenarios examined. The objective was to determine which factors had the greatest impact on present costs of woody biomass.
158
D. L. Rockwood, D. R. Dippon
Slash pine Growth measurements were collected periodically from studies ORNL10, ORNL-11, and 0-855 (Table 1 ). Data for economic analyses of slash pine were derived from studies ORNL- 10 and ORNL- 11 planting density tests. Equations from Campbell 6 were utilized to convert stand parameters to dry Mg ha- 1. The SRIC scenario assumed that site preparation included root rake, roller chop, burn and bedding at the start of each new rotation. After fertilization followed by planting, annual maintenance and monitoring were the only scheduled activities until stand harvest. Computations for break-even costs Mg-~ and G J- l were based on assumptions similar to those for E. grandis (Table 2). The northern Florida flatwoods had a rental price of USS75.00 h a - l
RESULTS A N D DISCUSSION
E. grandis The performance of 27 progenies on muck soil in ORNL-35 and 'palmetto prairie' in ORNL-36 brackets growth rates for E. grandis seedlings in southern Florida. Through 12 months, seedlings in ORNL35 were much taller than those in ORNL-36 (5.4 m versus 1.6 m). Before the first coppice rotation was initiated at age 18 months in ORNL-35, seedlings averaged 8.1 m, 4.9 cm and 61% in height, diameter at breast height (DBH), and survival, respectively. Adjusted for growing season months, this growth was similar to that previously observed in study ORNL-16. ~ However, under the relatively warm and dry conditions that followed the December 1986 harvest, only 3.6% of the trees coppiced. Coppicing after the March 1987 harvest was also very poor at 3-3%. Previous coppicing on muck soils was successful in cooler, wetter winters, ~ and E. grandis typically coppices successfully in the winter on 'palmetto prairie'. 7 Response of five E. grandis progenies to planting density was inconsistent for tree size but consistent for survival through 18 months. At 20 000 trees ha-~, tree height was 8-67 m and survival was 37"3%. Progenies planted at 10000 trees ha -~ were 8.03 m tall with 51.0% survival. Survival at 5000 trees ha- ~ was 74"1%, with an average height of 8.45 m. After harvest, coppice survival ranged from 6"0% at 20 000 trees ha-~ to 16.0% at 5000 trees ha-J Severe freezes from 1982 to 1985 facilitated the development of frost-resilient E. grandis. Four of the 55 clones in study ORNL-37 had
Eucalyptus grandis and slash pine as biomass energy crops
159
freeze-resilience and other merits for operational use 2 and by age 2.8 years regrew vigorously from the freezes. The excellent tree size (11.6-13.8 m in height, 11.7-12.8 cm in DBH) and survival (96.9-98.4%) of three of these clones in block plots after 5.3 years establish the current standard for E. grandis growth on the extensive 'palmetto prairie' sites in southern Florida under the most severe freezes. Through 15 months, differences among the three planting sites in ORNL-40 demonstrated the necessity for adequate site preparation/ cultural amendment on 'palmetto prairie'. The site with very thorough disking, high beds and recent application of phosphorus (P) averaged 94% survival and 3'0 m height, with individual clones as tall as 7.3 m. The site which had low beds had 84% survival, but the trees were only 1.4 m in height due to flooding caused, by periodic heavy rainfall. The third site, which had beds prepared in 1982, fertilizer applied in 1982 and 1984, and some herbaceous vegetation, had only 23% survival and trees averaging 0"8 m tall. The top three clones from ORNL-37 displayed good growth and survival in ORNL-40. Across the sites, the three clones averaged 3.2 m in height and 82% survival after 15 months. The 232 new cloning candidates had a mean height of 2-5 m and survival of 55%, and certain clones appear promising. Clonal propagation activities for ORNL-40 established the biological potential for rooted cutting production and for micropropagation. Rooted cutting production suggested a propagation period of as little as 160 days. Some 12 000 rooted cuttings were produced for a commercial planting in 1987, and more than 5000 cuttings were planted in ORNL40. Direct micropropagation 8 was successfully used by Hartman's Plants Inc. (Sebring, FL) for the commercial production of certain E. grandis clones. Because E. grandis clonal propagation may be more than twice as expensive as seedling propagation, seedling establishment was used in SRIC scenarios. Study ORNL-16 had calculated production costs as low as USS2.00 GJ -I at 10000 trees ha-t. j ORNL-35 estimated a somewhat lower level of production (Table 3) due to a later establishment date in the summer and poorer survival. However, the productivity of the best four progenies, whose annual yield exceeded the 20 Mg hareported for 2-7-year-old E. grandis planted at 6667 trees ha -t in Brazil, 9 highlights expectations for lower costs if better genotypes are developed. Break-even costs of several E. grandis systems on muck soil were under USS2.00 GJ -1 (Table 3), indicating some potential as an economic biomass source. ~ The actual cost was very sensitive to the
40-0
71"2
45.7
25.0
Muck/ORNL-35 four best progenies/ 10 000
Muck/ORNL- 16/ 10 000
Prairie/ORND37/ 10 000
49.1
20 000
Muck/ORNL-35 progeny/ 10 000
31-4
17-6
Mg ha t
10 000
Muck/ORNL-35 spacing/ 5 000
Site~study~density
Mg GJ
Mg GJ
Mg GJ
Mg GJ
Mg GJ Mg GJ Mg GJ
Cost basis
65"47 3"31
38-95 1"97
28-54 1'44
43.07 2-18
68"19 3"45 52.14 2-64 49-21 2-49
0
67'85 3"43
40"00 2"02
29"22 1"48
44.28 2.24
69"86 3"45 53"81 2.72 50"97 2"58
0.~
70"48 3"57
41"08 2"08
29"91 1"51
45.50 2.30
71"54 3-62 55-38 2-80 52-76 2-67
0.~
Discount rate (US$)
73"36 3"71
42"17 2"13
30"61 1"55
46.75 2.37
73-23 3-71 56"97 2"88 54-59 2"76
0.~
76"49 3-87
43'27 2"19
31"32 1"58
48.01 2.43
74-95 3"79 58"59 2"97 56'45 2"86
0"~
TABLE 3 Projected Dry Weight Production After 2 Years and Break-even Prices M g - t and GJ ~ for E. grandis as a Function of Site, Study, Density and Discount Rate
¢5
Eucalyptus grandis and slash pine as biomass energy crops
161
production function as well as the input parameters. Increasing planting density resulted in steadily decreasing per-unit production costs. Increasing the discount rate up to 8% caused the estimated present discounted costs to increase by approximately 16%. The net cost on 'palmetto prairie' sites was significantly higher than most muck scenarios. With yields expected to be about half those on muck soils, the discounted cost of production increased by approximately 170%. Cost competitive systems on 'palmetto prairie' will require better combinations of planting density, planting stock, and less intensive management. Harvest timing has a major impact on coppice productivity. Since coppicing can apparently only be expected during the winter months, the restriction of harvest operations to certain periods of the year requires stockpiling of the harvested biomass for later use. Whether the trees should be stored on the site, or chipped and stored in piles near the conversion facility, requires further study. The optimal planting density and rotation length may be affected by the method chosen to stockpile the fiber. The simulation analysis failed to indicate whether coppice productivity affects the optimal rotation. The rotation for either planting density was unaffected by the discount rates examined. Results indicate a discounted average annual cost Mg-~ of between USS20 and USS50. Assuming 19.2 GJ Mg -~, the unprocessed cost ranged from USS1.04 to USS2.60 GJ -I.
Slash pine After 8 years, slash pine responses to fertilization at the time of planting (Table 4) confirm earlier indications of significant increments on typical or poor sites and less response on good sites. In ORNL-10 (a poor site), all fertilizers except 50/50 increased tree size, especially the high level of sewage sludge. Few differences due to fertilizer level were detected for individual tree traits in ORNL-11 (good site). Planting density influenced tree size and survival through 8 years (Table 4). As had been observed by age 5 years, "~ tree height and DBH decreased with increasing density, and the greater competition at the higher densities reduced survival. These trends were supported by 10 000 trees ha- ~block plots in the fertilizer and progeny tests. Slash pine progenies in ORNL-10 and ORNL-11 were unexpectedly competition-tolerant. Compared to unselected slash pine progenies, ~ the progenies in ORNL-10 and ORNL-11 had over 30% higher survival at age 8 years. Nevertheless, progeny variation was still evident, suggesting that use of the better progenies can further increase productivity.
6-3b* 5"8b -5-6b 5-1a 4-8a
5-6c* 4.7c 6"5b 6-Obc 6'5b 7'8a
Ht (m)
6'7d 5'7c 5'5c 4"9bc 4-2b 3"2a
5'3bc 4.7c 5-6b 5"5b 5"7b 7-Oa
DBtt (cm)
ORNL-IO Ht (m)
8.4a 7.9a 9'1 b -8"5a --
95'1b 96.2b 94.2b 93-6b 94-3b 89"4a
8"4b 8-4b 8-4b 7-3a 7-3a 7-0a
Planting density tests
92.3a 87.7a 93"0a 92'7a 89"7a 87'7a
~ertilizer tests
Surv. (%)
Study
9-3f 8-0e 7.3d 6'5c 5'3b 4'5a
7.4a 7"5a 9"Ob -7"5a --
DBH (cm)
ORNL-11
93'0b 93"9b 91'2b 95'9b 91'4b 84.9a
93-0b 93-4b 84"8a -89"3ab --
Surv. (%)
*Means within a trait/test not sharing the same letter are significantly different at the 5% level. "Elemental units in kg ha ~; S = sewage sludge. ~Average of five progenies in block plots.
4 800 8 400 10000 ~' 14 600 25 100 43 300
Trees ha ~
0 50/50 150/50 175/135S 200/100 350/265S
Nitrogen/pho~whorus"
Treatment
40"32 51"41 53-71 58-16 61-92
102'6 116'0 139'7 188'6
USSMg i
71'3
M g h a -t
SR1C estimates
2"61 2"71 2"95 3"14
2"45
USSGJ-I
TABLE 4 Mean Height, DBH and Survival for 8-Year-Old Slash Pine in Fertilizer Tests and Planting Density Tests and Estimated SRIC Production and Average Costs in Response to Planting Density
e~
to
Eucalyptus grandis and slash pine as biomass energy crops
163
Slash pine's maximum productivity may be approximated by yields achieved through 5 years under the intensive culture practiced with superior progenies planted at 1518 trees ha-~ in 0-85. Tree height was increased to 5"9 m by complete fertilization, to 5.6 m by total vegetation control, and to 6.4 m by the two combined in comparison to a height of 3"8 m with conventional culture of bedding alone. Tree heights similar to the maximum culture were not achieved until ages 8 and 6 years in ORNL-10 and ORNL-11, respectively. While such increases may not occur at higher planting densities, the four- to seven-fold increases in biomass relative to conventional culture (up to 15.2 versus 2.2 Mg ha- ~) suggest the biological merit of very intensive culture. Slash pine is normally grown at densities between 1000 and 2000 trees ha-~ on 20- to 25-year rotations, and greatly increased initial planting densities were expected to slow the net biomass production function by age 8 years. However, the model developed from ORNL-10 and ORNL- 11 (Table 4) indicates that net growth is still expanding on all plots at all planting densities. Mortality has not yet significantly reduced stocking, and average tree data do not indicate that the productive capacities of the sites have been reached in 8 years. However, mean annual weight production is declining at the upper stocking levels (i.e. over 14 600 trees ha- ~). The average costs Mg-~ and GJ-~ for slash pine are encouraging (Table 4). At 4800 trees ha-~, average cost Mg-~ dropped from over USS79.16 to under USS40.32 by increasing the rotation from 4 to 8 years. The average cost G J - i also dropped from USS4.02 to USS2.45 with the same increase in rotation. If the initial planting rates are increased to 10 000 trees ha-~, average costs are increased for every rotation. Cost estimates are more sensitive to planting densities than to discount factor. Optimal rotation length for slash pine SRIC is affected by both the alternative rate of return for capital used to evaluate the investment and the initial planting density. At low alternative rates of capital costs, less dense plantations on a longer rotation (at least 8 years) provide less costly alternatives. If higher real rates of return are required to attract investment capital, higher density plantations with shorter rotations will provide the least cost alternative.
CONCLUSIONS The suitability of Eucalyptus grandis and slash pine for SRIC is influenced by various cultural amendment, planting density and genetic
164
D. L. Rockwood, D. R. Dippon
options. Growth of the best E. grandis progenies on muck soil suggested its maximum productivity to be approximately 35 dry Mg ha-l year-J. Coppicing success of E. grandis on muck soils is influenced by factors in addition to month of harvest, suggesting that coppice regeneration cannot presently be assured on these sites. Testing of E. grandis clones for frost-resilience and vigor can identify clones with improved productivity and reduced risks of freeze losses. If the risk of coppicing irregularities is reduced, economic analyses suggest that E. grandis may be profitably grown in SRIC. The economics of SRIC systems appear to favor denser stocking with a 6-year seedling/ coppice/coppice rotation. The optimal planting density is sensitive to the discount factor assumed while the optimal coppice/rotation is not. Break-even costs GJ-~ range from just under USS2.00 on muck soils to USS4.00 on sandy soils. The estimated cost Mg-~ is more sensitive to growth and rotation length assumptions than to modifications in the assumed production functions ( _ 20%) or real discount rates (0-8%). Eight-year growth of slash pine confirms that it responds well to amendments on typical sites and is unexpectedly tolerant of high planting densities. Site amendment combined with vegetation control increased yield more than seven times over conventional culture through 5 years, while optimum levels of each factor alone increased productivity ha- ~some four times. For slash pine SRIC, optimal planting density as well as rotation length is affected by the real rate of return. Based on data through 8 years, it appears that slash pine SRIC could produce biomass at a competitive cost, but better production functions and more detailed analysis are needed.
ACKNOWLEDGMENTS Journal series paper No. 9503 of the Florida Agricultural Experiment Station. Results reported are from Subcontract No. 19X-09050C with Oak Ridge National Laboratory under Martin Marietta Energy Systems, Inc., Contract DE-AC05-840R21400 with the US Department of Energy. This paper also reports research performed under a project that contributed to a cooperative program between the Institute of Food and Agricultural Sciences of the University of Florida and the Gas Research Institute entitled 'Methane from Biomass and Waste'. The assistance of ~ the following cooperators is gratefully acknowledged: Everglades Agricultural Research and Education Center, University of FloridaIFAS, Belle Glade, FL; ITT-Rayonier, Inc., Fernandina Beach, FL; Con-
Eucalyptus grandis and slash pine as biornass energy crops
165
tainer Corporation of America, Fernandina Beach, FL; Lykes Brothers, Inc., Palmdale, FL; Herren Nursery, Florida Division of Forestry, Lake Placid, FL; Hartman's Plants Inc., Sebring, FL.
REFERENCES 1. Rockwood, D. L., Comer, C. W., Conde, L. F., Dippon, D. R., Huffman, J. B., Riekerk, H. & Wang, S., Final report of energy and chemicals from woody species in Florida. ORNL/Sub/81-9050/1, University of Florida, Gainesville, FL, 1983,205pp. 2. Rockwood, D. L., Dippon, D. R. & Lesney, M. S., Woody species for biomass production in Florida: Final report 1983-88. ORNL/Sub/819050/7, University of Florida, Gainesville, FL, 1988, 153pp. 3. Meskimen, G. E, Rockwood, D. L. & Reddy, K. V., Development of Eucalyptus clones for a summer rainfall environment with periodic severe frosts. New Forests, 3 (1987) 197-205. 4. Das, S., Perlak, R. D., Brown, W. F. & Kroll, P., BIOCUT: A microcomputer based econometric model for wood energy plantations. Model description and users guide. ORNL/TM-9576, Oak Ridge National Laboratory, Oak Ridge, TN, 1985, 80pp. 5. Swindel, B. F., Neary, D. G., Comerford, N. B., Rockwood, D. L. & Blakeslee, G. M., Fertilization and competition control accelerate early southern pine growth on flatwoods. S. J. Appl. For., 12 (1988) 116-21. 6. Campbell, M. S. F., Biomass yields of young, heavily stocked slash pine stands in north Florida. MS thesis, University of Florida, Gainesville, FL, 1983, 56pp. 7. Webley, O. J., Geary, T. F., Rockwood, D. L., Comer, C. W. & Meskimen, G. F., Seasonal coppicing variation for three eucalypts in southern Florida. Aust. For. Res., 16 (1986) 281-90. 8. Warrag, E. E. I., Ortega, V., Lesney, M. S. & Rockwood, D. L., Recent progress in tissue culture methods for Eucalyptus species and implications for genetic improvement. In Proc. 9th S. For. Biota. Workshop, 8-11 June 1987, Biloxi, MI. Mississippi State University, Starkville, MI, 1988, pp. 71-80. 9. Suiter, W., de Rezende, G. C. & Mendes, C. J., Production of short rotation Eucalyptus for energy sources. Sociedade de Investigacoes Florestals. Boletin Technico, 3 (1980) 9pp. 10. Reighard, G. L., Rockwood, D. L. & Comer, C. W., Genetic and cultural factors affecting growth performance of slash pine. In Proc. 18th S. For. Tree Imp. Conf., 21-33 May 1985, Long Beach, MI, 1985. The National Technical Information Service, Springfield, VI, pp. 100-6. 11. Rockwood, D. L. & Frampton, L. J., Genetic variation in sand pine and slash pine for energy production in silvicultural biomass plantations. In Proc. 15th S. For. Tree Imp. Conf., 19-21 June, Starkville, MI, 1979. Eastern l'ree Seed Laboratory, Macon, GA, 1979, pp. 156-65.
Biological and Economic Potentials of Eucalyptus grandis and Slash Pine as Biomass Energy Crops D. L. Rockwood & D. R. Dippon Department of Forestry, University of Florida, Gainesville, Florida 32611-0303, USA
ABSTRACT Various cultural factors influence the biological and economic potentials of Eucalyptus grandis and slash pine as biomass energy crops for southern and northern Florida, respectively. On muck soil, superior E. grandis progenies may produce up to 70 dry Mg ha-I in 24 months. However, coppicing success on muck soil has been inconsistent. Clones superior in frost-resilience and vigor and propagated as rooted cuttings have increased productivity potential on sandy soils. Break-even costs GJ- 1 range from just under US$2 for E. grandis short-rotation intensive culture (SRIC) on muck soils (10000 trees ha-i with a 6-year rotation, i.e. seedling~coppice~coppice cycles of 2 years each) to USS4.00 GJ i on sandy soils. Planting density, but not coppice rotation, is sensitive to the discount factor. Through 8 years, slash pine yields responded well to soil amendments on typical sites and to high planting densities. Fertilization and vegetation control increased productivity some seven times over conventional culture through 5 years. For slash pine SRIC, higher discount rates increased initial stocking levels and shortened rotations. Break-even costs for slash pine are within the range of values estimated for E. grandis. Key words: Eucalyptus grandis, Pinus elliottii, biomass, energy crops, short-rotation intensive culture.
INTRODUCTION This paper compiles past and present data on biomass production of Eucalyptus grandis Hill ex Maid. and slash pine (Pinus elliottii var. elliottii Engelm.) in Florida to update estimates of their economic potentials. Previous short-rotation intensive culture (SRIC) research suggested that the two species were suitable biomass energy crops for Florida. ~ Recent research has further defined their biological responses to cultural a m e n d m e n t , planting density and genetic options. 155 Biomass 0144-4565/89/S03.50 - © 1989 Elsevier Science Publishers Ltd, England. Printed in Great Britain
D. l.. Rockwood, D. R. Dippon
156
MATERIALS A N D M E T H O D S
E. grandis To extend results from earlier E. grandis studies I (ORNL-16 on muck soil and ORNL-7 on sandy 'palmetto prairie' soil), studies ORNL-35 and ORNL-362 were established on adjacent muck and sandy soils, respectively, with additional progeny and planting density components (Table 1) using randomized complete block designs with three replications. In ORNL-35, coppicing following harvests in December 1986 and March 1987 was evaluated. Initial field evaluation of rooted cuttings of cloning candidates for frost-resilience and vigor on 'palmetto prairie' was conducted in study O R N L - 3 7 ) Three top clones in 16-tree square blocks replicated four times were remeasured at 5"3 years to estimate the maximum productivity that could be expected under extreme freezes. Additional cloning candidates were outplanted in ORNL-40 (Table 1) to test new clones in comparison to the top three from ORNL-37 and to evaluate site/site preparation effects. SRIC E. grandis systems tested densities ranging between 1600 and 20 000 trees ha-~ on both muck and sandy soils. Three harvests cornTABLE 1 Description of Eucal)ptus grandis and Slash Pine Studies Contributing to Updated Biological and Economic Assessments E. grandis study
(bmponent
ORNL-35 Location Latitude (N) Longitude(W) Ahitude (m) Date planted
Slash pine study
ORNL-36 ORNL-40 ORNL-IO ORNL-II
Belle Glade
LaBellc
Trenton
Gainesville
26°41' 80°39 ' 4 7/1985
26°46 ' 81°26 ' 10 7/1986
26°46 ' 81°26 ' 10 8/1987
29°46 ' 82013 , 29 1/1980
29o47 ' 82°47 ' 26 1/1980
29o46 ' 85°52 ' 28 1/1983
Muck
Sand
Sand
Sand
Sand
Sand
0 3 27 0 2
1 3 27 0 2
1 1 33 235 2
5 6 33 0 2
3 6 25 0 2
Soil
Treatments:" Fertilizers Planting densities Progenies Clone s Reference
"Number of treatment levels.
Palmdale Gainesville
0-85
1 1 4 0 5
Eucalyptus grandis and slash pine as biomass energy crops
157
prised each complete planting to replanting cycle. SRIC on muck soils consisted of 2-year seedling growth before the first harvest with two coppice harvests following at 2-year intervals, resulting in a 2/2/2 system with seedlings planted only once every 6 years. SRIC on 'palmetto prairie' involved a 3/3/3 system. Economic analyses assumed that coppice growth would be 20% greater than seedling growth. Yield data for economic analysis were primarily taken from ORNL-35. Derived growth functions updated preliminary production functions developed from ORNL-16. Coppicing production functions were extrapolated from ORNL-7, ~ ORNL-16, ~ and ORNL-35 data. Pertinent data were also derived from studies ORNL-36 and ORNL-37. SRIC break-even costs Mg-~ and GJ-L assumed that 1000 ha were placed under management for 35 years. The cost of such an operation was assumed to be divided into several components: regeneration activities at the start of each plantation and at coppices, initial and annual costs incurred, and the harvest/transportation cost incurred at the completion of each cycle. Tax effects were not considered. Costs were assumed to increase at the overall inflation rate. The costs for seedlings, planting, harvesting, processing and transportation (Table 2) were based TABLE 2 Cost Assumptions for E. grandis and Slash Pine SRiC Scenarios Input
Lease (USS ha-I) Infrastructure (USS ha i) Site preparation (USS ha -L ) Management expenses (USS ha +~) Fertilization (USS ha -~ ) Harvesting and chipping (USS Mg- ~) Transportation (USS Mg -~ ) Cost of seedlings (USS tree ~) Planting cost (USS tree ~)
E. grandis
Slash pine
247 5O 123 30 93
75 50 177 30 100
24 4
24 4
0' 15 O'O55
0"07 0"05
on data from ORNL-35 and ORNL-36. The annual rental price for land in southern Florida varied from USS247 ha -~ for muck soil to USS128.50 for sandy soil. These data were input values for the program BIOCUT ~ to derive the break-even analysis for the SRIC scenarios examined. The objective was to determine which factors had the greatest impact on present costs of woody biomass.
158
D. L. Rockwood, D. R. Dippon
Slash pine Growth measurements were collected periodically from studies ORNL10, ORNL-11, and 0-855 (Table 1 ). Data for economic analyses of slash pine were derived from studies ORNL- 10 and ORNL- 11 planting density tests. Equations from Campbell 6 were utilized to convert stand parameters to dry Mg ha- 1. The SRIC scenario assumed that site preparation included root rake, roller chop, burn and bedding at the start of each new rotation. After fertilization followed by planting, annual maintenance and monitoring were the only scheduled activities until stand harvest. Computations for break-even costs Mg-~ and G J- l were based on assumptions similar to those for E. grandis (Table 2). The northern Florida flatwoods had a rental price of USS75.00 h a - l
RESULTS A N D DISCUSSION
E. grandis The performance of 27 progenies on muck soil in ORNL-35 and 'palmetto prairie' in ORNL-36 brackets growth rates for E. grandis seedlings in southern Florida. Through 12 months, seedlings in ORNL35 were much taller than those in ORNL-36 (5.4 m versus 1.6 m). Before the first coppice rotation was initiated at age 18 months in ORNL-35, seedlings averaged 8.1 m, 4.9 cm and 61% in height, diameter at breast height (DBH), and survival, respectively. Adjusted for growing season months, this growth was similar to that previously observed in study ORNL-16. ~ However, under the relatively warm and dry conditions that followed the December 1986 harvest, only 3.6% of the trees coppiced. Coppicing after the March 1987 harvest was also very poor at 3-3%. Previous coppicing on muck soils was successful in cooler, wetter winters, ~ and E. grandis typically coppices successfully in the winter on 'palmetto prairie'. 7 Response of five E. grandis progenies to planting density was inconsistent for tree size but consistent for survival through 18 months. At 20 000 trees ha-~, tree height was 8-67 m and survival was 37"3%. Progenies planted at 10000 trees ha -~ were 8.03 m tall with 51.0% survival. Survival at 5000 trees ha- ~ was 74"1%, with an average height of 8.45 m. After harvest, coppice survival ranged from 6"0% at 20 000 trees ha-~ to 16.0% at 5000 trees ha-J Severe freezes from 1982 to 1985 facilitated the development of frost-resilient E. grandis. Four of the 55 clones in study ORNL-37 had
Eucalyptus grandis and slash pine as biomass energy crops
159
freeze-resilience and other merits for operational use 2 and by age 2.8 years regrew vigorously from the freezes. The excellent tree size (11.6-13.8 m in height, 11.7-12.8 cm in DBH) and survival (96.9-98.4%) of three of these clones in block plots after 5.3 years establish the current standard for E. grandis growth on the extensive 'palmetto prairie' sites in southern Florida under the most severe freezes. Through 15 months, differences among the three planting sites in ORNL-40 demonstrated the necessity for adequate site preparation/ cultural amendment on 'palmetto prairie'. The site with very thorough disking, high beds and recent application of phosphorus (P) averaged 94% survival and 3'0 m height, with individual clones as tall as 7.3 m. The site which had low beds had 84% survival, but the trees were only 1.4 m in height due to flooding caused, by periodic heavy rainfall. The third site, which had beds prepared in 1982, fertilizer applied in 1982 and 1984, and some herbaceous vegetation, had only 23% survival and trees averaging 0"8 m tall. The top three clones from ORNL-37 displayed good growth and survival in ORNL-40. Across the sites, the three clones averaged 3.2 m in height and 82% survival after 15 months. The 232 new cloning candidates had a mean height of 2-5 m and survival of 55%, and certain clones appear promising. Clonal propagation activities for ORNL-40 established the biological potential for rooted cutting production and for micropropagation. Rooted cutting production suggested a propagation period of as little as 160 days. Some 12 000 rooted cuttings were produced for a commercial planting in 1987, and more than 5000 cuttings were planted in ORNL40. Direct micropropagation 8 was successfully used by Hartman's Plants Inc. (Sebring, FL) for the commercial production of certain E. grandis clones. Because E. grandis clonal propagation may be more than twice as expensive as seedling propagation, seedling establishment was used in SRIC scenarios. Study ORNL-16 had calculated production costs as low as USS2.00 GJ -I at 10000 trees ha-t. j ORNL-35 estimated a somewhat lower level of production (Table 3) due to a later establishment date in the summer and poorer survival. However, the productivity of the best four progenies, whose annual yield exceeded the 20 Mg hareported for 2-7-year-old E. grandis planted at 6667 trees ha -t in Brazil, 9 highlights expectations for lower costs if better genotypes are developed. Break-even costs of several E. grandis systems on muck soil were under USS2.00 GJ -1 (Table 3), indicating some potential as an economic biomass source. ~ The actual cost was very sensitive to the
40-0
71"2
45.7
25.0
Muck/ORNL-35 four best progenies/ 10 000
Muck/ORNL- 16/ 10 000
Prairie/ORND37/ 10 000
49.1
20 000
Muck/ORNL-35 progeny/ 10 000
31-4
17-6
Mg ha t
10 000
Muck/ORNL-35 spacing/ 5 000
Site~study~density
Mg GJ
Mg GJ
Mg GJ
Mg GJ
Mg GJ Mg GJ Mg GJ
Cost basis
65"47 3"31
38-95 1"97
28-54 1'44
43.07 2-18
68"19 3"45 52.14 2-64 49-21 2-49
0
67'85 3"43
40"00 2"02
29"22 1"48
44.28 2.24
69"86 3"45 53"81 2.72 50"97 2"58
0.~
70"48 3"57
41"08 2"08
29"91 1"51
45.50 2.30
71"54 3-62 55-38 2-80 52-76 2-67
0.~
Discount rate (US$)
73"36 3"71
42"17 2"13
30"61 1"55
46.75 2.37
73-23 3-71 56"97 2"88 54-59 2"76
0.~
76"49 3-87
43'27 2"19
31"32 1"58
48.01 2.43
74-95 3"79 58"59 2"97 56'45 2"86
0"~
TABLE 3 Projected Dry Weight Production After 2 Years and Break-even Prices M g - t and GJ ~ for E. grandis as a Function of Site, Study, Density and Discount Rate
¢5
Eucalyptus grandis and slash pine as biomass energy crops
161
production function as well as the input parameters. Increasing planting density resulted in steadily decreasing per-unit production costs. Increasing the discount rate up to 8% caused the estimated present discounted costs to increase by approximately 16%. The net cost on 'palmetto prairie' sites was significantly higher than most muck scenarios. With yields expected to be about half those on muck soils, the discounted cost of production increased by approximately 170%. Cost competitive systems on 'palmetto prairie' will require better combinations of planting density, planting stock, and less intensive management. Harvest timing has a major impact on coppice productivity. Since coppicing can apparently only be expected during the winter months, the restriction of harvest operations to certain periods of the year requires stockpiling of the harvested biomass for later use. Whether the trees should be stored on the site, or chipped and stored in piles near the conversion facility, requires further study. The optimal planting density and rotation length may be affected by the method chosen to stockpile the fiber. The simulation analysis failed to indicate whether coppice productivity affects the optimal rotation. The rotation for either planting density was unaffected by the discount rates examined. Results indicate a discounted average annual cost Mg-~ of between USS20 and USS50. Assuming 19.2 GJ Mg -~, the unprocessed cost ranged from USS1.04 to USS2.60 GJ -I.
Slash pine After 8 years, slash pine responses to fertilization at the time of planting (Table 4) confirm earlier indications of significant increments on typical or poor sites and less response on good sites. In ORNL-10 (a poor site), all fertilizers except 50/50 increased tree size, especially the high level of sewage sludge. Few differences due to fertilizer level were detected for individual tree traits in ORNL-11 (good site). Planting density influenced tree size and survival through 8 years (Table 4). As had been observed by age 5 years, "~ tree height and DBH decreased with increasing density, and the greater competition at the higher densities reduced survival. These trends were supported by 10 000 trees ha- ~block plots in the fertilizer and progeny tests. Slash pine progenies in ORNL-10 and ORNL-11 were unexpectedly competition-tolerant. Compared to unselected slash pine progenies, ~ the progenies in ORNL-10 and ORNL-11 had over 30% higher survival at age 8 years. Nevertheless, progeny variation was still evident, suggesting that use of the better progenies can further increase productivity.
6-3b* 5"8b -5-6b 5-1a 4-8a
5-6c* 4.7c 6"5b 6-Obc 6'5b 7'8a
Ht (m)
6'7d 5'7c 5'5c 4"9bc 4-2b 3"2a
5'3bc 4.7c 5-6b 5"5b 5"7b 7-Oa
DBtt (cm)
ORNL-IO Ht (m)
8.4a 7.9a 9'1 b -8"5a --
95'1b 96.2b 94.2b 93-6b 94-3b 89"4a
8"4b 8-4b 8-4b 7-3a 7-3a 7-0a
Planting density tests
92.3a 87.7a 93"0a 92'7a 89"7a 87'7a
~ertilizer tests
Surv. (%)
Study
9-3f 8-0e 7.3d 6'5c 5'3b 4'5a
7.4a 7"5a 9"Ob -7"5a --
DBH (cm)
ORNL-11
93'0b 93"9b 91'2b 95'9b 91'4b 84.9a
93-0b 93-4b 84"8a -89"3ab --
Surv. (%)
*Means within a trait/test not sharing the same letter are significantly different at the 5% level. "Elemental units in kg ha ~; S = sewage sludge. ~Average of five progenies in block plots.
4 800 8 400 10000 ~' 14 600 25 100 43 300
Trees ha ~
0 50/50 150/50 175/135S 200/100 350/265S
Nitrogen/pho~whorus"
Treatment
40"32 51"41 53-71 58-16 61-92
102'6 116'0 139'7 188'6
USSMg i
71'3
M g h a -t
SR1C estimates
2"61 2"71 2"95 3"14
2"45
USSGJ-I
TABLE 4 Mean Height, DBH and Survival for 8-Year-Old Slash Pine in Fertilizer Tests and Planting Density Tests and Estimated SRIC Production and Average Costs in Response to Planting Density
e~
to
Eucalyptus grandis and slash pine as biomass energy crops
163
Slash pine's maximum productivity may be approximated by yields achieved through 5 years under the intensive culture practiced with superior progenies planted at 1518 trees ha-~ in 0-85. Tree height was increased to 5"9 m by complete fertilization, to 5.6 m by total vegetation control, and to 6.4 m by the two combined in comparison to a height of 3"8 m with conventional culture of bedding alone. Tree heights similar to the maximum culture were not achieved until ages 8 and 6 years in ORNL-10 and ORNL-11, respectively. While such increases may not occur at higher planting densities, the four- to seven-fold increases in biomass relative to conventional culture (up to 15.2 versus 2.2 Mg ha- ~) suggest the biological merit of very intensive culture. Slash pine is normally grown at densities between 1000 and 2000 trees ha-~ on 20- to 25-year rotations, and greatly increased initial planting densities were expected to slow the net biomass production function by age 8 years. However, the model developed from ORNL-10 and ORNL- 11 (Table 4) indicates that net growth is still expanding on all plots at all planting densities. Mortality has not yet significantly reduced stocking, and average tree data do not indicate that the productive capacities of the sites have been reached in 8 years. However, mean annual weight production is declining at the upper stocking levels (i.e. over 14 600 trees ha- ~). The average costs Mg-~ and GJ-~ for slash pine are encouraging (Table 4). At 4800 trees ha-~, average cost Mg-~ dropped from over USS79.16 to under USS40.32 by increasing the rotation from 4 to 8 years. The average cost G J - i also dropped from USS4.02 to USS2.45 with the same increase in rotation. If the initial planting rates are increased to 10 000 trees ha-~, average costs are increased for every rotation. Cost estimates are more sensitive to planting densities than to discount factor. Optimal rotation length for slash pine SRIC is affected by both the alternative rate of return for capital used to evaluate the investment and the initial planting density. At low alternative rates of capital costs, less dense plantations on a longer rotation (at least 8 years) provide less costly alternatives. If higher real rates of return are required to attract investment capital, higher density plantations with shorter rotations will provide the least cost alternative.
CONCLUSIONS The suitability of Eucalyptus grandis and slash pine for SRIC is influenced by various cultural amendment, planting density and genetic
164
D. L. Rockwood, D. R. Dippon
options. Growth of the best E. grandis progenies on muck soil suggested its maximum productivity to be approximately 35 dry Mg ha-l year-J. Coppicing success of E. grandis on muck soils is influenced by factors in addition to month of harvest, suggesting that coppice regeneration cannot presently be assured on these sites. Testing of E. grandis clones for frost-resilience and vigor can identify clones with improved productivity and reduced risks of freeze losses. If the risk of coppicing irregularities is reduced, economic analyses suggest that E. grandis may be profitably grown in SRIC. The economics of SRIC systems appear to favor denser stocking with a 6-year seedling/ coppice/coppice rotation. The optimal planting density is sensitive to the discount factor assumed while the optimal coppice/rotation is not. Break-even costs GJ-~ range from just under USS2.00 on muck soils to USS4.00 on sandy soils. The estimated cost Mg-~ is more sensitive to growth and rotation length assumptions than to modifications in the assumed production functions ( _ 20%) or real discount rates (0-8%). Eight-year growth of slash pine confirms that it responds well to amendments on typical sites and is unexpectedly tolerant of high planting densities. Site amendment combined with vegetation control increased yield more than seven times over conventional culture through 5 years, while optimum levels of each factor alone increased productivity ha- ~some four times. For slash pine SRIC, optimal planting density as well as rotation length is affected by the real rate of return. Based on data through 8 years, it appears that slash pine SRIC could produce biomass at a competitive cost, but better production functions and more detailed analysis are needed.
ACKNOWLEDGMENTS Journal series paper No. 9503 of the Florida Agricultural Experiment Station. Results reported are from Subcontract No. 19X-09050C with Oak Ridge National Laboratory under Martin Marietta Energy Systems, Inc., Contract DE-AC05-840R21400 with the US Department of Energy. This paper also reports research performed under a project that contributed to a cooperative program between the Institute of Food and Agricultural Sciences of the University of Florida and the Gas Research Institute entitled 'Methane from Biomass and Waste'. The assistance of ~ the following cooperators is gratefully acknowledged: Everglades Agricultural Research and Education Center, University of FloridaIFAS, Belle Glade, FL; ITT-Rayonier, Inc., Fernandina Beach, FL; Con-
Eucalyptus grandis and slash pine as biornass energy crops
165
tainer Corporation of America, Fernandina Beach, FL; Lykes Brothers, Inc., Palmdale, FL; Herren Nursery, Florida Division of Forestry, Lake Placid, FL; Hartman's Plants Inc., Sebring, FL.
REFERENCES 1. Rockwood, D. L., Comer, C. W., Conde, L. F., Dippon, D. R., Huffman, J. B., Riekerk, H. & Wang, S., Final report of energy and chemicals from woody species in Florida. ORNL/Sub/81-9050/1, University of Florida, Gainesville, FL, 1983,205pp. 2. Rockwood, D. L., Dippon, D. R. & Lesney, M. S., Woody species for biomass production in Florida: Final report 1983-88. ORNL/Sub/819050/7, University of Florida, Gainesville, FL, 1988, 153pp. 3. Meskimen, G. E, Rockwood, D. L. & Reddy, K. V., Development of Eucalyptus clones for a summer rainfall environment with periodic severe frosts. New Forests, 3 (1987) 197-205. 4. Das, S., Perlak, R. D., Brown, W. F. & Kroll, P., BIOCUT: A microcomputer based econometric model for wood energy plantations. Model description and users guide. ORNL/TM-9576, Oak Ridge National Laboratory, Oak Ridge, TN, 1985, 80pp. 5. Swindel, B. F., Neary, D. G., Comerford, N. B., Rockwood, D. L. & Blakeslee, G. M., Fertilization and competition control accelerate early southern pine growth on flatwoods. S. J. Appl. For., 12 (1988) 116-21. 6. Campbell, M. S. F., Biomass yields of young, heavily stocked slash pine stands in north Florida. MS thesis, University of Florida, Gainesville, FL, 1983, 56pp. 7. Webley, O. J., Geary, T. F., Rockwood, D. L., Comer, C. W. & Meskimen, G. F., Seasonal coppicing variation for three eucalypts in southern Florida. Aust. For. Res., 16 (1986) 281-90. 8. Warrag, E. E. I., Ortega, V., Lesney, M. S. & Rockwood, D. L., Recent progress in tissue culture methods for Eucalyptus species and implications for genetic improvement. In Proc. 9th S. For. Biota. Workshop, 8-11 June 1987, Biloxi, MI. Mississippi State University, Starkville, MI, 1988, pp. 71-80. 9. Suiter, W., de Rezende, G. C. & Mendes, C. J., Production of short rotation Eucalyptus for energy sources. Sociedade de Investigacoes Florestals. Boletin Technico, 3 (1980) 9pp. 10. Reighard, G. L., Rockwood, D. L. & Comer, C. W., Genetic and cultural factors affecting growth performance of slash pine. In Proc. 18th S. For. Tree Imp. Conf., 21-33 May 1985, Long Beach, MI, 1985. The National Technical Information Service, Springfield, VI, pp. 100-6. 11. Rockwood, D. L. & Frampton, L. J., Genetic variation in sand pine and slash pine for energy production in silvicultural biomass plantations. In Proc. 15th S. For. Tree Imp. Conf., 19-21 June, Starkville, MI, 1979. Eastern l'ree Seed Laboratory, Macon, GA, 1979, pp. 156-65.