Calculation of the Rate of Clearcutting in Plummer’s Hollow, 1805-1876

In order to calculate the rate that the iron company clearcut its properties in the hollow and the rest of its lands in the 19th century for charcoal production, it is necessary to know, or estimate, certain pieces of information. The amount of forest clearcut each year would depend on the rate at which wood grows in a Pennsylvania forest. The acreage also has to be based on the amount of charcoal that could be produced per cord of wood. The amount of charcoal needed for the forges depended on two factors: the efficiency of the forging of iron–how much charcoal was needed per ton of iron produced–and of course the amount of iron produced by the forges each year. Since the latter figures are easiest to determine, we will start from the amount of iron produced per year and work our way backwards to the probable acreage cut annually for wood to produce the charcoal.

First, the amount of iron produced each year. Africa indicates that, according to an estimate made in February 1826, the forges produced an estimated 500 tons of bar iron per year.[i] The census of 1820 did not report the amount of iron produced, but it did report that the forges consumed 600 tons of pig iron, which would have resulted in about 500 tons of bar iron.[ii] An 1832 report prepared by the owners of the company indicated that during the previous three years, the forges had produced an average of over 550 tons of iron–350 tons per year of blooms and 200 tons of bar iron, along with rods, spikes and nails.[iii] If the additional rods, spikes and nails can be estimated at 50 tons, then the figure for 1832 would have been 600 tons produced per year. An 1850 report indicated that the annual production of iron had jumped dramatically to 1543 tons as of 1849.[iv]

The second variable to enter into the calculation is the amount of charcoal needed at the Tyrone Forges to produce a ton of iron. Fortunately the 1832 report by the new owners, Lyon, Foster and Co., indicates that the forges used 225 bushels of charcoal per ton of iron produced.[v] This figure is within the range of other estimates of charcoal needs for forges. An 1828 estimate indicated that 175 bushels of charcoal were needed to produce one ton of bar iron[vi] while a later estimate, presumably made in the 1870s, was that 125 bushels of charcoal was needed per ton.[vii] Overman, in his lengthy discussion of 19th century techniques of iron making, indicates that the efficiency of the iron forges improved over time, and that the amount of charcoal consumed could vary considerably from forge to forge, depending of the quality of the iron ore. If the ore quality is good, only 150 bushels of charcoal would produce a ton, while poorer ore could consume 200 to 300 bushels per ton.[viii] Thus, the figure of 225 bushels per ton provided by the owners in 1832 seems reasonable, though improved technology may have diminished the figure somewhat over the following decades, perhaps to 200 bushels by 1850.

The third variable is the amount of wood needed to produce a bushel of charcoal. While there are unfortunately no figures available from the Tyrone Forges, other estimates from Pennsylvania forge and furnace operations provide the needed information. Based on the extensive records preserved at Hopewell Furnace in Berks County, Walker estimates that the good collier got 35 to 40 bushels of charcoal per cord of wood.[ix] Thomas Cooper, a writer on iron furnaces in 1813, estimated that a cord of oak would yield 40 bushels of charcoal while a cord of pine would yield 42. However, since a forge requires only the best charcoal, slightly more wood is necessary to produce forge charcoal than furnace charcoal.[x] It would appear that the figure of 40 bushels per cord of wood is reasonable to work with, and since the technology of charcoal production did not change during this period, the figure can be used for 1832 and 1850.

The fourth and final element in the calculation is the amount of wood produced on an acre of land. Overman indicated in 1854 that an acre of forest that is 30 years old contains an average of 30 cords of wood, a figure which the records at Hopewell Furnace during the same period verify–that an acre of woodland in southeastern Pennsylvania could be expected to grow one cord of wood per year.[xi] The managers of Hopewell Furnace expected to clearcut their property in rotation, with each section of woodland being timbered every 30 years.[xii] While it has been our observation that the trees grow very rapidly in the hollow nearest the stream, perhaps in a zone 600 feet wide (300 feet above the stream on each side), the end of Sapsucker Ridge appears to be extremely slow growing, as is the crest of Laurel Ridge. An average growth rate of one cord of wood per year for the whole hollow seems to be reasonable–faster nearer the stream and slower near the ridgetops.

On to the calculations. For 1820 we can multiply the 500 tons of iron produced by 225 bushels of charcoal per ton, and divide the result by 40 bushels of charcoal per cord of wood to determine that 2812 cords of wood were consumed at the Tyrone Forges that year. For 1832, using 600 tons of iron produced rather than 500 but keeping the other figures the same, the amount of wood consumed jumps to 3375 cords of wood. Eighteen years later in 1850, with the expansion of the forge operations, we would multiply the 1543 tons of iron produced by 200 bushels of charcoal per ton, and divide the result by 40 bushels of charcoal per cord of wood to find that 7715 cords of wood were used. If the Hopewell Furnace and Overman estimates are correct about the rate of growth of woodland per year, then 94 acres of forest would have been used in 1820 (2812 cords divided by 30), and 112 acres in 1832. By 1850, the figure would have jumped to 257 acres clearcut per year for the forges (7715 cords divided by 30). These calculations are completely in line with estimates provided by other secondary literature for the use of woodlands by the iron furnaces and forges.[xiii]


[i]. Africa, J. Simpson. History of Huntingdon and Blair Counties, Pennsylvania. Philadelphia: Everts, 1883, Huntingdon County vol., p.55.

[ii]. Census of Manufactures of 1820. Census schedule for Tyrone Forge in the National Archives, Record Group 29.

[iii]. Documents Relative to the Manufactures in the United States. U.S. House of Representatives, 22d congress, 2d Session, House Document 302, vol. 2. U.S. Serial Set vol. 223. Washington, 1833, p.344.

[iv]. Ironmasters Convention, Philadelphia, 1850. Documents Relating to the Manufacture of Iron in Pennsylvania. Philadelphia: The General Committee (of the Convention), 1850, Table titled “Detailed Statement of the Charcoal Forges in Eastern Pennsylvania, in the Year 1850.”

[v]. Documents Relative to the Manufactures in the United States. U.S. House of Representatives, 22d congress, 2d Session, House Document 302, vol. 2. U.S. Serial Set vol. 223. Washington, 1833, p.344-345.

[vi]. According to a Mr. Mitchell of Bellefonte, who presented testimony before Congress about the iron industry in Centre, Huntingdon, and Mifflin Counties (Pearse, John Barnard. A Concise History of the Iron Manufacture of the American Colonies Up to the Revolution, and of Pennsylvania until the Present Time. Philadelphia: Allen, Lane & Scott, 1876, p.216-217).

[vii]. This report is from the Freedom Forge in Mifflin County, presumably directly to John Barnard Pearse (A Concise History of the Iron Manufacture of the American Colonies Up to the Revolution, and of Pennsylvania until the Present Time. Philadelphia: Allen, Lane & Scott, 1876, p.250-251).

[viii]. Overman, Frederick. The manufacture of Iron in All Its Various Branches. 3rd edition. Philadelphia: Henry C. Baird, 1854, p.280.

[ix]. Walker, Joseph E. Hopewell Village: The Dynamics of a Nineteenth Century Iron-Making community. Philadelphia: University of Pennsylvania Press, 1974, p.242-249.

[x]. Thomas Cooper’s 1813 article as quoted by Sandford, Joseph E. “Charcoal Burning.” The Historian (Doylestown, PA) 1(5) winter 1960-61: 25-27.

[xi]. Overman, Frederick. The manufacture of Iron in All Its Various Branches. 3rd edition. Philadelphia: Henry C. Baird, 1854, p.84-85; Walker, Joseph E. Hopewell Village: The Dynamics of a Nineteenth Century Iron-Making community. Philadelphia: University of Pennsylvania Press, 1974, 135-136.

[xii]. Walker, Joseph E. Hopewell Village: The Dynamics of a Nineteenth Century Iron-Making community. Philadelphia: University of Pennsylvania Press, 1974, p.238-240.

[xiii]. Bining, Arthur Cecil. Pennsylvania Iron Manufacture in the Eighteenth Century. 2nd edition. Harrisburg: Pennsylvania Historical and Museum Commission, 1973, p.20, 63-64. Note, however, that Schallenberg (p.276) indicates that furnaces before the Civil War normally consumed no more than 100 acres of wood per year, but his figure is at variance with Walker, Bining, and the calculations given here.

–Bruce Bonta

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  1. The name Tyrone Forges seems to indicate that this was not a furnace. It would seem that a furnace would require much more charcoal than a forge. Interesting article.

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