Environmental Engineering Reference
In-Depth Information
Box 9.1
Wood Consumption in the Roman Empire
Average per capita rate is constructed by adding conservative estimates (based on the
i rst principles) for major wood consumption categories. I assume that bread baking
(mostly in urban
pistrinae
; only rich households baked their own bread) and cooking
(mostly in numerous
tabernae
) required 1 kg of wood/day per capita. At least 500
kg of wood/year were needed for space heating that was required for the roughly one-
third of the empire's population that lived beyond the warm Mediterranean in the
temperate climates of Europe and Asia Minor. To this must be added an average annual
per capita consumption of 2 kg of metals (much of it for military uses), which required
about 60 kg of wood per 1kg of metal.
This adds to annual per capita demand of 650 kg (roughly 10 GJ) or about 1.8
kg/day—but as the Roman combustion efi ciencies were uniformly low (no higher
than 15%), the useful energy derived from burning that wood was only on the order
of 1.5 GJ/year, a modern equivalent of just 35 kg of crude oil (or nearly 50 liters,
or one tankful, of gasoline). For comparison, when Allen (2007) constructed his two
Roman household consumption baskets he assumed average consumption of nearly
1 kg wood/capita a day for what he called a respectable alternative and just 0.4
kg/capita for a bare-bones budget (none of these rates included fuel for metallurgy and
manufacturing).
steam to power locomotives and boats. This use was almost everywhere rather
rapidly superseded by coal, but wood continued to supply small workshops and
local industries in many low-income countries throughout the twentieth century.
Quantifying preindustrial wood combustion is highly uncertain: there is no reliable
information either for antiquity or for the Middle Ages. My reconstruction of fuel
demand in the early Roman Empire (that is, during the i rst two centuries of the
Common Era) ended up with at least 10 GJ per capita (box 9.1), while Galloway,
Keene, and Murphy (1996) put the average annual wood consumption in London
around 1300 at 1.5 t of air-dried wood (20-25 GJ) per capita.
Recent studies of those Asian and African societies where phytomass remains
the principal source of heat show similarly low rates, with an annual per capita
consumption of less than 10 GJ among the poorest inhabitants in the warmest
regions. But typical wood consumption rates were always higher in heavily wooded
central and northern Europe. Some traditional manufacturing tasks were highly
wood-intensive. German medieval glassmaking required as much as 2.4 t of wood—
nearly all of it burned to obtain potassium rather than to generate heat—to produce
1 kg of glass (Sieferle 2001). Only about 3% of all wood heated the glassmaking
process, but that still translated to as much as 1 GJ/kg of glass; in contrast, today's
