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Encyclopedia of Physical Science and Technology EN002C-60 May 17, 2001 20:23

160 Biomass Utilization, Limits of

essential nutrients. This is the largest number and pro- tal biomass production about 36.5 billion metric tons or
portion of malnourished humans ever recorded in history. 145 × 10 15 kcal/yr. In contrast, the terrestrial ecosystem
Meanwhile, based on current rates of increase, the world produces about 3 t/ha/yr, making the total biomass about
15
population is projected to double to more than 12 billion 40.5 billion tons or 162 × 10 kcal/yr. The total biomass
in approximately 50 years. With a population growth of produced is approximately 77 billion tons or about 12.8 t
this magnitude, the numbers of malnourished could reach per person per year.
5 billion within a few decades. The need for biomass will The 40.5 billion tons of biomass produced in the terres-
continue to escalate. trial ecosystem provides an estimated 6.8 t/yr per person.
Associated with increasing human numbers are di- Giventhathumansharvestabout50%oftheworld’sterres-
verse environmental problems, including deforestation, trial biomass, each person is utilizing 3.4 t/yr. This 3.4 t/yr
urbanization, industrialization, and chemical pollution. includes all of agriculture, including livestock production
All these changes negatively impact on biomass produc- and forestry. The remaining 3.4 t/yr per person supplies
tion that is vital to human life and biodiversity. However, the other 10 million species of natural biota their energy
at present and in the foreseeable future the needs of the and nutrient needs.
rapidly growing human population will stress biomass Currently, approximately 50% of the world’s biomass
supplies. In our need to supply food and forest products (approximately 600 quads worldwide) is being used by
for humans from biomass, intense competition between humans for food, construction, and fuel. This major uti-
human needs for food and the conversion of biomass into lization of biomass, habitat destruction associated with
an energy resource is expected to intensify in the coming the rapid increase in the world population, and environ-
decades. mental pollution from about 100,000 chemicals used by
Furthermore, human intrusion throughout the natural humans is causing the serious loss of biodiversity world-
environment is causing a serious loss of biodiversity with wide. With each passing day an estimated 150 species are
as many as 150 species being lost per day. The present rate being eliminated because of increasing human numbers
of extinction of some groups of organisms is 1000–10,000 and associated human activities, including deforestation,
times faster than that in natural systems. Ecosystem and soil and water pollution, pesticide use, urbanization, and
species diversity are the vital reservoir of genetic material industrialization.
for the successful development of agriculture, forestry,
pharmaceutical products, and biosphere services in the
B. United States Biomass
future.
The limits of biomass energy utilization and how this In the North American temperate region, the solar energy
relates to food production and natural biodiversity and reaching a hectare of land per year is 14 billion kilocalo-
environmental quality are discussed in this article. ries. However, plants do not grow during the winter there.
Most plant growth occurs during 4 months in the summer
when about 7 billion kilocalories reach a hectare. In addi-
I. BIOMASS RESOURCES tion to low temperatures, plant growth is limited by short-
ages of water, nitrogen, phosphorus, potassium, and other
The amount of biomass available is limited because plants nutrients, plus the feeding pressure of herbivores and dis-
on average capture only about 0.1% of the solar energy ease organisms. At most, during a warm moist day in July
reaching the earth. Temperature, water availability, soil a plant, like corn, under very favorable conditions, might
nutrients, and feeding pressure of herbivores all limit capture only 5% of the sunlight energy reaching the plants.
biomass production in any given region. Under optimal Under natural and agricultural conditions for the total year,
growing conditions, natural and agricultural vegetation vegetationproducesapproximately12millionkilocalories
and produce about 12 million kilocalories per hectare per per hectare per year or about 3 t/ha dry biomass.
year (about 3 t/ha dry biomass). Total annual biomass produced in the United States is
an estimated 2.6 billion tons (Table I). This is slightly
more than 6% of all the terrestrial biomass produced in the
A. World Biomass
world. Based on the United States. land area of 917 mil-
The productive ecosystems in the world total an estimated lion hectares, this is the equivalent of 2.9 t/ha/yr and is
50 billion hectare, excluding the icecaps. Marine ecosys- similar to the world average of 3 t/ha/yr for all the terres-
tems occupy approximately 36.5 billion hectare while the trial ecosystems of the world. The total energy captured
terrestrial ecosystems occupy approximately 13.5 billion by all the United States plant biomass each year is ap-
hectare. Gross primary productivity for the marine ecosys- proximately 11.8 × 10 15 kcal (Table I). With the United
tem is estimated to be about 1 t/ha/yr, making the to- States currently consuming 87 quads (21.8 × 10 15 kcal)