Environmental Engineering Reference
In-Depth Information
1
Biomass: Dei nitions and Compositions
The classic life sciences—botany, zoology, plant and animal anatomy and physiology—
were for centuries preoccupied with classii cation. This concern was later extended
to life's assemblages, that is (in ascending order), communities, ecosystems, and
biomes. Such a focus is now seen as antiquated: the preoccupation has shifted to
the intricacies of genetic makeup and metabolism and to the dynamic processes of
evolution and adaptation. An undesirable side effect of this shift has been a lack of
attention to the precise meanings of many variables used to describe organisms and
their evolution. This declining rigor is not a trivial matter, as even apparently
straightforward dei nitions hide some complications; settling these matters (or
explaining clearly how unsettled they must remain) is an essential precondition for
using the variables with the least possible ambiguity. This clarii cation must proceed
along two tracks because biomass stores and productivities are not expressed in
mass terms only but are also quantii ed as reservoirs and l uxes of carbon, a choice
that requires reliable data on the element's content of major biopolymers.
Key Variables
Biomass
is the mass of any living organism. The term can be applied on scales
ranging from that of tissues and organs (the biomass of leaves, of muscles) through
that of individual species (the peak biomass of corn to be harvested for silage, the
biomass of migrating wildebeests) and narrowly circumscribed ecosystems (such as
the total plankton biomass of a small pond) all the way to that of the aggregates
of a biome (for example, the biomass of boreal forests), and on to the planetary
level (the biomass of all photosynthesizing organisms). Complications and uncer-
tainties arise as soon as we start analyzing the term, be it according to the two major
classes of life forms that it embraces or according to the physical or chemical com-
position of biomass.
