Energy Exchange
3
1 .I Microenvironments
Microenvironments are an intimate part of our everyday life, but we seldom stop to think of them. Our homes, our beds, our cars, the sheltered
side of a building, the shade of a tree, an animal's burrow are all examples
of microenvironments. The "weather" in these places cannot usually be
described by measured and reported weather data. The air temperature
may be 10" C and the wind 5 mls, but an insect, sitting in an animal
track sheltered from the wind and exposed to solar radiation may be at
a comfortable 25" C. It is the microenvironment that is important when
considering organism energy exchange, but descriptions of microclimate
are often complicated because the organism influences its microclimate
and because microclimates are extremely variable over short distances.
Specialized instruments are necessary to measure relevant environmental
variables. Variables of concern may be temperature, atmospheric moisture, radiant energy flux density, wind, oxygen and COz concentration,
temperature and thermal conductivity of the substrate (floor, ground, etc.),
and possibly spectral distribution of radiation. Other microenvironmental
variables may be measured for special studies.
We first concern ourselves with a study of the environmental
variables-namely, temperature, humidity, wind, and radiation. We then
discuss energy and mass exchange, the fundamental link between organisms and their surroundings. Next we apply the principles of energy and
mass exchange to a few selected problems in plant, animal, and human
environmental biophysics. Finally, we consider some problems in radiation, heat, and water vapor exchange for vegetated surfaces such as crops
or forests.
1.2 Energy Exchange
The fundamental interaction of biophysical ecology is energy exchange.
Energy may be exchanged as stored chemical energy, heat energy, radiant
energy, or mechanical energy. Our attention will be focused primarily on
the transport of heat and radiation.
Four modes of energy transfer are generally recognized in our common
language when we talk of the "hot" sun (radiative exchange) or the "cold"
floor tile (conduction), the "chilling" wind (convection), or the "stifling"
humidity (reduced latent heat loss). An understanding of the principles
behind each of these processes will provide the background needed to
determine the physical suitability of a given environment for a particular
organism.
The total heat content of a substance is proportional to the total random kinetic energy of its molecules. Heat can flow from one substance
to another if the average kinetic energies of the molecules in the two
substances are different. Temperature is a measure of the average random kinetic energy of the molecules in a substance. If two substances at
different temperatures are in contact with each other, heat is transferred
3
1 .I Microenvironments
Microenvironments are an intimate part of our everyday life, but we seldom stop to think of them. Our homes, our beds, our cars, the sheltered
side of a building, the shade of a tree, an animal's burrow are all examples
of microenvironments. The "weather" in these places cannot usually be
described by measured and reported weather data. The air temperature
may be 10" C and the wind 5 mls, but an insect, sitting in an animal
track sheltered from the wind and exposed to solar radiation may be at
a comfortable 25" C. It is the microenvironment that is important when
considering organism energy exchange, but descriptions of microclimate
are often complicated because the organism influences its microclimate
and because microclimates are extremely variable over short distances.
Specialized instruments are necessary to measure relevant environmental
variables. Variables of concern may be temperature, atmospheric moisture, radiant energy flux density, wind, oxygen and COz concentration,
temperature and thermal conductivity of the substrate (floor, ground, etc.),
and possibly spectral distribution of radiation. Other microenvironmental
variables may be measured for special studies.
We first concern ourselves with a study of the environmental
variables-namely, temperature, humidity, wind, and radiation. We then
discuss energy and mass exchange, the fundamental link between organisms and their surroundings. Next we apply the principles of energy and
mass exchange to a few selected problems in plant, animal, and human
environmental biophysics. Finally, we consider some problems in radiation, heat, and water vapor exchange for vegetated surfaces such as crops
or forests.
1.2 Energy Exchange
The fundamental interaction of biophysical ecology is energy exchange.
Energy may be exchanged as stored chemical energy, heat energy, radiant
energy, or mechanical energy. Our attention will be focused primarily on
the transport of heat and radiation.
Four modes of energy transfer are generally recognized in our common
language when we talk of the "hot" sun (radiative exchange) or the "cold"
floor tile (conduction), the "chilling" wind (convection), or the "stifling"
humidity (reduced latent heat loss). An understanding of the principles
behind each of these processes will provide the background needed to
determine the physical suitability of a given environment for a particular
organism.
The total heat content of a substance is proportional to the total random kinetic energy of its molecules. Heat can flow from one substance
to another if the average kinetic energies of the molecules in the two
substances are different. Temperature is a measure of the average random kinetic energy of the molecules in a substance. If two substances at
different temperatures are in contact with each other, heat is transferred