that the natural system is performing the service functions cheaper and in a
less energy intensive manner than would the replacement technology,

 What is needed now is a refined methodology coupling energy, sociology
and economics to quantify the components of the NSV equations, to better test
the hypothesis. One such beginning is implicit in this study as the societal
value of trees would include the following calculations:

 1. EQI = 2.8 billion Btu's/yr

 2. EU = mid range of energy saved by park functions

 = 10.9 billion Btu's/yr

 3. Therefore, the value of the natural system (in this case trees in
 Capitol Park) is:

 2.8
 10.9 = 0.26 NSV = 'Appropriateness'

 Even though the NSV represents less than unity, reflecting an efficient
pollution and climate control system by Capitol Park, this value is virtually
meaningless without other technologies and other values for comparison. Yet
it perhaps begins to quantify some of the difficult aspects energy modellers
and economists continue to grapple with in their separate and combined analyses.

 Energy analysis measures physical properties and many economists do not
view that measurement as indicative of the "real world" situation. Economists
add some social perspectives on the energy values, yet many represent some lags
and "slack" in the system. The overall system is a combination of the two,
with two masters being served simultaneously. True, the laws of thermodynamics
provide the baseline realms of possibilities, but the economics fine tune the
perspective, and the economics change more often than do the energetic of a
case study.

 Despite this cautious beginning of this combined approach to couple
energetic and economics to form the societal value of natural systems, much
more work needs to be done to perfect the theoretical basis of the evaluation
in addition to more calculations upon which to base some comparisons, and energy
planning decisions. Yet one point is very clear: the value of trees in cities
and urban centers is not trivial. In fact, cities are and have been running
on both fossil and solar fuels through trees and greenbelts, and the expansion
of this knowledge does not require a lot more calculation or debate. The
additional challenges lie in other natural system uses such as wetlands for
water purification, and nursery grounds for fishing economies, watersheds for
water management functions, and the like. The societal value of trees is just
a stepping stone from which to venture into future aggressive couplings of
urban and natural systems.