A Question

William S Currie wsc at kepler.unh.edu
Thu Oct 14 12:23:07 EST 1993


In article <1993Oct07.130921.11915 at rchland.ibm.com> joshuab at rchland.vnet.ibm.com (Joshua Blacksher) writes:
>Walking thru the park on my way to work today a question came to mind.
>how much land would it take (square miles whatever) for a forest,
>complete with animal life (up to and includeing large preditors)
>to be self sustaining?

	No forest is self-sustaining, in the sense that materials are
cycled only within the system.  Predators depend on herbivores, and
herbivores depend on plants that can photosynthesize.  The carbon
fixed in photosynthesis comes from the atmosphere.  To think of
a forest as a closed system materially, you'd have to include the
atmosphere.  Perhaps a small chunk of the atmosphere could suffice
in theory . . . but in practice, C atoms fixed in phototsynthesis
by plants in a forest come from around the globe, linking the
forest to the global C cycle.  This is true to varying degrees for
nutrients the forest requires, too.
	To think of the forest as self-sustaining in terms of energetics
requires an even larger system.  The energy fixed in photosynthesis,
passed to herbivores and then to predators, comes from 93 million
miles away.
	This is not meant to obfuscate; mereley to make the point that
such a question needs to be more precisely posed (I understand that
Josh is not an ecologist, and this is a fine question coming from
a non-ecologist).  If we're concerned about the land necessary to
sustain a predator population, then that's a population or community
ecology question, not an ecosystems (or 'forest') question unless
the cycles of nutrients on which the plant community depends is
considered . . . which means going outside the forest and looking
at larger systems.


-- 
William S. Currie / Complex Systems / Institute For the Study of Earth,
~~ ~/\^/\__/\~~ Oceans and Space / University of New Hampshire ~~/\^/\~
=======================================================================
	"There are liars, damn liars, and statisticians." -- Mark Twain
 



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