wwp@yahoogroups.com:
thoughts on "borders" - natural boundaries
G. Donald Bain 2006-Mar-12 20:00:00
A few notes on another type of border - edges in the natural world.
The crust of the earth is divided into tectonic plates. Most of
California is on the North American Plate, but a strip (including
both San Francisco and Los Angeles) is on the Pacific Plate. The
natural border between these is the San Andreas Fault - a very
significant feature for those of us living near it.
Stand at the waterline on a beach and you are on the greatest natural
border of all, the three-way division of lithosphere (earth),
hydrosphere (ocean), and atmosphere. Vastly different environments
and organisms, and most life clusters around the borders.
Ridgelines are natural borders (and often coincide with political
ones). They divide watersheds and may be barriers to travel. High
ranges often divide national groups and cultures, as in the Pyrenees.
Major rivers have similarly provided natural boundaries that become
political borders.
South facing slopes are warmer and drier than north facing slopes (in
the northern hemisphere) and there may thus be a clear environmental
border - often seen in different vegetation types. Ecotones are
natural borders - the abrupt change from grassland to forest, or from
wetland to upland. Many animal species exploit the inherent richness
of ecotones.
Both high altitude and high latitude create a tree-line (or
timberline), where conditions become too harsh for trees to
reproduce. Higher still is a snow line, where snow persists through
the summer, and a permafrost line, where the ground never thaws.
Geodesy, the science of measuring the earth, draws invisible lines
for us - the tropics and equator, which accord with the seasons,
boundaries in time.
Human activity, especially agriculture, often follows and accentuates
natural borders. In the valleys of northern California grapes are
planted only in areas with the right microclimate and soils, and some
varietals only on certain soils. Prime wine areas such as the Napa
Valley are defined by legislation (an appellation, from the French)
- you can only call it a Napa Valley wine if the grapes come from
within those borders.
In other areas agriculture stops abruptly at the edge of the flat
valley bottoms, constrained not only by the change in soil, but by
the technology of irrigation and mechanization. The border around the
Central Valley of California is easily visible from space, green
crops ringed by dry grasslands.
Administrative borders sometimes gradually produce natural borders.
Protected natural areas have increasingly obvious borders as
development of surrounding areas proceeds. Some species adapt to the
artificial borders better than others. In national parks like
Yosemite, bears will boldly raid your camp, but just outside the
park, where bears are hunted, they stay hidden and run away if they
encounter people.
Just a few more ideas about borders.
Don