The pollen records are not used to assess changes over evolutionary time -
too short term (unless pollen can be used from coal deposits). The most
recent feature on an evolutionary time scale is the rise of 'angiosperms'
which become dominant plants perhaps as long ago as 90 million years. In
terms of 'change' therefore there has been no significant change in the
major biomes during this time. Nivean and periglacial environments are
subject to almost constant change (which is obvious to anyone that skiis or
hikes in the mountains) whereas oceanic environments in the tropics are
unchanging....

There have been 29 major glaciations. The last one ended about 10,000 -
14,000 years ago. Thus in North America the main feature of ecological
change has been an expansion of the grassland biome. The grassland biome is
a relatively new ecosystem comprised mainly of gramminae angiosperms
[flowering plants] and an absence of ferns, liverworts, mosses and
horsetails except in very moist sites. The evolution of angiosperms has
perhaps resulted from the creation of a niche or habitat that was not
exploitable by earlier evolved plants such as ferns, cycads, and horsetails,
et cetera. The angiosperms are highly adapted to habitats which have
droughts, and if we consider what kind of environment existed when ferns and
other primitive plants existed as the dominant group of terrestrial plants,
these habitats did not lack abundant moisture. This is the reason why there
are huge fossil fuel deposits which formed during very wet and relatively
warm periods when large 'bogs' with spaghum and other mosses existed.

With the evolution of grasses and grasslands occurs the co-evolution of the
foraging equine species that first lived in forests as foragers. The early
horses did not live in grasslands but rather lived in forests and had
dentition which lacked teeth adapted to grazing.

The idea that ecosystems change is an inappropriate way of expressing what
occurs during the evolution of species. What actually occurs during speciati
on  may be discribed as a bifurcation of a descent group into one or more
species with adaptations to new environments and habitats (cf the primitive
horse which orginally lived in forests). For instance the descent of man
involves a bifurcation of one species in the Hominoid group and the rise of
the Hominid group which lasted until the demise of the Neanderthal about
16,000 years ago. Many species and habitats do not change significantly. For
instance there are still alligators and crocodiles, lemurs, and sloths.
Crocidiles existed prior to the dominance of flowering plants and the
habitats that these very primitive animals inhabit has not change much
(tropical rivers and lakes). The tropical rainforest still has tree ferns,
and many primitive plants, so there is another example of a 'constant' and
unchanging climatic environment. In fact the rainforests of Africa are about
90 million years old, and no major changes have occurred since then. The
ocean is one of the most 'unchanging' environments....

It may be generalized that as the global climate becomes drier and cooler
[due to various factors] the present expansion of the grassland biome, the
receding of forests worldwide will continue and perhaps will be accelerated
by man. One of the reasons why global climate is becoming drier and cooler
is due to a gradual reduction of the salt content of the oceans which raises
the freezing level of the ocean and a higher surface albedo at the polar
regions. Each glaciation results in large amounts of salt being removed from
sea water in the Meditterean Sea and other landlocked salt water bodies due
to evaporation.

The only change on an evolutionary time scale of any significance are the
expansion of angiosperms [flowering plants] as a result of a change in the
global climate over a period of 90 million years. The glaciations had some
effect on the tropical rain forests. For instance during the height of the
last glaciation, the Amazon rainforest was reduced in size to about 10% of
what is at present.

Over the last few million years hominids have not had a significant effect
on nature. But over the last few hundred years humans have had a significant
effect on global climate, forests, grasslands, and many individual species.
In fact George Perkins Marsh claimed that man is a 'factor in geological
change' (citing the massive erosion and flooding of the Yanzte River in
China which claimed the lives of 2 million persons at the turn of the last
century).

Thousand year time scales are not adequate for describing evolutionary
time.....and thus there can be no 'moral' or 'ethical' analogies made about
'justifications' nor 'excuses' for environmental 'tradeoffs' or
'damage'....based on a comparison derived from post-Wisconsin 'drying'
out.....at least in my opinion....

chao

"I believe that we are ultimately directed Godward but that this journey is
often impeded by emotion. I don't think you are a jellyfish. But I suspect
you of being a Romantic." [Flannery O'Connor, letter to "A"] [The Habit of
Being]



> >From Leopold "Cons in whole or part" (collected in The River of the
Mother
> of God and other essays): "The wisconsin land was stable....for a long
> period before 1840 [when settled by europeans].  The pollens embedded in
> peat bogs showed that the native plants comprising the prairie, the
hardwood