[permaculture] Prairies and Forests
mpludwig at facstaff.wisc.edu
Mon Jul 15 13:32:49 EDT 2002
Once again, i'll try not to repeat myself
>I also believe that it's possible for us to accelerate and exacerbate our
>present warming trend. Clearing the land by burning has no doubt been
>affecting all of the macro cycles of global climate for the past 10,000
>years, if not the past 100,000 years. It's probably time for us to
>seriously ask ourselves if we want to keep burning the earth as a way of
>managing it, or if we want to steer the earth away from fire adapted,
>pyro-phillic plant communities.
I think scale is critical here. I'm advocating much smaller burns than
would have historically occured or are sometimes seen in the developing world.
>However, since I cannot find any historical mention of naturally occurring
>fires, at least in Texas, I have a much harder time embracing the use of
>controlled burning across Texas prairies.
Dry lightning, nuf said.
> WI is certainly different than
>Texas, so for that region my concerns are with the recommended frequency of
>burning the same piece of land. Once every seven years is too often, IMO -
>that's what's recommended by the USNRCS in Texas.
Each situation is differant. Two years of sucessive burning knocks out
many weedy biennials. Perhaps the 7 year prescription is for brush
supression. My point is that fire is a tool of limited use, but really is
essential in some phases of retoration an managemet.
>Across much of Texas, however, grasslands and woodlands are so interwoven it
>really becomes counter-productive to attempt to untangle the two. This is
>exactly why the French Explorers coined the phrase prairies when they
>arrived in Texas, to distinguish them from plains and grasslands..
My understanding is that the term prairie was coined because the french had
no equiveilent TREELESS landscape. Their traditional medows had fencerows
etc. making the need for a new term.
> >> It [intensive, rotational grazing] is not however all that easy to do in
>prairie systems, much simpler to use C3 grasses and annual C4's. <<
>In lou of ungulates? I'm just learning about the differences between C3 and
>C4 plants. The reference is to pathways for photosynthesis (PS) that
>involve Carbon molecules, relate to the placement and behavior of stomata,
>seasonal temperatures and night time or dark PS pathways? One is made up
>more of forbes and brushy species and the other composed more of cool season
Most prairie grasses are warm season (C4), most forbes are cool season
C3. C4 is more water efficent and requires higher temperatures. The
problem with native C4's (speaking generally here) is that they store more
carbohydrates in their stems than typical introduced c3's. It's much
easier to overgraze. Plus it takes three years to get a good stand going
compared to 1/2 a season for the typical c3. Hard to make the $
work. Native C4's make more sense the dryer and hotter a landscape becomes
or possibly as 'drought insurance".
>There was also the Mid-West's dust bowl phenomena in the 1930's, which our
>generation tends to quickly forget about. How much soil, species diversity
>and bio-mass did we loose as a result of that, how much have we lost since?
How quickly they forget where the dust bowl was. That would be the high
plains and southern and western most portions of the midwest, where the
native grass land was plowed up and planted to small grains. Once the
wheat died it was quite predictable that the losses (wind deposited soil)
blew away. This is why I want to see the region re grassed first, it holds
the soil down long enough to try and plant the trees you want.
>Desertization as opposed to desertification is the naturally occurring
>migration of the true hyper-arid deserts of the earth, resulting from
>planetary climate change. True deserts move very slowly and when talking in
>terms of millenniums neither increase nor decrease in area significantly.
>Desertification is the result of human disturbance and is quickly converting
>most of the earth's arid and semi-arid grasslands into desert. Point,
>being, I wouldn't underestimate mankind's ability to turn grasslands into
>deserts, especially with a fire brand in his hand.
Overgrazing is a much bigger threat IMO. There is little insentive to
"overburn", essentially burning a grazable landscape means some ammount of
forage was left unconsumed, a rather rare situation in most well stocked
pasture systems and certianly comes with a lost oprotunity to graze. There
is however an insentive to overgraze if one has need for more animals or
> >> And turn the prevailing continental wind direction. Good luck. <<
>It's documented that woodlands themselves our a source of precipitation.
>The O18 molecule is found in rains that originate from the transpired water
>from trees. The O16 molecule is from evaporated sea water and often doesn't
>make it all the way to the continental interior. So the majority of the
>rain in the interior of a large continent such as ours comes from trees. As
>you mentioned, the Rocky Mountains wring (via topographical uplifting) most
>of the water out of the air from the west, without the coastal forests there
>would be much less precipitation in the Central Grasslands.
Grass also transpires of course. The real enemy here is bare soil which
rapidly looses water, co2 and tends to heat up much more than covered land.
>I can only surmise that with a robust coastal forest along the Gulf of
>Mexico and the Pacific Rim we could increase the amount of rainfall and
>humidity of the continental interior. Let's keep the grasslands but aim for
>cooling and re-humidifying the planet.
I still don't see more water making it over the Rocky's if the pacific rim
forest if restored (not to say it should't be). As for the Gulf costal
forests, I'm all for more trees there.
> >> Re grassing the central plains before the ogalala aquifer is blown might
>be a bit more pragmatic and much more stable than trying to grow trees in a
>I'm all for regrassing the Central Grasslands and protecting the aquifers.
>Let's do it right, though, and make the most out of those areas already
>cleared of trees and native grasses.
It's almost all been plowed. plenty of work to be done just getting the
grass right again. The ag system out there is pretty marginal
already. One the irrigation is played out grass will be the only resonable
> > >I've been following this topic [the effect of burning on insects] on the
>prairie mailing list. It seems to be a double edged sword.
> > huh?
>Meaning, it can be used as an argument either for or against the use of
>controlled burning. Some use the increase of the insect population,
>resulting from a fire, as a reason to burn, while I'm hearing warnings from
>others that you can severely set back the insects if you don't leave them
>some sanctuary. In other words a burn wipes out a lot of the insects it
>moves over - whether the insects are able to quickly recognize is a risk
>factor based on the knowledge and experience of those executing the burn. A
>risk I'm leery to take.
Most of the burners round here or prairie philes, they want the bugs, the
birds and the grass, so I think this isn't that big of an issue.
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Mark P. Ludwig
Poultry Research Lab
University of Wisconsin -Madison
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