Brittle vs. non-brittle pastures

One of the most fascinating
points in Small-Scale
Livestock Farming
was the distinction between brittle and nonbrittle environments. 
The term was coined by Allan Savory to explain why rainforests (the
extreme of non-brittle environments) respond differently to grazing
than deserts (the extreme of brittle environments).  Most
locations are partway between the two extremes, and understanding where
your farm lies on the scale can help you make management decisions.



Brittle environments
generally don’t have much precipitation, and what rain does fall is
often concentrated at one season of the year.  Wooden fence posts
(and other plant matter left on the ground) tend to rot slowly by
weathering and oxidation from the top down in these areas, and there’s
little leaching to suck minerals out of the soil.  Bunch grasses
are common, with lots of space between each plant, and if you
overgraze, you tend to see more exposed soil that will erode
away.  If you undergraze pastures, you end up with more bare
ground between plants, while if you use high-impact
grazing properly,
plant spacing will tighten up.  When left alone, brittle pastures
tend to lose species and only slowly (if ever) turn into forest.



Nonbrittle environments
are just the opposite.  Places like our southwest Virginia farm
get lots of rain spread throughout the year, so wooden fence posts rot
quickly via biological decay starting at the soil line, and we lose a
lot of minerals from our soil by leaching.  Grasses in nonbrittle
environments tend to form a solid sod, and if you overgraze, the
spacing just gets tighter.  If left alone, pastures quickly grow
up in briars, then in trees, and eventually close up into forest.



The map at the top of this
post shows that most of the east is nonbrittle and most of the west
(except for the Pacific Northwest) is brittle.  Interestingly,
most mob grazing experts (like Greg
Judy) are located in
brittle environments, and even Joel Salatin (in northern Virginia)
explained in Folks,
This Ain’t Normal
that his valley microclimate veers toward brittle.  On the other
hand, Bill
Murphy, who wrote
about Voisin-style grazing, farmed in the nonbrittle east. 



I’d be tempted to say
that the big divide between Voisin and mob grazing is due to the
brittleness of the environment, but Matron of Husbandry illustrates that mob grazing
can work quite well on the rainy side of Washington state.  I’d
love some more data points from rotational grazers — are you brittle
or nonbrittle and what kind of rotation works for you?