[Prev][Next][Index][Thread]

Re: Trees sitting in depressions

> > What got me thinking about this was the realization that trees
> > don't seem to form the bulk of their substance from what they get
> > from the soil.  If they did, you'd expect them to be sitting in
> > depressions.  Instead, the soil around them actually seems to rise
> > up a little.  
>
>      From what I have seen you are wrong about this.  While the soil
> immediately around the trunk of the tree may seem a bit higher, the larger
> area encompassed by its roots is always lower.  


More likely, it is the first observation that is most
common--that soil is higher under trees. 

In agricultural lands, and especially on sloping land, 
trees planted on the contour are viewed as hedgerows against 
erosion.  So are shrubs and coarse/stiff grasses such as vetiver, 
switch grass, and many others. 

When water encounters the hedgerow, it slows down and pools
up.  Sediment carried by the water settles out and the
result is that you actually end up with a berm of soil on 
the uphill side of the hedgerow.  Additionally, the water
infiltrates the soil instead of running off.  The cumulative
effect of increased soil moisture reserves can be
substantial when the rains stop and the plants are left to
fend for themselves.  Keyline Agriculture - Water for Every
Farm is a good book to learn more about water management
such as this.  

Even on very gently sloping land (1-3% slope) which is true
of many states considered to be flat (western Oklahoma and 
Kansas), water runs downslope.   

In Missouri, I attended a field day to observe black walnut alley
cropping.  Black walnut trees were spaced 10 feet in the row
and 40 feet between the row.  In the alleyways between the
rows, the plantation planted corn-sorghum-soybeans in the
summer and winter wheat in the winter.  

The point is that a berm of soil was noticeable in the tree row, 
and the researchers specifically pointed this fact out. 

Indeed the USDA recognizes stiff-grassed hedgerows and alley
cropping with tree crops as conservation measures to reduce
erosion to tolerable levels, and this means farmers can
avoid the very expensive practice of terracing by simply 
employing one of these common sense practices.
References: