agroforestry question

truffler1635 at truffler1635 at
Sun Jan 23 15:20:01 EST 2000

In article <28079-388928BA-35 at>,
  TREEFARMER at wrote:
> In response to DVK's response about Locust fixing nitrogen: It's my
> understanding that the legume (in this case Locust) must be killed for
> the nitrogen to be released. Some years back we interplanted Black
> Walnuts with Black Locust. The idea was to eventually kill out the Black
> Locust to fertilize the Black Walnuts. Needless to say, the Black Locust
> beat out the Black Walnuts so fast that they effectively choked out the
> Walnuts. It may have worked on a better site, but why waste space on a
> good site growing Black Locust.
> Truffler, I'm glad you responded to this problem as I'm running out of
> reasons for low yields in seeps (wet areas). Lack of mycorrhizal fungi
> or some bacteria in seeps seems to be the yield limiter whether one is
> talking of grain yields or board feet.
You're not the only one stimied by this situation. My botany teacher at
Oregon State University, Helen Gilkey, once told me she could go into a
forest, analyze leaf samples from two adjacent trees, and determine that
one was nitrogen deprived, and the other nitrogen rich. Yet both were
growing at approximately the same rate. The answer did not appear until
after her death, unfortunately. Studies from Oregon State and the
University of British Columbia have shown that some mycorrhizae
(Rhizopogon, Hysterangium sps) for matt communities, which apparently
share nutrients between non-related species. It can be between Western
hemlock and Douglas fir, or between Red Alder/Birch/Douglas fir stands.

This symbiotic relationship between non-related species via mycorrhizal
fungi is one of the strange aspects to forestry not thought of in
Gifford Pinchot's time. If you consider tree species as being
competitors for air/water/soil/light, then the relationship makes little
sense. But consider it from the fungi's viewpoint.

According to Dr. William Dennison, direct sunlight kills most
mycorrhizal fungi upon direct exposure. That may explain why thinned
tree stands which have chanterelle production may lose chanterelles
production when the stand is thinned. Thinning by 10-50% may not kill
the mycorrhizal fungi present with other trees, but it certainly
decreases their growth by decreasing association with other trees, many
of which such as Red alder, may be benefitting nearby conifers via the
production of nitrogen via nitrogen-fixing bacteria associated with
mycorrhizal fungi specific to Red alder. The more that is learned of
these relationships, the most complex the relationships become.

And yet, it is possible to find in nature stands disturbed or destroyed
by high-winds, where the neighboring standing trees do just fine. Little
reseach in this area often translates into little data for even
hypothesis into how trees actually grow rapidly. One thing is certain:
mycorrhizal fungi are no longer "optional" symbiotic partners. And
fertilizing over 80 lbs. urea/acre/year can cause mycorrhizal fungi to
disassociate from trees. Lack of mycorrhizal association can cause this
over-fertilized trees to die soon afterwards.

> What can one do to better the environment for these fungi?
The best thing is to keep track of what mycorrhizal fungi you have. Most
tree-farmers don't know how to identify the thousands of fungi found on
their property, especially the fungi which are hypogeal (underground).

Inoculating trees with some of the few mycorrhizal fungi which can be
cultivated is a first step. But many of these fungi are species
specific: found only with one host tree or plant. While they _may_ be
associated with other tree/shrub species, they often _fruit_ with only
one species of tree. Ergo, inculation with these fungi is important to
establishing long-term productive tree stands.

Cautious, judicious thinning practices also help. Instead of taking 50%,
30%, or 10% of the tree overstory out during thinning operations, try to
leave the majority of trees, even if they seem weak or light-deprived.
Judging which trees to remove during each thinning is extremely complex,
and more of an art than a science at this time. The Alamanor Forest of
Northern California does not allow a cruiser to harvest a single tree
until they have gone through a 5-year apprenticeship program.
Oftentimes, the single-species, larger trees are left as seed sources/
mycorrhizal sources/wildlife habitat/canopy cover to decrease thinning
stress on the remaining trees.

In other words, there are no simple answers.
> Using several years of GPS yield monitoring equipment and mapping we've
> found that yields can't be increased by increasing potash and potassium
> amounts. Also, deep tillage has helped little. The only thing that has
> helped is tiling, but to date the tiled areas can't match the better
> areas of the  field. Even as severe as the drought was here last year it
> was still a 3/4 average yield year.
The mycorrhizal fungi associated with watery or boggy soils is still
mostly unknown. There are probably naturally occuring sites in the same
state as you which have naturally occuring mycorrhizal fungi which allow
the trees to grow considerably faster than at your site. The key is
somehow transferring these fungi from the other sites to your site.
That's one of the reasons why the Northern Spotted Owl is so important
in the PNW. The owl can daily inoculate several hundred species of
mycorrhizal fungi through defecation/regurgitation of owl pellets. While
at least 60 species of animals are known to disperse mycorrhizal fungi,
many of these animals are specific to given habitats. Owls may not
inoculate swampy areas, since their food supply is more likely to be
found on drier land (and California Red-backed vole tunnels underground
often help drain such areas).
> It seems like soil temperature may
> have something to do with it but I haven't had a chance to study this
> realm yet.
Certainly soil temperatures affect mycorrhizal fungi production also. I
would not be surprised to see some correlation. Cooler temperatures are
often the best for mycorrhizal fungi, which may account for one reason
they form matt communities with several non-related nearby species.
Mycorrhizal fungi do best with closed canopies.
> Sometimes in constructing dry dams for water control as
> little as a few inches are removed for construction of the dam. Yields
> in these areas are drastically decreased eventhough there is plenty of
> "topsoil" left.
The problem may be mycorrhizal depletion: most mycorrhizal fungi survive
in the upper 6 inches of soil, including the duff layer.
> There seems to be something very important in the top
> few inches of the soil that contributes significantly to the crops
> yield.  I guess I've taken up enough space.
I encourage you to take up _more_ space. This is important discussion
for long-term tree survival, IMHO.

Daniel B. Wheeler

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