SThis posting is for those interested in discussing silviculture.
Question: How does one go about determining the "optimum" seedling
for use in reforestation?
Background: There are many seedling grade studies that have determined
the "minimum" seedling standards for a plantable seedling. Once these
"minimums" are established, nurseries tend to produce seedlings that
are just above the minimum. These seedlings are then (gradually)
accepted as the norm or "ideal." Any seedlings that are larger than
the norm would be "too hard to plant" (read too hard to plant quickly
by hand). Therefore, there is a tendency to reduce cost of seedling
production by producing seedlings near the minimum standards.
I believe silvicultural research aimed at identifying the "optimum"
seedling for reforestation is lacking. For example, I just read a
paper that used seedlings grown in small containers (313 or 3 cm
diameter with a depth of 13 cm). Much detail was provided in the
paper (except the initial size of the seedlings). After one year in
the field, the diameter growth of the seedlings was less than 1 mm!
IMHO, I doubt these very small seedlings are "optimum" for
regeneration on these sites. Such small seedlings may need a lot of
help in the form of intensive weed control and mechanical site
preparation) in order to get them to grow.
Of course there are two "optimum" stock types. One is the
biologically "optimum" (performs better than other ideotypes). The
other is the economically "optimum" (produces a higher NPV than other
ideotypes). I expect the "biologically" optimum seedling to have a
larger root mass than the "economically" optimum since the costs
associated with producing, shipping and planting enter into the
equation when determining the "economically" optimum seedling.
Defining the biologically "optimum" seedling is relatively easy.
Seedlings of various sizes (and conditions) can be produced and
outplanted to determine the best field performance (say at a 2 meter
average height in the field). If the stock with the biggest roots
performs best (no point of diminishing returns identified), the study
is repeated using even larger "balanced" stock (until a plateau or
node is identified).
A problem with identifying the "economic" optimum planting stock is
taking early growth results and predicting volume (or value) at
harvest. A big stumbling block is a lack of growth models that have
been developed for the establishment phase. One way to get around
this problem is to estimate the "years gained" from establishment.
This simply estimates the time gain from planting larger stock (see
for example: Blake, J.I., L.D. Teeter, and D.B. South. 1989. Analysis
of the economic benefits from increasing uniformity in Douglas-fir
nursery stock. Forestry Supplement 62:251-261). The estimation of
"years gained" is not a precise estimate (may vary with individual) but it seems
to be an accepted method (until adequate regeneration models are developed).
Costs of site preparation will affect the "biologically" optimum seedling. If
costly methods of site preparation are used, then savings might result by
lowering the intensity of mechanical preparation while increasing the root mass
(and RCD) of the planting stock. For example, planting 12.5 mm stock with a
single bed and no herbicides sometimes does better than planting a 2.5 mm stock
on double beds plus herbicide. (see
www.forestry.auburn.edu/coops/sfnmc/data/ipm.html).
Conclusion: If studies to determine the "economically" optimum planting
stock have been established, then we may have some confidence that we are not
wasting establishment money on helping small seedlings get established. If we
have not determined the "economically" optimum planting stock, then there is a
good chance we have accepted sub-optimum stock as the norm.
==============
Looking forward to a good internet discussion.
David South
School of Forestry
Auburn University
A member of the Forester's Chapter for ZPG
www.forestry.auburn.edu/people/faculty/biology/south/zpg/forester.html
As always, views expressed here are my own
(and I am not speaking on the behalf of others).
I use only 100% post-consumer paper in my home printer. (discarded used office
paper printed on one side)
====================================================================== The world
population is expected to double by the year 2100.
Therefore the annual demand for wood for energy (etc.)
will increase and might double (to more than 7 billion m3/yr). To provide
plantation wood for people in the future,
support the planting of trees on pastureland.
Set a goal of converting 8 million ha of pastureland/yr for the next 55 years.
This would increase tree plantations to about 5% of the world's landbase.
======================================================================
Support Zero Population Growth for the United States
http://www.igc.apc.org/zpg/index.html
Mail converted by
MHonArc 1.1.0