PE EIE[R-Rg RESEARCH ON - HJ Andrews Experimental Forest

ported little photosynthate basipetally in contrast
with the preferential translocation of
photosynthate toward the stem by 2-year-ol d
needles may be explained by the ability of a
sink such as the stem to mobilize photosynthate
falling off with distance in a n
approximately logarithmic manner .
These studies give clues to the relationships
between CO 2 assimilation in the leaves an d
the formation and differentiation of new cells
in apical and cambial growth . These relationships
are not simple, and care must be take n
to avoid oversimplified connections . For
example, net assimilation rates can give an
index of amounts of photosynthate availabl e
for growth only if position and age of th e
foliage studied are taken into account (Ros s
1972). With caution, however, net assimilation
rates taken in different parts of th e
crown can be used to estimate daily mean
assimilation and the total photosynthate production,
on the basis of the whorls o f
branches of different heights (Woodman
1968, 1971) .
In the Coniferous Biome studies, effort s
must be made to bring together net assimilation,
translocation, and terminal and lateral
growth into a workable model . It may be
necessary in such efforts to take into accoun t
growth inhibitors and promoters in such a
model, since Lavender and Hermann (1970 )
have pointed out the importance of thes e
substances in their studies of light and photo -
period effects in Douglas-fir . Although there
is information to build on with respect to re d
pine and Douglas-fir (see above), further wor k
will be necessary with Douglas-fir to utiliz e
the information effectively . Clearly, specifi c
studies of translocation and growth in wester n
hemlock, ponderosa pine, and a true fir ar e
needed .
Mineral Nutrition
A number of books cover the general field
of mineral nutrition and specifically that of
forest tree species (Baule and Fricker 1967 ,
Bengtson 1968, Epstein 1972) . The aspects of
particular concern in the Coniferous Biom e
are mineral uptake and cycling, and the role
of mineral elements in metabolic processes .
Mineral cycling studies in second-growt h
Douglas-fir forests have been carried out for
over a decade (Grier and Cole 1972) . Mineral
cycling is important in the nutrition of th e
trees since limited nutrient capital is available .
These studies need to be extended to th e
other species of special importance in th e
Coniferous Biome program .
The importance of nitrogen in chlorophyll
production and the close correlation between
chlorophyll contents and CO 2 uptake were
pointed out by Keller and Wehrmann (1967 )
with reference to Picea abies and Pinus sylvestris
. The widespread occurrence of nitrogen
deficiency in Douglas-fir in western Washington
and Oregon (Gessel et at . 1965) give s
reason for careful attention to this element i n
studies of coastal Douglas-fir in the Coniferous
Biome . Also it will be wise to make a
sufficiently broad spectrum of mineral analyses
to detect low levels of other element s
which might be limiting photosynthesis or
growth .
The foregoing indicates that a large back -
ground of information on terrestrial production
processes in woody plants is already
available. With respect to Douglas-fir, the
species currently receiving most emphasis i n
the Coniferous Biome, the background i s
appreciable and useful, but often lacking i n
specific data needed for the construction of
mathematical models . These deficiencies must
be made up for adequate modeling of processes
in this species. With other species of
special concern in the Biome-western hemlock,
ponderosa pine, and true firs-muc h
more background information as well as
specific data is needed in order to develo p
effective production models .
A cknowledgments
The work reported in this paper was sup -
ported in part by the University of Washingto n
and in part by National Science Foundatio n
Grant No. GB-20963 to the Coniferous Fores t
Biome, U .S. Analysis of Ecosystems, Inter -
national Biological Program . This is Contribution
No . 37 to the Coniferous Forest Biome .
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