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FSH 2409.26f - SEED HANDBOOK
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CHAPTER 400 - PLANNING FOR CONE AND SEED COLLECTION
Contents
410
411
PLANNING AND ORGANIZATION FOR CONE AND SEED
COLLECTION
Planning
420
421
422
423
424
CONE AND SEED CROP ESTIMATES
Forecasting Cone Crop Estimates Using Reproductive Buds
Cone Crop Surveys
Cone Crop Rating
Seed Crop Evaluation
430
431
432
433
DETERMINING SEED MATURITY
Cone Color
Seed Cut Test
Specific Gravity
440
CONE COLLECTION METHODS
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410 - PLANNING AND ORGANIZATION FOR CONE AND SEED COLLECTION.
Planning and organization are two of the most important steps involved in the cone
collection process. The planning process for cone collection actually begins when
silvicultural prescriptions are written and a decision is made on the method of
stand regeneration. If he regeneration method involves direct seeding or planting,
then the entire planning process for seed collection is set into operation. Planning
and organization for cone collection includes several steps beginning with the
determination of long-term seed needs and ending with delivery of cones or seed at
the extractory or storage facilities (seedbank). Because of the relatively short time
available for cone collection, most arrangements must be made in advance to ensure
efficient cone collection and shipment to the Bessey Nursery for seed extraction and
storage.
411 - Planning. Planning for cone collection involves basic planning and
implementation planning.
1. Basic Planning. Included in the basic portion of the cone collection
planning process are:
a. Estimate long-term needs. This is accomplished by reviewing reforestation
needs and including these needs in the ten-year seed plan. The need for current
year collection is determined by using the ten-year seed plan and seed inventory
data. If the inventory shows that the current seed supply is below required needs,
it will be necessary to collect seed when the first collectible crop is available.
b. Establish cone collection priorities. After priorities are determined, include
cone collection as part of the District and Forest work schedule.
c. Establish collection area and stand priorities. This requires consideration
of seed zones and elevations, seed collection stands, seed production areas, special
areas, and so forth.
d. Determine collection method. Existing timber sales or special sales for the
purpose of cone collection should be utilized whenever possible. Note: only mature
cones and seed from freshly cut trees should be collected.
Cones should be collected from good individual trees (phenotypes) within good
stands. In timber sales, good phenotypes from which seed is to be collected should
be marked prior to felling.
If good phenotypes are to be retained for repeated collection and for tree
improvement purposes, cones should be collected by climbing. If funding for cone
collection is limited, select only trees which can be climbed and picked efficiently.
The following guidelines can be used to determine if a tree is commercially pickable.
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Species
Engelmann spruce
Blue spruce
Ponderosa pine
Lodgepole pine
Douglas-fir
White fir
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Minimum Pickable
Cones per Tree
600
200
100
1000
500
75
2. Implementation Planning. After basic planning has been completed,
develop an action plan for the actual cone collection or seed purchase.
420 - CONE AND SEED CROP ESTIMATES. Once seed needs are known, the next
important step in the planning process for cone and seed collection is estimation of
potential seed crops. If little seed is available, considerable time and effort can be
saved by deciding very early in the planning process not to collect. However, if a
potential moderate to bumper seed crop is available the entire planning process for
seed collection can be developed and executed in a timely and efficient manner.
Estimates of potential seed crops should only be made when there is a need
identified in the Ten-year Seed Plan for cone collection.
421 - Forecasting Cone Crops Using Reproductive Buds. When reproductive buds
have formed, 1 to 2 years before seed fall occurs, seed collectors can determine, by
appropriate sampling, if a potential cone crop is developing. Only potential cone
and seed crops can be estimated because many factors may cause reproductive
structures to abort or destroy developing seeds. It cannot be determined if a seed
crop is available until shortly before seed maturation and collection.
Early forecasting is based upon sampling to determine the numbers and proportion
of female reproductive buds relative to vegetative buds. An estimate of potential
cone crops can be determined for all conifers by sampling a minimum of three
branches from each of ten dominant trees well distributed throughout the collection
area.
Since female reproductive buds are produced in different areas in the crown
depending upon species, sample branches should be collected only from the cone
producing portion of the crown for the species involved. In the spruces and true firs
collect samples only in the uppermost 1/3 of the crown. For all other species collect
sample branches in the upper 2/3 of the crown. Do not sample branches in the
lowest 1/3 of the crown since no seed should be collected in this part of the crown
because of increased potential for self-pollinated seed.
When sample branches have been collected during late fall or winter prior to
"flowering," a distinction must be made between reproductive buds (male and
female) and vegetative buds. Depending on species and time of collection, female
buds which develop into cones may be recognized externally. However, sometimes
the buds need to be sectioned or sliced in half longitudinally to reveal internal
structures. Another method of recognizing bud types is by "forcing" the sample
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branches to flush by placing the sample branches in water in a warm, well-lighted
room. This will cause the buds to break dormancy and open, permitting
identification of female, male and vegetative buds.
Generally, reproductive buds are larger than vegetative buds, and female buds tend
to be more pointed than male buds. When buds are sliced (sectioned) or bud scales
are removed, female buds have an oval or football-shaped structure resembling a
miniature cone with their spirally arranged cone scale primordia. Male buds are
flatter and wider than the females and have a characteristic miniature raspberry
shape.
Generally, female buds tend to be located subterminally and sometimes along the
branch near the terminal end of the branch. They are usually produced on vigorous
terminal or lateral branches, and greater numbers occur on branches exposed to
sunlight. Males are usually found on the basal 2/3 of branches and frequently occur
on shaded and often less vigorous and smaller branchlets. The greater the
proportion of female buds to vegetative buds, the greater the potential cone crop.
Unfortunately, the quantitative relationship between bud counts and actual cone
crops is not well defined and considerable variation exists between species, areas,
and years. Repeated evaluations and keeping of good records on flowering, cone,
and seed production are necessary to establish these relationships by species, areas,
and years.
Excellent illustrations and photographs of seed production cycles, reproductive
cycles, reproductive structures, and cone and seed development are included in the
following publications:
Several species
Dobbs, et al. 1976. Guideline to collecting cones in B.C. conifers.
Lodgepole pine
Owens, John N. 1984a. The reproductive cycle of lodgepole pine.
Engelmann spruce
Owens, John N. 1984b. The reproductive cycle of interior spruce.
Douglas-fir
Allen, George S., and Owens, John N. 1972. The life history of
Douglas-fir.
422 - Cone Crop Surveys. Forecasting availability of potential cone crops must be
coordinated with estimating the size of the potential cone and seed crop. The best
method to estimate cone crop size is by counting female strobili before they become
cones. With experience it is relatively easy to count female strobili, using
binoculars, on elongating branches of trees up to 50 feet tall. It is best to observe
the trees in early July because any female strobili have appeared by then and they
are not yet obscured by needles. By early July, second year pine conelets can also
be estimated. These conelets will be the current year's pine cone crop. Cone crop
surveys should be conducted in areas of high cone collection priority. It is
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recommended that District staff responsible for cone collection visit potential cone
collection areas in the field in early July to estimate potential crops. Although
these reports are due in the Regional Office each year by July 15, periodic
inspection of developing crops should be continued throughout the summer.
Additional observations are necessary to check progress of the developing crop,
especially when determining time of seed maturity and collection. Problems that
may result in partial to complete crop failure, such as insect attack, can be
evaluated during these inspections.
Weather conditions affect flowering and cone and seed development from time of
flowering and pollination until time of seed maturity in late August or early
September. As cones and seed approach maturity they become less susceptible to
damage resulting from weather extremes but more susceptible to cone and seed
insect damage.
Cones and seed are susceptible to attack and destruction by a variety of cone and
seed insects (Hedlin et al. 1980). During light seed years higher percentages of
cones and seed may be damaged by insects. Insect damage may occur at any time
during cone and seed development. Brown, discolored or aborted flowers, discolored
areas on cones, exist holes and frass (insect work), pitch exudations, and deformed
cones are evidence of insect attack. Cone cutting tests are the best method of
determining the extent of damage. When certain types of cone or seed insect
damage are anticipated or detected at an early stage of development, corrective
control measures should be evaluated and utilized, if warranted. Most types of
damage and the insects causing the damage are described and illustrated in the
publication entitled "Cone and Seed Insects of North American Conifers" (Hedlin et
al. 1980).
423 - Cone Crop Rating. To estimate cone crop size, use a numerical rating system
based on visual observations of tree crowns and subjective assessments of the
relative amounts of cones present. Personnel conducting the examinations to
determine cone crop ratings should walk through the stands and observe the
volume of the current year cones on a number of well-distributed, representative
dominant and co-dominant trees. The more trees observed, the better the rating
will be. To insure best visibility, the observer should stand with the sun to his/her
back. The following rating system should be used and recorded on form R2-2470-8,
Request for Cone/Seed Collection Funds (See sec. 730, exhibit 01).
CONE CROP RATINGS AND CRITERIA
Crop Ratings
None
Light
Medium
Heavy
1
2
3
4
Criteria
Few cones on less than 25% of seed trees
Few cones on more than 25% of seed trees
Many cones on 25-50% of seed trees
Many cones on more than 50% of seed trees
"Few" and "many" cones are relative and subjective determinations based on species
and experience. For example, 50-100 cones on true firs would be classified as
"many". This number on spruce or Douglas-fir would be rated as "few." When
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rating cone crops, observations should be made in that part of the crown where
cones are normally produced. In true firs, cones are produced in the top 4-6 whorls
of branches; in spruces and Douglas-fir, cones are produced in the upper 2/3 of the
crown; in the pines, cones may be produced over the entire crown. Generally, the
smaller the crop the greater the chances are that they will occur in the upper crown.
Generally, collectable crops are those rated as medium and heavy (ratings 3 and 4).
Light crops may be collected when seed is critically needed. Collection of light seed
crops, however, will significantly increase costs.
Two common errors in rating cone crops are: (1) estimating numbers of old cones
that have already shed their seeds, especially non-serotinous lodgepole pines, and
(2) evaluation of roadside trees which may produce more cones than trees inside the
stand because of their increased exposure to sunlight. Ratings should be
determined separately for each species to be collected.
424 - Seed Crop Evaluation. Once cone crop estimates have been determined and
potential collection areas have been designated, estimates of seed yield and seed
maturity are obtained from cone cutting tests. These tests, conducted in late July to
mid-August, are necessary for determining if the developing seed crop will yield
adequate amounts of high quality seed. Cutting tests are used to determine when
seed has reached maturity and can be collected. Evaluation of the potential seed
crop involves slicing cones longitudinally and cutting of extracted seeds (see sec.
432).
Estimates of a collectable seed crop can be determined at this evaluation. Cone
samples for cutting tests should be taken from a minimum of five trees well
distributed throughout a collection stand. Sample cones should be obtained from
various aspects and levels within the cone-producing portion of the crowns.
As with cone crop rating, determination of sound seed can be done in conjunction
with other field work.
Sample cones should be sliced longitudinally through the center of the cone, except
true firs which should be cut 1/4-1/2 inch from center, with a sharp knife or cone
cutter. A count is made of the exposed filled seed on one face of the cut cone
(ex. 01). The half-section count provides a measure of the number of filled seed per
cone.
A more accurate method is to extract and count the total number of filled seed per
cone determined by crushing the seed with the finger or the tip of a knife to reveal a
firm, white to cream colored female gametophytic tissue (endosperm) (sec 432, ex.
02.) This method is especially good to use with lodgepole pine since lodgepole cones
are hard and difficult to section. It is easy to extract the seeds from lodgepole by
dipping the cones in boiling water for 10 seconds, then placing them in an oven at
65 degrees C (150oF) for 3 to 4 hours.
Cone crops are collectable when the average number of seed filled with mature
endosperm and embryos on one face of a cut cone, or the percent of sound seed per
scale, equals or exceeds the minimum standards shown in the following table. It
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should be remembered that little sound seed is produced in the tip of the cone and
essentially no seed is produced in the basal 1/5 of the cone. Therefore, in
determining percent of sound seed per scale, count the number of sound seed and
scales in the center 3/4 of the cone.
Minimum Sound Seed per Cone for Collectable Crop 1/
Species
Spruces
Ponderosa pine
Lodgepole pine
Douglas-fir
True firs
Number/Cut Cone Face
7
7
5
5
10
Percent Sound Seed/Scale Area
66-2/3
66-2/3
50
50
50
1/ These minimum amounts should be raised 2-3 per cut face or 5-10 percent in a
good seed year when yield is above average. When seed reserves are very low,
minimum can be reduced 1-3 per cut face or 10-15 percent.
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424 - Exhibit 01
DOUGLAS-FIR CONE ILLUSTRATION
SEE THE PAPER COPY OF THE MASTER SET
FOR SECTION 424 EXHIBIT 01.
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430 - DETERMINING SEED MATURITY. Seed must be mature before cones are
collected. Degree of seed maturity at time of cone collection will greatly affect seed
viability and seedling quality. Low viability caused by immature seed often results
in low vigor and abnormal seedlings. Seed germination may be as much as 40 to 60
percent lower when seed is collected two to three weeks before the seed is fully
mature. This problem is especially acute in high elevation stands where low
viability rates may be a normal problem. Early cone collection may also result in
cones that are difficult to open (case-hardening); thus, little or no seed may be
extracted. Collection of immature cones often results in rapid molding and heating,
because of high moisture levels, which may further reduce seed viability.
Cones must also be collected before natural seed fall or the seed crop may be lost.
Once cones begin to open, seed dispersal may be very rapid. The total cone
collection period for some species may be only 10 to 14 days; consequently, early
determination of seed maturity is extremely important.
August 20 is an approximate date to use for planning to begin collecting. Generally
cone collectors tend to want to pick cones before seed is mature. Cutting and
caching of cones by squirrels usually begins considerably before cone and seed
maturity; therefore, squirrel activity does not indicate when seeds are mature. This
further emphasizes that cones collected from squirrel caches should be very
carefully assessed for seed maturity.
Because seed maturity will vary with species, climate, geographic location,
elevation, field sampling is required. Several cone and seed traits can be used to
determine maturity and time of collection (ex. 01). The following criteria can be
used in determining seed maturity.
431 - Cone Color. As cones develop and seeds mature, a change in cone color
usually occurs. The normal green cone color changes to various shades of brown,
olive green, purple or other colors depending upon species. Cone color is only an
indicator of ripeness, and there are many color variations within species. Cone color
changes are often subtle and may be difficult to distinguish.
Immature cones, when cut in half lengthwise, will display a light-colored interior
surface. When exposed to air for a few minutes this surface will begin to turn
brown, much as the surface of a peeled apple turns brown when exposed to air.
Conversely, a mature cone will show dark interior surfaces immediately upon being
cut open.
432 - Seed Cut Test. Seed maturity can best be determined by cutting the cone and
individual seeds lengthwise and inspecting color and development of the seed coat,
seedwing, and endosperm. This procedure can be used to estimate seed counts,
effects of insects or diseases, and stage of development. The seed is cut
longitudinally with a razor blade or scalpel and the contents examined with a 10X
hand lens (ex. 01 and 02).
Cut seed tests should be made on seeds collected from all aspects and levels within
the crown because of early maturation associated with locations exposed to the sun
and lower portion of the crown.
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430 - Exhibit 01
SEED MATURITY CRITERIA
Species
Engelmann spruce
Picea engelmannii
Cone and Seed Appearance
Cones - green tinged with red to shiny brown.
Specific Gravity 1
0.90
Seedwing - detaches from cone scale, golden
brown.
Seedcoat - firm, brittle, brown to black, seed snaps
when cut with sharp instrument.
Embryo - yellow-green, 90% of cavity length.
Blue spruce
Picea pungens
Cones - green tinged with red to pale shinybrown.
0.95
Seedwing - detaches from scale, brown.
Embryo - yellow-green, 90% of cavity length.
Ponderosa pine
Pinus ponderosa
var. scopulorum
Cones - green to yellow-green to brownish-yellow,
russet brown to purplish-brown.
0.85
0.95 Black
Hills
Seedwing - detaches from scale, light brown.
Seedcoat - firm, golden brown to brown.
Embryo - white to yellow, nearly fills cavity
endosperm color is yellow to cream.
Lodgepole pine
Pinus contorta
var. latifolia
Cones - light brown, yellow brown (avoid old, grey
cones).
Not good indicator
Seedwing - detaches from scale, brown.
Seedcoat - dark brown to black.
Embryo - white to yellow-green, nearly fills cavity,
endosperm yellow to cream color (avoid
collecting seeds with grey-white endosperms).
Douglas-fir
Pseudotsuga menziesii
var. glauca
Cones - green with brownish or purplish tinge.
Information
unavailable
Seedwing - detaches from bract, golden
brown.
Seedcoat - golden brown
Embryo - yellow-green, almost filling
cavity.
White fir
Abies concolor
Cones - yellow-green, green-purple, to bright
yellow-brown.
Seedwing-detached from scale 2 ,
0.85
brown with deep magenta edge.
Embryo - pale yellow-green, almost filling embryo
1 Test for specific gravity immediately after picking.
2Cones disintegrate rapidly after reaching maturity. Timing of cone collection is therefore very
critical. Cones must be stored in a cool, moist condition for after ripening.
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cavity, endosperm firm, nonmilky, cream
color.
432 - Exhibit 01
(from Dobbs et al. 1976)
THE SEED CUTTING TEST
This test should be used with other indices of maturity to arrive at a tentative date
to begin cone collection. (The cutting test should not be confused with the less exact
procedure described on page 19 for evaluating lodgepole pine cone crops.)
In the cutting test, each seed is sliced exactly in half longitudinally with a razor
blade or scalpel (Figure 12A, B). The contents of 20 to 30 filled seeds are then
examined with a 10X hand lens (Fugure 12C). Generally, as conifer seeds mature,
their embryos elongate and become yellow in color, while the endosperm changes
from a viscous milky condition to a firm consistency (similar to the meat of a
coconut); the seedcoat and seedwing also darken in color. In most cases, embryos
must have elongated to 75% of their potential length to assure seed viability. An
embryo's potential length is the length of its cavity within the endosperm (Figure
12D, E). After picking, some further development, called "after-ripening" may
occur.
The cutting test should not be made earlier than the final week of July, because up
to this time unfertilized ovules may appear to be developing normally; i.e., they will
contain endosperm and will appear to be filled. However, because they have not
been fertilized, they lack embryos and cannot become viable seeds. Between late
June and mid-July, most of these unfertilized ovules cease development and their
endosperm tissue will shrivel. Therefore, by delaying the cutting test until after
this period, the danger of inflating seed yield estimates by counting these
unfertilized ovules will be avoided. The extent to which embryos in fertilized ovules
have developed will also depend in part on the date at which the cutting test is
made. At the beginning of August, embryos may not exceed 50% of their potential
length and further checks are advised. Once the embryos begin to elonagate past
this stage, they usually do so rapidly and may react 90% or more of full size within
2 to 3 weeks.
For most species, collection of cones can begin when the majority of embryos exceed
75% of the length of the cavity within the endosperm, and the endosperm is firm. A
further check on seed ripeness can be obtained by leaving the sliced seeds
uncovered overnight at room temperature. If the seeds are sufficiently developed,
the embryo and endosperm will show little shrinkage and curling and will retain a
relatively firm, fresh appearance. Considerable shrivelling and shrinkage away
from the seed coat indicates that the moisture content of the seed is still too high
and that collection should be delayed. Mature and immature Douglas-fir seeds are
illustrated in Figure 12D,E.
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432 - Exhibit 1--Continued
Seed Cutting Test
SEE THE PAPER COPY OF THE MASTER SET
FOR SECTION 432 - EXHIBIT 01--CONTINUED.
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432 - Exhibit 02
SEE THE PAPER COPY OF THE MASTER SET
FOR SECTION 432 - EXHIBIT 02.
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433 - Specific Gravity. As seeds and cones of conifers mature, specific gravity of the
cones decreases because of water loss. Guides to cone ripeness based on specific
gravity of freshly picked, sound cones are available for several species (sec. 430, ex.
01). Tests for specific gravity should be made immediately after picking fresh cones.
These tests are not valid for cones on the ground, in squirrel caches, picked from
felled trees with a delay in time of testing, or cones with insect damage, because
cone moisture loss is related to factors other than cone and seed maturity. Specific
gravity of cones within the same species may vary with geographic location. For
example, ponderosa pine cones are considered mature when specific gravity has
dropped to about 0.85; however, ponderosa pine cones in the Black Hills, for
example, are considered mature and collectable when specific gravity decreases to
about 0.95. Cone ripeness also appears to be related to latitude. In the Black Hills
it has been reported that cone ripening progresses from north to south (Van Deusen
and Beagle 1973).
Fast and accurate measurements of cone specific gravity can be made using a
graduated cylinder to determine cone weight and volume. The size of cylinder
needed depends on species involved. A 1,000 ml cylinder is probably best to use for
most ponderosa pine cones. Smaller cylinders are better to use for species with
smaller cones because graduations on these cylinders permit more accurate
readings.
Determination of seed maturity should not be based on estimates of cone specific
gravity alone because of possible variation within species in specific gravity of
mature cones. A combination of cone and seed characteristics should always be
used in determining when to collect seed.
The following procedure for determining cone specific gravity is fairly simple:
1. Fill the cylinder to a convenient level with water and record amount; such
as, 600 ml (Figure 1A).
2. Place a cone in the cylinder without splashing water out. If the cone sinks,
specific gravity is greater than 1.00 and cannot be determined more accurately. The
difference between the measurement with a floating cone and the initial
measurement is the cone weight. For example, if the water level with floating cone
is now 750 ml, cone weight is 750-600 = 160 grams (Figure 1B).
3. With a thin wire or needle (dissecting) submerge the cone and record new
water level. The difference between the submerged cone water level and the initial
level is the cone volume. For example, if the water level with submerged cone is
775, cone volume is 775-600 = 175 grams (Figure 1C).
4. Specific gravity = weight divided by volume: 150 :175 = 0.86.
When a minimum of five cones from five trees have specific gravities equal to or
lower than those listed in section 430, exhibit 01, cone collection can begin.
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433 - Exhibit 01
Figure 1
(Barnett 1979)
SEE THE PAPER COPY OF THE MASTER SET
FOR 433 - EXHIBIT 01.
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440 - CONE COLLECTION METHODS. Several methods of collecting cones or
seed are used in the field. The most common methods are summarized below and
are listed in decreasing order of control of genetic quality of seed and recommended
collection methods.
1. Standing Trees. Collection of cones from standing trees is possible for most
species in the central and southern Rockies including Engelmann spruce, ponderosa
pine, Douglas-fir and the true firs. In general, it is not a recommended procedure
for lodgepole pine except when small seedlots are required for special purposes.
Collection of seed from standing trees is recommended when seed is to be collected
from individual superior trees or several good phenotypes in small stands and when
the seed trees are to be retained for tree improvement or other reasons. Cones may
be collected from standing trees by climbing and hand picking, clipping from within
the tree or from the ground, tree shakers, picking by hand or clipping from
mechanical lifts, shooting with rifles, or by topping.
2. Felled Selected Individual Trees. Collection of cones from felled trees is the
method of collection generally used for species which are not readily or safely
climber or which cannot be efficiently picked such as spruces, true firs, and
lodgepole pine. Small timber sales may be programmed for cone collection by this
method. Merchantable material can then be utilized after cones are collected.
Tree felling must coincide with seed ripening. Prior to felling selected trees, it is
necessary to test for quantity of seed per cone and seed maturity (see sections on
seed crop estimates and determining seed maturity). These tests can be made on
cones collected by climbing and hand picking, by clipping, or by shooting the cones
with a rifle.
Seed must be collected from a minimum of 20 widely scattered individual trees in
order to maintain a broad genetic base in the seedlot.
Seed collection by this method should be limited only to those areas where quantity
and quality of cones and seed are acceptable and where the wood can be salvaged.
Cone pickers can pick approximately 3-4 bushels of Engelmann spruce and
lodgepole pine and 6-8 bushels of Douglas-fir cones per picker-day from felled trees
with medium to heavy cone crops (Dobbs et al. 1976).
3. Timber Sales. Cones may be picked from trees felled during logging
operations. Cone collection from slash and debris in a logging operation is difficult.
Frequent inspections of cones by the collector are necessary to ensure that the cones
and seed were mature at the time of felling and that the cones have not opened and
a part or all of the seed crop lost. Arrangements with loggers for felling selected
trees in units to be harvested in advance of the regular operation avoids slash
problems. Cone collection rates for this method are similar to those for collecting
from felled selected individual trees, but large volumes of slash may reduce
collection speed.
Seed must be collected from a minimum of 20 individual trees.
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4. Squirrel Caches. The least desirable method of cone collection is to collect
from squirrel caches. Quality of seed from caches is always questionable since
parent trees are usually unknown and some cones in caches may have been
collected too early for normal seed maturation. Squirrels usually collect seed from a
few individual trees, often related, resulting in a limited genetic base which is
undesirable. Often the majority of cached seed was collected from the most prolific
seed producers, irrespective of tree quality. Squirrel caches may be very small in
some areas even in good seed years if there are few squirrels. Occasionally squirrel
caches may be totally lacking even when squirrels are present.
Collection of squirrel cached cones is acceptable in designated seed production areas
where the caches are located well within the seed production area (minimum of 200300 feet of stand boundary). Collect only current year cones having fully mature
and undamaged seed. Wet cones and partially rotted cones should not be collected.
Moist cones should be at least air dried prior to shipment to the nursery for
extraction.
If seed from squirrel caches is to be used, then seed from a minimum of seven
caches should be mixed together to maintain a minimum genetic base (squirrels
usually cache cones from 3 to 4 trees per cache).
5. Open Market. Little seed should be purchased on the open market since
this collection method offers very little or no control of seed origin and quality. This
does not preclude local cone purchases from areas designated by the Forest Service.
Shrubs. Specialized procedures for various shrub species are documented in "Seeds
of Woody Plants in the United States." (USDA forest Service 1974).