Genetics of Giant Sequoia1
Lauren Fins W. J. Libby2
Besides being a national treasure because it is so spectacularly beautiful, giant sequoia is a genetically fascinating
species. These most massive of all living organisms, some of
which live more than 3,000 years, once flourished around
the world in natural populations, and are currently planted
worldwide as ornamentals and as a renewable wood resource.
Yet their natural range today is confined to a narrow distribution along the west side of the Sierra Nevada Mountains in
California, with eight disjunct populations, or groves, in
the northern part of the range and a series of generally larger
and more continuous populations in the southern part of the
range. Fossil evidence indicates that the gross morphology
of the species has changed little since the Miocene and early
Pliocene, that is, for the past 20-30 million years! Given
these facts, questions about the patterns and magnitude of
genetic variation almost ask themselves.
In this paper, we try to answer broadly the question: "If
you have seen one giant sequoia, have you, indeed, seen
them all?" In more scientific terms, we have tried to detect,
quantify and describe patterns of genetic variation in natural
populations of this species. It is important to study this
genetic variability for at least three practical reasons:
(1) Some populations may prove to be better adapted
and faster growing than others when planted outside of the
native range. Which populations do well may not be the
same for different regions. Thus, a series of common-garden
tests that sample many populations should be conducted
in each region before a serious commitment to planting
sequoia in that region is made.
(2) If planting is to be done in or near a native grove, it
is important to know whether the propagules (seeds or
cuttings) should be obtained from local parents only, or whether
propagules from other parts of that grove, or even from
outside the grove, should be permitted or even preferred.
(3) When giant sequoia is purposefully bred for one or
more purposes, it will be useful to know the patterns of
variation for a variety of traits in order to better devise
effective breeding schemes.
More than 30 of the 73 named giant sequoia groves have
been sampled, and various combinations of trees from these
groves are now growing in common-garden provenance tests3
1
An abbreviated version of this paper was presented at the Symposium
on Giant Sequoias: Their Place in the Ecosystem and Society, June 23-25,
1992, Visalia, California
2
Professor, Department of Forest Resources, University of Idaho,
Moscow, ID 83844-1133; and Professor, Department of Environmental
Science, Policy and Management - Forestry, University of California,
Berkeley, CA 94720
3
Provenance tests are usually common-garden studies whose purpose
is to describe and quantify genetic differences among the origin populations
of the samples.
USDA Forest Service Gen. Tech. Rep.PSW-151. 1994.
in California, Idaho, France, Germany, and New Zealand.
Data are available from 4-, 7- and 12-year-old plantations in
New Zealand, from a 5- and 6-year-old plantations in Idaho,
from 9-year-old plantations in Germany, and from 11-year-old
plantations in California.
At the risk of oversimplifying the answer to our question, we will state here for the record that if you have seen
one giant sequoia, you have not seen them all. Although we
do not yet have a complete picture of its genetic architecture,
its levels of genetic variation appear to be lower than the
average of those observed for other gymnosperms. Nonethe
less giant sequoia displays substantial genetic variation in
the biochemical, morphological, physiological, and growth
traits thus far studied.
Variation Among Populations
Biochemical Traits
We began our studies of giant sequoia with the expectation that we would find high levels of biochemically
expressed genetic variation distributed throughout the
species' range. We based that expectation on the observation
that many long-lived, woody species maintain high levels
of genetic variation (Hamrick and others 1979), although
recent analyses indicate that those with relatively narrow
distributions tend to have lower levels of genetic variation
than those that are widespread (Hamrick and others 1992).
Our analyses of isozymes4 showed giant sequoia to be below
average in this kind of genetic variability compared to other
long-lived, woody perennials. For example, giant sequoia's
average heterozygosity (one measure of variation) is 0.140
(Fins and Libby 1982) compared to an average of 0.177 for
other long-lived, woody perennial species or compared to an
average of 0.165 for those with narrow distributions (Hamrick
and others 1992). Of this isozyme variability, about 10
percent was distributed among different giant sequoia groves;
the remaining 90 percent occurred within groves. This pattern
is similar to that of most of the long-lived, woody species thus
far studied, or perhaps indicates slightly more variability
among groves than the 7 percent variation among populations
that is common for other gymnosperms (Hamrick and others
1992).
We also found clear differences between the northern
and southern giant sequoia grove samples, with the northern
groves less variable than the southern ones and a progressive
4
Isozymes are alternative forms of enzymes and are used frequently to
describe and quantify genetically determined biochemical variation within
and among populations.
65
increase in within-grove isozyme variation from north to
south. Although the differences we observed were relatively
small, they were nonetheless statistically significant and may
be important considerations both for the wise management of
the native populations and for the distribution of seeds from
the native populations for planting elsewhere.
Morphological Traits
Individual giant sequoias differ in traits such as foliage
color, crown shape, and stem taper. Occasional trees have
such deviations as variegated foliage or drooping branches.
Yet, with a casual glance, most young giant sequoias appear
to be remarkably similar in appearance. Although giant
sequoia generally has a more predictable crown form in
youth than is typical of most other conifers, a small study of
rooted cuttings sampling five of the native populations and
planted in northern Idaho showed statistically significant
differences among populations in average branch angle, crown
diameter, and crown shape (Du and Fins 1989).
In a study of seedlings from 26 of the native giant
sequoia groves, cotyledon numbers ranged from 3 to 6 and
varied in frequency among regions, among groves, and among
families within groves. Twelve percent of that variation
occurred among groves, 21 percent among families within
groves, and 67 percent among individuals within families
(Fins 1979; Fins and Libby 1982). The sample from the
Placer Grove (the most northern native population) was
particularly interesting, because, unlike other grove samples,
it included a high proportion of 6-cotyledon seedlings and
no 3-cotyledon seedlings.
Physiological Traits
Germination tests using seeds from 26 native groves
showed significant differences among the population samples
and among families within populations (Fins 1979; Fins and
Libby 1982). Germination ranged from 2.1 percent for the
Case Mountain Grove to 50 percent for the Cabin Creek
Grove, with 13 to 17 percent of the observed variation
attributable to variation among populations (groves) depending
on whether nongerminating families were included in
the analysis.
Work done in Germany found highly significant differences among populations in frost resistance of 2-year-old
sequoias (Guinon and others 1982). This same study showed
a large, negative, statistically highly significant correlation
between frost resistance and winter damage of seedlings
from the same populations. Correlations between frost
resistance and elevation of the origin populations were
statistically significant, but were weak or absent between
frost resistance and grove latitude or longitude.
In the study conducted in northern Idaho, differences
among populations were statistically significant for amount
of winter damage to field-planted rooted cuttings in one of
two years of assessment. Although seasonal patterns of the
development of freezing tolerance were similar among
four of the five population samples, the Cedar Flat Grove
66
displayed a seasonal pattern that was significantly different
(P<0.05) or nearly so (P<0.10) compared to the patterns of
the other four populations (Du and Fins 1989).
In the Idaho plantation, the dates when shoots began
and ceased elongation were not statistically different among
populations. However, in the Foresthill experiments in
California, flushing date (measured as amount of new shoot
growth in early May) varied both among groves and among
individuals (clones) within groves, and there was a tendency
for trees from the more northern groves (nearer to Foresthill)
to flush earlier than trees from the more southern (distant)
groves. But, like other traits, there was much variation in
flushing date within the grove samples.
Early survival was generally high in the Idaho and New
Zealand plantations. Substantial early mortality occurred in
some German and California experiments, but in no case
in these studies was there statistical significance for the
differences observed among groves, or for differences among
families or clones within groves.
Growth Traits
Table 1 presents a summary of results from the samples
of nine groves that were included in most of 10 commongarden tests, plus results from the Placer and Deer Creek
Groves in the few tests that included them.
With respect to height and stem-volume index, the
provenance tests were consistent only for the small outlying
Placer Grove (only six mature sequoias), the southernmost
Deer Creek Grove (about 30 sequoias), the Raincliff Forest
in New Zealand, and two trees at Hermeskeil in Germany
(data for the latter are not shown in table 1), all of which
exhibited below-average growth in all tests in which they
were included. The likely explanation is that many of the
propagules from these origins are inbred and do poorly as a
result. For the rest of the 30+ groves that were sampled, the
common-garden experiments that have data available do
not provide a consistent picture, either with respect to the
statistical significance of among-grove variation, or with
respect to the relative performances of the various grove
samples (table 1; Libby, Fins and Mahalovich, manuscript
in preparation).
At the three German plantations, differences among
grove samples in 9th-year height were statistically highly
significant (Dekker-Robertson and Svolba 1993), as were
several age-trait combinations in three experiments in two
plantations at Foresthill, California (table 1; Libby, Fins and
Mahalovich, manuscript in preparation). Differences among
populations in 4th-year height, diameter, and terminal shoot
elongation were statistically significant for the field-planted
rooted cuttings from five populations growing in northern
Idaho (Du and Fins 1989). Statistical tests were not available
from the New Zealand plantations.
Performance of samples from the North Calaveras,
Redwood Mountain (sometimes called Whitaker's Forest),
and Mountain Home Groves is particularly interesting. Most
early plantings, particularly in Europe, came from the North
USDA Forest Service Gen. Tech. Rep.PSW-151. 1994
Table 1 -Comparison of heights (H) and stem volume index (SV) for selected provenances of giant sequoia in ten common-garden experiments. 1
Grove
1
H
2
United States
F1stek
SV
H
SV
---
F1seed
H
SV
Es
H
---
-
-
-
---
+
+
Placer
---
---
North Calaveras
+
-
Nelder
-
---
McKinley
+
++
+
+
Redwood Mountain
+
++
++
++
+
-
+
Giant Forest
+
++
-
-
+
+
Atwell Mill
-
-
-
-
---
+
---
+
Germany
BG
H
Us
H
Ra
H
Ka
H
+
+
---
New Zealand
Ha
Be
H
H
SV
--+
+
-
++
+
-
+
++
+
++
+
---
---
+
++
+
+
+
+
++
+
-
+
---
---
-
+
-
+
+
-
---
-
++
Mountain Home
++
+
+
++
+
+
+
+
++
---
+
-
Wheel Meadow
+
++
+
++
-
-
-
---
+
-
-
---
Black Mountain
+
-
+
-
++
-
---
-
---
Deer Creek
---
---
Flstek = Foresthill Experiment I, stecklings (rooted cuttings); age 11
Fl seed= Foresthill Experiment l, seedlings: age 11
F2stek = Foresthill Experiment 2. stecklings; age 11
Es = Escherode, seedlings and stecklings; age 9
BG = Bad Grund. seedlings and stecklings; age 9
Us = Uslar. seedlings and stecklings; age 9
Ra = Rai, stecklings; age 4
Ka = Kakahu, seedlings: age 7
Ha= Hamner, seedlings; age 7
Be = Beaumont, seedlings; age 12
Calaveras Grove, the discovery site of giant sequoia in 1852.
More recently, many seed collections have been made and
distributed from Mountain Home State Demonstration
Forest and from the University of California's Whitaker's
Research Forest in the Redwood Mountain Grove. Surprisingly, the North Calaveras Grove sample is performing poorly
in the three Foresthill experiments, where (other than Placer
Grove) it is the nearest native population. However, both the
Mountain Home and Redwood Mountain/Whitaker's Groves
samples are performing well at most of the test locations.
Atwell Mill, earlier touted as doing well on cold sites, does
not seem to be a generally good performer.
Variation Within Populations
Biochemical Traits
The genetic variation that occurs within a population is
distributed among and within families largely as a function
of the mating system. The isozyme analyses indicate that
some inbreeding occurs in most natural populations of
giant sequoia. This interpretation is based on an excess of
homozygotes (same form of the isozyme within a gene-pair)
among newly germinated embryos, compared to expectations
based on observed allele frequencies (proportions of the
different isozyme forms within the populations) and assumed
random mating within the population. However, the mature
trees in these same populations have a deficiency of
USDA Forest Service Gen. Tech. Rep.PSW-151. 1994.
-
+, - indicates slightly above or below average for the plantation (including
provenances not listed above).
++, -- indicates substantially above or below average for the plantation.
2
Groves listed north to south.
homozygotes, both compared to embryo data and to
theoretical expectation. This indicates that there is selection
against inbred offspring during the development of natural
populations of giant sequoia (Fins and Libby 1982).
Growth Traits
At Foresthill, California, we have three experiments
with giant sequoia that allow us to estimate the amounts and
distribution of variation in growth traits. Two 21-grove
experiments are designed to allow estimates of within-grove
genetic variation. Both are clonal experiments and were
begun when cloning of giant sequoia was not yet reliably
done. Recognizing the uneven quality of propagules available
at the time of planting, the better and more uniform propagules
were allocated to the second experiment, which was also
allocated a better balance of open-pollinated families per
grove and cloned siblings per family. Thus, the data should
be and probably are better in the second experiment than
in the first.
To summarize the more reliable second Foresthill
experiment, with one marginal exception, the families-withingroves components of genetic variation and most of the
clones-within-families genetic components were all positive
for the 17 traits tested (height at several ages, and stem
diameter, stem volume, and crown shape at later ages). These
components of variation were statistically significant
more often than would be likely by chance alone. In general,
67
the families-within-groves component was slightly more
than half as large as the clones-within-families component,
indicating a high degree of relatedness among siblings.
Matings in and among very large-crowned giant sequoia
trees might be expected to produce a combination of some
half-siblings, and many inbred siblings and full-siblings in
open-pollinated families.
The third experiment at Foresthill has eight large
"standard clones" interplanted in the first experiment. These
were mostly drawn from different groves, so the among-clones
component contains all three levels of genetic variation. Of
the 17 traits analyzed in the standard clones experiment, all
had positive among-clones variance components; only three
were statistically non-significant, two were significant, four
were highly significant, and the remaining eight were very
highly significant (P < 0.001).
Discussion and Recommendations
Several lines of evidence indicate that there is a smallto-modest amount of genetic variation among populations of
giant sequoia, and some north to south trends are evident.
For the most part, the studies indicate at least modest levels
of genetic variation within populations. The second Foresthill
21-grove experiment and the cotyledon data both indicate
that approximately one-third of the within-population
genetic variation occurs among open-pollinated families
within groves; the remainder is segregating among siblings
within families.
With the exception of samples from the probably inbred
Placer and Deer Creek Groves, the differences among groves
that have been observed for growth traits in the California
tests have been small. Nonetheless, there was a wide diversity
of tree sizes and growth rates within the population samples.
Except for Placer and Deer Creek, the largest trees in
samples from any of the other groves greatly exceeded the
mean of the best of them, and the smallest trees in each
grove sample were smaller than the mean of the worst of
them (Mahalovich 1985).
The different relative performances of grove samples at
different locations (table 1) may indicate either true
genotype-by-environment interaction or inadequate and/or
different sampling of groves for different experiments. In
some cases, the sample may have been largely composed of
one or a few above-average families; in other cases, of one
or a few below-average families.
There are some indications that the genetic differences
among groves, among families, and among clones within
families are all increasing with age in the common-garden
tests. This is not surprising and, in fact, is to be expected as
the various test locations accumulate unusual environmental
events. Thus, although these first-decade data indicate
relatively small amounts of among-grove genetic variation,
the conservative approach is to treat giant sequoia as if
this among-grove variation might become more important.
68
This approach should be followed until such time as more
extensive and longer-term data are available.
For the extant native populations, we recommend that
the groves be managed to encourage and enhance natural
regeneration. If, however, planting is necessary in the native
groves, seeds should be used from at least 20 different trees
from the part of the grove where planting is to occur. Such a
strategy will maintain diversity and avoid increasing
next-generation inbreeding. Isolated trees should not be used
as sources of seeds for routine reforestation.
If giant sequoia is to continue to be planted as a renewable wood resource around the world, genetic information
on population, family, and/or individual differences will
become more critical for selecting the most appropriate sources
to meet the long-term objectives of the plantings. Thus, the
native groves of giant sequoia are not only a national
treasure just as they are but will also be important sources of
reliable genetic material for plantings in many other parts of
the world. In this sense, we have a responsibility not only to
maintain the genetic health of our native groves, but to
maintain their genetic integrity as well.
Acknowledgments
We are grateful to John Miller for providing recent New
Zealand data, to Thimmappa Anekonda, Larry Binder, Dave
Harry, Sue Kloss, Deborah Rogers, Kerry Rouck, and Al
Stangenberger for assistance in measuring and analyzing the
recent Foresthill data, to Sierra Forest Products of Terra Bella,
Calif., and the Pacific Southwest Region, USDA Forest
Service, for financial support for the Foresthill measurements and analyses, and to Peg Kingery for reviewing an
earlier version of the manuscript.
References
Dekker-Robertson, D.L.; Svolba, J. 1993. Results of a Sequoiadendron
giganteum ([Lindl.] Buch.) provenance experiment in Germany. Silvae
Genetica 42(45):199-206.
Du, W.; Fins, L. 1989. Genetic variation among five giant sequoia populations. Silvae Genetica 38(2):70-76.
Fins, Lauren. 1979. Genetic architecture of giant sequoia. Berkeley:
University of California; 255 p. Dissertation.
Fins, L.; Libby, W.J. 1982. Population variation in Sequoiadendron: Seed
and seedling studies, vegetative propagation, and isozyme variation.
Silvae Genetica 31:102-110.
Guinon, M.; Larsen, J.B.; Spethmann, W.1982. Frost resistance and early
growth of Sequoiadendron giganteum seedlings of different origins.
Silvae Genetica 31:173-178.
Hamrick, J.L.; Godt, M.J.W.; Sherman-Broyles, S.L. 1992. Factors influencing levels of genetic diversity in woody plant species. New Forests
6:95-124.
Hamrick, J.L.; Linhart, Y.B.; Mitton, J.B. 1979. Relationships between
life history characteristics and electrophoretically detectable genetic
variation in plants. Annual Review of Ecology and Systematics
10:73-200.
Mahalovich, Mary Frances. 1985. A genetic architecture study of giant
sequoia: early growth characteristics. Berkeley: University of California; 98 p. MS Thesis.
USDA Forest Service Gen. Tech. Rep.PSW-151. 1994