GENETIC CONSIDERATIONS IN ECOSYSTEM RESTORATION USING NATIVE TREE SPECIES
.••,
The development of forest
tree seed zones in the Pacific
Northwest of the United States
Brad St Clair
United States Department of Agriculture Forest Service, Pacific Northwest Research Station,
United States
Seed zones and seed movement guidelines con­
tribute to the restoration of native ecosystems
by ensuring adapted and resilient plant popula­
tions. Seed zones have a long history in the Pacific
Northwest of the United States. Plantation for­
estry was initiated in the early twentieth century
with the establishment of the Wind River Nursery
by the United States Forest Service in 1910. The
nursery was establ ished in southwestern Wash­
ington State to reforest and restore large areas
of bare land and understocked forests result­
ing from large forest fires and logging. Initially,
foresters did not pay particular attention to the
off-site sources increased as stands aged, with a
particularly sharp increase in the years after an
extreme cold-weather event.
These observations led in the 1940s to the es­
tabl ishment of the first seed collection zon es and
seed collection gu idelines for Douglas-fir. A sys­
tem to cert ify the sta nd orig in of forest tree seed
was established by the mid-1960s, and in 1966
seed zone maps for Washington and Oregon were
published. These maps were widely used and
have served their purpose of ensuring adapted
planting stock for reforestation and restoration.
In the meantime, rese archers have learned much
source of forest tree seed. Seed came from eas­
ily accessible locations, often lower elevation
more about geographic patterns of genetic vari­
ation in adaptive traits for a va riety of forest tree
species, primaril y from short-term genecological
studies such as those by Campbell {1986) and by
forests near population centres and at logging
operations. By the 1930s, however, it was be­
coming evident that not all plantations were as
productive as they could be, particularly those
at higher elevations, when compared with adja­
cent natura ll y regenerated stands. The gradual
Sorensen (1992). Genecological studies co nsider
genetic variation as found in common garden
trials, and relate that variation to the cl imates or
physiography of seed sources . Consistent, sensi­
decline of trees from non-local sources was also
ble correlations between genetic variation and
evident in two pioneering research studies begun
in 1912: the Wind River Arboretum, wh ich tested
seed-source environments indicate that a trait
has responded to natural selection and ma y be of
trees from around the world for their suitability
io the Pacific Northwest, and the Douglas-Fir He­
redity Study, which addressed questions of type
and location of Douglas-fir {Pseudotsuga men­
ziesii (Mirb.) Franco) parents from which to collect
seed . Mortality and poor growth of trees from
adaptive importance. Based on results from gene­
colog ical studies, se ed zones in Washington and
Oregon were revised, primarily enlarging them in
latitudinal directions, but mostly maintaining ele­
vation lim its (Randall, 1996; Randall and Berrang,
2002). This is because forest trees in temperate
49 THE STATE OF THE WORlD'S FOREST GENETIC RESOURCES- THEMAT IC STU DY
and boreal regions are pr im arily adapted to mini­
mum winter temperatures, which are largely as­
maintaining genetic d iversity and structure of for­
est trees at landscape scales that are likely most
sociated with elevation. Adaptation to aridity is
also important in some regions, and may be par­
ticularly important in the trop ics. Species may also
d iffer in the scale and patterns of genetic va ria­
tion and adaptation, and the revised seed zones
in Oregon and Washington take t hese differences
into account. Some species, such as Douglas-fir,
are tightly adapted to their environments and
may be considered specialist species . Other spe­
cies, like western red cedar (Thuja plicata Donn
ex D. Don), are more generally adapted and may
be considered genera li st species. Consequently,
Douglas-fir has many seed zo nes with relatively
narrow elevation bands of 150 m, whereas west­
ern red cedar has fewer seed zones with elevation
bands of 450 to 600 m (Figure 15-1). An additional
benefit of seed zones is that they contribute to
important for adaptation.
Seed zones and seed -movement guidelines
have he lped to ensure productive, healthy and di­
ve rse fo rests in the Pacific Northwest for the past
half-century and mo re. What have we learned?
First, even with limited or no knowledge of
genetic structure of a species, a reasonable as­
sumption is that native populations are at least
approximately adapted to their local environ­
ments (Savolainen, Pyhajarvi and KnOrr, 2007) .
The question then becomes, how local is local?
Start somewhere. Make assumptions about the
climatic or other environmental variables that
are most important for adaptation , and deline­
ate seed zones based on those assumptions. In
the Pacific Northwest. initial seed zones were
based on climatic variables of cold and drought,
Figure 15-1.
Seed zones for Douglas-fir and western red cedar in Oregon and Wash in gton State, United States
for Douglas-fir
Source: adapted from Randall (1996); Randall and Berrang (2002).
50
western red cedar
GENETIC CO NSI DERATIONS IN ECOSYSTEM RESTORATION USING NAT IVE TREE SPECI ES
vegetation t ypes and p hysiography, especially el­
References
evation . Genecolog y studies indicated th at many
of those zones were too conservative, part icularly
in t he north- south direction and particularly for
some species that were later determined to be
generalists. Revised seed zones t ook int o account
t his new knowledge, but in t he meantime, or igi­
nal se ed zon es based primaril y on cl imat e served
Cam pbell, R.K. 1986. Mapped genetic vanat1on of
Douglas-fir to guide seed transfer 1n southwest
Oregon . Silvae Genet., 35: 85-96 .
Randall, W.K. 1996 . Forest tree seed zones for western
Orego n . Salem, OK, USA, Oregon Department of
Forestry.
their purpose.
Second, short-t erm g en ecology studies are val­
uable for indicating genetic structure important
f or adaptati on and for delineating seed zones
Randall, W.K. & Berrang, P. 2002. Washin g ton tree
seed tran sfer zones. Olympia, WA, USA, Washington
Department of Natural Resou rces.
and seed-movement guidelines. These may be
f ollowed by longer-t erm reciprocal transplant
studies or provenance tests to evaluate long­
term adaptive respon ses, including estimat ­
Savolainen, 0 ., Pyhajarvi, T. & Knurr, T. 2007. Gene
flow and local adaptation in trees. Annu. Rev. Ecol.
Evo/. Syst. , 38: 595-619.
ing productivity g iven climates at the locations
of seed sources and plant ing sites (see Wang,
O'Neill and A itken, 2010) . An important f inding
from these studies is that each species must be
cons idered individuall y, and that t he pattern s
and scale of adaptation are not always obvious
beforehand.
Finally, during t he last fe w decades, scientists
and land manag ers have recogn ized t hat cl i­
mates are changin g and have begun to conside r
management responses. Knowledge of genet ic
variation in adapt ive traits is important for un­
derstanding responses of n at ive population s t o
Sorensen, F.C. 1992 . Genetic varia tion and seed transfer
guidelines for lodgepole pine m cen tral Oregon .
Research Paper PNW-RP-468. Portland, OR, USA,
USDA Forest Service, Pacific Northwest Resea rch
Station.
Wang, T., O'N eill, G.A. & Aitken, S.N. 2010.
Integrating environmental and genetic effects to
predict responses of trees to clima te. Ecol. Appl., 20:
153-163 .
climate change and f or evaluating managem ent
option s to adapt t o climate change, includin g
planting populations adapted to future climates
and ensuring genetic diversity for future evolu­
t ion. The primary lesson from the development of
seed zones in the Pacific Northwest is that, rather
t han w aiting for the genetic knowledge t o accu­
mulate, it is bett er to act based on the best avail­
able knowledge, w hich may be from other spec ies
in other regions, and th en to adjust management
responses based on new knowledge from genetic
studies.
51
Recommended citation: Bozza no, M., Jalonen. R.. Thomas. E., Boshier. D., Gallo, L., Cavers, S., Bordiics, S., Smith, P. & Loo, J., eds. 2014. Genetic considerations in ecosystem restoration using native tree species. State of the World's
Forest Genetic Resources- Thematic Study. Rome, FAO and Bioversity International.
Photo credits:
p. 47 A. Borovics
p. 69 Leonardo Gallo, Paula Marchelli pp. 139-140 Nik Muhamad Majid and team members p. 154 Mauro E. Gonzalez
p. 158 Philip Ashmole
p. 162 Dannyel de Sa, Cassia no C. Marmet, Luciana Akemi Deluci
p. 163 Luciano Langmantel Eichholz (top photos), Osvaldo Luis de Sousa, Elin R0mo Grande
p. 170 Wilmer Toirac Arguelle
p. 171 Orlidia Hechavarria Kindelan
p. 197 Lewis Environmental Services Inc. pp. 217-218,220 Luis Gonzalo Moscoso Higuita pp. 231-232 Fulvio Ducci p. 234 Sandor Bordacs. Istvan Bach
p. 238 Jesus Vargas-Hernandez
p. 239 Alfonso Aguirre
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