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Poplar research in Canada - A historical perspective with a view to the future

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This paper provides a brief history of the development of poplar research in Canada within the broader North American context, as background to the present collection of papers on current Canadian poplar research. After the earliest times and European settlement, a few individual scientists played a pioneering role in early selection and breeding of poplars. The development of farm shelterbelts in the prairies over the last 100ayears, including the widespread distribution of adapted poplars, has had a significant impact on the landscape. In the last 30ayears, industrial strategies for the development and use of poplars have been the most important driver for poplar research. All of these components have in some way foreshadowed the present dramatic leading-edge research in poplar genomics. With the increasing diversity and sophistication of poplar research, particularly in recent years, a need is seen for identification of research priorities and coordination of research activities by disparate parties.
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MINIREVIEW / MINISYNTHE
`SE
Poplar research in Canada — a historical
perspective with a view to the future1
J. Richardson, J.E.K. Cooke, J.G. Isebrands, B.R. Thomas, and K.C.J. Van Rees
Abstract: This paper provides a brief history of the development of poplar research in Canada within the broader North
American context, as background to the present collection of papers on current Canadian poplar research. After the earliest
times and European settlement, a few individual scientists played a pioneering role in early selection and breeding of pop-
lars. The development of farm shelterbelts in the prairies over the last 100 years, including the widespread distribution of
adapted poplars, has had a significant impact on the landscape. In the last 30 years, industrial strategies for the develop-
ment and use of poplars have been the most important driver for poplar research. All of these components have in some
way foreshadowed the present dramatic leading-edge research in poplar genomics. With the increasing diversity and so-
phistication of poplar research, particularly in recent years, a need is seen for identification of research priorities and
coordination of research activities by disparate parties.
Key words: Populus, research history, breeding, shelterbelts, plantations, genomics.
Re
´sume
´:Les auteurs pre
´sentent une bre
`ve historique du de
´veloppement de la recherche sur les peupliers au Canada, dans
le contexte e
´largi de l’Ame
´rique du Nord, comme mise en sce
`ne pour la pre
´sente collection de publications faisant e
´tat de
la recherche canadienne actuelle sur les peupliers. Apre
`slede
´but de la colonisation par les Europe
´ens, quelques chercheurs
individuels se sont faits les pionniers des premie
`res se
´lections et croisements de peupliers. Le de
´veloppement de brise-vent
dans les Prairies, au cours des 100 dernie
`res anne
´es, impliquant une large distribution de peupliers adapte
´s, a exerce
´un
impact significatif sur le paysage. Au cours des 30 dernie
`res anne
´es, les strate
´gies industrielles pour le de
´veloppement et
l’utilisation du peuplier ont propulse
´la recherche sur ces essences. Tous ces e
´le
´ments ont en quelques sortes jete
´les bases
de la recherche de pointe actuelle en ge
´nomique des peupliers. Avec la diversite
´croissante et la sophistication de la re-
cherche sur les peupliers, au cours des re
´centes anne
´es, le temps est venu d’identifier des priorite
´s de recherche et de coor-
donner les activite
´s de recherches par des acteurs he
´te
´roclites.
Mots-cle
´s : Populus, histoire de la recherche, croisement, brise-vent, plantations, ge
´nomique.
[Traduit par la Re
´daction]
Introduction
Poplars (Populus spp.) have always been a distinctive ele-
ment of the natural landscape of Canada, and for the last
century or more, the human-influenced landscape as well.
The aspen (Populus tremuloides Michx.) stands of the Bor-
eal Forest and the aptly named aspen parkland, as well as
the cottonwoods (Populus deltoides Bartr. ex Marsh.) of the
more southern ecoregions of the country play an important
role in our natural ecosystems. Other native Populus species:
black cottonwood (Populus trichocarpa Torr. & A. Gray),
balsam poplar (Populus balsamifera L.), narrowleaf cotton-
wood (Populus angustifolia James), and largetooth aspen
(Populus grandidentata Michx.) also play significant eco-
logical roles. From the time of European settlement, other
poplars, both introduced and domestically bred species and
cultivars, have accompanied and provided support and bene-
fits to human activities. The more striking example of the
latter is the farm shelterbelts of the prairies in which poplars
have a very significant presence.
The history of poplars in Canada is long and complex. A
brief history of poplar research in Canada provides some
background and context to the present collection of papers
on current Canadian poplar research. The diversity and so-
Received 14 February 2007. Published on the NRC Research Press Web site at canjbot.nrc.ca on 19 December 2007.
J. Richardson.2Poplar Council of Canada, 1876 Saunderson Drive, Ottawa, ON K1G 2C5, Canada.
J. Cooke. Department of Biological Sciences CW 405, University of Alberta, Edmonton, AB T6G 2E9, Canada.
J. Isebrands. Environmental Forestry Consultants LLC, P.O. Box 54, E7323 Highway 54, New London, WI 54961, USA.
B. Thomas. Genstat Consulting, P.O. Box 45086, Lansdowne Postal Outlet, Edmonton, AB T6G 2H1, Canada.
K. Van Rees. College of Agriculture & Bioresources, 51 Campus Drive, University of Saskatchewan, Saskatoon, SK S7N 5A8, Canada.
1This minireview is one of a selection of papers published in the Special Issue on Poplar Research in Canada.
2Corresponding author (e-mail: jrichardson@on.aibn.com).
1136
Can. J. Bot. 85: 1136–1146 (2007) doi:10.1139/B07-103 #2007 NRC Canada
phistication of that research has increased dramatically, par-
ticularly in recent years.
The approach taken is essentially chronological, starting
from the earliest times prior to European settlement and out-
lining the major trends up to the present day. Key elements
in the history include the pioneering role of a few individual
scientists in early selection and breeding of poplars, the im-
pact of poplars developed for farm shelterbelts in the prai-
ries, industrial strategies for the development and use of
poplars in the last 30 years and, most recently, the dramatic
leading-edge research in poplar genomics. Poplar research in
Canada and the United States has been closely linked
throughout history. This overview describes how the close
ties between these countries have complemented one another
and led to major advances in poplar research. Some conclu-
sions and lessons can be drawn from the past. An assess-
ment of the present status of poplar research in Canada
must also include consideration of the actual and potential
role of organizations such as the Poplar Council of Canada
(PCC) in identifying research needs, and bringing disparate
parties together to coordinate research activities.
In the beginning
Poplars have been growing in Canada since the retreat of
ice sheets after the last glaciation. Poplar research in Canada
can be said to have a history almost as long, if the gradual
discovery and adoption of uses of poplars in the activities of
native peoples can be considered a simple form of research.
The indigenous peoples of North America regarded poplars
as powerful and sacred medicine trees (Altman 1994;
Moerman 1998, cited in Dickmann et al. 2001). Black
cottonwood was used by tribes on the west coast for dugout
canoes (Moerman 1998). Twigs, leaves, bark, and wood of
native poplars were used variously for medicine, food,
shelter, and heat for people and domestic animals (Marles
et al. 2000; Dickmann et al. 2001).
The early European explorers, prior to the establishment
of the Canada – USA boundary at the Treaty of Paris in
1783, were impressed with the poplar species they observed,
took seeds back to Europe, and planted them in their gar-
dens. According to Sudworth (1934), European botanical
taxonomists Linnaeus and Michaux, named North American
poplars including P. deltoides and P. balsamifera that had
been brought back from explorations in the 1750s to 1770s,
before either Canada or the USA were countries.
Populus tremuloides was named in 1803, and P. trichocarpa
and P. angustifolia were discovered by Lewis and Clark and
named in 1814 before the Canada – USA boundary was fixed
in the Treaty of 1818.
Populus trichocarpa was introduced to Europe from seed
in 1889. Numerous hybrids (putative) between North Ameri-
can and European poplars occurred accidentally in Euro-
pean gardens in the 1750s (Stout 1929; Johnson 1939).
Those poplar hybrids were brought to Canada and the
USA by early settlers when they immigrated to western
Canada and the USA during the Homestead Act of 1862
in the USA and the similar Canadian Dominion Lands Act
in 1872. Homesteaders planted native cottonwood trees as
well as P. deltoides Populus nigra L. hybrids, including
the Carolina poplar and Robusta that are still being planted
today (Stout et al. 1927). The first planned crosses of
North American poplars with European poplars were made
in the United Kingdom by A. Henry in 1912 (Johnson
1939). These hybrids became known as
Populus canadensis Moench (Eckenwalder 1984, 2001)
with reference to a Canadian parent (this cross is also
known, though incorrectly, as P. euramericana.)
Pioneers
Research on poplars began in a more systematic way in
the 20th century. The focus in this paper is on selection and
breeding, but there was also work on the properties and
utilization of poplar timber and fibre. It is important to
recognize that much of the breeding work was stimulated
by the forest industry’s interest in securing and improving
their wood supply, products, and profitability.
The history of poplar research in Canada for most of the
20th century is a story of a few individual scientists who
were pioneers in this field. Their work formed much of the
basis for what we know about poplars in Canada today and,
more particularly, the poplar genetic material currently used
in cultivation. We focus on three key individuals, none of
whom, sadly, are still with us: F.L. ‘‘Frank’’ Skinner, Carl
C. Heimburger, and Louis Zsuffa. All three of these pio-
neers came to Canada from Europe early in their careers.
Frank Leith Skinner (1882–1967) (Fig. 1) was a self-
taught horticulturist who lived and worked in the Dropmore
District of Manitoba where his family moved in 1895 from
Scotland. He studied the flora of Manitoba and experi-
mented with adapting plants to the challenging continental
climate of west-central Manitoba. As well as developing
hardy new strains of ornamental fruit trees and garden flow-
ers such as chrysanthemums and roses, he was the first to
produce fast-growing poplar hybrids suitable for shelterbelts
(Manitoba Culture, Heritage and Tourism 2007). Poplars
were reported to be Skinner’s favourite species, and he in-
troduced several Asiatic species from Kew, England, in the
late 1920s from which he made successful crosses with na-
tive poplars (Roller 1968). The enduring legacy of his life’s
work remains in the Frank Skinner Arboretum located be-
tween Russell and Roblin, Manitoba (Frank Skinner Arbore-
tum Corporation 2007)
Carl C. Heimburger (1899–1990) (Fig. 2) has been de-
scribed as the ‘‘father of forest genetics and tree improve-
ment’’ in Canada (Fowler and Meagher 2002). He was born
in St. Petersburg, Russia, and studied forestry in Denmark at
the Royal Veterinary and Agricultural College, Copenhagen.
He arrived in Canada in 1925, graduating in forestry from
the University of Toronto in 1928. He received his Ph.D.
from Cornell University in 1933, and joined the then Do-
minion Forest Service, at the Petawawa Forest Experiment
Station in 1934 where he finally returned to his first
love — plant breeding — an interest that had started during
his youth in Russia. At Petawawa he initiated breeding
studies on Pinus,Picea, and Populus, subsequently moving
to Maple, Ontario, where he started and led, for more than
20 years, an ambitious research program in forest genetics
for the Ontario Department of Lands and Forests (Fowler
and Meagher 2002). The collection of poplar selections and
cultivars at Maple, started by Heimburger, is still interna-
tionally known though the Maple station has been overtaken
by Toronto’s suburban development.
Richardson et al. 1137
#2007 NRC Canada
Louis Zsuffa (1927–2003) (Fig. 3) devoted his entire pro-
fessional life to the study, cultivation, and breeding of pop-
lars and willows. Born in Yugoslavia, he received his
forestry education and doctorate in forest genetics at the
University of Zagreb. Zsuffa began his work on poplar ge-
netics at the Poplar Research Institute in Novi Sad, Yugosla-
via. He came to Canada in 1966 with a post-doctoral
fellowship at the Faculty of Forestry, University of Toronto.
A year later he moved to the Research Branch of the
Ontario Ministry of Natural Resources where for 17 years
he continued and expanded the poplar research and breeding
program that had been started by Heimburger. The program
expanded beyond Maple, and in eastern Ontario achieved
considerable success in a collaborative effort involving the
Ministry of Natural Resources, Domtar Inc. (a major pulp
and paper company), local farmers, and landowners. The
collaboration expanded to include the University of Toronto
when Zsuffa returned to the Faculty of Forestry in 1984 and
a number of other faculty members became engaged in other
aspects of poplar research, including diseases, economics,
and utilization, as well as breeding and genetics (Balatinecz
and Richardson 2004). Zsuffa was active internationally as
well as within Canada, particularly through the Bioenergy
Agreement of the International Energy Agency and the In-
ternational Poplar Commission.
In Quebec, the Ministry of Natural Resources and Wild-
life started a program of breeding and genetics of poplars in
1969. The program began in southern Quebec with the aim
of developing material suitable for that region. Since then it
has expanded to focus also on poplars suitable for the more
northerly regions of Gaspe
´, Saguenay-Lac St. Jean, and
Abitibi-Te
´miscamingue (Valle
´e 1995). Originally under the
direction of Gilles Valle
´e, who established it and led it for
almost 30 years, the program has continued since his retire-
ment under the direction of Pierre Pe
´rinet.
The work of those Canadian poplar pioneers described
above, as well as others, has given Canada an international
reputation as a leader in poplar breeding and genetics. That
reputation has been enhanced by the international exchanges
of poplar genetic material, research experience, and results,
and researchers from graduate students to post-doctoral fel-
lows and beyond that have taken place particularly in the
last 40 years. Informal bilateral exchanges were comple-
mented by Canada’s formal participation in organizations
such as the International Poplar Commission and the Inter-
national Energy Agency’s Bioenergy Agreement.
History of poplar on the prairies
During the settlement of the prairie region in the 18th and
19th century, immigrants typically brought cuttings of pop-
lar to plant in the New World since they were very familiar
with poplar in their home country (Isebrands and Karnosky
2001). Poplars, whether from their homeland or native
cottonwoods, were planted on the homestead for wind and
snow protection for their farmsteads and livestock, for fuel,
and to decrease soil erosion. Besides settlers bringing plant-
Fig. 1. Frank Leith Skinner (1882–1967). Fig. 2. Carl C. Heimburger (1899–1990) from D.P. Fowler and
M.D. Meagher. 2002. Proceedings of the Royal Society of Canada,
7th series, Vol. 1. Part 2, pp. 128–130. Reproduced with the
permission of the Royal Society of Canada, #2002 Royal Society
of Canada.
1138 Can. J. Bot. Vol. 85, 2007
#2007 NRC Canada
ing material from Europe or the USA, there was a concerted
effort by the government to establish trees on the prairies.
According to Watters (2002), after Canada had acquired the
western interior in 1870, which was considered to be a bar-
ren wilderness, scientific expeditions were sent out to assess
the prairies for large-scale farming. Although the expedi-
tions found the soils to be fertile, the treeless landscape
raised concerns about aridity and the future success of agri-
culture. In addition, the scientific theories of that day sug-
gested that trees also increased rainfall.
Therefore, a large tree planting program was initiated by
the government to afforest as much as one third of the land
base with the goal of increasing settlement through the de-
velopment of successful agriculture, increasing rainfall, de-
creasing evaporation, moderating temperatures, and
providing fuel and building materials (Watters 2002). To
help with this initiative, the government passed the Experi-
mental Farm Station Act in 1886, which would create farms
to provide the trees and extension expertise to change the
prairie landscape. In 1901, tree seedling propagation was
started at the tree nursery in Indian Head, Saskatchewan, by
the Forestry Branch of the Department of the Interior, which
in 1963 was transferred to the Prairie Farm Rehabilitation
Administration (PFRA) under Agriculture Canada where it
remains today as the Shelterbelt Centre (Howe 1986). De-
spite these initiatives, the massive undertaking of planting
the prairies with trees never fully materialized owing to the
lack of planting material and settlers unwilling to participate
in afforesting the landscape. Thus the emphasis from 1887
to 1914 shifted more towards shelterbelt planting, which
continues to this day.
Between 1910 and 1919, cottonwood (P. deltoides) and
Russian poplar (Populus berolinensis Dippel ‘Petrow-
skyana’) were the two dominant poplars utilized in the Tree
Nursery at Indian Head. Other poplar genotypes were bred
in later years (Table 1). Cottonwood trees, considered to be
the fastest growing tree at the nursery, were 9.2 m in height
and 20 cm in diameter after 12 years of growth when
planted in the early 1900s and were often used as fence
posts (Indian Head Forest Nursery Station, unpublished
data, 1908). Cottonwoods were also grown for fuelwood
and 3-year-old plantations could yield three and one-half
cords in 1906. These plantations were generally planted at
1.2 m spacings and often would be intermixed with maple,
ash, elm, and larch. Thinnings were used for fuel. Planta-
tions of Russian poplar were also grown at the Tree Nursery
to determine best cultural practices and yields, since planta-
tion systems were seen to be a viable approach for an eco-
nomic yield (Fig. 4). The production and shipping of poplars
across the prairies varied from year to year, but peak pro-
duction occurred in the 1920s when approximately 32% of
all trees shipped were poplars (Fig. 5). From the 1990s to
the present, the number of poplars shipped ranged from 3%
to 9% of the total trees shipped. In the 1950s, the practice of
shipping poplar cuttings was stopped owing to poor survival,
and the use of rooted cuttings became the norm for planting
at wider spacings of 1.8–2.4 m to reduce competition (Howe
1986). Since 1910, over 32 million poplars have been
shipped and planted across the prairie provinces (Fig. 6).
There was active exchange of materials across the border
to improve poplars for the prairies by the PFRA at Indian
Head and the Prairie Nursery at Morden, Manitoba. John
Walker of PFRA selected a putative hybrid of P. deltoides
obtained from North Dakota and an imported ‘Petrow-
skyana’ clone in the nursery at Indian Head. This clone, sub-
sequently named ‘Walker’, became one of the most widely
planted shelterbelt poplars in the prairies (Cram 1960; Eck-
enwalder 1996). In the late 1960s David Dawson of the
US Forest Service in Rhinelander, Wisconsin, obtained
poplar clones from William Cram at Indian Head and
Louis Zsuffa at Maple, Ontario, when he initiated the US
Forest Service’s North Central Short Rotation Intensive
Culture Program. This program is still active today and
many of the poplar clones acquired from Canada are still
in use in the program (Dickmann et al. 2001).
Industry takes hold — with research support
Industrial activities involving poplar in Canada have
mainly occurred in the last few decades. These activities
have involved development of hybrid poplar plantations
(Fig. 6), and harvesting of natural aspen stands. Both en-
deavours have benefited — and continue to benefit — from
the input of poplar researchers and their research.
One of the first and most successful regional programs in
intensive hybrid poplar plantation management was that in
eastern Ontario, where it was known latterly as the Fast
Growing Forests Program. This programme, which was a
cooperative agreement between the Ontario Ministry of Nat-
Fig. 3. Louis Zsuffa (1927–2003) from J. Balatinecz and
J. Richardson, Poplar Council of Canada, 20 Feb. 2004. Repro-
duced with the permission of the Poplar Council of Canada,
#2004 Poplar Council of Canada.
Richardson et al. 1139
#2007 NRC Canada
ural Resources and Domtar Inc., operated from 1976 to
1995, when Domtar took over management of the planta-
tions (Strobl and Fraser 1989; van Oosten 2000). As men-
tioned earlier in the context of the pioneer Louis Zsuffa
who was the leading scientist in developing and supporting
the program, this was truly a collaborative effort involving
the University of Toronto, the Domtar pulp and paper mill
in Cornwall, Ontario, and local farmers and landowners as
well as the provincial ministry. The eastern Ontario program
produced much practical technical and scientific information
about all aspects of hybrid poplar growing as well as
breeding and was widely recognized internationally (Ontario
Ministry of Natural Resources 1983, 1991). During the
1990s, however, the endeavour shrank considerably with the
gradual withdrawal of Ministry support, and the last activ-
ities ended with the closure of the Domtar mill in Cornwall
in 2005.
Trembling aspen is particularly prominent in the boreal
forests and aspen parkland of the prairie provinces, and thus
it is not surprising that much of the industrial focus on trem-
bling aspen as a commercial species has been centred on the
prairies. Aspen has been sustaining a forest industry produc-
ing pulp, oriented strand-board, and other products in west-
ern Canada for nearly two decades. In the early 1990s,
enormous operations were given license to operate in Alberta
with tenure holdings of 2.9 million ha by Daishowa Maru-
beni International Ltd. (DMI) (1991), and 5.8 million ha
by Alberta-Pacific Forest Industries Inc. (1993). Combined,
these two companies alone produce more than 1 million
air-dried metric tonnes (ADMT) of deciduous pulp per
year (about 90% aspen, 10% balsam poplar). Other decidu-
ous operators include Slave Lake Pulp (210 000 ADMT
pulp, start-up 1991), Ainsworth Engineered (harvests
960 000 m3, start-up 1995), and Tolko (start-up 1996), the
latter two producing oriented strand-board (OSB). Millar
Western and Weyerhaeuser Canada began operations in
Alberta in 1988, and 1989, respectively. These mills pro-
duce pulp and OSB. The combined harvests of DMI,
Weyerhaeuser Canada, Ainsworth, and Footner Forest
Products totals 4.5 million m3/year of aspen and poplar
(Alberta Forest Products Association and Government of
Alberta 2005). These four companies constitute the mem-
bership of the Western Boreal Aspen Corporation.
With this massive expansion in the use of the deciduous
component of the 38 million ha of boreal forest lands in Al-
berta, interest soon developed in enhancing this resource
through tree breeding. In conjunction with these large land
holdings for timber rights being allocated by the provincial
Government, the largest oil-sand deposits in the world were
also being recognized and developed under much of the
same landbase (Schneider 2002). The expanding interests in
the current development of breeding programs were diverse
and include many of the following drivers:
1. Flexibility in land management planning (e.g., imple-
mentation of the TRIAD approach to forest management
including protected, extensive and intensive management
options).
2. Control over fibre flow to the mill with a guaranteed har-
vest from intensive plantations.
3. Dwindling public landbase to operate on with expanding
oil and gas development and therefore reduced fibre
availability.
4. Ability to select and breed for specific fibre characteris-
tics to enhance operational production of mill products
(e.g., pulp).
5. With a reduced rotation to 18–25 years in the boreal, and
7–12 years in the BC coastal regions, private land man-
agement options could be maximized for fibre produc-
tion.
Poplars and aspens lend themselves well to breeding pro-
grams and have attracted a great deal of attention for several
key reasons which include the following:
1. Poplars are relatively easy to breed using the ‘‘cut branch
technique’’, which does not require maintenance of
breeding or seed orchards.
2. There is a wide diversity of species to work with in a
breeding program from both local and exotic sources.
3. Thousands of individuals can be produced in each breed-
ing cycle for screening.
4. Through selection of individual clones, trees exhibiting
hybrid vigour can be propagated (Fig. 7), reducing the
rotation length to harvest from 60 years to 20 years.
5. Both pure native species and hybrid species programs
can be developed and geared to fit within the provincial
and federal government regulations in each region.
Regional programs have developed from one extreme to
the other, from single company programs (e.g., Alberta-
Pacific Forest Industries Inc.) to multi-company programs
(e.g., Western Boreal Aspen Corporation with four member
companies) to government programs such as those of the
Quebec Ministry of Natural Resources and the British
Columbia Ministry of Forests.
Combined with each breeding program is also a need for
both basic and applied research, often in conjunction. Sev-
eral common threads exist between the various programs,
highlighting the need for publishing findings, and sharing of
both material and information. Diseases such as Septoria
canker, Melampsora rusts, Marssonina leaf spot, and Ventu-
Table 1. Types of poplar trees shipped from the Shelterbelt Centre in Indian Head, Saskatchewan during 1910–1970
(PFRA Shelterbelt Centre).
Year Brooks Cottonwood Dunlop Griffin Northwest Russian Sask. Tristis Wheeler
1910–1919 HH
1920–1929 HHHH
1930–1939 HHHH
1940–1949 HHHH
1950–1959 HH HHH HH H
1960–1969 HH HHH HHHH
Note: Sask., Saskatchewan.
1140 Can. J. Bot. Vol. 85, 2007
#2007 NRC Canada
ria shoot blight have had — and continue to have — devas-
tating impacts on plantation-grown poplars and aspens
(Riffle and Peterson 1986). In fact, a major factor contribu-
ting to the demise of the eastern Ontario plantation program
described above was the high incidence of disease that af-
fected the plantations, particularly Septoria (Strobl and
Fraser 1989). Abiotic factors such as cold hardiness, drought
and flood tolerance, and sunscald, often in conjunction with
biotic factors, are also key drivers in research programs
geared at improving and selecting superior poplars and as-
pens (www.poplar.ca/resneeds.htm). Maximizing product
yields and optimizing mill production based on form and fi-
bre quality can also play a key role in a research program.
All of these issues, and others, are receiving attention from
poplar researchers, particularly at universities. The ability to
screen large numbers of genotypes for a series of different
traits is becoming even more important, particularly if pre-
dictions for climate change unfold as expected.
There has been active exchange of aspen provenance ma-
terial between the Western Boreal Aspen Corporation in Al-
berta and the Aspen and Larch Genetics Project and
Cooperative in Minnesota. As a result, Canadian aspen-
based materials are currently under test in the Lake States
of the USA. Reinhard F. Stettler of the University of Wash-
ington, Seattle, Washington, made collections of
P. trichocarpa from British Columbia as part of a major
poplar breeding program (Stettler et al. 1996). The
P. trichocarpa P. deltoides hybrid poplars from this pro-
gram have been widely used for short rotation plantations by
industry throughout western Canada and the USA.
The operational reality of implementing intensive planta-
tion programs also requires answers related regionally to op-
timizing stock type and production methods, site preparation
and maintenance, best silvicultural practices, and harvest
methods. Although information on these aspects can be
shared, local conditions and sites will likely dictate what is
best regionally. The method of producing planting material
will depend on whether aspen or poplar is being grown. For
poplars, either stooling beds can be maintained with selected
clones, or side-branching cuttings can be taken from young
plantations. For aspen, a number of root propagation meth-
ods exist or a micropropagation method can be used in steri-
lized media culture. Aspen do not root from lignified
cuttings. The diversity of operational poplar research is be-
coming ever wider, and extends to assessment of public per-
ceptions of using and growing hybrid poplars (e.g.,
Huybregts et al. 2007, LeBoldus et al. 2007, Neumann et
al. 2007). Industry is often the most direct beneficiary of
such research.
Genomics: a bright future rooted in a rich past
The emergence of genomics has been arguably the most
exciting development in poplar research within the last dec-
ade. The foundation of genomics is the availability of se-
quence information for a significant proportion of the genes
within an organism’s genome. Having access to large-scale
sequence information is akin to having a molecular blue-
Fig. 4. A Russian poplar test plantation planted in 1908, Indian Head Forest Nursery Station (photo by N.M. Ross (1913) found in the
Report of the Director of Forestry, Department of the Interior, Ottawa, 1913).
Fig. 5. Distribution of plant material (total and poplars) across the
prairies from the AAFC-PFRA Shelterbelt Centre since its incep-
tion (PFRA Shelterbelt Centre).
Richardson et al. 1141
#2007 NRC Canada
print, giving researchers unprecedented license to investigate
questions pertaining to the regulation, structure, function,
and genetic variation of large numbers of genes simultane-
ously. The recent publication of the assembled, annotated
draft genome sequence for P. trichocarpa — which features
several Canadians on the author list — is a landmark ac-
complishment for this rapidly evolving discipline (Tuskan
et al. 2006).
Poplar genomics builds upon an exceptional tradition of
tree breeding, genetics, molecular genetics, molecular biol-
ogy, and biotechnology research in poplar, and indeed
would not be possible without the solid foundation of
knowledge, resources, and technologies that continues to
arise from these disciplines. While much of the contempo-
rary molecular-based research has been predicated on a de-
sire to advance the state of commercial poplar applications,
the rise in prominence of Populus spp. as the forest tree of
choice for molecular research also stems from the amenabil-
ity of this genus to experimental manipulation. The suite of
attributes that make Populus spp. tractable to molecular re-
search are eloquently described elsewhere (Bradshaw et al.
2000; Taylor 2002; Tuskan et al. 2006). These same traits
also make Populus attractive for genomics research. Impor-
tantly for genomics, Populus has a modest genome size. The
sequenced genome of P. trichocarpa is estimated to be
485 ± 10 megabases, or approximately 5-fold larger than
the Arabidopsis genome (Tuskan et al. 2006). This relatively
small genome size has facilitated classical genetics ap-
proaches such as the construction of linkage maps (reviewed
in Cervera et al. 1997), and was an important consideration
in the sequencing of the poplar genome.
Canada frequently has been a leader within the interna-
tional poplar genetics, molecular biology, and molecular ge-
netics research communities that have paved the way for
poplar genomics. While many Canadian research groups
have made laudable contributions to this arena, the scientists
of the now-defunct Petawawa National Forestry Institute
(PNFI 1918–1996) merit special mention for their pioneer-
ing research in forest tree molecular biology, molecular ge-
netics, and biotechnology, and in particular for advancing
poplar molecular research. Many researchers passed through
the doors of this research station over the 78 years that it
was in operation, and a large number of Canadian research-
ers active in poplar molecular research today have collabo-
rated with or have been mentored by PNFI researchers.
As described in previous sections, there has been a long
and storied history of tree improvement in Populus in Can-
ada, and these programs laid an essential foundation for the
advent of contemporary genetics research. The classical
breeding and selection programs of individuals such as
Fig. 6. Hybrid poplar plantations in northwestern Saskatchewan (photo courtesy of Mistik Management Ltd.)
1142 Can. J. Bot. Vol. 85, 2007
#2007 NRC Canada
Louis Zsuffa and Gilles Valle
´e made possible the next gen-
eration of poplar genetics research that included quantitative
genetics, molecular genetics, genecology, and systematics.
The first studies were based largely on isozyme techniques
(e.g., Farmer et al. 1988; Rajora and Dancik 1992), which
gave rise in the 1990s to a variety of DNA-based marker ap-
proaches (e.g., Lin et al. 1994; Dayanandan et al. 1998). The
indefatigable Louis Zsuffa, together with colleagues such as
Bill Cheliak (then PNFI) and Bruce Dancik (University of
Alberta), were instrumental in establishing poplar molecular
genetics in Canada. Robert Farmer (Lakehead University,
retired) also used classical and early molecular genetic ap-
proaches to carry out ground-breaking studies on the gene-
cology of Populus.
The 1990s also saw the advent of poplar molecular biol-
ogy and biotechnology. These experimental approaches per-
mitted cloning and functional characterization of specific
genes, as well as manipulation of gene expression. In Can-
ada, poplar molecular biology and biotechnology research
evolved largely from a tradition of research in forest tree bi-
ochemistry and tissue culture. Much of the early research
activity was centred at PNFI. Don Durzan, who carried out
graduate studies with the legendary F.C. Steward (Cornell
University, deceased), was a pioneer of conifer biochemistry
and conifer tissue culture research at Petawawa in the 1960s
and 1970s. Bill Cheliak assumed this mantle after Durzan’s
departure from PNFI, and he and others in this group de-
serve credit for their role in establishing poplar molecular
biology and biotechnology in Canada.
Genomics is a natural progression from molecular genet-
ics and molecular biology. The poplar genome sequence is
in its essence an ultra-fine-scale genetic map, and thus pro-
vides an overarching link between the two nonoverlapping
disciplines. With this genome sequence and other resources
of the poplar genomics toolkit in hand, it becomes feasible
not only to identify and characterize suites of genes that
play a functional role in a trait of interest, but also to iden-
tify the genes that exert genetic control over the trait. In
other words, genomics provides us with the potential to link
genotype with phenotype. Because of this exciting possibil-
ity, genomics is poised to play a role not only in shedding
light on fundamental phenomena of poplar biology, but also
in resolving issues germane to poplar breeding and opera-
tional programs detailed in the previous section.
Poplar genomics burst onto the Canadian research scene
in the early part of this decade, in part owing to the success
of two Genome Canada-sponsored large-scale projects,
Treenomix and Arborea. These two projects have played im-
portant roles in developing poplar genomics resources that
are essential for carrying out genomics research. Notably,
researchers associated with the Treenomix project (www.
treenomix.ca), situated at the University of British Columbia
and the British Columbia Genome Sciences Centre, played
an active role in the development of the Populus tricho-
carpa genome sequence. Together with collaborators at the
British Columbia Genome Sciences Centre, the Treenomix
project carried out essential sequencing required for assem-
bly of the raw genomic sequence fragments into the linkage
groups that correspond to chromosomes, as well as for iden-
tification of genes within these uncharacterized linkage
groups.
Researchers associated with the Arborea project (www.
arborea.ca), located at Universite
´Laval, Laurentian Forestry
Centre, and Queens University, have also contributed to the
poplar expressed gene databank. A major focus of the Ar-
borea project was creation of a large set of activation-tagged
poplars in which the expression of at least one gene has
been constitutively upregulated. This valuable resource can
be used to discover in an unbiased manner novel genes in-
volved in a given biological phenomenon. This group of re-
searchers also generated a suite of transgenic poplars for 24
different genes hypothesized to be involved in wood forma-
tion and defense. These trees also represent an important re-
source for functional characterization of these genes. Both
the Arborea and Treenomix groups have produced cDNA
microarrays for carrying out large-scale surveys of gene ex-
pression.
In addition to these two large-scale genomics projects,
there are several other active poplar genomics research pro-
grams in Canada. This growing, vibrant poplar genomics
community is addressing many questions central to poplar
biology. Some of these groups have contributed to this spe-
cial issue. The advent of poplar genomics and the establish-
ment of a Canadian poplar genomics research community
have almost certainly contributed to the renaissance in pop-
lar research that we are currently enjoying in Canada. As il-
Fig. 7. Block planting of Manitou poplar (male progeny of Walker
poplar) at age 13 in north-central Alberta (photo courtesy of
B. Thomas).
Richardson et al. 1143
#2007 NRC Canada
lustrated here, we are indebted to a number of predecessors
who laid the foundation for genomics research in Canada.
The story goes on
The history of poplar research in Canada has many facets.
This brief review has described some of the more important
ones, including culture and improvement of poplars, shelter-
belts on the prairies, industrial involvement and most re-
cently poplar genomics. Until quite recently, the focus has
been on practical, applied research with immediate and di-
rect benefits to Canadians. Poplar research in Canada today
covers a wide diversity of topics, often with a more basic-
research-oriented approach than in the past. There is also a
diversity of players involved in the research: universities,
federal and provincial governments, and industry. Some-
times a poplar research project is carried out independently
by an individual scientist or organization. Often, however,
there are several partners involved, each with different roles,
e.g., a university carrying out the research on material or a
site provided by industry and with government funding.
Such cooperation is vital to ensure optimal use of intellec-
tual, material, and economic resources and to ensure that
important and practical questions are addressed. In addition,
since issues requiring scientific investigation are many and
researchers and resources are limited, prioritization of re-
search needs is important. Assessment of research needs for
poplars at the national level in Canada has not often been
undertaken, except for limited sectors, such as the manage-
ment of natural aspen and mixedwood ecosystems.
The PCC has tried to identify research needs for poplar
through consultation among its members. One series of is-
sues for research initially identified in 2001 is available on
the PCC Web site (Poplar Council of Canada 2004). More
recent efforts by the PCC, as yet unpublished, have also
been undertaken. The PCC is a national nonprofit organiza-
tion committed to the wise use, conservation, and sustain-
able management of Canada’s poplar resources. First
established in 1977, PCC has members from industry, wood-
lot owners, universities, research establishments, and provin-
cial and federal governments. Its members include most of
the key players in the poplar sector (Zsuffa 2002). As such,
it is perhaps uniquely placed to provide information about
and facilitate communication and coordination amongst the
different stakeholders and their needs. An example of PCC
activities in communication and coordination is a recent
workshop convened by PCC to build bridges between play-
ers in poplar genomics and poplar breeders and growers to
realize the full potential of recent developments in poplar
genomics (Poplar Council of Canada 2006).
Prior to the separate establishment of the PCC, a North
American Poplar Council was formed in the 1970s, under
which scientists from Canada and the USA met jointly in
Ontario, Michigan, and Wisconsin. In recent years, the PCC
and the Poplar Council of the USA (in operation since the
1960s) have met jointly on several occasions, including the
21st Session of the International Poplar Commission organ-
ized jointly by Canada and the USA in Portland, Oregon, in
2000. Proceedings of that session were published in different
forms in both Canada (a special issue of The Forestry
Chronicle, Vol. 77, No. 2, March/April 2001) and the USA
(Isebrands and Richardson 2000).
Probably the most important state-of-the-art publications
on poplar biology and poplar culture in North America are
the two books published by the National Research Council
of Canada, NRC Research Press, in 1996 and 2001 (Stettler
et al. 1996; Dickmann et al. 2001). These books were the
result of the combined efforts of dozens of chapter co-authors
in Canada and the USA who collaborated on updating the
recent advances in our fundamental understanding of the
biology of poplars (Stettler et al. 1996), and on relevant
practical information on how to grow and use poplars in
North America (Dickmann et al. 2001). These two books,
in combination, remain the most up-to date scientific infor-
mation on poplar research in North America today.
Canadian scientists are very prominent in several current
international collaborations involving poplars. The Aspen
FACE research project is the world’s largest field study of
the effects of climate change on the health and productivity
of trees, with emphasis on aspen. The study’s findings on
the altered performance of forest pests under elevated CO2
and O3, published by Canadian senior author and Aspen
FACE steering committee member, K. Percy, have major
significance for future aspen forests in North America
(Percy et al. 2002). Research on riparian ecosystems of
cottonwoods in North America is headquartered at the
University of Lethbridge under S.B. Rood. The program has
revealed the major impacts of river damming on down-
stream environments (Rood et al. 2003).
A number of driving forces have given direction to poplar
research in Canada in the past. In the early years, meeting
basic human needs, particularly for shelter and fuel, were
primary reasons for looking at poplars. In the last century,
however, the scientific motivation has been a desire to im-
prove survival and growth of poplar trees and the quality of
products derived from poplar. These scientific aims were
coupled directly or indirectly with the more basic economic
objective of profit or, to put it less crudely, improving the
value of poplar trees, stands, products, or the ecosystems in
which they grow. Ultimately, curiosity has also been a
deeper motivator. Looking ahead, the drivers for poplar re-
search that are emerging now and will likely become in-
creasingly important in the future are climate change
mitigation, including bioenergy use, and environmental re-
habilitation and enhancement.
Lessons from the past
A number of lessons can be drawn from the past. In sum-
mary these are the following:
.the important role of individuals, such as Heimburger
and Zsuffa, in leading and inspiring others, and of organiza-
tions, such as the AAFC-PFRA Shelterbelt Centre and the
Quebec Ministry of Natural Resources, in supporting the
work;
.the value of long-term continuity, displayed most clearly
by the 100-year history of the PFRA Shelterbelt Centre;
.the different, but complementary, roles of different play-
ers, e.g., the Ontario Ministry of Natural Resources, Univer-
sity of Toronto, Domtar and private land-owners in the
Eastern Ontario hybrid poplar program; and
.the need for cooperation — across disciplines, interests
and borders — to achieve real benefits, seen most recently
in the efforts to bridge the gap between the spectacular sci-
1144 Can. J. Bot. Vol. 85, 2007
#2007 NRC Canada
entific accomplishments of poplar genomics and the applied,
practical needs of poplar growers.
Let us hope that today’s poplar researchers can appreciate
what has already been learned — both the specific scientific
conclusions, and the general principles and strategies — and
build on these for the future.
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... Exotic hybrids were restricted to disturbed urban areas and were not found in natural forests. For over a century, exotic poplar cultivars have been planted as ornamentals and windbreaks throughout North America (Richardson et al. 2007). More recently, poplar cultivars are being used for bioenergy production, carbon sequestration, and phytoremediation (Doty et al. 2007;Richardson et al. 2007;Hinchee et al. 2009;Harfouche et al. 2011). ...
... For over a century, exotic poplar cultivars have been planted as ornamentals and windbreaks throughout North America (Richardson et al. 2007). More recently, poplar cultivars are being used for bioenergy production, carbon sequestration, and phytoremediation (Doty et al. 2007;Richardson et al. 2007;Hinchee et al. 2009;Harfouche et al. 2011). Human activities, especially in urban areas, have brought these exotics into contact with native poplar populations, thereby providing opportunities for exotic genes to escape into native gene pools (Dodet and Collet 2012). ...
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Trees bearing novel or exotic gene components are poised to contribute to the bioeconomy for a variety of purposes such as bioenergy production, phytoremediation, and carbon sequestration within the forestry sector, but sustainable release of trees with novel traits in large-scale plantations requires the quantification of risks posed to native tree populations. Over the last century, exotic hybrid poplars produced through artificial crosses were planted throughout eastern Canada as ornamentals or windbreaks and these exotics provide a proxy by which to examine the fitness of exotic poplar traits within the natural environment to assess risk of exotic gene escape, establishment, and spread into native gene pools. We assessed postzygotic fitness traits of native and exotic poplars within a naturally regenerated stand in eastern Canada (Quebec City, QC). Pure natives (P. balsamifera and P. deltoides spp. deltoides), native hybrids (P. deltoides × P. balsamifera), and exotic hybrids (trees bearing Populus nigra and P. maximowiczii genetic components) were screened for reproductive biomass, yield, seed germination, and fungal disease susceptibility. Exotic hybrids expressed fitness traits intermediate to pure species and were not significantly different from native hybrids. They formed fully viable seed and backcrossed predominantly with P. balsamifera. These data show that exotic hybrids were not unfit and were capable of establishing and competing within the native stand. Future research will seek to examine the impact of exotic gene regions on associated biotic communities to fully quantify the risk exotic poplars pose to native poplar forests.
... Besides conifers, poplars (Populus spec.) play an important ecological and economical role in western Canada (Peterson & Peterson, 1992, Richardson et al., 2007). The genus Populus is tightly linked to human history. ...
... The data also suggest that vessel diameter may be a key trait in evaluating growth performance in a boreal environment. play an important role in North American ecosystems, particularly in the boreal forest and the aspen parklands of the prairie provinces (Alberta, Saskatchewan, Manitoba) in western Canada (Richardson et al., 2007). Poplars (Populus ssp.) are among the fastest growing temperate trees and are considered to be vegetational pioneers (Eckenwalder, 1996, Bradshaw et al., 2000 ). ...
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This study contains a series of experiments to evaluate growth performance and survival of hybrid poplars (Populus spp.) and trembling aspen (Populus tremuloides Michx.) in boreal planting environments in western Canada. Ecophysiological traits related to drought resistance and winter survival were studied and compared with growth in long-term field trials, within and between these two plant groups. The results showed that trembling aspen is more resistant to drought stress and more water-use efficient than hybrid poplars, suggesting that these two groups employ different water-use strategies. Tree height was negatively correlated with branch vessel diameter in both plant groups and was highly conserved in aspen trees from different geographic origins. Hybrid poplars with wider xylem vessel were also more prone to freezing-induced embolism, suggesting that smaller vessel diameters may be an essential adaptive trait to ensure frost tolerance and long-term productivity of hybrid poplar plantations in boreal planting environments. For aspen, provenances ranging from northeast British Columbia to Minnesota were tested in a series of reciprocal transplant experiments across western Canada. The analysis found pronounced increases in productivity as a result of long-distance transfers in northwest direction. Commonly reported trade-offs between freezing tolerance and growth rate were not found in this study. Seed transferred from Minnesota to northeast British Columbia (2,300 km northeast and 11°� latitude north), still outperformed local sources by 17 % in height had more than twice the biomass at age ten. Increased productivity as a result of northwest transfers was not associated with reduced survival. The results suggest that the potential benefits of northward movement of aspen populations in forestry operations outweigh the potential risks, especially in the context of climate change.
... Promising results were also obtained under Mediterranean climatic conditions, where poplar was able to accumulate high amounts of Cu (180 g ha À1 yr À1 ) and Zn (3,500 g ha À1 yr À1 ) (Guidi Nissim et al. 2018). In Canada, poplars are grown for wood and energy production on plantations and under intensive culture (Richardson et al. 2007;Yemshanov and McKenney 2008). However few experiments using poplars for TE phytoextraction have been carried out in the cold temperate countries where willow generally outperforms poplar. ...
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Fast-growing hybrid poplars have been tested for their potential to remove trace elements (TE) from polluted soil in several temperate regions. Despite their potential, they have rarely been tested in countries with a cold temperate climate. The current study screened four different Populus hybrids for phytoextraction of four TEs (i.e., As, Cu, Pb, and Zn) on an abandoned brownfield site in southern Quebec (Canada). The main results showed that under the current experimental conditions, the most important traits determining the actual phytoextraction rate are Biological Concentration Factor (BCF) and TE accumulation in the aboveground biomass, rather than biomass productivity. Although the overall performance of the chosen hybrids was rather poor, the presence of poplar stands enhanced the movement of mobile contaminants in soil, which led to an increase in their concentration in the root zone. This aspect suggests possible strategies for using these plants with high transpiration rates in future phytoremediation projects, including either possible rotation with more effective TE phytoextractor plants (e.g., hyperaccumulators) that can remove high TE amounts that have migrated from the deeper soil layers following poplar plantation, or phytostabilization.
... The first species tested were jack pine (Pinus banksiana Lamb.), tamarack (Larix laricina (Du Roi) K. Koch), and hybrid poplars. The conifers were from local improved seed sources, and the hybrid poplars were imported from poplar programs in Saskatchewan and Ontario, Canada (Richardson et al. 2007). The first experimental plantings were established in small plots in the nearby Hugo Sauer Nursery in Rhinelander. ...
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The United States Department of Agriculture Forest Service established three regional Institutes of Forest Genetics in the United States in the 1950s to improve trees for reforestation and improve the management of forests. The institute in Rhinelander, Wisconsin, started in 1956 as part of the Lake States Forest Experiment Station. Since that time, the “Rhinelander Lab” has undergone changes in research priorities, organizational changes, and name changes while becoming an international center of forest scientific excellence. Many of the researchers’ key findings over the years were published in the Canadian Journal of Forest Research. In this paper, for the 50<sup>th</sup> anniversary edition of the journal, we reflect upon one part of those accomplishments – the history of the contributions of Populus research at Rhinelander. We discuss major research programs and the scientists conducting this work, including: 1) physiology of wood formation, 2) short rotation intensive culture and short rotation woody crops, 3) intensively cultured plantations, 4) physiology and utilization of short rotation poplar yields, 5) breeding and selection, 6) biotechnology and molecular genetics, 7) atmospheric pollution and climate change, 8) phytotechnologies, and 9) ecosystem services. Also, we describe four major international conferences held in Rhinelander and/or hosted by Rhinelander researchers.
... ʀ ʀ ɳ > ʁ ɳ ɷ> ɳ ʄ ɷ> @ ʀ ʀ ʀ ʀ ʈ ʀ ʀ ʈ ʀ ʀ ʀ ʀ @ɳ ʀ ʀ ʀ ʀ ʈɳ >ɳ ʀ ʀ P. deltoides ɿʈ . ɸɳ ʇ> ʀ ɳ ʆ ʀ ɸ ʀ ʇʈ @ ʀ @ >ɳ ʆɳ ʀ ʇ ʀ ɸ @ ʀ > ɷ ʈ ʀ ʀ ʀ ) Richardson et al., 2007 .( ɷ> ʀʀ ɳ > ʀʀ ɳ> ʀ ʀʀ ʀʀ @ʈɷ @ ʀ ʀʀ ʀʀ ʀʀ Perinet, 2007 .( ...
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Because of adaptability to different ecological conditions, cross pollination and heterozygosity, Populus euphratica has high genetic diversity. It could have an important role in superior phenotypes selection, inter and intra specific hybridization processes. The aim of this study was identifing and selection of superior phenotypes of P. euphratica and seed propagation for new genotypes and also selection of elite genotypes by evaluation of growth rate and stem form traits. A total of 29 superior trees from 13 natural stands were selected. Seedlings were produced by seed culture in greenhouse condition. Evaluation of seedlings was performed in a nursery of Karaj Research Station (RIFR) during 2011 to 2013. Quantitative and qualitative characteristics including plant diameter, height, survival percent, number of branches, stem form and branch angle with main stem were recorded. Analysis of variance showed significant differences among the seedlings of superior phenotypes with different habitats for quantitative and qualitative characters. Also Duncan multiple range test showed the diameter progenies of the superior trees of Kerman and Khojir, also height progenies of the Kerman, Khojir, Ahvaz and Zabol displayed the most growth values. Finally, some of seedlings had a suitable qualitative and quantitative growth that can be used in next phase study.
... Populus species and their natural hybrid strains are vitally important in their local ecological roles. Canada has had a long and strong tradition in studying poplars (Richardson et al., 2007). ...
... Finding markets for hybrid poplar timber is crucial for ensuring profitability of this silviculture. Many genomics projects are carried out to increase yields and fiber quality of hybrid poplar (Richardson et al. 2007). Improved fiber quality could lead to use of hybrid poplar wood in the production of high-quality goods, thus increasing the value of the fiber by diversifying its potential uses. ...
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The intensification of forest management through afforestation of high-yielding species such as hybrid poplar is considered a possible solution for re-establishing Quebec's forest industry. However, lack of financial data seems to limit the development of poplar cultivation. This paper is a financial analysis of poplar cultivation for private landowners in the province of Quebec and is based on a scale of actual cost and six different silvicultural scenarios. This study showed that poplar cultivation is profitable when subsidized. Using a sensitivity analysis, we identified the main factors defining a window of profitability for this type of intensive silviculture. The two main factors were the price of wood and government grants. The profitability of poplar farming is sensitive to three other secondary factors: cost of transportation, cost of harvesting, and timber yields. Consideration of these factors is crucial in establishing profitable hybrid poplar plantations.
... These patterns are consistent with those observed in other poplar hybrid zones in North America (e.g., Keim et al. 1989;Martinsen et al. 2001;Floate 2004) and Europe (Lexer et al. 2010;Vanden Broeck et al. 2012). In addition to these two native species, many exotic varieties of poplar have been planted as horticultural trees and used in commercial applications, such as biomass production (Richardson et al. 2007;Hinchee et al. 2009). Given the complex nature of the poplar community in eastern Canada, we needed to understand the fitness dynamics of the native P. balsamifera and P. deltoides hybrid zone before we could identify differences between native and exotic hybrid formation and then assess the potential impacts of exotic hybrids on this native system, which is addressed in our companion paper (Roe et al. 2014). ...
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Hybridization and introgression are pervasive evolutionary phenomena that provide insight into the selective forces that maintain species boundaries, permit gene flow, and control the direction of evolutionary change. Poplar trees (Populus L.) are well known for their ability to form viable hybrids and maintain their distinct species boundaries despite this interspecific gene flow. We sought to quantify the hybridization dynamics and postzygotic fitness within a hybrid stand of balsam poplar (Populus balsamifera L.), eastern cottonwood (P. deltoides Marsh.), and their natural hybrids to gain insight into the barriers maintaining this stable hybrid zone. We observed asymmetrical hybrid formation with P. deltoides acting as the seed parent, but with subsequent introgression biased toward P. balsamifera. Native hybrids expressed fitness traits intermediate to the parental species and were not universally unfit. That said, native hybrid seedlings were absent from the seedling population, which may indicate additional selective pressures controlling their recruitment. It is imperative that we understand the selective forces maintaining this native hybrid zone in order to quantify the impact of exotic poplar hybrids on this native system.
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The principal broadleaves in Interior British Columbia (trembling aspen, paper birch, balsam poplar and black cottonwood) are well distributed across all of the major Interior ecological zones but their occurrence is greatest in the northern areas. Their utilization has gradually increased over the last 20 years, especially in the north. Economic values are low compared to conifer species but shortage of conifer timber as a result of the mountain pine beetle epidemic could drive demand for broadleaves higher. The ecological and non-timber values of broadleaves are very high; however, management practices still favour conifer species. Retention of broadleaves in harvesting and reforestation programs is widely implemented, but at a very low intensity and with little attention to broadleaf silvics. Future management of broadleaves is likely to be based largely on natural regeneration of broadleaves and not nursery production. Investments in genetic research should focus on genecology and gene conservation, as well as facilitated migration studies and investigation of pest resistance.
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This book entitled 'Poplars and Willows: Trees for Society and the Environment' contains twelve chapters. The poplars could equally well be willows, since they are clearly of a single, identified taxon (Chapter 2), selected originally from naturally occurring genetic resources (Chapter 3), but having undergone a process of domestication (Chapter 4) to enhance productivity and perhaps resistance to diseases (Chapter 8) and damaging insects (Chapter 9). The procedures for operationally producing poplar planting material, and for ensuring successful establishment and growth once planted, have been developed, honed and adapted to different regions of the world (Chapter 5). The trees provide shelter, an environmental benefit, to the field crop (Chapter 6). The scientist needs to be aware of the stresses placed on the agroforestry ecosystem by abiotic factors such as drought, salinity and the changing global climate (Chapter 7). The trees in the older plantation in the photo will soon be ready to harvest for a variety of products (Chapter 10) and the person managing this agroforestry system will need to consider the market trends and future outlook for different poplar products (Chapter 11), as well as for the field crops. By its very nature, the scene is one of support for rural livelihoods and sustainable development (Chapter 12).
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At the turn of the century, trees and shrubs were not a noticeable feature on the grasslands of Western Canada. With the settlement of the prairies, tree plantings became widespread as farmers realized the benefits of shelterbelt plantings. The history of prairie tree plantings is closely tied to programmes sponsored by the federal and provincial governments. The federal tree planting programme has remained much the same for over 80 years - to promote tree plantings for shelter and to aid in soil conservation. There has been an increase in field shelterbelt plantings in the past 10 years as farmers become more concerned with soil conservation. In spite of drought, insects and adverse climatic conditions, prairie shelterbelt plantings have been successful and epitomize the faith of prairie farmers.-Author
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In Alberta, Canada, the provincial government currently restricts the establishment of hybrid poplars to private land or small research plantings on Crown lands, because of the unknown risks associated with using non-native trees. Industry is interested in utilizing hybrid poplars on a larger scale for fibre production and reclamation. This interest has driven the need to better understand the genetic risks associated with the deployment of these non-native trees within a matrix of natural poplar stands and agricultural plantings. The first step to understanding the potential risks associated with the use of non-native poplars is to assess flowering phenology and seedling development of both native and non-native poplars growing in the same region. Flowering data were collected and graphed for 38 clones of native Populus balsamifera, 20 clones of native P. tremuloides, and 13 non-native poplar clones (seven hybrid poplar clones and six P. davidiana seedlings) in north-central Alberta. Based on the overlapping flowering patterns and the development of normal seedlings, some potential for hybridization between native and non-native poplars exists.
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This work is NOT from Taxon. It is a book published by Timber Press in 1989, 908 pages, listing 46,000 uses of plants by native American people.
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Survival of seventeen poplar clones six years after planting in 1951 ranged from 0 to 100 per cent. Total height of the surviving 13 clones in 1956 varied from 11 to 25 feet. FNS No. 44-52, a natural hybrid of P. deltoides, was the outstanding clone in the test with a survival of 94 per cent and height of 25 feet. Three clones, FNS No. 44-52, Saskatchewan, and BNW No. 4 demonstrated resistance to disease (Cytospora canker), while ten clones proved highly susceptible. Survival and growth for FNS No. 44-52, 38P38, tristis No. 1 and gelrica were superior to those of Northwest poplar, which exhibited a survival of 75 per cent and height of 18 feet.
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Isozyme analysis was conducted on individuals of Populus alba L., P. tremula L., and P. × canescens Smith to genetically characterize and differentiate species, hybrids, and individuals, and to determine genetic relationships among them. Thirty gene loci, with 71 alleles, coding for 15 enzymes were observed. Individuals could be identified on the basis of their multilocus genotypes. There were 21 unique multilocus genotypes among 23 P. alba clones. Five P. alba clones from Canada were genetically distinct from each other. Each of the 18 P. tremula and 15 P. × canescens clones had unique multilocus genotypes. Thirteen clones had a unique genotype at a single locus. Percentage of polymorphic loci, average number of alleles per locus, and mean observed heterozygosity were, respectively, 50.0, 1.86, and 0.085 in P. alba, 51.7, 1.66, and 0.096 in P. tremula, and 51.7, 1.86, and 0.157 in P. × canescens. Populus alba and P. tremula were genetically distinct from each other and could be distinguished by mutually exclusive alleles at Aco-3, P. tremula-specific gene Mdh-3, and allele frequency differences at 6 loci. Populus × canescens had allele contributions of P. alba and P. tremula. However, their allele frequencies were closer to those of P. alba than being truly intermediate. The mean genetic identity was 0.749 between P. alba and P. tremula, 0.987 between P. alba and P. × canescens, and 0.817 between P. tremula and P. × canescens. Canonical discriminant analysis of multilocus genotypes separated P. alba, P. tremula, and P. × canescens into three distinct groups and portrayed similar interspecific relationship as above. Our results suggested that the putative P. × canescens individuals consisted of a mixture of F1 hybrids of P. alba and P. tremula and their backcrosses to P. alba.
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Five of 6 possible hybrid combinations of the 2 native North American species of Populus sect. Aigeiros with the 3 native species of sect. Tacamahaca have been found in nature. Putative hybrids occur wherever species of the 2 sections are sympatric and sometimes even beyond the range of one or both parents. Although the five hybrids can easily be recognized as a group, each parentage yields hybrids of unique morphology. Hybrids are morphologically intermediate between their putative parents and have an additive chromatographic profile combining leaf flavonoids of each pair. Trees of P X generosa (P. deltoides X P. trichocarpa) and P. X jackii (P. deltoides X P. balsamifera) from natural populations closely resemble artificial hybrids between their presumed parents. Three natural hybrids, P. X acuminata (P. deltoides X P. angustifolia), P. X jackii, and P. X parryi (P. fremontii X P. trichocarpa), are all cultivated as shade trees. Keys distinguish the 5 hybrids from each other and from their parents; each hybrid is described; its nomenclature is clarified; and its range is mapped in relation to those of its parents. -from Author