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Manuscript of dissemination article. Will be published in the international
journal “Journal of Tree Sciences” after the end of the conference
Choice of willow (Salix spp.) clones for establishment short rotation
forest plantations in Estonia
Katrin Heinsoo, Andres Koppel
Estonian Agricultural University, Institute of Zoology and Botany, Riia 181, 51014,
Tartu, Estonia; katrin@zbi.ee
Keywords: energy crop, Estonia, production, Salix, willow
Abstract: We estimated wood production in different Salix viminalis and S.
dasyclados clones during 9 consecutive years in one of experimental fields in Estonia.
The main aim of this study is to evaluate annual yield and suitability of a set of
willow clones originating from the Swedish Energy Forest Programme in Estonian
environmental conditions. The only clone of S. dasyclados, used in the current study
showed the highest growth potential throughout the whole experiment. The ranking of
six S. viminalis clones according to productivity differed in different years. We
conclude that suitability of certain clone for commercial use can not be evaluated by
short-term experiments. Clone evaluation period should exceed the first rotation
cycle. In long run genetic diversity of plantation ensures optimal yield during variable
climatic conditions and possible attacks of pathogens.
Introduction
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Willow (Salix ssp.) plantations have been found to be among the most perspective
short rotation crops in Nordic countries. The average annual wood dry matter (WDM)
yield of willow plantations is about 5 t dry matter per hectare (Aronsson et al., 2002;
Heinsoo et al., 2002). Fast growing species like willow have high nutrient demand
and fertilisation (either mineral fertilisers or municipal sewage) increases in most
cases WDM more than twice. Production over 8…16 t ha-1 is needed in Swedish
commercial willow plantations in order to reach economic break-even level
(Rosenqvist, 1997). The major climatic factor limiting willow productivity in high
nutrient supply is precipitation during the growing season (Lindroth and Båth, 1999).
Water use efficiency of willows is clone-specific (Weih and Nordh, 2002). Hence
clone selection is important for maximising short rotation forest production.
In
Nordic conditions late frost could reduce willow production. A single occasion of late
spring frost may cause severe damage of a plantation and reduce its productivity for
many years (Verwijst et al., 1996; Ögren, 1999). Frost sensitivity of willows is clonespecific and depends on fertilisation regime. Willow clones differ also in their
pathogen tolerance. Therefore choice of suitable genetic material before plantation
establishment is a crucial problem.
In Estonia systematic study of willows was initiated in 1993-1994, when seven
experimental willow plantations were established by using several Salix viminalis and
S. dasyclados clones selected within the Swedish Energy Forest Programme (Koppel
et al., 1996). The local climatic conditions in Estonia are rather similar to that of the
southern part of Sweden, where the area of willow plantations is over 12 000 ha
(Lindroth and Cienciala, 1996). Willow plantations can be used also as vegetation
filters in order to purify wastewater or to utilise municipal sludge (Perttu, 1998).
According to the development plan of Estonian energy sector, the share of renewable
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energy sources should be almost doubled in the next decade. We predict increase in
the area of willow plantations for various purposes in Estonia during next years.
Hence, additional information about suitability of planting material in local
environmental conditions is needed. The main aim of the current study is to evaluate
the suitability of different clones in terms of their productivity for practical use in
Estonia.
Material and methods
Experimental field site
The studied plantation is situated in eastern Estonia on a typical poor mineral soil. A
detailed description of the site is published earlier (Koppel et al., 1996). In May 1993,
the plantation was established with cuttings of six S. viminalis clones (78101, 82007,
78112, 78021, 78183 and 78195) and one S. dasyclados clone (81090). Clone
numbers correspond to the Swedish clone numbering system. Below, only numbers
written in bold are used for each clone. Cuttings of each clone were planted in four
randomly selected plots (16*16 m2 or 8*16 m2) in double rows (distance between the
rows 1.25 and 0.75 m) (Fig. 1). Planting density was 20,000 plants per hectare. In
May 1994, shoots were cut at 5 cm above the ground to promote denser sprouting.
Two plots per clone were fertilised with mineral fertiliser in June every year. In first
two years 60 kg of N, 0…26 of P and 0…40 of K was applied to these plots. From
1996 the annual application of fertiliser was 160, 40 and 70 kg of N, P and K,
respectively. Mechanical weed control was carried out in 1993 and herbicides (Quick
+ Expand) were applied in 1994. Plantation was harvested by a harvester in March
1998.
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Mix of 7
clones
Clone trial,
32
clones
1995,
21
12
07
07
83
fertilised
83
control
21
95
12
90
95
07
01
01
12
95
01
90
83
12
90
21
21
01
83
07
90
16 m
16 m
mm
Figure 1. Scheme of the willow plantation.
Methods
For wood production studies we used the allometric relations between shoot diameter
and biomass. We measured once per year diameter of all living shoots at 55 cm above
soil surface (D55), if D55  4 mm in 20 stools (from two different row sections) per
plot. Thus the calculated wood dry matter (WDM) yield included the wood and bark
dry biomass of only living shoots. The exclusion of dead shoots caused a difference
between actual shoot productivity and WDM. The latter represents the harvestable
biomass. All measurements were carried out during shoot dormancy period in late
autumn.
The biomass of shoots was calculated with the help of power equation: DW =
0.953*D552.494. The parameters of this allometric relation were found on the basis of
shoot D55 and dry weight (DW) data of more than 1000 shoots from both species from
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different years, fertilisation levels and clones. Adjusted R2 of the equation was 0,953.
Shoot dry weight was determined after drying the shoots at 80 C until constant
weight.
Average stool DW was calculated from the corresponding parameter values for plots
with same clone and fertilisation level. The values of the annual WDM yield were
found as the difference between the average stool DW of the current and previous
year. The only exceptions are WDM in 1995 that includes biomass increment during
1994 and 1995; and WDM in 1998, the first year of the second rotation period of the
plantation.
Results
Average stool dry weight (DW) of willows increased exponentially during both
rotation cycles. The differences between DW of fertilised and control plants increased
over time of a rotation cycle (Fig. 2).
g per plant
3000
2000
control
fertilised
1000
0
1993
1995
1997
1999
2001
2003
year
Figure 2. Average dry weight (DW) of all studied willow stools.
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Annual WDM yield in the same year/fertilisation level showed high variability –
standard error of a dataset varied from 8 to 25 % of the average value. The highest
growth potential during the whole experiment was shown by fertilised plot of the
clone of S. dasyclados. In non-fertilised plots WDM of S. dasyclados was lower than
that of some S. viminalis clones. The ranking of six S. viminalis clones according to
annual WDM yield differed throughout the study period (Table 1). For example,
fertilised plots of clone 07 that showed the poorest growth during the first rotation
cycle ranked the third among S. viminalis clones during the second rotation cycle.
Furthermore, the ranking of clones differed if the fertilised and control plots were
compared in the same year. For example, at the end of both rotation cycles (1997 and
2002) clone 12 was one of the most productive among fertilised plots. In control plots
the same clone was the least productive.
Table 1. Ranking of studied willow clones according to their productivity in different
years in descending order
Fertilised
Control
1995
1997
2002
1995
1997
2002
90
90
90
01
01
90
95
95
83
95
07
01
83
12
12
90
95
07
01
01
07
12
21
95
21
83
95
07
90
83
12
21
01
83
83
21
07
07
21
21
12
12
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Discussion
In last decades bioenergy production in Sweden has increased up to 17 % in 2000
(Swedish Energy Agency, personal communication). In the other Baltic region
country, Estonia 12.1 % of primary energy was produced from peat and wood fuels
(2.2 and 9.9 * 1012 Wh, respectively) in 1996. (Eesti …, 2001). The share of
renewable sources in the primary energy is expected to increase more than 1.6 times
by 2010 (Kütuse…, 1998). Therefore information about productivity of energy crops
in Estonian climatic conditions is urgently needed. Moreover, we foresee expansion
of willow plantations as vegetation filters for wastewater purification in small
communities. In spring 2003 we are planning to establish more than 20 hectares of
willow plantations for wastewater purification in three villages. Which clones should
be used in these new plantations?
Data analysis of experimental willow plantation show that on poor mineral soil the
average annual WDM yield of a stool over eight years is 274 g. Fertilisation increases
stool WDM yield up to 490 g. In plantation of 20 000 plants per hectare the
productivity figures are 5.5 and 9.8 tons of dry wood per hectare, respectively. These
are smaller numbers than reported previously (Heinsoo et al., 2002). Moreover, our
data show significant decrease in the actual density of plantation during the second
rotation cycle that decreases the actual productivity figures even more. There could be
many reasons, e.g. drought during the vegetation period, late frost in the spring,
pathogen attacks etc. that should be analysed in detail in future.
Growth of different clones in the same year/fertilisation level showed high variability.
However, ranking clones according to annual WDM yield throughout the first two
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rotation periods showed that among S. viminalis clones there was no unique dominant.
The leader in control plots, clone 01, was not among the best in fertilised plots. The
best producers in fertilised plots at the end of one rotation cycle (clones 95 and 83, in
the first and second rotation cycle, respectively) showed less than average WDM in
the other rotation cycle. Almost all the studied clones showed advantage in some
particular case.
Therefore we conclude that the suitability of certain clone for commercial use can not
be evaluated by the short-term experiments or even by the results of only the first
rotation cycle. Furthermore, genetic diversity of plantation should be positive to
ensure optimal yield during various climatic conditions and attacks of several
pathogens and pests. We decided to use four clones of S. viminalis (01, 12, 21, and
83) for establishment of new plantations. Clones 01 and 95 were excluded from the
list because of their frost-sensitivity as reported earlier (Heinsoo et al., 2002). Despite
partial recovery their productivity was low in fertilised plots during the second
rotation cycle.
Acknowledgements: The study was supported by Estonian Science Foundation grant
ETF 4831 and by EC grant LIFE 00 ENV/EE/000924.
References:
Aronsson, P., Heinsoo, K.; Perttu, K., Hasselgren, K. 2002. Spatial variation in aboveground growth in unevenly wastewater-irrigated willow Salix viminalis plantations.
Ecological Engineering 19, 281-287.
Eesti energeetika 1991-2002. http://www.mkm.ee/dokumendid/[Energeetika]91-00.doc
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Heinsoo, K., Sild, E., Koppel, A. 2002. Estimation of shoot biomass productivity in
Estonian Salix plantations. Forest Ecology and Management 170, 67 –74.
Koppel, A., Perttu, K., Ross, J., 1996. Estonian energy forest plantations – General
information. In: Perttu, K., Koppel, A. (Eds.) Short Rotation Willow Coppice for
Renewable Energy and Improved Environment. Swedish University of Agricultural
Sciences, Department of Short Rotation Forestry 57, 15-24.
Kütuse- ja energiamajanduse pikaajaline riiklik arengukava. 1998. Riigi Teataja, I
05-.03.1998, 19, 295.
Lindroth, A., Båth, A., 1999. Assessment of regional willow coppice yields in
Sweden on basis of water availability. Forest Ecology and Management 121, 57-65.
Lindroth, A., Cienciala, E., 1996. Water use efficiency of short-rotation Salix
viminalis at leaf, tree and stand scales. Tree Physiology 16, 257-262.
Ögren, E., 1999. Fall frost resistance in willows used for biomass production. II.
Predictive relationships with sugar concentration and dry matter content. Tree
Physiology 19, 755-760.
Perttu, K., 1998. Environmental justification for short-rotation forestry in Sweden.
Biomass and Bioenergy 15, 1-6.
Rosenqvist, H., 1997. Salixodling – kalkylmetoder och lönsamhet. Acta Universitatis
Agriculturae Sueciae, Silvestria. Swedish University of Agricultural Sciences 24,
Uppsala.
Verwijst, T., Elowson, S., Li, X., Leng, G., 1996. Production losses due to a summer
frost in a Salix viminalis short-rotation forest in southern Sweden. Scand. J. For. Res.
11, 104-110.
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Weih, M., Nordh N.-E. 2002. Characterising willows for biomass and
phytoremedation: growth, nitrogen and water use of 14 willow clones under different
irrigation and fertilisation regimes. Biomass and Bioenergy 23, 397-413.
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