Download Growing Mixed Forests – waste or value for the future?

NordGen Forest Conference, 20 – 21 September 2016
Growing Mixed Forests
– waste or value for the future?
SUMMARY OF PRESENTATIONS
Nordic Forest Solutions, with reference to mixed forests
Adalsteinn Sigurgeirsson
Icelandic Forest Research / Icelandic Forest Service
____________________________________________
Abstract
At their meeting in Turku on June 29. 2016, the Nordic forestry ministers adopted a roadmap
for the future forest sector co-operation, called Nordic Forest Solutions (NFS)i. The roadmap
builds upon the Selfoss Declaration of the Nordic forestry ministers from 2008ii, and
highlights the important challenges and promotes the solutions that forests can provide. It
aims to strengthen the Nordic voice at regional, European and global level, and identifies
areas where the Nordic forest sector co-operation can help provide solutions – Nordic Forest
Solutions – consolidating and extending collaboration between existing platforms. The
document may also serve as a source of inspiration for further work.
NFS also aims to promote the role of forests in attaining economic, ecological and social
sustainability. Rapidly increasing demand for biomass will affect market development and
associated land use. Finding a balance between biomass production and use, increase and
maintenance of carbon stocks, and protection of biodiversity will be important.
The forest sector plays a major role in meeting these and other challenges by:




replacing non-renewable resources with renewable forest-based materials
promoting economic development and creating new jobs in a bioeconomy
providing general ecosystem services and mechanisms addressing climate change
providing an arena for developing policies to combat social exclusion and stimulate
equality
The multifaceted challenges that societies are facing require many innovative solutions.
Collaboration, research, education and information are important tools in meeting these
challenges.
In this presentation, the NFS-roadmap will be presented with reference to the role of mixed
forests towards reaching the NFS-goals of securing greater forest productivity, ensuring
adaptation in future forests, protecting and enhancing forest biodiversity and improving the
general well-being of Nordic societies.
i
https://www.norden.org/en/nordic-council-of-ministers/council-of-ministers/nordic-council-of-ministers-forfisheries-and-aquaculture-agriculture-food-and-forestry-mr-fjls/nordic-forest-solutions-roadmap-pdf
ii
http://www.nordicforestresearch.org/blog/2014/11/20/selfoss-declaration-achievements-report/
What’s natural? Forest composition and land use changes
in the Nordic countries during 5000 years
Both for conservation reasons and social value, understanding of a landscapes history, such as
changes in species composition and land use, can be crucial.
Forest composition has always been determined by natural properties such as soil and
precipitation, both local and regional, while a considerably newer source of influence is
human land use such as grazing, meadow management, cultivation of cereals and changes in
fire frequencies.
In large parts of the Nordic area, anthropogenic impact has been significant during several
centuries, and in order to understand e.g. an areas long-term biodiversity, outlooks even
further back in time can be valuable. It is however important to remember that the Nordic
countries by no means share the exact same history, but that all areas are the result of natural
properties and traditional management at that specific site – at least up to modern time.
Today’s often comparably homogenous landscapes are a result both of rational forestry
focusing on coniferous forest (often with denser and darker forests as a result) and rational
agriculture with little room for edges, fallows and shrub habitats, but also of coniferous
colonization as an indirect effect of the abandonment of grazing and mowing.
Tove Hultberg, PhD.
Söderåsen National Park
The County Administrative Board of Skåne
Skäralid 747, 264 53 LJUNGBYHED
Tel: 010-224 14 05
Epost: [email protected]
www.soderasensnationalpark.se
The effect of species mixing on tree and stand growth
Hans Pretzsch, Technical University of Munich, Germany
Mixed-species forests can fulfil many forest functions and services better than monospecific stands and receive growing attention in forest science and practice. A string of
recent publications quantifies overyielding of mixed-species stands versus
monocultures of 10-30 % in terms of volume growth.
This presentation will first report to what extent mixed-species stands consisting of
typical European species combinations can overyield mono-specific stands in terms of
volume growth. Second, will be shown how species mixing modifies population
characteristics such as the stand density, tree size distribution, and canopy space filling.
Third, the mixing effects are analysed at the individual tree and tree organ level.
So far, the knowledge about mixed-species stands consists rather of a collection of
phenomena than of general rules or even an overarching theory. However, the
discussion will introduce working hypotheses on how the shown mixing effects result
from niche complementarity and depend on site conditions. Furthermore the effects of
the three dimensional stand structure, the intra-individual volume growth partitioning,
and the specific wood density will be discussed.
Selection of the author’s publications on mixed-species forest stands
Liang, J, … Pretzsch, H, …Reich, PB (2016) Positive Biodiversity–Productivity Relationship
Predominant in Global Forests. Science. ISSN 0036-8075 (In Press)
Forrester, D.I., Pretzsch, H. (2015): Tamm Review: On the strength of evidence when comparing
ecosystem functions of mixtures with monocultures. Forest Ecology and Management, 356, 41-53.
Pretzsch, H., … Bravo-Oviedo, A. (2015): Growth and yield of mixed versus pure stands of Scots pine
(Pinus sylvestris L.) and European beech (Fagus sylvatica L.) analysed along a productivity
gradient through Europe. Eur J Forest Res, 134 (5): 927-947.
Pretzsch, H., Forrester, D.I., Rötzer, T. (2015): Representation of species mixing in forest growth
models. Ecological Modelling 313:276-292.
Pretzsch H. (2014) Canopy space filling and tree crown morphology in mixed-species stands compared
with monocultures. Forest Ecology and Management, 327: 251-264.
Pretzsch H., … Zingg A. (2010) Comparison between the productivity of pure and mixed stands of
Norway spruce and European beech along an ecological gradient. Annals of Forest Science, 67
(7): 712.
[email protected], Chair for Forest Growth and Yield Science, Technische Universität München,
Hans-Carl-von-Carlowitz-Platz 2, 85354 Freising, Germany, http://waldwachstum.wzw.tum.de/
Establishment of high-productive mixtures
Magnus Löf
Two-storied mixed plantations can be designed to meet social, economic and environmental
objectives during forest reforestation and restoration. In addition, the rapid re-establishment of
forests following large disturbances is being seen as one option to increase the contribution of
forests to climate change mitigation. The temporary inclusion of pioneer trees as nurse crops
on disturbed sites can facilitate the establishment of target tree species and may additionally
improve productivity and soil fertility. This presentation reports how nurse trees influence the
growing conditions, and report results from different studies around the world concerning the
influence of fast growing nurse tree species on the growth and performance of target tree
species. Transgressive over-yielding has been observed in several studies that measured
productivity in forests with e.g. aspen or birch growing over shade tolerant target species in
North America, Scandinavia and elsewhere. The use of fast growing poplars or improved
birch as nurse trees and exotic shade tolerant conifer tree species may further increase
production. Such experiments are presently being established in southern Scandinavia.
However, even if productivity probably is increased, more complex forests structures may be
an obstacle for cost-effective management.
Climate change, adaptation and management of risks to boreal forests
Prof. Heli Peltola, School of Forest Sciences, University of Eastern Finland
Under the projected climate change, the mean annual temperature is expected to increase in
Northern Europe until 2100 by 3–6 C° and mean annual precipitation by 11–18% compared to the
current climate, depending on the scenario used for the concentration of greenhouse gases. As a
result, the carbon sequestration and wood production are in general expected to increase in boreal
forests. This is because currently short growing season, relatively low summer temperatures and
small supply of nitrogen limit them. The carbon sequestration and wood production are also
expected to increase in relative sense more in northern than in southern boreal conditions, where the
growth and success of tree species like Norway spruce with shallow rooting may suffer drought
especially on sites with low water holding capacity. In all, the future development of forest
resources is affected both by the current forest structure (age, tree species), intensity of forest
management and projected climate change together with associated increase of various abiotic and
biotic damage risks to forests. Climate change is expected to increase the risk of forest damages,
e.g. by wind storms, bark beetles and fungus, and especially in Norway spruce. Risk of wind
damages are also expected to increase despite of increase of windiness, due to the increase of
duration of unfrozen soil during the most windy season of year, i.e. from late autumn to early
spring. This is because frozen soil improves tree anchorage. However, various damage risks to
forests (e.g. by wind storms) may be decreased at least in some degree by considering them in forest
management and planning (e.g. tree species preference in regeneration and in pre-commercial
thinning, timing and intensity of thinning, final cut). The process-based forest ecosystem and
mechanistic risk models could also offer useful means to study how current forest structure together
with intensity of forest management and projected climate change may affect future development of
forest resources and various abiotic and biotic risks to forests. As a result, proper adaptive
management strategies needed in different regions and time spans could be developed, considering
also the uncertainties related to the projected climate change.
Mixed forests and fungal diseases: potential solutions or problems?
Iben M. Thomsen, Senior adviser, Department of Geosciences and Natural Resource Management,
University of Copenhagen
Most natural forest systems contain a mixture of tree species and tree ages, either conifer / broadleaf
mixtures, or forests containing different conifer species or different broadleaf species. In contrast,
traditional managed forest has often focused on even-aged monocultures, and when they are devastated
by pests or diseases it is tempting to conclude the damage could have been avoided or lessened if the
stands had been contained a mix of tree species.
The concept of using mixed forest stands to lessen the impact of diseases has mostly been based on
indirect evidence via observation, and there are few research based studies. The arguments for and against
may be difficult to prove or disprove.
Possible advantages of mixed forests:
 Fewer host trees mean lower risk of build-up of inoculum and higher likelihood of disease escape.
 Non-hosts act as barriers to spread of pathogens (especially via root systems).
 If one tree species is decimated by disease, the whole stand is not lost.
Possible disadvantages of mixed forests:
 If the pathogens have more than one host, mixing the wrong tree species can increase risks of disease,
especially if more susceptible species cause a rapid disease development.
 The microclimate in mixed stands can be more favourable for infection.
Examples of potential consequences
 Mixing conifer species means fewer root grafts and therefore less transfer of Heterobasidion sp. On the
other hand using Pinus sylvestris to help establish Picea abies may introduce H. annosum early in the
rotation, rather than H. parviporum later.
 Presence of Armillaria sp. in deciduous stands of e.g. Fagus silvatica is thought to give rise to infection
of Phaeolus schweinitzii in Pseudotsuga menziesii, Pinus sylvestris or Larix sp. mixed into the stand.
 Presence of pines susceptible to Gremmeniella abietina or Dothistroma septosporum (e.g. Pinus nigra
and P. contorta) can start an epidemic which spreads to P. sylvestris and Picea abies under the right
weather conditions.
 Young Fraxinus excelsior stands are generally lost due to infection by Hymenoscyphus fraxineus, but if
they are mixed with e.g. Acer sp. or other broadleaves, the forester can build on those trees rather than
clear cut due to ash dieback.
 In Britain Larix sp. has been devastated by Phytophthora ramorum in certain areas, but Picea sitchensis
survived and could be kept as forest cover.
 Presence of Abies concolor and A. lasiocarpa may increase risk of outbreak of Neonectria
neomacrospora in e.g. A. nordmanniana or A. alba.
 Mixing the alternate hosts of various rust fungi (e.g. Larix sp. and Pinus sp. with Populus sp. and Salix
sp.) may increase likelihood of severe infections.
Conclusions
The decision to maintain or switch to mixed forest stands should not be based on a desire to avoid
problems with pest or diseases. But diversification can be an advantage if new threats appear, and
knowledge of specific diseases should be employed when planning and managing mixed stands.
Examples of literature
Ennos, R.A. 2015. Resilience of forests to pathogens: an evolutionary ecology perspective. Forestry 88(1):
41-52. http://forestry.oxfordjournals.org/content/88/1/41.full
Koricheva, J.; Vehviläinen, H.; Riihimäki,J.; Ruohomäki, K.; Kaitaniemi, P.; Ranta, H. 2006. Diversification of
tree stands as a means to manage pests and diseases in boreal forests: myth or reality? Canadian Journal of
Forest Research 36(2): 324-336. http://www.nrcresearchpress.com/doi/abs/10.1139/x05-172#.V9veU1H30U
Nguyen, D. Castagneyrol, B.; Bruelheide, H.; Bussotti, F.; Guyot, V.; Jactel, H.; Jaroszewicz, B.; Valladares,
F.; Stenlid, J.; Boberg, J. 2016. Fungal disease incidence along tree diversity gradients depends on latitude
in European forests. Ecology and Evolution 6(8): 2426–2438.
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4788975/
NordGen conference 2016, Växjö
Presentation summary
Broadleaved forest reproductive material: is it available and should we use it?
Katri Himanen, Natural Resources Institute Finland
In most environments, an abundance of broadleaved seedlings appear shortly after final felling
and/or soil preparation. This natural seedling material is used in establishment of mixed stands. In
many cases, such as in areas with heavy browsing, this is an economically sound approach.
Broadleaved forest reproductive material (FRM) is also not always available for artificial
regeneration. With natural regeneration, however, the benefits of using FRM are lost.
In artificial regeneration the amount, spatial distribution and genetic quality of the seedlings can be
controlled. Advances in production of FRM, regeneration methods and tree breeding may give
reason to re-evaluate the usefulness of artificial regeneration of broadleaved trees.
In Finland three new silver birch seed orchards have been registered, giving seed material with +30%
volume growth compared to natural populations. New oak, maple and black alder seed orchards are
also beginning to produce seed. New seedling types for silver birch have been launched and studied.
With smaller birch seedlings compared to traditional seedling types, the cost of the regeneration
chain decreases and even mechanical planting can be used.
The value of afforestation for recreation in Iceland
Hreinn Óskarsson
Icelandic Forestry Service & Heklaforest
Abstract
People do not usually think of Iceland in relation to forests. The lowlands of Iceland were
however covered with birch woodlands from the seashore to the mountains (25-40% of the
country). whereupon the country was settled by humans who quickly deforested the island. By
year 1900 the woodland cover had been reduced to less than 1% of the land area owing to
unsustainable land use, mainly overgrazing. Severe soil erosion, a dramatic ecosystem
destruction has continued to the present in some parts of the country. Since the establishment
of Icelandic Forest Service in 1908 the forest cover has risen to 2%, of which 0,5% can be
defined as plantations mainly of exotic species. Most of the early afforestation efforts during
the 20th century was carried out by converting semi-natural birch woodlands to conifer forest,
but since 1990 afforestation has taken place on treeless land mainly through state-supported
afforestation on private land. The birch woodlands have expanded in the recent years due to
natural regeneration mainly on land protected from grazing. In the last decades tree planting
has been used to restore desertified land with good results. Examples of such efforts are Land
Reclamation forests and Hekla-forests.
The presentation will give some insight into afforestation in Iceland and furthermore look
on the value of afforestation for recreation. The main conlusion is that the value of forests and
woodlands for recreation in Iceland is high, both for local people and the fast growing
tourism.
Keywords: afforestation, recreation, Iceland
Adam Felton
The biodiversity benefits of mixtures: Overcoming the implementation gap
Mixed-species production stands are often suggested to support higher levels of
biodiversity and provide a more balanced suite of ecosystem services than their
monoculture alternatives. Whereas there is evidence that mixtures in general can
provide positive outcomes relative to monocultures, it is less clear to what extent
multiple benefits can be derived from specific mixture alternatives. To provide such
insights requires evaluations of the biodiversity, ecosystem services, and additional
forest management considerations provided by specific mixtures and monocultures
within a region. Such studies should provide either a more justified basis for motivating
the adoption of mixtures, or alternatively, a better understanding of the reasons behind
the continued widespread reliance on monocultures. Starting with stand-level
biodiversity, we have synthesized the available evidence regarding whether mixtures of
Norway spruce (Picea abies) and birch (Betula spp.) are more likely to support a higher
biodiversity than Norway spruce monocultures in southern Sweden. Our findings
suggest positive outcomes from the adoption of this mixture for a distinct range of
taxonomic groups, including vascular plants, lichens, saproxylic beetles, and birds. We
subsequently contrasted the ecosystem services, biodiversity, and forest management
considerations provided by mixtures of spruce and birch, or spruce and Scots pine
(Pinus sylvestris) relative to Norway spruce monocultures. We identified positive
outcomes from these mixtures including increased biodiversity, water quality, aesthetic
and recreational values, as well as a likely reduced stand vulnerability to damages
associated with pests, pathogens, and storms. However, some uncertainties and risks
were projected to increase with the adoption of these mixture alternatives. We use
these findings, and additional studies of post disturbance planting decisions by Swedish
forest owners, to discuss the likely obstacles and opportunities for the increased
implementation of production forest mixtures in Sweden.
2016-09-12
Rappe- von Schmiterlöwska Stiftelsen
Rappe- von Schmiterlöwska Stiftelsen
The last private owner of the estate Tagel (Tagels gård), who then had owned Tagel
for 77 years, died in 1959. In her will she donated most of her property including
Tagel to a foundation, Rappe- von Schmiterlöwska Stiftelsen. It was named after the
family names on her mothers and fathers side respectively.
The land area of Tagels gård is approximately 1.400 hectares, of which 1.200
hectares is productive forest land. The agricultural land is leased out. There are some
40 bildings of different types to take care of. Thirteen holiday cottages and four
aparetments are let out. The annual cut is about 5.500 cubic metres and the total net
turnover is about 3 million SEK
According to the regulations of the foundation, its purpose is “to support scientific
research regarding agriculture and forestry and their subsidiary industry at Tagel”.
Research and development activities had been carried out long before the
establishment of the foundation, but were intensified after that. R&D regarding
agriculture was comparatively extensive during the first decades of the foundation,
but ceased in 1992 when the agricultural land was leased out. The dominating
activites in that area was sort testing in the field of different crop species as potatoes,
clover, timothy and oats. Effects of different management of grazing land on the flora
and meat production on different types of grazing land was also studied.
Since 1992 R&D in the area of forestry has been totally dominating. It has included a
big variety of trials as testing of different tree species and provenances, afforestation
of agriculture land, regeneration of forest land, precommercial and commercial
thinning, impact of soil treatment on vegetation, shifting cultivation, production of
blue berries etc. Most of the research is done by SLU, but some also by Skogforsk
(the Forestry Research Institute of Sweden). A few years ago the board of the
foundation adopted a strategy for allocation of resources to research and appointed a
scientific leader/coordinator, Ulf Johansson, SLU.
The average annual grants for research is approximately half amillion (SEK) . The
intention is to increase the level to three quarter of a million.
Jan-Åke Lundén
Secretary of the foundation
Pre-commercial thinning in Norway spruce and birch mixes
Emma Holmström SLU
Visit to newly established experiment with Norway spruce and birch and presentation of some earlier
findings in measured experiments and simulations of PCT and stand developments.
Keeping the even aged mixed stand through the full rotation may be possible if the stand density and
height development between species is considered already in the early management.
Pre-commercial thinning (PCT) and control treatments were applied to planted Norway spruce (Picea
abies L. Karst) and naturally regenerated birch (Betula pendula Roth, Betula pubescens Ehrh) stands in
forest experiments in southern Sweden (lat. 56 -57 ° N) containing 1.1-5.5 m tall saplings. The
treatments were retention of 1000 or 2000 stems ha-1 of Norway spruce, with no birch or birch at
1000 stems ha-1. Treatments were replicated with and without annual removal of birch sprouts from
stumps. The periodic annual increment (PAI) over five years was calculated for total stand volume and
individual trees. The mean PAI of dominant trees was significantly higher both following all PCT
treatments than controls, and following low rather than high density PCT. Birch retention did not
affect growth of the dominant trees but PAI were lower in plots with uncontrolled sprouting. The PAI
of birch was significantly higher in low density Norway spruce plots than in control plots and the high
density plots. The treatment response was significant even in stands with initial heights of only 1 to 2
m.
Pre commercial thinning of young establishments could be done in various ways, many are the
opinions regarding PCT intensity, timing of season and timing in stand age, birch percentage and
spatial distribution of saplings. Most importantly, the reduction of density, from more than 10 000 to
3000 stems ha-1 or less, are the major difference in growth and yield for future crop trees. The largest
saplings before PCT will keep their dominance regardless of treatment and the size of the neighbor
affect more than the species. If the goal with the establishment is a mixed stand throughout the stand
rotation, the density has to be regulated already in PCT to ensure vital birches. Density reduction have
an effect on the seedlings already at heights of 1-1.5 m but the competition from birch stump sprouting
could be significant, at least the first years after PCT.
Tree seedling data from experiments with planted Norway spruce (Picea abies L. Karst) and naturally
regenerated species, mainly Silver birch (Betula pendula Roth), were used for six simulated precommercial thinning (PCT) scenarios. The scenarios included both monocultures and mixed stand
alternatives with various initial spacing of the planted Norway spruce (0, 1600 or 2800 seedlings) and
selection of main stems based on relative heights. Further stand development and individual tree
growth wereas simulated until final harvest. Potentially, based on findings of the seedling
measurements, the stands could be mixed with five to six species but the browsing pressure from
ungulates reduced this possibility since the height growth for all species except Norway spruce was
highly affected by browsing. The simulated mixtures had a small variation between the PCT scenarios
for the maximum mean annual increment (about 10%). Although the growth was similar for Norway
spruce, the proportion of birch in the final stands differed from 3 % to 21 % between treatments and
none of the high density planting treatments generated a mixed Norway spruce-birch forest at time of
final felling.
Holmström, E., Ekö, P. M., Hjelm, K., Karlsson, M., & Nilsson, U. (2016). Natural Regeneration on
Planted Clearcuts—The Easy Way to Mixed Forest?. Open Journal of Forestry, 6, 281-294.
doi:
10.4236/ojf.2016.64023.
.
Open
Journal
of
Forestry,
6,
281-294.
doi:10.4236/ojf.2016.64023
Holmström, E., Hjelm, K., Karlsson, M., & Nilsson, U. (2016). Scenario analysis of planting density
and pre-commercial thinning: will the mixed forest have a chance? European Journal of
Forest Research, 1-11. doi:10.1007/s10342-016-0981-8
Holmström, E., Hjelm, K., Johansson, U., Karlsson, M., Valkonen, S., & Nilsson, U. (2015). Precommercial thinning, birch admixture and sprout management in planted Norway spruce
stands in South Sweden. Scandinavian Journal of Forest Research, 1-10.
doi:10.1080/02827581.2015.1055792
Mixed forests within a forest owners association
Magnus Lindén, Södra skogsägarna
Södra is a forest owners association with approximately 50 000 members owning extensive
pulp and sawmill industry. Forestry is the dominant source of income but profits from the
industry are increasingly important for the members.
Forestry products and processing includes a ten of tree species. The most significant forest
products are pulpwood and saw timber from Norway spruce, Scots pine and naturally
regenerated Birch. Mixed species forests are abundant.
The main recommendations for high economic return are stands dominated by one site
adapted tree species - Norway spruce and Scots pine complemented by naturally
regenerated Birch. Heavy browsing on Scots pine and broadleaves is a challenge. The
stands often have a significant admixture of a second tree species.
Effect of the density of shelterwood of natural regenerated birch to damage and
growth to planted Douglas fir seedlings
Kristina Wallertz, Asa Research station SLU
The use of non-native species, such as Douglas fir (Pseudotsuga menziesii (Mirb.) Franco), is
of interest mainly because of its potentially fast growth and valuable and usable wood.
Planted Douglas fir is however sensitive to frost damage, early spring frost, autumn frost and
winter desiccation. Planting underneath a shelterwood of another tree species could be one
way of reducing the risk of frost damage. Douglas fir is considered to be relatively tolerant to
shade during the time of establishment. In many other countries Douglas fir is growing well in
mixtures with other tree species.
The experiment consists of 4 blocks with 5 treatments in each, in total 20 plots. The size of
the plots is about 17 x 20 meters and the corners are marked with painted oak poles (45 x 45
mm) with colours according to the list below. The treatments are:
1.
2.
3.
4.
5.
Control (no shelter trees) (White)
Birch 1500 per ha (Blue)
Spruces 1500 per ha (Red)
Birch+Spruce 1500 per ha (Yellow)
Birch 3000 per ha (Purple)
On each plot 36 Douglas fir seedlings are planted (6 rows with 6 seedlings in each). Site
preparation before planting the Douglas fir seedlings was conducted with an excavator.
The experiment was established in early spring of 2014. Measurements have been conducted
directly after planting and in the autumn 2014, 2015 and 2016. An extra measurement was
made after a period of frost in the spring of 2015.
Mortality after three years in the field was low, between 3.5-5.6 % and there were no
significant differences between treatments. Dead and severely damaged seedlings were
highest for seedlings planted in control plots (11.2%) and in mixture of Norway spruce and
birch (10.4%). Douglas fir seedlings growing in the densest shelter had in average the highest
height after three seasons and also the longest leading shoot.
Tabell 1. Result from measurements in May 2014, autumn 2014, autumn 2015 and autumn
2016. Mortality and severe damage to seedlings 2016, average height in cm during three
seasons and leading shoot in cm the third season.
Treatment
Mortality
2016
Control
Birch 1500
Spruce 1500
S+B 1500
Birch 3000
Severe
damage 2016
4.9 %
4.9 %
3.5 %
5.6 %
4.2 %
Height time of
planting
6.3 %
2.1 %
1.4 %
4.9 %
2.1 %
Height first
season
18.0
17.0
17.4
18.3
18.2
Height second
season
25,2
23,6
25,1
25,2
25,6
Height third
season
36.0
38.7
39.0
38.6
41.8
Leading shoot
third season
45.1
53.9
51.8
51.3
56.6
In May 2015 when the Douglas fir seedling had begun their bud burst, the temperature
decreased to around -2°C for a few nights. Around 50 % of the seedlings on the control plots
were severely damaged by frost while for the seedlings planted in medium dense shelter the
damage was minor; approximately 25 % of the seedlings were recorded with severe damage.
In the densest shelter, only 8% of the seedlings got severely damaged by frost and 85 % of the
seedlings were recorded as undamaged.
Severe damage
Strong damage
Some damage
Easy damage
No damage
100 %
80 %
60 %
40 %
20 %
0%
Control
Birch 1500
Spruce 1500
B+S 1500
Birch 3000
Figure 1. Damage by early spring frost in May 2016 to Douglas fir seedlings planted in five
different treatments.
9.0
14.1
12.9
12.8
14.3
Early development of single-storied mixtures of Norway
spruce and birch spp. in Southern Sweden
Nils Fahlvik, Swedish University of Agricultural Sciences
During recent years there has been an increasing interest within forestry in Sweden for admixture of
broad-leaves in coniferous stands, mainly for environmental purposes. The aim is to retain the
broadleaves in the mixture throughout the rotation which is in contrast to previous forest
management when broadleaves typically were removed at thinning. In the present study the
development and yield of a long-term mixture of Norway spruce (Picea Abies (L.) Karst.) and Birch
(Betula pendula Roth. and Betula pubescens Ehrh.) was compared with that of monocultures of
Norway spruce.
The experiment was established 1998 in a stand with 16-years-old planted Norway spruce and
naturally regenerated birch. At that time, the average height was 4.5 m for spruce and 5.8 m for
birch. Nine 0.1 ha plots were established and the treatments included pre-commercial thinning to a
birch proportion of 0 %, 20 % and 50 % of total stem number. The total number of stems after
thinning was equal for all treatments. Growth data was measured at the establishment and after 4,
10 and 18 growing seasons.
There were no significant differences in average diameter, average height or dominant height for
Norway spruce between the treatments at the last measurement. The initial difference of 2 m in
dominant height between Norway spruce and birch decreased during the study period and at the last
measurement the dominant height was equal for both species. There were no significant differences
in total basal area growth and volume growth between the treatments. However, there was a
tendency towards a reduced growth in the mixed stands during the last period compared to the
spruce monoculture. The proportion of spruce trees with severe top damages was 3-6 % with no
significant difference between the two levels of birch admixture.