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-for-

fisheries-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: tove.hultberg@lansstyrelsen.se

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 mono-

specific 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.

H.Pretzsch@lrz.tum.de, 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#.V9v-

eU1H30U

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 pre-

commercial 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). Pre-

commercial 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. Control (no shelter trees) (White)

2. Birch 1500 per ha (Blue)

3. Spruces 1500 per ha (Red)

4. Birch+Spruce 1500 per ha (Yellow)

5. 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

Severe damage 2016

Height time of planting

Height first season

Height second season

Height third season

Leading shoot third season

Control 4.9 % 6.3 % 18.0 25,2 36.0 45.1 9.0

Birch 1500 4.9 % 2.1 % 17.0 23,6 38.7 53.9 14.1

Spruce 1500 3.5 % 1.4 % 17.4 25,1 39.0 51.8 12.9

S+B 1500 5.6 % 4.9 % 18.3 25,2 38.6 51.3 12.8

Birch 3000 4.2 % 2.1 % 18.2 25,6 41.8 56.6 14.3

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.

Figure 1. Damage by early spring frost in May 2016 to Douglas fir seedlings planted in five

different treatments.

0 %

20 %

40 %

60 %

80 %

100 %

Control Birch 1500 Spruce 1500 B+S 1500 Birch 3000

Severe damage Strong damage Some damage Easy damage No damage

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.