Non -native tree species: Strategies for Development in Southeast Europe [602188]

Non -native tree species: Strategies for Development in Southeast Europe
Keča L jiljana *, Nicolescu Valeriu Noroce l, Marčeta M ilica, Božič Gregor., Perić Sanja, Tsvetkov
Ivaylo, Andreassen Kjell, Hernea Cornelia, Stijović Aleksandar, Mandžukovski Dejan
Department of Forestry, University of Belgrade, Faculty of Forestry, Belgrade, 11030, Serbia
Department of Forest Physiology and Genetics, Slovenian Forestry Institute, Ljubljana, 1 000, Slovenia
Department of Silviculture, Croatian Forest Research Institute, Jastrebarsko, 10 450, Croatia
Forest Research Institute , Bulgarian Academy of Science, 1040, Sofia, Bulgaria
Department of Forestry and Forest Resources, Norwegian Institute of Bioeconomy Research, 1431 Aas,
Norway
Depar tment of Forestry, Banat University of Agricultural Sciences and Veterinary Medicine, 300645,
Timișoara, Romania
Institute of Forestry, 81000, Podgorica, Montenegro
Department of Forest Management Planning, PE "Makedonski šumi", Skopje, Republic of Macedo nia
Department of Forest Management, University of Banja Luka, Faculty of Forestry, 78 000, Banja Luka,
Bosnia and Herzegovina
*Corresponding author: Tel: + 381 11 3053 959 ; Fax: + 381 11 2545 485 ; Email: [anonimizat]
ABSTRACT
We analyzed the prospects and challenges for non-native tree species (NNTSs) in Southeast Europe (SEE) using the
strengths (S), weaknesses (W), opportunities (O), and threats (T) approach in combination with analytic hierarchy
process. We used preference d ata from opinion leaders who have had extensive knowledge about silviculture,
ecology and climate changes on NNTSs in the Region of Balkan Peninsula. We identify three groups of opinion
leaders in each country: researches, practice and decision makers. 72 people were included in research Results
reveal that strengths and opportunities for all three analyzed elements adoption outweigh its weaknesses and
threats. The participants perceive that in segment of NNTSs Ecology dominant are SO elements such as: potential
for phytoremediation of polluted soils and for soil erosion control and revitalization of high degraded land,
accumulation of carbon and using of NNTSs to filling gaps after calamities, faster adaptation to changing ecological
conditions, enhance ment of soil fertility, cover all ecological characteristics as well as broad usage in highly
degraded land, fast growing species of NNTSs for biomass production, high resistance to shallow soils and drought
of some species. In segment of Silviculture SO e lements are: high productivity, valuable wood assortments,
adapted to afforestation of degraded areas , filling the gaps in forest ecosystems after disappearance of native tree
species, creating better options for stability on landscape level, higher timber increment of NNTSs comparing to
native tree species. SO elements in segment of Climate changes are: adaptive management which responses to
climate changes and increase length of the growing period, help to natural regenerations in case of shifting limits
and possibility of better -adapted NNTSs mixtures to climate changes , replacement of species that are sensitive to
the pests and outbreaks due to climate changes. These results provide important insights for strategy of
development of NNTSs relating to management practices in SEE .

INTRODUCTION
The introduction of non -native tree species (NNTSs) causes ecological concern globally . There have been
published significant numbers (Manchester and Bullock, 2000) of articles of their effects on climate,
silviculture and ecology aspects. Ecological and economic impacts of alien species are usually studied
separately, but they are likely to be highly correlated (Olson LJ. 2006, Vila M., 2009). "Non-native ", "non –
indigenous" , "alien " or "exotic " refers to a species o r race that does not occur natu rally in an area, i.e. it

has not previously occurred there, or its dispersal into the area has been mediated by humans (Holmes
J.S. & Simons, J.R. , 1996 , Ehrenfeld 2011 ). Researches into the theoretical basis of NNTSs have focused
primarily on: invasiveness, ecology, taxonomy, evolution and biodiversity (Mooney & Drake 1984 ,
Arthington 1991 ). Most theories and empirical re search on exotic invasiveness are based on the
assum ption that problematic exotics are much more abundant in the regions where they invade than in
the regions where they are native ( Mooney 1999, Hierro et al., 2005). It is important to mention as has
long been acknowledged, not all introduced species have n egative effects (Williamson M., 1996).
Non -native species do not have the same cultural and historical value as native species, but they have
been used as acceptable ecological substitutes in cases where the benefits of their ecological function
are percei ved to exceed the potential risks of introducing a non -native species (Schlaepfer M. A . et al.,
2011).
Biological invasions have been chronicled for centuries. The book The ecology of animal and plant
invasions (by Charles Elton) was the starting point of what has come to be known as invasion ecology
(Richardson and Pyšek, 2006). Alien ( non-native, non-indigenous, introduced species, exotic) are those
species that occur in different places from their current are a of their natural distribution and very often
are aggressive when successfully established, some of them threatening biotic systems and disrupt
ecosystem processes and cause direct economic losses and environmental damages (Mooney, 1999 ;
Hobbs and Humphri es, 1995 ). The most of non-native species usually are naturalized in adjacent heavily
disturbed areas under human land use types (Pauchard and Alaback 2004). Invasive plants are a subset
of naturalized plants that produce reproductive offspring, often in l arge numbers, at considerable
distances from parent plants, and thus have the potential to spread over a large area (Richardson and
Pyšek, 2006 ). Plant invasions are a serious threat to natural and managed ecosystems worldwide (Hobbs
and Humphries, 1995 , Maskell et al. 2006 ). During its long history as an introduced species, the way it
has been perceived and used has changed radically. The investigation program SCOPE (Scientific
Committee on Problems of the Environment 1982) studied the ecology of biologic al invasions worldwide
for 10 years (Hoenicka H. and Fladung M., 2006 ) and results indicate that invasiveness of plant species
into a new ecological system is complex phenomenon ( Kowarik I ., 2003 ). The number of species involved
and the scale of the probl em make invasiv e plants one of the major prob lems facing land managers
(Hobbs and Humphries , 1995). Binggeli’s (1996) reported 653 invasive woody plants species world -wide.
He classified 184 from this as highly invasive and 134 of the invasive species have been spread by
forestry for years (Hoenicka H. and Fladung M., 2006 ). Eurasia is recognized as the main source of non –
native species for all other continents. With only 4.4% of the total flora of the world, Eurasia contributes
with 58.9% of naturalized no n-native species ( Pauchard and Shea, K. , 2006 , Pyšek 1998). Early detection
and control must become an important component of the management of plant inva sions (Hobbs and
Huenneke , 1992). An estimated 138 nonindigenous tree and scrub species have invaded native in US
forest and scrub ecosystem ( Pimentel , 2000 ) and some of them have displaced native trees . These
phenomena are present both in urban and in forest ecosystems. The proportion of non -native plant
species in hu man settlements always increases through time ( McKinney, 2006) . For example, New York
City has lost 578 native species (a loss of roughly 43% of the original native species) while gaining 411
non-native species (DeCandido et al., 2004). The proportion of n on-native plant species rises from 6% in
nature preserves outside the city of Berlin, Germany to 25% in the suburbs to 54% in the most
intensively urbanized central areas (Kowarik, 1995). Most of the invasive weeds of a region were
originally introduced in tentionally for economic and other purposes and now their control incurs high
expenses (Pimentel et al., 2000). App. 12.5% is a share of non -native vascular plants in Europe (Vitousek
et al., 1996).
The significance of invasive species as a global environm ental problem is widely recognised, and article
8(h) of the Biodiversity Convention asks for measures ‘‘to prevent the introduction of, control or
eradicate those alien species which threaten ecosystems, habitats or species’’ (Weber and Gut, 2004) .

This paper considers non-native tree species, which are spread on Southeast Europe, with focus on
elements of strengths, weaknesses, opportunities and threats (SWOT) in their development . The work is
based on a broader review of elements that are relevant for d evelopment of NNTSs, such as: climate
changes, forest management and silviculture, and ecology elements . The paper focuses on the effects of
non-native tree species within Southeast Europe .

METHODOLOGY

The intention of the article is to analyze the pros pects and challenges for NNTSs in southeastern Europe
using the strengths, weaknesses, opportunities, and threats approach in combination with analytic
hierarchy process. We used preference data from opinion leaders who have had extensive knowledge
about NNTSs state in the field of forest management and silviculture, ecology and climate changes in
each analyzed country. Results reveal that strengths and opportunities for t hese segments outweigh its
weaknesses and threats. SWOT is a tool designed to be used in the preliminary stages of decision –
making on the one hand and as a precursor to strategic management planning on the other (Shrivastava
et al ., 2005).
In this study, we attempt to assess the effect of different factors relating to NNTSs adoption decisions.
We use the strengths, weaknesses, opportunities, and threats (SWOT) approach in combination with
analytic hierarchy process (AHP) to achieve this task. The result of SWOT analysis is a list of factors that
can be used for further analysis (AHP) and selecting decision criteria for NNTS s in SEE.
The SWOT –AHP allows us to define NNTSs adoption decision process in a hierarchical structure of
factors, evaluate factors in pairs, and quantify the relative importance of each factor to the adoption
decision (Shrestha R.K. et al, 2004). We utilize preference data from selected opinion leaders involved in
NNTSs practices in South -European countries. Although SWOT –AHP is an estab lished method in
strategic planning literature, to our knowledge, this is the first study to apply it to NNTSs.
The SWOT approach is used extensively in strategic planning and allows analysts to categorize factors
into internal (strengths, weaknesses) and external (opportunities, treats) as they relate to a decision and
thus enables them to compare opportunities and threats with strengths and weaknesses (Saaty T.L.,
Vargas L.G., 2001, Smith J.A., 1999). Stages in SWOT -AHP methodology involves identification key
respondents on NNTSs in each country, classification of critical factors influencing the decision and
evaluation of factors using SWOT -AHP (Kurttila et al., 2000) Kurttila et al. (2000) developed a hybrid
method to eliminate the weaknesses in the meas urement and evaluation steps of the SWOT analysis .
The research was based on expert interviews, which were structured according to the principles of
value -focused thinking and A’WOT analysis. A’WOT is a hybrid method combining the well -known SWOT
analysis and the A nalytic Hierarchy Process (AHP) (Kajunus et al., 2004 , Kangas and Kangas, 2005 ). The
further utilization of SWOT is usually based on qualitative and quantitative analysis of internal and
external factors, as well as on the capabilities and expertise of the people involved in the planning
process (Anselin et al., 1989).
The main limitations of this approach is that the importance of each factor in decision -making cannot be
measured quantitatively, but in a combination with analytic hierarchy process, however, SWOT
approach can provide a quantitative measure of importance of each factor on decision -making (Kurttila
et al., 2000) . Ident ification and classification of critical decision factors was accomplished using SWOT
questionnaire , focus group discussions, and field visits to r espondents in each country.
We identify three groups of opinion leaders in each country: researches, practice and decision makers.
72 people were included in research, and most of them are male (79%). Average age is 45 and they have
app. 19 years of working experience in forestry. The respondents identify the key factors that influence

decision and weight it in a range from 1 to 5. The “1” is the lowest influence on the NNTSs issue in the
field of ecology/silviculture (forest management)/climate changes. The “5” is the highest importance of
the component. The relative priority value of each factor within each SWOT group is computed using the
eigenvalue method (Shrestha R.K. et al, 2004).
After preparing the preliminary list of decision factors, they were categorized into 12 major factors, few
of which were placed in each SWOT group. Input from the focus group discu ssions helped us in
aggregating factors into major groups. While it is beneficial to consider as many factors as possible, it is
important to keep in mind that the number of pair -wise comparisons in AHP grows exponentially with
the number of factors (Shres tha R.K. et al, 2004). We worked with different number of key factors in
each SWOT category. The SWOT factors were used to develop a questionnaire for pair -wise comparison
using SWOT –AHP methods. The questionnaire included a rating scale to weigh each fact or relative to
the other. The respondents were asked to evaluate if both factors are equally important or one is more
important than the other. The data from pair -wise comparisons were used to estimate a priority value
for each factor within each SWOT grou p. We developed scale parameters for each SWOT group using a
rating scale as detailed in Saaty and Vargas (2001). This approach requires a specification of control
criteria. In this study, we considered forest management, climate changes and ecology object ives as
three equally important control criteria. Each strength, weakness, opportunity, and threat was rated
based on these three control criteria and five intensity ratings (very high, high, medium, low, and very
low – from 1 to 5 ).
Using this rating proc ess, we obtained scale parameters that were used to calculate the overall priority
score of each factor within each SWOT group. Thus, scale parameters also reflect the priority scores of
each SWOT group. We used the computer software Expert Choice 2000 to analyze data generated from
pair-wise comparisons and ratings (Expert Choice, 2001).

Map 1. Studied countries on NNTSs in Europe

Southeast Europe or Southeastern Europe is a geographical region of Europe , consisting primarily of the
Balkan Peninsula . The participants in this study are representatives from: Bosnia and Herzegovina,
Bulgaria, Croatia, Macedonia, Montenegro, Romania, Serbia Slovenia and Norway (Map 1) . Norway is
taken in account for analysis because of diverse of NNTSs and diversity of d ata. The percent of NNTSs
area ranges from 0,54% in Norway to 11,18% in Serbia, average value is 2,18% (Table 1).

Table 1. NNTSs in Southeastern Europe and Norway
Country NNTSs (%) of total
forest area
Bosnia and Herzegovina 1,00
Croatia 1,26
Macedonia 0,72
Montenegro 1,00
Norway 0,54
Romania 0,72
Serbia 11,18
Slovenia 0,99
Average 2,18

The diversity of NNTSs is high. Therefore, they will be presented separately .

RESULTS

BOSNIA AND HERZEGOVINA
The l ist of the most important NNTSs in Bosnia counts 1,00% of total forest area (Table 2). Dominant
tree species are Pseudotsuga menziessii, Pinus strobus, Larix decidua. Dominant management systems
for all species are clear cut and selective cuts. There is no legal restrictions on growing NNTSs in B osnia
and Herzegovina.
Table 2. NNTSs in Bosnia and Herzegovina
Dominant
NNTS Area
(ha) % of
total
forest
area Places Aim/Role Management
systems Key risks
Pseudotsuga
menziessii
(Mirb.
Franco) 342 0.06 Grows in
various
ecological
conditions .
Alongside
sessile oak
with
hornbeam,
beech and
European
silver fir. Shows
significantly
better results in
DBH and height in
comparison with
other species .
Becoming the
species local
stakeholders have
an interest for it.
Clear cuts and
selective cuts,
depending on
area and
timber order.

Undefined climate
conditions – climate
changes . Undefined
areas suitable for
introduction . Not
enough experimental
plots to monitor
development and
potential of introduced
species. The local
market is unfamiliar
with int roduced species
such as the Douglas fir.

Pinus strobus 654 0.1 grows in
various
ecological
conditions,
The market
demands are
mostly for
cellulose wood
and lamp poles.
Widely used and
the market
absorbs all the
available wood . Clear cuts and
selective cuts,
depending on
area and
timber order. It shows
significantly better
results in DBH and
height in comparison
with other species.
Patterns are different,
depending on the origin
of the seedlings (seed
zone).
Larix decidua 861 0.1 Grows on all
kinds of sites,
at lower
altitudes . Clear cuts and
selective cuts,
depending on
area and
timber order.

Table 3. SWOT/AHP Analysis for B&H
Element of
analysis Strengths Opportunities Weaknesses Threats Dominant
strategy
Ecology 0,2741 0,3807 0,1218 0,2234 SO
Silviculture 0,1787 0,3191 0,1957 0,3064 WO
Climate changes 0,2348 0,2609 0,2261 0,2783 ST

Figure 1. Category weights in AHP analysis for B&H

Dominant strengths in Ecology analysis are: potential for phytoremediation and revitalization of high –
degraded land and opportunities are: accumulation of carbon and using of NNTSs to filling gaps after
calamities. In Silviculture analysis prevail opportunities is improving conditions for production of 0,0000 0,1000 0,2000 0,3000 0,4000 Strengths
Opportunities
Weaknesses Threats
Ecology Silviculture Climate changes

bioenergy and in Climate change analysis dominant threat is high uncertainty of prediction of climate
changes (Table 3, Figure 1).

BULGARIA
The most important NNTSs in Bulgaria counts 5,00% of total forest area are: Pseudotsuga menziessii,
Robinia pseudoacacia, Quercus rubra , which are located in forests and urban areas (Table 4).
Table 4 . NNTSs in Bulgaria
Dominant
NNTS Area
(ha) % of
total
forest
area Places Aim/Role Management
systems Key risks
Pseudotsuga
menziessii
(Mirb. Franco) 7
372 0.68 Forests
and
urban
areas Successful natural
regeneration,
Ornamental tree, basic
seed material Rhabdocline
pseudotsugae,
Phaeocryptopus
gaumannii,
Phomopsis
pseudotsugae
Droughts, early
autumn and late
spring frosts,
snowbreaks, heavy
snow and wind
uproots, windfalls/
windbreaks. Damages
caused by game.
Quercus rubra
L. 11
132 0.30 Urban
areas Successful natural
regeneration, seed
material High stem
management
systems Dry period 1983 -1993
Robinia
pseudoacacia
L. 150
590 4.00 Forests,
parks,
gardens Anti-erosion
afforestations,
Reclamation and
remediation purposes
Basic seed material ,
Establishment of short –
rotation plantations for
biomass production
predominantly on
terrains with better
humidity conditions and
complying with initial Clear felling,
Selective felling
Selected clones
vegetative
Propagated
saplings,
specific designs
and on
appropriate
habitats. Etiella zinkenella TR,
Polyporus (Laetiporus )
sulfureus ,
Phyllonorycter
robiniella ,
Gracillariidae ,
Lepidoptera ,
Parectopa robiniella ,
Pyralidae, Damaged
seeds can reach 80%.

planting density, site
conditions and rotation
period .
*Executive Forests Agency, 2010
Numerous plantations of NNTSs in Bulgaria have been established without clear economic target. These are:
protective plantations – protection against erosion, landslides, snowdrifts, industrial pollution and land restoration;
landscape improvement and green zones. These plantations are conformable to landscape and ensure ecological
benefits, typical for the n atural stands. Depending on the main objectives NNTSs can be used for: 1) industrial
plantations (plantations for timber and non -timber products and plantations for intensive production of wood and
biomass) 2) protective plantations – protection against er osion, landslides, snowdrifts, industrial pollution and land
restoration; 3) landscape improvement and green zones. There are numerous legal restrictions on NNTSs in
Bulgaria (Table 5).
Table 5. Legal restrictions on NNTSs in Bulgaria
Biological Diversity Act (BDA 2002, 2007) Art. 35, 6. Control and regulation of non -native
species that are or could be introduced intentionally
or accidentally in nature and threaten native species.
Art. 67, 2. The introduction of non -native species into
the wild is only possible after a positive scientific
expertise and a positive decision of the National
Council on Biological Diversity.
Regulation No. 4 (2003) Conditions and procedures for issuing permits for
introduction of non -native or reintroduction of native
plant and animal species in the wild.
Regulation No. 14 (2005) Concerns the conditions and procedures for issuing
permits for the introduction of non -native or
reintroduction of native trees, shrubs and game
species in nature and consideration of the public
opinion in the region of the reintroduction
Regimes for sustainable management of forests in
Natura 2000 On 60% of the forest area, it is forbidden to plant
non- native tree species.
Prohibition for afforestation with non -native species
exce pting the actions towards controlling of torrents
and erosion processes.
Temporal standard of Rainforest Alliance for
assessment of forest management in Bulgaria
(2010) – Forest certification Use of exotic species shall be carefully controlled
Exotic species may only be used when they
outperform native species in meeting the
management objective .

Table 6. SWOT/AHP Analysis for Bulgaria
Element of analysis Strengths Opportunities Weaknesses Threats Dominant strategy
Ecology 0,2030 0,3008 0,1203 0,3759 ST
Silviculture 0,1961 0,3813 0,1351 0,2876 SO
Climate changes 0,2032 0,3499 0,1490 0,2980 SO

Figure 2. Category weights in AHP analysis for Bulgaria

Dominant threats in Ecology analyses are : management to maintenance biodiversity and
multifunctionality as well as mapping of pathways of introduction of NNTSs . In Silviculture analysis
prevail strengths high productivity, valuable wood assortments, adapted to afforestation of degraded
areas . In opportunities reasons we can count necessity for introduction of new clones and provenances
as well as establishing of energy plantations. In Climate change analysis dominant strengths and
opportunities are adaptive management which responses to climate change s and increase length of the
growing per iod. (Table 6, Figure 2).

CROATIA
The most important NNTSs in Croatia are: Populus sp., Robinia pseudoacacia, and Pinus strobus. NNTS s
counts 1,26% of total forest area in Croatia and located in forests, parks and plantations (Table 7) .

Table 7. NNTSs in Croatia
Dominant
NNTS Area
(ha) % of
total
forest
area Places Aim/Role Management
systems Key risks 0,0000 0,1000 0,2000 0,3000 0,4000 Strengths
Opportunities
Weaknesses Threats
Ecology Silviculture Climate changes

Populus
deltoides,
Populus
canadensis 13
219 0,49 Plantations Afforestation FSC, preserve
natural structure
and biodiversity,
clear cutting Inappropriate
afforestation areas
Robinia
pseudoacacia L. 12
004 0,45 Forests,
parks,
gardens Reforestation Selective thinning,
clear felling Phyllo norycter
robiniella, Perectopa
robiniella, Obolodiplosis
robiniae, Platygaster
robiniae,
Pinus strobus 3
219 0,12 Pineus strobi, Tends to
suffer when sited in wet
soils. Intolerant of salt
and air pollution;
sensitive to soil
compaction.
Introduction of new species in nature forests is prohibited except with permission of Ministry (Nature
protected act, 2010). More legal restrictions are mentioned in: Strategy of conservation of poplars
(2003), National Forestry Strategy and Policy (2003), Forest Law (2008), and Act on Forest Reproductive
Material (2009).

Table 8. SWOT/AHP Analysis for Cro atia
Element of
analysis Strengths Opportunities Weaknesses Threats Dominant
strategy
Ecology 0,32636 0,271966527 0,251046 0,150628 SO
Silviculture 0,181319 0,43956044 0,137363 0,241758 SO
Climate changes 0,232044 0,248618785 0,143646 0,375691 ST

Figure 3. Category weights in AHP analysis for Croatia

Dominant strengths in Ecology analysis are: faster adaptation to changing ecological conditions of NNTS
and enhancement of soil fertility/soil melioration. Opportunities that are dominant are: fillin g the gaps 0 0,1 0,2 0,3 0,4 0,5 Strengths
Opportunities
Weaknesses Threats
Ecology Silviculture Climate changes

in the forest with NNTS after calamities and lowering risks for carbon pools. In Silviculture analysis,
prevail strengths like f illing the gaps in forest ecosystems after disappearance of native tree species (e.
g. Ulmus leavis) and enhanced woo d production . Opportunities are: enhancement of options for
bioenergy production and creating better options for stability on landscape level (combination of stands
consisted of native tree species and those of NNTS). In Climate changes, analysis main strengths are
possibility for better -adapted mixtures to clima te changes . On the other side threats are: limited
legislation as well as uncertainty of predictions of climate changes (Table 8, Figure 3).
MACEDONIA
The l ist of the most important NNTSs in Macedonia counts 0,72% of total forest area . These species are
located mainly in forests and urban areas, and the mail roles are: timber production (R. pseudoacacia),
afforestation (Cupressus sp.) and ornamental species (P. menziessii) (Table 9) .
Tabl e 9. NNTSs in Macedonia
Dominant NNTS Area
(ha) % of total
forest
area Places Aim/Role Management
systems Key risks
Cupressus sp. 2
640,00 0,29 Public land Afforestation Regeneration after
fire Rot and butt
rot diseases
Robinia
pseudoacacia L. 2
622,00 0,29 Forests and
urban areas Timber
production Coppice
management
Pseudotsuga
menziessii (Mirb.
Franco) 670,00 0,07 Forests Ornamental
tree Thinning, this
stands are still
mature Insects and
pests

Table 10. SWOT/AHP Analysis for Macedonia
Element of
analysis Strengths Opportunities Weaknesses Threats Dominant
strategy
Ecology 0,2432 0,2703 0,1622 0,3243 ST
Silviculture 0,1875 0,3606 0,1442 0,3077 SO
Climate changes 0,2394 0,4521 0,1170 0,1915 SO

Figure 4. Category weights in AHP analysis for Macedonia

Ecology analysis shows that the dominant threats in Macedonia are inappropriate selection of NNTSs
and their invasiveness and opportunity is high quality of assortment structure of NNTSs and strength is
high quality assortment structure . Silviculture prevail strength such as afforestation of poor habitats and
main opportunity is higher timber increment of NNTSs comparing to native tree species. Climate
changes opportunities are: mitigation of global climate changes . (Table 10, Figure 4).
MONTENEGRO
The list of the most important NNTSs in Montenegro counts 1,00% of total forest area. These species are
located mainly as plantations and urban areas, and the mail role is afforestation (Table 11).
Table 11. NNTSs in Montenegro
Dominant
NNTS Area
(ha) % of total
forest area Places Aim/Role Management
systems Key risks
Pinus
strobus 714 0,09 Plantations Afforestation Selective
thinning Unappropriate
afforestation areas
Pseudotsuga
menziesii 834 0,11 Plantations Afforestation Selective
thinning Unappropriate
afforestation areas
Larix
europea 228 0,03 Forests, parks,
gardens Afforestation Selective
thinning Unappropriate
afforestation areas
Ailanthus
altissima N.A. 0,4 Close to the
roads, in suburbs No management
system Invasiveness

Table 12. SWOT/AHP Analysis for Montenegro
Element of Strengths Opportunities Weaknesses Threats Dominant 0,0000 0,1000 0,2000 0,3000 0,4000 0,5000 Strengths
Opportunities
Weaknesses Threats
Ecology Silviculture Climate changes

analysis strategy
Ecology 0,2879 0,2786 0,2229 0,2105 SO
Silviculture 0,2043 0,4489 0,1610 0,1858 SO
Climate changes 0,2576 0,2273 0,1717 0,3434 ST

Figure 5. Category weights in AHP analysis for Montenegro

The mail strengths in Ecology analysis are NNTSs cover all ecological characteristics in the country as
well as broad usage in highly degraded land. Opportunities are: fast growing NNTSs f or biomass
production and enhancement of landscape. Silvicultural analysis shows that the main opportunities are:
enhancement of options for bioenergy production and higher wood production. Strengths are: better
conditions for business of SMEs in wood processing , and higher wood production. The climate changes
analysis shows that the dominant strategy is ST strategy. Stren gths elements are : help to natural
regenerations in case of shifting limits and possibility of better -adapted NNTSs mixtures to climate
changes. Threats are lack of good practice and introductions of insects and pathogens.
NORWAY
List of the most important NNTSs in Norway counts 0,54% of total forest area. There are 11 most
important species, prevailing Picea sitchensis and Pinus contorta (Table 13) in forests and plantations.
Table 13. NNTSs in Norway
Dominant
NNTS Area
(ha) % of
total
forest
area Places Aim/Role Management systems Key risks
Picea 50 0,417 Plantations Increase in
carbon Monoculture even – aged
system , the predicted Extreme weather like
hurricanes and heavy 0,0000 0,1000 0,2000 0,3000 0,4000 0,5000 Strengths
Opportunities
Weaknesses Threats
Ecology Silviculture Climate changes

sitchensis 000 sequestration
and the shelter
function on
windy sites. long –
term yield trials
and biomass
expansion
factors climate change for
Norway with increased
precipitation in the
coastal area, prolonged
growing season and a
little bit higher
temperature will
increase the fitness for
Sitka spruce compared
to the native tree
species , Conversion storms hit the coast
occasionally and cause
wind throws resistant
to wind and salt spray
from sea higher and
more frequent seed
production
Pinus
contorta 8
000 0,066 Forests Great volume
production Replanting after cutting
is problematic because
of new restrictions due
to concerns for
biodiversity. Natural
regeneration is too small
for establishing new
stands. Length of
rotation period is
discussed with respect
to what is optimal.
Present practice is to cut
rather young stands
mainly on poorer sites.
The species is more
resistant to pathogens The critic from
environmentalists and
lack of knowledge
about the exotics are
may be the main
bottlenecks
Picea x
lutzii 5
000 0,041 Forests Great volume
production Higher resistance to
frost and drought ,
regeneration
NNTSs in Norway are regulated by the Act of Nature (2009) . Restrictions mean that the forest owner has
to apply local authorities for permission. Also the Forest Act (1997) motivate for using native tree
species as far as possible. In addition, a list of Alien species in Norway – with Norwegian Black list has
been published Species considered having severe (SE) and high (HI) impacts are what form the 2012
Black List.
Table 14. SWOT/AHP Analysis for Norway
Element of
analysis Strengths Opportunities Weaknesses Threats Dominant
strategy
Ecology 0,223881 0,447761 0,089552 0,238806 SO
Silviculture 0,246269 0,335821 0,119403 0,298507 SO

Climate changes 0,268966 0,413793 0,124138 0,193103 SO

Figure 6. Category weights in AHP analysis for Norway

Dominant strengths and opportunities in Ecology segment are: long time experiments on NNTS and
higher production e.g. Sitka spruce 30 % faster growth . Silvicultural analysis shows dominant strengths
are l ong-term 30 -80 years scientific experiments in silviculture and higher volume production of some
NNTS s vs NTS s. Main opportunity is that i ncreased price of fossil fuel increases the demand for wood
and then NNTS s. In a field of climate changes, analysis main strength is that NNTSs are better adapted to
climate changes than NTSs and opportunity is that i ncreased pric es of fossil fuel can fasten the planting
of NNTS due to increased bioenergy prices .
ROMANIA
NNTS s in Romania counts 0,72% of total forest area. There are app. 20 NNTSs. The most important are
Robinia pseudoacacia, Populus sp., and Pseudotsuga menziesii in a form of forest stands or plantations
(Populus sp.).
Table 15. NNTSs in Romania
Dominant
NNTS Area
(ha) % of
total
forest
area Places Aim/Role Management
systems Key risks
Robinia
pseudacacia L. 250
000 3,92 Forest stands,
mostly mixed
stands, parks,
gardens, seed
orchards Good market
potential , High
ecological
protective values
for stabilization of
sands and
degraded lands, Afforestation and
reforestation ,
Tending
operations ,
Silvicultural
systems Early frosts; low
temperatures;
cold winds; heavy
snows 0 0,1 0,2 0,3 0,4 0,5 Strenghts
Opportunities
Weaknesses Threats
Ecology Silviculture Climate chnge

fast growing .
Populus x
canadensis
Moench. and P.
deltoides x P.
trichocarpa 49
840 0,78 Pure plantations,
tested basic
material Good market
potential , High
ecological
protective values
(grows on
sandy and
shallow soils.
Withstand
relatively long
floods, fast
growing Afforestation and
reforestation ,
Tending
operations ,
Silvicultural
systems Melampsora
larici -populina
Pseudotsuga
menziesii
(Mirbel) Franco 12
700 0,20 Forest stands,
parks, arboreta,
botanical
gardens Valuable wood
and resin , h igh
ecological
protective values,
medium growing Afforestation and
reforestation ,
tending
operations Phaeocryptopus
(Adelopus)
gaumannii Petr. ,
Rabdocline
pseudotsugae
Sidow ,
Melolontha,
Grylotalpa
Quercus rubra
L. 2
500 0,04 Forest stands
(including seed
stands), in
mixture stands
parks, arboreta,
botanical
gardens, seed
orchards Local market
potential , average
ecological
protective values
moderate –
growing Afforestation and
reforestation Early frosts, dry
periods .
Pinus strobus L. 1
500 0,02 Forest stands
(including seed
stands), parks,
arboreta,
botanical
gardens, seed
orchards . High resin
production High
ecological
protective values ,
medium -growing Afforestation and
reforestation Dioryctia
abietella Sciff. ,
Agaricum meleus
Vahl .,
Peridermium
strobe Kleb
Legal restrictions are numerous and indicated in laws and norms (Table 16).
Table 16. Legal restrictions on NNTSs in Romania
Law no. 107/2011 the use of forest reproductive materials of exotic
species or non -local provenances in forest cultures is
possible only after testing them in several site

conditions in Romania.
Technical norm no. 1/2000 the use of exotic species (in terms of native forest
types, stocking, planting spacing, etc.) is strictly
limited (on species compositions, planting schemes
and forest regeneration technologies and
afforestation of degraded lands) to the situations
described in point no. 8.
Technical norms no. 2/2000 the app lication of Tending operations and of
Silvicultural systems in stands with exotic species .

Table 17. SWOT/AHP Analysis for Romania
Element of
analysis Strengths Opportunities Weaknesses Threats Dominant
strategy
Ecology 0,216216 0,315315315 0,144144 0,324324 ST
Silviculture 0,20339 0,338983051 0,254237 0,20339 WO
Climate changes 0,251613 0,322580645 0,116129 0,309677 SO

Figure 7. Category weights in AHP analysis for Romania

In Ecology analysis main strength is high growth rate of NNTSs, and treat high invasiveness of NNTSs.
Silviculture results shows dominant WO strategy. Weakness is l ack of specific technical norms/regulation
for NNTS and opportunity i ncreased yield (mixtures of native and non -native species ). Climate changes
shows dominant SO strategy. Strength is NNTS s better adapted to local climate condition compare with
NTSs and opportunity is to id entif y the best most adapted and productive NNTS.
SERBIA 0 0,1 0,2 0,3 0,4 Strengths
Opportunities
Weaknesses Threats
Ecology Silviculture Climate changes

List of the most important NNNTs in Serbia counts 11,18 % of total forest area . Robinia pseudoacacia and
Populus sp. are the dominant species (Table 18) in a form of plantations.
Table 18. NNTSs in Romania
Dominant
NNTS Area
(ha) % of
total
forest
area Places Aim/Role Management
systems Key risks
Robinia
pseudoacacia
L. 156
000 6,93 Plantations,
stands Mixed with
birch and
aspen .
Afforestation .
Honey
production Clear cutting,
mostly natural
regeneration by
sprout from
root, seldom
artificial
establishment by
seedlings Invasive tree species ,
Phoma pseudoaccaciae ,
Phyllonorycter robiniella,
Parectopa robiniella,
Obolodiplosis robiniae
Populus
deltoides 48
000 2,13 Intensive
plantations Increasing of
biological
diversity of the
country,
increasing of
genofond,
consuming CO2 clear cutting,
artificial
establishment by
seedlings with
278-400
seedlings
per hectare Low temperature ,
Dothichiza populea Sacc. &
Briard, Drepanopeziza
punctiformis Gremmen
Marssonina brunea (Ellis &
Everh.) Magnus].,
Melampsora spp .,
Melasoma populi
(Stephens, 1834),
Phyllodecta vitellinae L.
(Col., Chrysomelidae),
Parenthrene tabaniformis
Rott., Cryptodiaporthe
populea , Pemphigus
spirothecae, Sciapteron
tabaniformis, Cosus cosus
Pseudotsuga
taxifolia 2
600 0,12 Mountain
forests,
small areas Increasing of
biological
diversity of the
country,
increasing of
genofond,
consuming CO2 Clear cutting,
artificial
establishment by
seedlings with
2500 seedlings
per hectare. Rhabdoclyne pseudotsugae
Hylastes ater
Pinus strobus 2
000 0,09 Mountain
forests, Increasing of
biological
diversity of the Clear cutting,
artificial
establishment by Cronartium ribicola

small areas,
parks country,
increasing of
genofond,
consuming CO2 seedlings with
2500 seedlings
per hectare.
Legal restrictions:
There are not legal restrictions for growing non -native tree species in Serbia . But all state forests are sertificated so
increasing the area of non -native species at the expense of native species is not allowed. Increasing the area of
non-native species is possible in special cases, at sites that is not covered by forest vegetation, with the approval of
the Ministry of Agriculture, Forestry and Water Management.
Table 19. SWOT/AHP Analysis for Serbia
Element of
analysis Strengths Opportunities Weaknesses Threats Dominant
strategy
Ecology 0,2550 0,2750 0,1700 0,3000 ST
Silviculture 0,2277 0,2902 0,1607 0,3214 ST
Climate changes 0,3022 0,2518 0,1007 0,3453 ST

Figure 8. Category weights in AHP analysis for Serbia

Dominant strengths in Ecology segment are: faster adaptation to changing ecological conditions and
enhancement of soil melioration. Threats are: negative impact on nat ive tree species in terms of
competitiveness and fact that NNTS change habitat type characteristics . Silvicultural analysis shows
dominant strengths are well-adaptation to the local conditions and filling the gaps in forest ecosystems
after disappearance of native tree species . Main threat is that NNTSs are not recognized in state
strategies or programs. In a field of climate changes, analysis main strengt h is that NNTSs are better 0,0000 0,0500 0,1000 0,1500 0,2000 0,2500 0,3000 0,3500 Strenghts
Opportunities
Weaknesses Threats
Ecology Silviculture Climate changes

adapted to climate changes than NTSs particularly in mixed forests and main threat is reduction of the
tree's physiological status and increase of susceptibility to pathogens .
SLOVENIA
NNTSs in Slovenia counts 0,99 % of total for est area . Dominant species are: Robinia pseudoacacia and
Pinus strobus. Both of the species are invasive (Table 20).

Table 20. NNTSs in Slovenia
Dominant
NNTS Area
(ha) % of
total
forest
area Places Aim/Role Management systems Key risks
Robinia
pseudoacacia
L. 157
148 7,76 Forests,
plantations Afforestation
Quality
timber, but
market low
influence
comparing
to native
species,
Honey
production Close -to-nature
sylvicultural system,
selection system,
irregular shelterwood
system, freestyle
system. Invasive , Danger of
using unknown
provenances and
untested forest
reproductive
material
Pinus strobus 38
735 1,91 Planted in
forest Invasive
Pseudotsuga
menziesii 18
066 0,89 Planted in
forest
Quercus
rubra 11
978 0,59 Planted in
forest Invasive

Legal restrictions for NNTSs are present in Forest reproductive material act (2002) where are listed 77
tree species and Order on the list of forest tree species and hybrids (2010) where are listed NNTSs.

Table 21. SWOT/AHP Analysis for Slovenia
Element of
analysis Strengths Opportunities Weaknesses Threats Dominant
strategy
Ecology 0,218182 0,353535354 0,161616 0,266667 SO
Silviculture 0,242697 0,370786517 0,134831 0,251685 SO

Climate changes 0,265487 0,486725664 0,053097 0,19469 SO

Figure 9. Category weights in AHP analysis for Slovenia

In Ecology segment dominants strengths are: high flexibility regarding site conditions of some NNTSs,
high resistance to shallow soils and drought of some species, resistance and vitality of species and go od
adaptation to the sites . The main opportunities are: p otential use for phytoremediation on polluted soils
and for soil erosion control. In Silvicultural segment main strengths are: reforestation of areas unsuitable
for native species , because of environmental changes and NNTS s are used as minority -introduced
species during artificial regeneration . Opportunities are: h igh economic value of some NNTS s logs and
use of NNTS s for shaping the future forests with special ecological or/and soc ial values . In segment of
Climate changes main strengths are: r eplacement of species that are sensitive to the pests and
outbreaks due to climate change s, and opportunities are sustaining forestlands, wood production and
ecosystem services.

To address th is added complexity, we analyzed ecology, silvicultural and climate changes impacts
described in the Millennium Ecosystem Assessment framework (MA 2005), in order to link them with
NNTSs for all analyzed countries , by assuming that the effect of any change influences NNTSs existence
and, in turn, human well -being. After applying SWOT AHP decision -making tool for ranking ecological,
silvicultural and climate changes characteristics in each of analyzed countries, we obtain the strategies,
which are dominant in each segment (Table 22) .

Table 22. Internal and external factors affecting the NNTSs in SEE
Country ECOLOGY SILVICULTURE CLIMATE CHANGES
S O W T S O W T S O W T
Bulgaria 0,2030 0,3008 0,1203 0,3759 0,1961 0,3813 0,1351 0,2876 0,2032 0,3499 0,1490 0,2980
Croatia 0,3264 0,2720 0,2510 0,1506 0,1813 0,4396 0,1374 0,2418 0,2320 0,2486 0,1436 0,3757 0 0,1 0,2 0,3 0,4 0,5 Strengths
Opportunities
Weaknesses Threats
Ecology Silviculture Climate change

Macedonia 0,2432 0,2703 0,1622 0,3243 0,1875 0,3606 0,1442 0,3077 0,2394 0,4521 0,1170 0,1915
Norway 0,2239 0,4478 0,0896 0,2388 0,2463 0,3358 0,1194 0,2985 0,2690 0,4138 0,1241 0,1931
Romania 0,2162 0,3153 0,1441 0,3243 0,2034 0,3390 0,2542 0,2034 0,2516 0,3226 0,1161 0,3097
Serbia 0,2550 0,2750 0,1700 0,3000 0,2277 0,2902 0,1607 0,3214 0,3022 0,2518 0,1007 0,3453
Slovenia 0,2182 0,3535 0,1616 0,2667 0,2427 0,3708 0,1348 0,2517 0,2655 0,4867 0,0531 0,1947
Bosnia and Herzegovina 0,2741 0,3807 0,1218 0,2234 0,1787 0,3191 0,1957 0,3064 0,2348 0,2609 0,2261 0,2783
Montenegro 0,2879 0,2786 0,2229 0,2105 0,2043 0,4489 0,1610 0,1858 0,2576 0,2273 0,1717 0,3434

It is obvious that the dominant strategy in SEE on NNTSs is SO strategy in three analyzed segments of
ecology, silviculture and climate changes (Table 23).

Table 23. Dominant strategies in different segments of NNTSs
ECOLOGY SILVICULTURE CLIMATE CHANGES
SO ST SO ST WO SO ST
Croatia Bulgaria Bulgaria Serbia Romania Bulgaria Croatia
Norway Macedonia Croatia B&H Macedonia Serbia
Slovenia Romania Macedonia Norway B&H
B&H Serbia Norway Romania Montenegro
Montenegro Slovenia Slovenia
Montenegro

When summarizing all results in a segment of Ecology SO strategies of NNTSs refers to: potential for
phytoremediation of polluted soils and for soil erosion control and revitalization of high degraded land ,
accumulation of carbon and using of NNTSs to filling gaps after calamities , faster adaptation to changing
ecological conditions , enhancement of soil fertility , cover all ecological characteristics as well as broad
usage in highly degraded land, fast growi ng species of NNTSs for biomass production, high resistance to
shallow soils and drought of some species . In a segment of Silviculture dominant strategy is also SO and
main elements refers to : improving conditions for production of bioenergy , high productivity, valuable
wood assortments, adapted to afforestation of degraded areas , filling the gaps in forest ecosystems
after disappearance of native tree species, creating better options for stability on landscape level, higher
timber increment of NNTSs comparing to native tree species, better conditions for business of SMEs in
wood processing . SO strategy is main in a field of Climate changes and the dominant elements are:
adaptive management which responses to climate change s and i ncrease lengt h of the growing period ,

help to natural regenerations in case of shifting limits and possibility of better -adapted NNTSs mixtures
to climate changes, better adapted to climate changes than NTSs and opportunity is that i ncreased
prices of fossil fuel can f asten the planting of NNTS s due to increased bioenergy prices , replacement of
species that are sensitive to the pests and outbreaks due to climate change s.
DISSCUSION
In this paper, we present a rating system to assess the potential of NNTSs in a Southeastern countries,
regarding 3 elements: ecology of NNTSs, silviculture and climate changes on NNTSs. We designed the
rating system to meet the specific needs for South east Europe and focused on tree species that may
become invasive in this region. W e then validated the rating system by applying it to NNTSs using SWOT –
AHP analysis. Efforts to manage non -native species generally focus on two approaches that have proven
effective: preventing the introduction of novel species that are likely to become in vasive and, in the
event a non -native species is introduced and rapidly detected, controlling or eradicating the species
(Lodge et al. 2006). Challenges to managing non -native species that are firmly established include
uncertainties over future effects of a non -native species, divergent values among stakeholders, varying
interpretations of sometimes sparse historical records, and dynamic conservation goals. (Schlaepfer, M.
A. et al., 2011). The plethora of UK legislation and guidelines developed to reduce impacts of non -native
species only go part of the way towards ameliorating impact (Manchester and Bullock, 2000). In
analyzed countries, some of them have rigorous legislation on NNTSs (f.e. Bulgaria, Romania). The
difficulties of making general pre diction s on NNTSs suggest that every proposed species introduction
should be subject to rigorous ecological characterization and risk assessment prior to introduction . In
this way application of SWOT -AHP analysis is more than welcome. There are a few leading conc erns
about non -native species relates to their potential to cause economic losses through damage to crops or
forestry and ecology disturbances of NTSs (Mooney, 1999, Manchester and Bullock, 2000) all around the
world. The IUCN (1987) guidelines state that planning of an introduction should involve assessment of
the probability of an increase in numbers of the intro duced species to a level that damages the
environ ment , and the probability of invasion into other habitats . That has been particularly indicated by
the respondents in Macedonia, Romania and Serbia. The most NNTSs in USA have been introduced for
ornamental cultivation (Pimentel et al., 2000) . The spread of non -natives into native communities is a
global issue (Sala et al. , 2000) . This is the case also in SEE result in major disruptions to communities,
changes in ecological functioning and species extinctions in forest stands. Non-native species are seen
generally as a threat by many authors because some possess the ability to become pernicious
domi nants (Maskell et al., 2006), which has been indicated in Bulgaria, Macedonia, Romania and Serbia.
More than 70% of the naturalized exotic plants in Australia had been introduced as ornamentals or for
agricultural purposes (Nairn et al., 1996). It is poss ible to avoid damage to native ecosystems by optimal
mix of exotic species (Weber and Gut, 2004). According to Weber and Gut 2004 the most invasive NNTSs
in Europe are: Robinia pseudoacaciaa and Pinus strobus with risk class III (the highest class), which are
present and cited in almost all countries of SEE. On the other side , Robinia pseudoacacia provides cover
and restores soil fertility on mined lands and it is obvious its role as catalyst for native species (Ashby,
1987). Negative impacts of R. pseudoac acia include shading and changes of soil conditions as a result of
nitrogen fixation (Cierjacks et al., 2013) .
Hiebert & Stubbendieck (1993) developed a decision -making tool for prioritizing control efforts against
exotic plant species by ranking them according to their: ecology, spread potential, costs, and impacts on
the native communities. We applied iIn this article SWOT -AHP analysis to establish ranking of ecology,
silviculture and clima te changes characteristics of NNTSs and point out the strategy for their
development in SEE. This longterm perspective is essential because forests can take several decades to

respond to changes in management and the habitats that they provide today are of ten a function of
decisions made years ago (Mason, 2007) .
Non -native species can cause the loss of biological diversity (i.e., genetic, species, and ecosystem
diversity) and threaten the well -being of humans when they become invasive. In some cases, howeve r,
they can also provide conservation benefits (Schlaepfer et al., 2011) . It has been indicated in the SWOT –
AHP analyses in Macedonia, Romania and Slovenia. The management of non -native species and their
potential integration into conservation plans depends on how conservation goals are set in the future
(Schlaepfer et al., 2011) . It has been particularly emphasized in Bulgaria in Regimes for sustainable
management of forests in Natura 2000, where is prohibited afforestation with non -native species ex cept
the actions towards controlling of torrents and erosion processes .
Non -native species could come to fill important ecosystem and aesthetic functions, particularly in places
where native species cannot persist due to environmental changes and climate c hanges (Byers, 2002). It
is expressed ability of NNTSs to tolerate and adapt to a broad range of biotic and abiotic conditions, as
well as to expand their ranges rapidly, and persist under a variety of future climate scenarios (Williams
and Jackson, 2007). Populus sp., Robinia pseudoacacia, and Pinus strobus are adaptable to different
climate scenarios .
However, some trials have also shown the potential for establishing a wide range of exotic species, some
of which may ultimately prove to be better suited than certain native species for maintaining woodland
cover in lowland England , if predicted future extreme climate change scenarios do come to pass
(Willoughby et al., 2007) . Increasing evidence is that climate change is already affecting t ree growth and
tree mortality (Bran g et al., 2014). A large part of the industrial roundwood of the world is still produced
in short rotation monocultures, often with NNTSs (Roessiger et al., 2011) .
The dynamic behavior of forest trees and stands is being changed constan tly by interactions between
cover, biotic and abiotic conditions, and especially climatic and microclimatic conditions (Aussenac ,
2000 ). Adaptive strategies of NNTSs may include: "(i) persistence of the current forest types, thanks to
the acclimatization to local conditions and to phenotypic plasticity of the populations; (ii) evolution, or
local adaptation, i.e., change in genotype (frequencies) within the same species due to environ mental
pressure. It is favored by large within population diversity and (when possible) gene flow among
populations; (iii) migration and substitution of species; and (iv) extinction of populations with low
ecological plasticity, especially at the edges of their distribution or in the case of isolated (relict)
populations " (Bussotti et al, 2015) .
Several fungal diseases on trees may become more devastating , because of the following factors: (i)
abiotic stresses; (ii) temperature and moisture affect pathogen sporulation and dispersal, and changes in
climatic conditions ; (iii) migration of pathogens triggered by climatic change may increase disease
incidence or geographical range; and (iv) new threats may appear either because of a change in tree
species compos ition or because of invasive species (La Porta et al, 2008) . It has been indicated also on
NNTSs in Bulgraria, Croatia, Macedonia, Romania and Serbia.
Introduced tree species are increasingly being considered for use in production forestry due to
producti on targets, and demand for a diversity of wood products (Felton et al, 2013) . It is especially
obvious in Pseudotsuga menziesii and Populus sp. A striking feature of the list of invasive trees and
shrubs of the world is that 325 species (52%) are currently known to us as invasive, in Europe is 107
(Richardson and Rejmánek, 2011) .

CONCLUSIONS

The results of this study indicate that SO strategy is expected to be a success factor in ecologz,
silviculture and climate changes of NNTSs in research area. The research results emphasise the
importance of forest management to strengthen and raise importance of NNTSs in SEE . The results of

the case studies were rather clear and easily interpreted. Although our case study results bring new
dimens ions or considerable empirical contributions to the research in strategy analysis of NNTSs , the
application of the value -focused thinking approach and A’WOT -based methodology, were pioneering
attempts in the field. Thus future research needs to addr ess spe cific cases. Identifica tion of potential
problem NNTSs will be possible only following reviews of the ecology of species, assessment of potential
effects on biodiversity, and population s tudies to determine processes connected to NNTSs in Europe .

Acknowledgements

The authors gratefully acknowledge …., and reviewers’ valuable suggestions and constructive comments
on the earlier version of this paper .

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