Robinia pseudoacacia in Europe: distribution, habitat, usage and threats

Abstract

Robinia pseudoacacia L., commonly known as black locust, is a tree native to North America and is one of the most important and widespread broadleaved alien trees in Europe. It is a medium-sized, deciduous, fast-growing thorny tree with high suckering capacity. It has been extensively planted in Europe and now it is naturalised in practically the whole continent. Growing on a wide range of soil types, this tree species only avoids wet or compacted conditions. It is mainly distributed in sub-Mediterranean to warm continental climates and requires a rather high heat-sum. As a light-demanding pioneer species, it rapidly colonises grasslands, semi-natural woodlands and urban habitats, where it can persist for a long time. Owing to the capacity of fixing di-nitrogen through symbiotic rhizobia in root nodules, black locust can add high rates of nitrogen to soil which becomes available to other plants. The wood of black locust is durable and rot-resistant, making it adequate for multiple purposes such as fire and pulp wood, for fences, construction and furniture. In several parts of Europe, black locust is considered an invasive alien plant, because of shading and its ability to change soil conditions.

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European Atlas of Forest Tree Species | Tree species
166
< 25%
25% - 50%
50% - 75%
> 75%
Frequency
Annual precipitation (mm)
Uncertain, no-data
Marginal/no presence < 5%
Low presence 5% - 10%
Mid-low presence 10% - 30%
Medium presence 30% - 50%
Mid-high presence 50% - 70%
High presence 70% - 90%
Very-high presence > 90%
Robinia pseudoacacia
T. Sitzia, A. Cierjacks, D. de Rigo, G. Caudullo
Robinia pseudoacacia L., commonly known as black locust, is a tree native to North America and is one of the most
important and widespread broadleaved alien trees in Europe. It is a medium-sized, deciduous, fast-growing thorny tree
with high suckering capacity. It has been extensively planted in Europe and now it is naturalised in practically the whole
continent. Growing on a wide range of soil types, this tree species only avoids wet or compacted conditions. It is mainly
distributed in sub-Mediterranean to warm continental climates and requires a rather high heat-sum. As a light-demanding
pioneer species, it rapidly colonises grasslands, semi-natural woodlands and urban habitats, where it can persist for a long
time. Owing to the capacity of fixing di-nitrogen through symbiotic rhizobia in root nodules, black locust can add high rates
of nitrogen to soil which becomes available to other plants. The wood of black locust is durable and rot-resistant, making
it adequate for multiple purposes such as fire and pulp wood, for fences, construction and furniture. In several parts of
Europe, black locust is considered an invasive alien plant, because of shading and its ability to change soil conditions.
The black locust (Robinia pseudoacacia L.) is a medium-sized
deciduous tree that commonly reaches 20 m as a single tree and
30 m within stands1, 2 , but capable of attaining heights up to 35 m
in some locations3. It has a typical life span of about 60-100
years4, although the current longevity record in Europe is for more
than 300 years5. The tree is usually bent-stemmed with greyish-
brown to dark brown bark, becoming longitudinally fissured with
age. The leaves are composed, pinnate, 10-30 cm long, usually
with a pair of spines at the base which persist on young shoots.
The leaflets are commonly in 2-12 pairs, usually opposite, with an
additional one at the end of the rachis. Leaf blades are oblong,
elliptic or ovate, 2-5 × 1.5-2.5 cm, with entire margin. Black locust is
a monoecious species: the hermaphrodite scented flowers have a
white to cream corolla with yellow spots inside, up to 2 cm long and
grouped in pendent, many-flowered, axillary racemes 10-20 cm
long6. Black locust is a monoecious species: the hermaphrodite,
white and fragrant flowers are arranged in pendulous racemes 10-
20 cm long6. The fruit is a legume, 5-10 cm long dark brown pods
hanging in winter and containing 4-10 seeds, mainly dispersed by
gravity and wind7. Fruiting takes place once or twice per year at a
tree age from 6 to 30-40 years8.
Distribution
Black locust is widespread across Europe, occurring from Sicily
in Italy to South Norway and longitudinally from the Portugal littoral
regions up to the Caucasus9-11 . Core areas in the alien range of this
species are in sub-Mediterranean to warm continental climates, where
a rather high heat-sum is available7 and prolonged drought is rare12.
It can be found from sea level up to 1 640 m in the Southern Alps
(Prosser F., pers. comm., July 1, 2015). The species was introduced
in Europe in the early 17th century. Linnaeus dedicated the genus
name to Jean Robin, who, with his son Vespasien, was among the
first arborists to introduce and cultivate this tree in Europe5. In the late
18th and early 19th century extensive planting of black locust trees
started in Central Europe. Currently it occurs in 42 European countries
and is naturalised in 3213, covering with pure and mixed stands, for
example, 400 000 ha in Hungary14, 200 000 ha in France15, 250 000 ha
in Romania16 and 230 000 ha in Italy17. Although accounted among
the 100 most invasive alien species in Europe11, only a few countries
have policies and initiatives to tackle it18.
Habitat and Ecology
Black locust is a light-demanding pioneer species and
grows either as an upright, single- or multi-stemmed tree or, in
harsh environments, as a multi-stemmed shrub. It tolerates a
remarkably diverse range of soil conditions, being only limited by
low soil aeration and waterlogging. On steep slopes, black locust
is usually less vigorous19. The tree is easily damaged by extreme
frosts in winter and presents low adaptability to arid conditions6, 20.
Climate warming is expected to favour its further expansion21. Its
reproduction is primary asexual through horizontal root elongation22.
It is able to produces a high number of root suckers and therefore
exhibits the capacity for clonal growth, up to an area of 100 square
metres23. Disturbance favours clonal growth and causes an increase
in the number of suckers19. The invasion of black locust is well
documented in early succession habitats, like abandoned gravel-
sand pits and landfills, brownfields, secondary forests, coppiced
forests, lowland pastures, roadsides, and burned sites6. As with
other species of the Fabaceae (syn. Leguminosae) family, the roots
of black locust host rhizobia bacteria in symbiotic relationship within
structures called root nodules. These bacteria have the capacity to
take di-nitrogen gas (N2) out of the air and convert it to a form usable
to the host plant (nitrogen fixation). This process makes nitrogen
available to other plants, mainly through mineralization of leaf litter,
and improves the quality of the soils. Black locust can add between
23 and 300 kg of nitrogen in a hectare every year6. So stands of
black locust may generate substantial soil alterations, increasing the
total soil nitrogen, the litter and the organic carbon, also changing
soil pH and decreasing the total phosphorus6. Its adaptability and
the capacity of transforming ecosystem processes are the reason
for its adverse effects on biodiversity. However, inferior competitive
ability in later successional stages is reported where stands have
been left unmanaged for a sufficient time24. Black locust commonly
contributes to the composition of deciduous woodlands, mainly oak
and riparian woods, which are the most frequently invaded12. Stands
dominated by black locust are cultural forest communities, which
can totally differ from native forest vegetation25. As such, they have
been either classified within the phytosociological separate class
Robinietea or included in other units, as a derivative community26.
Several associations have been described in Central Europe, among
which Balloto-Robinietum (diagnostic species include Ballota
nigra, Bromus sterilis, Dactylis glomerata) on poor aeolian sandy
soils, Solidagino-Robinietum (diagnostic species include Solidago
Robinia pseudoacacia in Europe: distribution, habitat, usage and threats
Robinia pseudoacacia
Black locust invasion has been proven to have an impact on biodiversity
when compared with the native habitats. This applies to both plant34-36 ,
bird37 and lichen38 communities. These effects depend on the stand
age and the landscape type. For example, the presence of black locust
in recent secondary stands in rural landscapes does not seem to play
a major role in shaping the diversity of the understorey plant groups
compared to native stands39. In urban areas, it seems to have the
ability to homogenize processes at the plant community level36. Further
research is needed to elucidate the effect of different management
techniques on the ability of black locust to invade adjacent forest and
semi-natural habitats30.
Biodiversity concerns
Black locust in Berlin, Germany.
(Copyright Giovanni Trentanovi: CC-BY)
Map 1: Plot distribution and simplified chorology map for Robinia pseudoacacia.
Frequency of Robinia pseudoacacia occurrences within the field observations
as reported by the National Forest Inventories.
Map 2: High resolution distribution map estimating the relative probability of presence.
JRC_EFDAC_forest_atlas.indd 166JRC_EFDAC_forest_atlas.indd 166 05/07/2021 17:1405/07/2021 17:14

Tree species | European Atlas of Forest Tree Species 167
Annual average temperature (°C) Potential spring-summer solar irradiation (kWh m-2)
Annual precipitation (mm)
Average temperature of the coldest month (°C)
Sum of precipitation of the driest month (mm)
Seasonal variation of monthly precipitation (dimensionless)
Uncertain, no-data
Tundra, cold desert
Negligible survivability
Low survivability
Mid-low survivability
Medium survivability
Mid-high survivability
High survivability
Field data in Europe (including absences) Observed presences in Europe
Robinia pseudoacacia Robinia pseudoacacia
gigantea) on river valley soils, Chelidonio-Robinietum on slightly
humid soils rich in humus, characterised by an understorey with the
greater celandine (Chelidonium majus) and other species (Sambucus
nigra, Galium aparine, Urtica dioica, Geranium robertianum), and
Poo nemoralis-Robinietum, with herb layer dominated by Poa
nemoralis, on slopes with acid bedrock26.
Importance and Usage
Black locust has been strongly encouraged as a forestry tree
in Europe. The yellow and greenish wood is durable, resistant to
stem rot and insect damage, with a marked contrasted colour
between young and mature wood. Black locust is appreciated
as firewood because of its high calorific potential and the
high suckering capacity which makes coppicing the most cost-
effective management system. The mechanical properties of the
wood is moderate to high, but shrinkage has been observed6, 27.
The potential uses include fence posts, boatbuilding, flooring,
furniture, mine timbers, railway sleepers, turned objects, and
veneer. Moreover, it is a promising fast-growing tree species for
biomass production28. Finally, black locust produces a fruity and
fragrant honey29, and its blossoms are used for cooking. However,
all these uses should consider the risk of further expansion of
black locust in adjacent threatened habitats30.
Threats and Diseases
Large herbivores cause only minor damage to black
locust trees in Europe. Until now, exclusively one gall midge
(Obolodiplosis robiniae) and two moths (Phyllonorycter robiniella
and Parectopa robiniella) are known to cause some damage31, 32.
Many lignicolous fungal species have been detected in the alien
range, of which more than 40 are parasitic. Moreover, 11 mildews
and leaf-spot diseases have been recorded in Germany6. Finally,
some viruses, potentially pathogenic to crops, are known from
the alien range33. In general, threats for black locust in Europe are
much fewer and of lower intensity than those in its native range6.
This is an extended summary of the chapter. The full version of
this chapter (revised and peer-reviewed) will be published online at
https://w3id.org/mtv/FISE-Comm/v01/e014e79. The purpose of this
summary is to provide an accessible dissemination of the related
main topics.
This QR code points to the full online version, where the most
updated content may be freely accessed.
Please, cite as:
Sitzia, T., Cierjacks, A., de Rigo, D., Caudullo, G., 2016. Robinia
pseudoacacia in Europe: distribution, habitat, usage and
threats. In: San-Miguel-Ayanz, J., de Rigo, D., Caudullo, G., Houston
Durrant, T., Mauri, A. (Eds.), European Atlas of Forest Tree Species.
Publ. Off. EU, Luxembourg, pp. e014e79+
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Long legume which can contain 4-10 seeds.
(Copyright Marinella Zepigi, www.actaplantarum.org: AP)
Fragrant white flowers clustered in a long raceme.
(Mezzana, Northern Italy).
(Copyright Giulia Corradini: CC-BY: CC-BY)
A stand with a dense carpet of celandines (Chelidonium majus) (Berlin, Germany).
(Copyright Giovanni Trentanovi: CC-BY)
Autoecology diagrams based on harmonised
field observations from forest plots.
Map 3: High resolution map estimating the maximum habitat suitability.
JRC_EFDAC_forest_atlas.indd 167JRC_EFDAC_forest_atlas.indd 167 05/07/2021 17:1405/07/2021 17:14