# *Robinia pseudoacacia*

**Black locust**

**Fabaceae**

Plants are shrubs or trees, generally spreading from underground parts.
Leaves are alternate and deciduous. *Robinia pseudoacacia* occurs along
roadsides, canyon slopes, and stream banks, between 50 m and 1900 m
elevation. Seeds, leaves and bark may be fatal to humans and livestock
if ingested (Hickman, 1993).

The genus *Robinia* has four species native to temperate regions of
eastern North America, and is noteworthy for its ability to tolerate
severe frosts. *P. pseudoacacia* is a symbiotic nitrogen-fixing species,
and is among the few leguminous trees adapted to frost-prone areas. It
is also adaptable to environmental extremes such as air pollutants and
high light intensities. Rapid growth, dense wood, and N~2~-fixing
ability make it ideal for colonizing degraded sites. Its natural
distribution includes the Appalachian and Ozark mountains of the US.
Trees tolerate temperatures from 35 to 40°C. *Robinia pseudoacacia* is
found on a variety of soils with pH of 4.6 to 8.2, but grows best in
calcareous, well-drained loams, and does not tolerate water logging or
shade. The trees are pioneers on disturbed soils or burned sites. It
spreads aggressively into disturbed sites by root sprouts, becoming the
main tree colonizer (Dzwonko and Loster 1997). The drought tolerance of
black locust is unclear; while it is sometimes referred to as "drought
tolerant," Elliot and Swank (1994) provide contrasting evidence that
drought can cause high levels of mortality.

*Robinia pseudoacacia* rivals poplar as the second most extensively
planted genus after eucalyptus (Ali 1994). It is becoming one of the
most sought after agroforestry tree species because of its cash value as
fuelwood and fodder (Ali 1994).

*Robinia pseudoacacia* is thought to be fairly specific in its Rhizobium
requirements. While it can form nodules with a variety of exotic
strains, those from native trees work best for effective N-fixation.
Although black locust is relatively frost-tolerant, there is some
evidence that lower soil temperatures limit the amount of nitrogen that
can be fixed (Stoyanova, 1996).

The effects of N-fixation by *R. pseudoacacia* on site fertility may be
large: Ali (1994) estimates that under closed stand conditions, one ton
of black locust litter can release the equivalent of 56 pounds of
nitrogen per acre annually. A 20-year-old monoculture of *R.
pseudoacacia* accumulated 600-700 kg nitrogen per ha (Keresztesi, 1988).
Even in young black locust woods the nitrogen content of soil can be
considerably higher than in woods of the same age of other species
(Boring and Swank 1984a). In invaded regions in Poland, enrichment of
soil nitrogen by *R. pseudoacacia* is thought to favour the appearance
of certain combinations of associated species (Dzwonko and Loster 1997).

Because black locust is considered a desirable species, for both grazing
purposes and as a source of biomass, there are relatively few studies
which describe control methods. However, there is evidence that
susceptibility to anthracnose caused by the fungus Colletotrichum
gloeosporioides could cause decreases in productivity of black locust
(Whiting and Roncadori, 1994).

**Literature cited**:

Ali, Shaukat. 1994. Effect of nitrogen and phosphorus fertilizers on
root growth and nodulation in black locust (Robinia pseudoacacia L.)
seedlings. Pakistan J. Forestry 65-72.

Dzwonko, Z. and S. Loster. 1997. Effects of dominant trees and
anthropogenic disturbances on species richness and floristic composition
of secondary communities in southern Poland. J. Appl. Ecol. 34:861-870.

Elliott, K. J., and W. T. Swank. 1994. Impacts of drought on tree
mortality and growth in a mixed hardwood forest. Journal of Vegetation
Science 5:229-236.

Hickman, J. C. (ed.). 1993. The Jepson manual: Higher plants of
California. Berkeley: University of California Press. 1400pp.

Hui-Juan, S. and Z. Bin. 1993. Increased drought resistance of black
locust seedlings via pretreatment of seeds with paclobutrazol. Can. J.
For. Res. 23:2548-2551.

Keresztesi, B. 1988. The Black Locust. Hungary, Academiai Kiado.

Stoyanova, J. 1996. Growth and N2-fixation in Robinia pseudoacacia L. as
affected by: I. Root temperature. Nauka za Gorata, v. 33, n.1:34-42.

Whiting, E.C. and R. W. Roncadori. 1994. First report of black locust
anthracnose caused by *Colletotrichum gloeosporioides* in Georgia and
South Carolina. Plant Disease 78:529.