BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Robinia pseudoacacia | Black Locust 



GENERAL BOTANICAL CHARACTERISTICS : 
Black locust is a medium-sized, native, deciduous tree [45].  Mature
height ranges from 40 to 60 feet (12-18 m), and 12 to 30 inches (30-76
cm) d.b.h.  On better sites, maximum height may be 100 feet (30 m) [45].
The bark is thick (1 to 1.5 inches [2.5-4 cm] and deeply furrowed
[24,31].  Open grown trees have short boles, branching at 10 to 15 feet
(3-5 m) above the ground.  On good sites, however, black locust trees
with longer, clear, straight trunks may be produced.  The roots of black
locust are usually shallow and wide spreading, but deep roots of up to
26 feet (8 m) or more can also be produced, especially on xeric sites
[14].  Radial root spread is usually 1 to 1.5 times tree height [45].
The leaves fold and droop with cloud cover or at evening [24].  The
paired stipules at the base of each leaf develop into persistent woody
spines [31].  The inflorescence is a large, pendant raceme [45].  The
fruit is a flattened legume 2 to 4 inches (5-10 cm) long.  The fruit
opens while still on the tree [45].

Black locust grows rapidly, reaching mature heights in 20 to 40 years
[86].  It is short-lived; decadence may begin at 40 years of age [75],
and it rarely lives over 100 years [24].


RAUNKIAER LIFE FORM : 
   Phanerophyte


REGENERATION PROCESSES : 
Sexual reproduction:  Black locust reaches sexual maturity at
approximately 6 years of age.  The best seed production occurs between
15 and 40 years of age.  Seed production continues until about age 60.
Good seed crops are produced every 1 to 2 years [45].  Seeds are hard
and require scarification for germination to take place [75].  Seedlings
established on good sites free of competition show rapid early growth
[45].

Vegetative reproduction:  Black locust produces root and stump sprouts.
Sprout production is stimulated by top damage.  Root suckers are usually
more important to reproduction than are seedlings.  Root suckers first
appear when stems are 4 or 5 years old [45].  Sprouting is an important
mechanism for colonizing areas that have herbaceous plant cover but no
woody canopy.  Grasses form a sod that does not allow black locust
seedling establishment, but black locust root sprouts are able to
colonize these areas [40].


SITE CHARACTERISTICS : 
Black locust can grow on a wide range of sites, but grows best on rich,
moist, limestone-derived soils [45].  It does not do well on heavy or
poorly drained soils [46], although it appears to be tolerant of some
flooding.  In the Northeast, it is found on floodplain sites with a 40
to 100 percent probability of flooding in any given year [64].
Acceptable soil pH ranges from 4.6 to 8.2 [45].  Vogel [79] reported the
lower pH limit for black locust growth as 4.0.  In the Appalachians,
black locust grows best on moist eastern slopes below 3,400 feet (1,040
m).  In the Great Smokey Mountains, black locust occurs up to 5,300 feet
(1,620 m) elevation [45].


SUCCESSIONAL STATUS : 
Facultative seral species

Black locust is intolerant of shade [5].  It is a pioneer on old fields
within and outside of its original range [68].  It is often a prominent
member of postclearcut communities if it occurred in the pretreatment
community [5].  Black locust sprouts quickly from roots and stumps and
grows more rapidly than other tree species for the first 10 to 20
postdisturbance years [10].  In southwestern Ohio black locust is a
dominant member of 40-year-old oldfield stands that include white ash
(Fraxinus americana), American elm, black cherry (Prunus serotina),
honeylocust (Gleditsia triacanthos), and other species.  In the same
area, black locust is a minor canopy member of 60-year-old oldfield
stands dominated by sugar maple (Acer saccharum), white oak (Quercus
alba), northern red oak (Q.  rubra), American elm (Ulmus americana), and
other species [28].  Black locust colonizes canopy openings by root
sprouts [10].  It is not usually found in old-growth forests; its
presence in mature forests usually indicates disturbance [56].

Black locust is sometimes present in self-sustaining Table Mountain pine
(Pinus pungens) populations in Virginia.  Usually a fire-maintained
type, Table Mountain pine is apparently climax on steep, dry slopes.
The presence of black locust in these stands is probably due to
gap-phase recruitment, indicated by the uneven distribution of black
locust age-classes [82].

As a nitrogen fixing species, black locust can achieve early dominance
on open sites where nitrogen is limiting to other species.  As soil
nitrogen levels rise, however, other plants can replace black locust.
Other factors in black locust replacement include its short lifespan and
lack of reproduction under closed canopies [10,46].


SEASONAL DEVELOPMENT : 
Black locust flowers from April to June.  Fruits ripen from July to
November.  Seeds are released from the persistent fruits until the
following spring [86].

Related categories for Species: Robinia pseudoacacia | Black Locust