BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Juglans nigra | Black Walnut 



GENERAL BOTANICAL CHARACTERISTICS : 
Black walnut is a native, deciduous tree that can grow to a height of
125 feet (38 m) but ordinarily grows to around 80 feet (25 m) [10,43].
Black walnut develops a long, smooth trunk and a small rounded crown
when growing in the forest.  In the open, the trunk forks low with a few
ascending and spreading coarse branches.  The root system usually
consists of a deep taproot and several wide-spreading lateral roots.
The bark on young trees is dark and scaly but becomes darker with
rounded intersecting ridges on mature trees [17,39].


RAUNKIAER LIFE FORM : 
   Phanerophyte


REGENERATION PROCESSES : 
Seed production:  Black walnut produces abundant seed crops irregularly,
perhaps twice in 5 years.  Although open-grown trees produce seed as
early as 8 years after planting, the minimum seed-bearing age for
commercial quantities of seed is about 12 years.  Best seed production
begins when the tree is about 30 years old and continues for another 100
years [31,43].

Dispersal:  Black walnut seed is heavy. The seeds are dispersed by
squirrels carrying seed from beneath the tree and burying them at a
distance [29,36].

Seedling development:  Many black walnut seedlings germinate from the
nuts cached by squirrels in the fall.  Normal freezing and thawing
usually causes the seeds to break dormancy the following spring, but
germination is often delayed, sometimes until the second year [3,35].

Vegetative reproduction:  Small black walnut trees usually sprout from
the stump when they are cut or killed back by fire.  Shoots originating
high on the older stumps often decay, but shoots from the root crown
generally are free from defect [22,43].


SITE CHARACTERISTICS : 
Black walnut is found on a variety of sites but grows best on deep,
well-drained neutral soils that are moist and fertile [43].  It grows
slowly on wet bottomlands, dry ridges, and slopes.  Black walnut is
common on limestone soils [9,10] and grows extremely well on deep loams
and fertile alluvial deposits.  Good agricultural soils are generally
favorable sites for black walnut.  In the Appalachians, the best wlanut
trees are found on bottomlands and coves below 4,000 feet (1,200 m) [5].

Principal associates are identified in the Distribution and Occurrence
frame.  Other common tree associates include American elm (Ulmus
americana), hackberry (Celtis laevigata), green ash (Fraxinus
pennsylvanica), box elder (Acer negundo), and butternut (Juglans
cinerea) [29].


SUCCESSIONAL STATUS : 
Black walnut is classified as shade intolerant.  In mixed forest stands,
it must be dominant to survive, although it can survive in the
relatively light shade of black locust [43].  Black walnut is found in
many of the climax associations but because of its intolerance is not
classified as a climax tree in the strict sense.  In general, black
walnut maintains itself in most stands as scattered single trees
occupying openings in the canopy [15].


SEASONAL DEVELOPMENT : 
Black walnut normally begins flowering about mid-April in the southern
part of its geographic range and mid-June in the northern part of its
range.  The fruit ripens in September or October of the same year,
dropping shortly after the leaves fall [10,29].

Related categories for Species: Juglans nigra | Black Walnut