BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Juglans major | Arizona Walnut 



GENERAL BOTANICAL CHARACTERISTICS : 
Arizona walnut is a native, deciduous, small to medium tree that may
grow up to 65.6 feet (20 m) tall and to 4 feet (1.2 m) in diameter
[4,24,44,46].  The stout branches spread widely and form a rounded
crown.  Pinnately compound leaves are 7 to 14 inches (17.8-35.6 cm) long
[13,29].  Arizona walnut is monoecious with separate staminate and
pistillate catkins [44,56].  The fruit is 1 to 1.5 inches (2.5-3.8 cm)
in diameter with a husk and a thick, hard shell surrounding a single
seed [29,46].


RAUNKIAER LIFE FORM : 
   Phanerophyte


REGENERATION PROCESSES : 
Arizona walnut reproduces sexually.  It produces large amounts of fruits
every 2 to 3 years [41,56].  Periodic crops are attributed to the need
for above-average spring precipitation for seed production [50].  Female
flower production decreases during times of stress, for example, during
drought years [49].  Seedlings grow rapidly and have a well-developed
taproot [56].  Beyond the seedling stage, Arizona walnut grows
relatively slowly at 1 foot per year (0.3 m/yr) until it reaches
maturity [12,45].  Arizona walnut is long-lived and may reach 400 years
old [17].

Some seed predation occurs; moderate amounts of seed are consumed by
Arizona gray squirrel [48,50].

Germination rates of Arizona walnut are usually less than 50 percent
[17,56].  Seeds germinate in the shell during the year following
production [9,48].  Buried seeds had higher germination rates than seeds
lying on the soil surface [48].  Seed viability increases as seed size
increases; however, seed weight declines as trees become larger and
older [50].  Germination rate is influenced by light.  Arizona walnut
germination was lower under dense herb cover than under open canopy
cover [48].  High densities of Arizona walnut occurred in stands with a
sparse overstory canopy cover in southwestern New Mexico [33].

Arizona walnut seedlings establish over wide elevational and moisture
gradients from wet streambanks to dry hillsides [50].  Seedlings are
susceptible to drought.  In a central Arizona study where drought
occurred annually, only one seedling from a cohort of 374 was alive
after 2 years [48].  Seedling recruitment is decreased by grazing and
flooding [45].



SITE CHARACTERISTICS : 
Arizona walnut is the only walnut to occur in the desert; it is a
facultative riparian species [4,50].  It occurs along ephemeral streams
with subsurface flows or perennial streams in moist sites that are
occasionally flooded [8,10,21,27,36].  Arizona walnut also is found
scattered along river bottoms, canyons, floodplains, dry terraces and
hillsides [28,35,49].  It occurs at elevations from 2,600 to 6,500 feet
(800-1,981 m) and may extend up to 8,200 feet (2,500 m) in elevation
[11,49,53].

The alluvial soils that Arizona walnut commonly occurs on have a wide
range of textures; they are often coarse, rocky, or cobbly sandy loams
[4,20,21,34].  The soils often are stratified and may be up to 28 feet
(8.5 m) deep [11,33].  Two examples of epipedons that Arizona walnut can
occur on in southwestern New Mexico are mollic soils on terraces and
aquic soils in active channel zones [33].  The nutrient status of the
soils is variable; organic matter is usually low due to the coarse
textures and frequent flooding [1].


SUCCESSIONAL STATUS : 
Facultative Seral Species

Arizona walnut occurs in various seral stages from early to climax.  It
is present in early seral riparian communities following periodic
flooding disturances such as scouring.  Arizona walnut may be seral to
or climax with any of the species in the mixed broadleaf and coniferous
communities [3,33].  It is relatively shade tolerant [33,48].


SEASONAL DEVELOPMENT : 
The flowers of Arizona walnut appear shortly before or after the leaves
in the spring [4,9,44].  Fruits mature in 3 months.  Depending upon
elevation, fruits ripen from July to September [50].

Related categories for Species: Juglans major | Arizona Walnut