BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Pinus leiophylla var. chihuahuana | Chihuahua Pine 



GENERAL BOTANICAL CHARACTERISTICS : 
Chihuahua pine is a native, small to medium, monoecious tree that grows
35 to 60 feet (10.7-18.3 m) tall and 1 to 2 feet (0.3-0.6 m) in trunk
diameter [30,34,39,55,70].  Large branches form a narrow crown.  The
bark of Chihuahua pine is 0.9 to 1.5 inches (2.3-3.8 cm) thick [30,55].
The evergreen needles are in bundles of three, are 2 to 4.7 inches (5-12
cm) long, and persist for 3 or more years [22,30,34,57,70].  The cones
are 1.5 to 2.7 inches (3.8-7 cm) long and persist for 5 or more years
[30,34,39].  The seeds of Chihuahua pine are 0.13 inch (0.33 cm) long
with large (0.33 inch [0.84 cm]) wings [70].


RAUNKIAER LIFE FORM : 
   Phanerophyte


REGENERATION PROCESSES : 
Chihuahua pine sprouts from cut stumps or from the root crown [10,39,45,55].

The minimum seed-bearing age of Chihuahua pine is 28 to 30 years [35].
It has persistent, serotinous and semiserotinous (delayed dispersal)
cones that may remain closed for 5 or more years [20,57,68].  Reports of
cone crop size are variable.  While some cones mature every year,
Chihuahua pine produces large seed crops about every other year [30];
however, Krugman and Jenkinson [35] report that intervals between large
seed crops are 3 to 4 years.  Cone and seed collection and seed
germination procedures are discussed in the literature [35].

The small seeds of Chihuahua pine weigh an average of 0.003 ounce (0.01
g) and are wind dispersed [66].  Recruitment is often sparse in
undisturbed stands which may be partly due to closed cones that delay
seed dispersal [30].  Birds consume Chihuahua pine seeds, but it is not
known whether they facilitate Chihuahua pine dispersal and establishment
[45].

Chihuahua pine seedlings are sensitive to intense light and heat [30].
Deep litter reduces Chihuahua pine seedling emergence [6].  In a study
that evaluated relative drought resistance, Chihuahua pine established
beneath nurse plants such as older trees and shrubs, and beneath logs
and boulders [7,30].

Near the lower elevation limit of this species, Chihuahua pine seedlings
occur in relatively moist microsites.  Just below the lowest elevational
limit, Chihuahua pine seedlings die from water stress [7].  Chihuahua
pine seedlings were less drought tolerant than Mexican pinyon seedlings
and more drought tolerant than Apache pine seedlings [8].

Humphrey [33] suggested that a 100-year drought from 1869 to 1956 was
responsible for high Chihuahua pine mortality during the 1950's in
southeastern Arizona.



SITE CHARACTERISTICS : 
Chihuahua pine grows in climates that range from semiarid with bimodal
precipitation to temperate-subhumid with most precipitation falling in
summer [12,62,69].  

Chihuahua pine is common on upland slopes, mesas, canyon bottoms,
alluvial terraces, and intermittent washes [9,10,62].  Chihuahua pine
occurs at elevations from 4,920 to 7,800 feet (1,500-2,377 m) throughout
its range [9,39,69].

Chihuahua pine occurs on soils of varying textures ranging from sandy to
clayey sand with gravel [69].  Soils are often shallow and cobbly
[9,10].  Parent materials are igneous, rhyolite, basalt, or schist [10,69].

Along a moisture gradient from mesic to xeric sites in Arizona,
Chihuahua pine was not present at the most mesic or xeric ends of the
gradient.  It had 50 to 100 stems per hectare at the midmesic point [71].


SUCCESSIONAL STATUS : 
Facultative Seral Species

Chihuahua pine is climax in pine-oak woodlands and forests [9,12].  

Young Chihuahua pine is shade tolerant beneath oaks and junipers.
Depending on the site characteristics, Chihuahua pine may become
dominant and replace the oaks and junipers [20].  It is seral in white
fir forests [38].  Chihuahua pine becomes shade intolerant after it is
about 20 feet (6.1 m) tall [30,68].


SEASONAL DEVELOPMENT : 
Chihuahua pine requires 3 years for cones to mature [17,22,30,53,57].
Reproductive buds are initiated in the summer of the first year [53,57].
Pollination occurs in spring or early summer of the second year
[35,53,70].  Fertilization occurs the following spring.  Seeds mature in
the fall of the third year [30,35,53].  Some seeds may disperse December
through January [35].

Related categories for Species: Pinus leiophylla var. chihuahuana | Chihuahua Pine