BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Pinus sabiniana | Gray Pine 



GENERAL BOTANICAL CHARACTERISTICS : 
Gray pine is a drought-tolerant, native evergreen conifer.  Mature
trees average from 40 to 80 feet (12-24 m) in height and from 12 to 36
inches (30-90 cm) in d.b.h. [38,40].  Trees usually maintain a pyrimidal
growth form until the pole stage.  Mature trees typically have multiple
trunks [40].  Gray pine is self-pruning, and lower branches are often
a considerable distance above the understory [35].  Gray pine grows a
deep taproot where soil depth permits [4,40].  In hardpan soils, it
develops a spreading, shallow root system with a weak taproot extending
through the duripan [40].  The bark of young trees is thin [40], while
older trees have thick bark [35].  Needles grow from 8 to 12 inches
(20-30 cm) long and are shed every 2 to 3 years [39].  Gray pine's
heavily spined female cones are among the largest and most massive in
the genus.  Fresh cones average from 0.7 to 1.5 pounds (0.3-0.7 k), and
may exceed 2.2 pounds (1 kg) [40].  The cones are typically from 6 to 12
inches (15-30 cm) long.  They do not form an abcission layer and are
retained long after seeds are shed.  The hard-coated, heavy seeds are
from 0.6 to 1.0 inch (15-25 mm) long and have short-winged seeds
[17,38,39].  The lifespan of gray pine is unclear because most older
specimens were cut by early settlers, but it is believed to be 200+
years [40].


RAUNKIAER LIFE FORM : 
   Phanerophyte


REGENERATION PROCESSES : 
Gray pine produces seed at 10 to 25 years of age [33].  It is a
consistent seed producer, with large crop outputs at 2- to 3-year
intervals [40].  Gray pine has delayed seed dispersal [10,46].  Cones
open slowly, shedding seed over a period of several months [40].  Seeds
are disseminated by animals, gravity, and water [1,40].  Scrub jay and
acorn woodpecker are the most effective animal disseminators [40].

Seeds require cold stratification for approximately 30 days prior to
germination [27,33].  The exact stratification period varies with
ecotype.  Seedbank-stored seed remains viable for up to 5 years [33].
Germination rates improve when the seed is scarified and increase
greatly when the nuclear cap is removed [40,48].  Germination is epigeal
[33].  Seedlings establish best on bare mineral soil under partial
shade.  Most first-year growth occurs in the taproot.  Subsequent top
growth is rapid; early growth rates of gray pine are among the most
rapid of all conifers.  Rate of top growth averages 28 inches (70 cm)
per year for the first 8 years of life [40].

Gray pine does not reproduce vegetatively [40].


SITE CHARACTERISTICS : 
Gray pine grows on exposed, dry, rocky slopes at elevations from 100
to 6,000 feet (30-1,800 m) [23,26].  The climate is Mediterranean, with
mild winters and hot, dry summers [35].  Annual mean precipitation is 21
inches (530 mm), ranging from 3 to 40 inches (76-1,000 mm) [6,40].
Eighty percent of precipitation occurs during winter and early spring.
Snow falls occasionally [35].  The annual mean temperature is 61 degrees
Fahrenheit (16 deg C), with maximum summer temperatures sometimes above
105 degrees Fahrenheit (41 deg C) [6,9].  Relative humidity is often 5
percent or lower in summer [9].


SUCCESSIONAL STATUS : 
Facultative Seral Species

Blue oak-gray pine communities are fire climax and are replaced by
ponderosa pine or other coniferous forests in the absence of fire
[16,26,32].  Gray pine readily establishes from seed on disturbed sites
and is common in all seral stages of the blue oak-gray pine community
[30].  Young trees tolerate partial shade [40].  Mature trees are shade
intolerant [25].


SEASONAL DEVELOPMENT : 
The seasonal development of gray pine is as follows:

     growth starts:    March to April [35]
     pollination:      March to April [15,40]
     fertilization:    Spring following pollination [40]
     cones mature:     September to October [40]
     seeds dispersed:  October to February [40]

Related categories for Species: Pinus sabiniana | Gray Pine