BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Arbutus menziesii | Pacific Madrone 



GENERAL BOTANICAL CHARACTERISTICS : 
Pacific madrone is a native broadleaved sclerophyllous evergreen tree
[9,16].  Heights range from 25 to 130 feet (7.6 to 40 m) [2,28,44,52].
Trees occupying favorable sites typically range from 50 to 80 feet (15
to 25 m) in height with diameters of up to 2 feet (0.6 m) [52].  Single
or multiple curved trunks support a broad, spreading crown composed of
heavy, irregularly shaped limbs [2].  The bark is freely exfoliating,
peeling off in large, thin scales.  Once the bark is shed, the remaining
surface typically exhibits a smooth, polished appearence and a
distinctive reddish color [2,44].  Color of young bark varies widely but
darkens to a deep red with age; younger stems may range from green to
chartreuse, while young trunks are frequently orange [2,28].  Older
portions of the bark become dark, brownish-red in color and are
fissured.  The glossy, leathery leaves are dark green above and paler
green below and are arranged alternately on the stem.

Inconspicous, bisexual urn-shaped flowers are borne in showy, terminal
clusters [52].  Flowers range from white to pink in color and are sweet
smelling [2].  The fruit is a bright red to orange-red, pea-sized berry
consisting of a mealy pulp and numerous, bony seeds [2].  At the base of
the stem, Pacific madrone possesses a woody, globe-shaped, underground
regenerative organ known as a burl [31,58].  The massive, widespreading
root system is associated with ericoid mycorrhizae [41,46].  Once
established, Pacific madrone is windfirm, drought enduring, and somewhat
tolerant of wet, freezing conditions [16,40].

Growth:  Best growth occurs on humid, coastal sites [11,16].  Trees may
live to 200 years of age or more [2,24].  Sprouts grow quite rapidly
following disturbances which kill the aboveground stems [40,59].


RAUNKIAER LIFE FORM : 
   Undisturbed State:  Phanerophtye (mesophanerophyte)
   Burned or Clipped State:  Cryptophyte (geophyte)


REGENERATION PROCESSES : 
Pacific madrone regenerates both sexually and vegetatively.  Disturbed
environments and early seral situations are extremely conducive to
madrone regeneration; plants produce abundant seed and prolific sprouts
[40,46,59].

Reproduction from seed:  Unlike many evergreen hardwoods, Pacific
madrone is a regular seeder.  Abundant seed is produced almost every
year, with seed production occurring as early as 3 to 5 years of age
[16,52].  Birds and mammals are important long-distance dispersal agents
for the boney seeds which are contained in brightly colored, pea-sized
berries [16].  If not animal-dispersed, berries fall directly beneath
parent plants [40].  Although most seed is viable, a stratification
period of approximately 60 days at 33 to 40 degrees F (0.6 to 4 degrees
C) on a moist seedbed is required to stimulate germination [52].
Germination rates of previously stratified seed are high.  In laboratory
tests, 94 percent germination occurred over 38 days at temperatures of
approximately 70 degrees F (21 degrees C) [52].  Scarification with
sulfuric acid does not enhance germination.  Seeds remain viable for at
least 2 years when stored at room temperature [16].

Natural germination takes place from February to April [16].  On
mixed-evergreen sites in southwestern Oregon, seedling emergence
occurred from early March to early May; more than 90 percent of
seedlings emerged within a 1-month period and no second or third year
emergence was observed [59].  Despite high rates of germination and
emergence, seedling survival is poor on most sites.  Approximately 90 to
100 percent of seedlings die within the first year [46,59].  Few
seedlings survive beneath well-stocked conifer-hardwood stands.  Forest
floor layers contain damping-off fungi and invertebrates (probably
slugs) which kill large numbers of seedlings.  Since hypocotyls are soft
and flabby, first year seedlings are also very susceptible to mortality
from litterfall.  Seedlings are sometimes able to survive their first
summer under light canopy densities in conifer-hardwood stands; however,
most die from litterfall over the winter [59].  Other factors
contributing to poor seedling establishment on forested sites include
drought, seed predation, and perhaps insufficient light.

Successful germination and establishment occurs most frequently on
moist, partially shaded, mineral soil [4,16,40].  Favorable nursery
conditions are present in young clearcuts where logging has exposed
mineral soil and reduced overstory litterfall [40].  Recent studies of
Pacific madrone seedling establishment on mixed-evergreen sites indicate
that first year survival appears significantly related to overstory
canopy density (P=0.05) [59].  On these southwestern Oregon sites,
better average seedling survival occurred on clearcut versus forested
environments.  Seedling survival was highly variable even within
clearcuts, however, and depended on microsites protected from direct
radiation, frost heaving, and cold temperatures.  Litterfall from
associated shrubs and sprouting hardwoods also contributed to seedling
mortality on clearcuts.  On recently logged redwood (Sequoia
sempervirens) sites, madrone seedlings readily established in open
environments on relatively hot, dry sites with poor soils [62].

Madrone seedlings grow slowly [40].  First year seedlings are typically
0.6 to 1.4 inches (1.5-3.5 cm) tall with a taproot less than 4 inches
(10 cm) long.  Average height of second year seedlings is approximately
1 inch (2.5 cm) [59].  Once established, seedlings are extremely drought
tolerant [16].
 
Vegetative regeneration:  Pacific madrone regenerates vegetatively by
adventitious budding from stumps and basal burls following fire and
other disturbance [2,21,26,61].


SITE CHARACTERISTICS : 
Pacific madrone is widely distributed throughout the Pacific Coast
region, occurring from coastal redwood forests to oak woodlands and
chaparral communities [9,18,54].  This species is generally restricted
to sites having mild oceanic winters [2,16].  Temperature and moisture
regimes vary considerably throughout its distribution; annual
precipitation may range from 15 to 150 inches (37.5 to 373 cm) [2,16].
Although ubiquitious throughout its range, Pacific madrone rarely occurs
in pure stands [16].
  
Southern range:  Pacific madrone is often associated with dry foothills,
wooded slopes and canyons in California and southwestern Oregon [44,53].
In California, elevations range from 300 to 4,000 feet (91 to 1,220 m)
[53].  A common component of coastal redwood and mixed-evergreen
forests, Pacific madrone reaches greatest stature and abundance on dry
sites at low to moderate elevations along the east slope of the Coast
Ranges and in the Siskiyou Mountains [21,49,54].  Common conifer
associates include redwood, Douglas-fir (Psuedotsuga menziesii),
ponderosa pine (Pinus ponderosa), sugar pine (P. lambertina), and
incense-cedar (Libocedrus decurrens) [54].  Common hardwood associates
include tanoak (Lithocarpus densiflora), canyon live oak (Quercus
chrysolepis), and chiquapin (Chrysolepsis chrysophylla); ceanothus
(Ceanothus spp.), manzanitas (Arctostaphylos spp.), and raspberries
(Rubus spp.)  are common associated shrubs [11,16,18,59].  Pacific
madrone is also a characteristic species of oak woodlands in the
interior valleys of northern California and southern Oregon where it
occupies harsh sites with Oregon white oak (Quercus garryana), canyon
live oak, California black oak (Q. kelloggii), and poison-oak
(Toxicodendron diversiloba) [17,40,56].  On particularly severe sites,
Pacific madrone often grows as a shrub [16].  Shrubby ecotypes are most
prevalent from northern California southward [61].

Northern range:  Farther northward, Pacific madrone typically grows as a
small tree [11,30].  It is widespread west of the Cascades in Oregon and
Washington and is associated with relatively hot, dry lowland sites
within coastal Douglas-fir and western hemlock forests [18,65].
Increased regional rainfall apparently allows Pacific madrone to occupy
drier habitats than in mixed-evergreen forests [64].  Greatest abundance
is usually attained on sites unfavorable to conifer growth [2,17].
Sites include ridgetops and south-facing slopes up to 5,000 feet in
elevation (1,524 m) [60].  Towards the northern edge of its distribution
in southern British Columbia and northwestern Washington, Pacific
madrone is restricted to areas along the immediate coast [18].  The only
broadleaved evergreen tree native to Canada [30,35], Pacific madrone
rarely extends inland more than five miles (8 km) in southern British
Columbia [18,30,34].  Sites consist of rocky bluffs along the seacoast;
elevations do not exceed 1,000 feet (305 m) [23,30].  Common associated
species include Douglas-fir, lodgepole pine (Pinus contorta), Rocky
Mountain juniper (Juniperus scopulorum), Oregon white oak, salal
(Gaultheria shallon), and Idaho fescue (Festuca idahoensis) [18].

Soils: Although soil types are highly variable, soils supporting Pacific
madrone usually exhibit a low soil moisture content thoughout most of
the summer.  Pacific madrone grows on glacial tills or shallow rocky
soils in the northern portion of its range.  Soils may also be fine
textured, ranging from loam to clay loam.  Towards the southern end of
its distribution, soils are often derived from granite, quartz diorite,
sandstone, or shale [16].


SUCCESSIONAL STATUS : 
Within coastal redwood and mixed-evergreen forests, Pacific madrone is a
long-lived, moderately shade-tolerant, seral species which survives
disturbances such as fire, logging, blow-down, insect devastation, or
mass soil movement [10,16,18].  Not only is madrone capable of vigorous
sprouting following disturbances which kill aboveground stems, but
exposed mineral soil and light canopies associated with early seral
situations are optimal conditions for madrone seedling establishment
[46,59].  Consequently, Pacific madrone is a strong competitor during
early stages of succession, particularly on drier sites within redwood
and mixed-evergreen forests [54].  Although frequently abundant within
young stands, coverage gradually declines as the conifer canopy closes
[18,62].

Pacific madrone is fire maintained throughout most of its range,
depending on periodic fire to eliminate or greatly reduce the conifer
overstory [4,62].  With continued fire exclusion, madrone is replaced by
more shade-tolerant competitors [3,62].  Pacific madrone is often a
component of broad sclerophyll forests and brushfields in northern
California and southwestern Oregon [18].  In the Klamath Mountains,
Pacific madrone is a common species in chaparrallike brushfields
dominated by evergreen shrubs [20,54].  Repeated fires have converted
many of these brushfields into semipermanent communities [18].


SEASONAL DEVELOPMENT : 
Pacific madrone typically flowers from March to June [52].  Fruits ripen
in the fall and persist until December or January [16,61].  Leaves
remain on the plant for 2 years before they turn red to orange and fall;
abscission typically coincides with the development of a new leaf crop
[2,16].

Generalized trends in the phenological development of Pacfic madrone are
presented below [16]:

                              Southern range          Northern range

Leaf bud swelling begins       February               late March
Flower bud swelling begins     March                  May
Flowering begins               March                  May
Full bloom                     April                  June
Second year leaves fall        June                   June - July
Bark exfoliates                June - July            June - September
Fruits mature                  September - October    October

Related categories for Species: Arbutus menziesii | Pacific Madrone