BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Heteromeles arbutifolia | Toyon 



GENERAL BOTANICAL CHARACTERISTICS : 
Toyon is a native, broad-leaved, sclerophyllous, arborescent shrub which
typically grows from 6 to 10 feet (1.8 to 3 m) tall [9,24,45,56,58].  On
more favorable sites toyon may occasionally attain tree stature,
reaching heights of approximately 33 feet (10 m); however, in these
instances it typically retains a shrublike form [9].  Plants are erect,
freely branched, and unarmed [45].  Older branches have gray bark [45].
The dense foliage is composed of simple, evergreen leaves which are from
2 to 4 inches (5 to 10 cm) long and arranged alternately on the stem;
leaf margins are sharply toothed and bristly pointed [56,58].  The
inconspicuous, bisexual flowers are white in color and occur in loose,
somewhat flat, terminal clusters [56].  The bright red, berrylike fruits
are approximately 0.25 inch (5 to 6 mm) in diameter and contain one or
two, small brown seeds [37,45,46].  Toyon has a strong and much-branched
root system that is deeply penetrating and wide spreading [24].  Feeder
roots are abundant in the surface humus around the plant base as well as
elsewhere throughout the extensive root system.  In response to repeated
postburn sprouting, toyon sometimes develops an enlarged rootcrown which
is irregularly shaped and platformlike [30]; this structure, however, is
not a lignotuber [30,31].  Longevity of toyon is estimated to be from
100 to 200 years [30].

Morphological distinctions between varieties are presented below
[45,46]:

H. a. var. arbutifolia - typical variety; fruit red
H. a. var. cerina  - fruit yellow
H. a. var. macrocarpa - large fruited form; fruit red; leaves subentire


RAUNKIAER LIFE FORM : 
   Phanerophyte


REGENERATION PROCESSES : 
Toyon regenerates by both sexual and vegetative means.  Within the
fire-prone chaparral environment, it maintains itself primarily through
vigorous sprouting [29,31,32].  Little or no seedling establishment
occurs immediately following fire [31,63].  Extended fire-free periods
are required for successful seedling establishment and population
expansion [32,33].

Vegetative regeneration:  During extended fire-free intervals, toyon
rejuvenates its crown by continually producing new sprouts from
established rootcrowns [31,33].  Following disturbances such as fire or
cutting, toyon sprouts from surviving adventitious buds on the rootcrown
[55,58].

Seedling reproduction:  Onset of seed production occurs early in toyon;
2-year-old transplants can produce seed during the second season
following outplanting [13].  Abundant seed is produced annually after
the first flowering [37,54], and seed production apparently does not
decrease with age [29].  Seeds are dispersed in the late fall and winter
[32].  Significant, widespread dispersal of the persistant, fleshy
fruits occurs through animals, particularly birds [11,30,43,63,64,66];
if not dispersed by animals, seeds fall directly beneath the parent
plant.  Seeds are short lived and retain their viability for not more
than 9 months when dried at room temperature [32].  Germination occurs
readily under favorable moisture and temperature conditions, often
within 10 to 40 days [37,41].  Seeds germinate without the stimulus of
heat or charred wood; in fact, heat treatments are generally lethal to
toyon seed [32].  Germinative capacity under greenhouse conditions
ranges from 73 to 99 percent [32,37,41].  Although fresh seeds do not
need stratification, stored seeds require stratification for 3 months at
temperatures of 35 to 41 degrees F (1.6 to 5 degrees C) to enhance
germination [37,41].

Toyon seedlings are never very abundant within chaparral communities
[63].  Limited observations suggest that seedling establishment is
episodic and coincides with periods of above-normal rainfall [31,63].  A
series of wet years apparently produces an abundant seed crop and also
creates a moisture regime conducive to seedling establishment [31].
Successful establishment occurs within mature chaparral in gaps
resulting from the death of senescing, shorter lived species [64].
Although abundant initial establishment may occur in burned or unburned
stands during years of above-normal precipitation [64], continued
survival is favored beneath mature stands on sites that are relatively
mesic (north slopes) and which possess a well-developed litter layer
[31].  Seedlings are frequently stunted and susceptible to browsing from
small mammals [26].  Consequently, long-term survival beneath mature
chaparral is rare [31].

Established seedlings are most common in very old stands (60 to 100+
years) [31,32].  Toyon seedling densities (plants established in recent
decades) within a 117-year-old stand of scrub oak chaparral equalled
approximately 50 per hectare [33].  Long fire-free intervals apparently
allow for the buildup of seedling populations resulting from episodes of
establishment.  Zedler [64] speculates that gap size is crucial to a
seedlings ability to survive to the stage where it can resprout
following fire.  The average size of unoccupied gaps tends to be larger
in infrequently burned stands where the size of senescing individuals is
also larger [63,64].  Obligate sprouters such as toyon apparently
require fire-free intervals of 100 years or more for significant
recruitment of new individuals [31].
  
Newly emerged toyon seedlings have been observed as early as
mid-February on undisturbed mixed-evergreen sites in central California
[49].  Mortality was high within these communities with nearly all
seedlings dying from damping-off fungus or leaf spot disease [49].



SITE CHARACTERISTICS : 
Toyon is a characteristic species of chaparral and foothill woodland
communities throughout its distribution [20,45].  It usually grows in
scattered stands [9,56] on semidry, rocky slopes within foothills,
mountains, and canyon bottoms at elevations below 4,000 feet (1,220 m)
[37,45].  Soils supporting toyon are typically dry and well drained and
may occasionally be somewhat saline [58].  Although occurring on a
variety of aspects, toyon is most often associated with relatively mesic
chaparral communities, occupying cool, north exposures, erosion
channels, arroyos, depressions, and toeslopes [20,60].  


SUCCESSIONAL STATUS : 
Toyon is a long-lived and relatively shade-tolerant species which is
highly persistent within chaparral and woodland chaparral communities
[20,22,30].  Although widespread, toyon is not usually abundant [9].  It
becomes more common within mesic types of chaparral, particularly stands
dominated by scrub oak.  Scrub oak chaparral typically experiences
reduced fire frequencies relative to chamise chaparral [30].  During
extended fire free intervals, toyon is able to outlive, overtop, and
shade out many shorter lived species [64]; seedling establishment then
occurs in newly created gaps beneath the mature canopy [47,63].
Successional studies in scrub oak chaparral indicate that limited toyon
seedling establishment may occur in stands which remain unburned for 10
to 20 years [23,25].  As a stand matures, toyon gradually increases in
prominence until it is an important codominant of 65-year-old stands
[47].  In stands beyond 65 years of age, scrub oak and hollyleaf cherry
increase in dominance while toyon decreases in size and prevalence
[19,23].  However, toyon typically persists within mature chaparral
until the next fire occurs, at which time resprouted individuals become
part of the initial postburn vegetation [7,33,58].  Toyon is also
capable of pioneering eroded sites [58].


SEASONAL DEVELOPMENT : 
Studies of seasonal cambial growth indicate that toyon is active from
December through mid-June, with peak activity occurring between February
and April; stem growth ceases from late June to December during the
prolonged summer drought [1,43].  Leaves are initiated in the early
spring, and maximum size is reached soon afterwards; secondary leaf
growth occurs during the remainder of the growing season, resulting in
increased tissue density [11].  Flowering occurs from June through July
[45,56].  Fruit development is prolonged; berries first appear in August
or September and persist until December when they reach maturity
[11,58].

Although toyon is able to photosynthesize year-round, carbon is
partitioned differentially among plant functions and varies according to
season [11].  During the stem growth period in the spring, most fixed
carbon goes to the development of the canopy (new leaf and stem tissue)
which gives toyon a competitive advantage.  During periods of little
stem growth, carbon is allocated to root growth, fruit production, and
into compounds which apparently provide a degree of predator protection
[43].  Although leaves are characterized by high levels of both tannins
and cyanogenic glucosides from the time of initiation, tannin levels
reach a maximum in September and October when herbivore pressures are
particularly high.  The pulp of immature fruits contains a toxic
cyanogenic glucoside that protects developing fruits from bird
predation.  During the long maturation process, however, bird dispersal
of the seeds is encouraged as cyanogenic glucosides are gradually
shifted from pulp to seed, pulp carbohydrate levels increase, and fruits
turn from green to bright red.  Subsequent seed predation is prevented
by the localization of cyanogenic glycosides in the seeds [11].

Compared with other chaparral shrubs, toyon apparently has moderate
water use requirements [53].  Maximum water stress generally declines
well before before the onset of fall rains, apparently in response to a
decrease in ambient air temperatures [50].

Related categories for Species: Heteromeles arbutifolia | Toyon