• GENERAL BOTANICAL CHARACTERISTICS
• RAUNKIAER LIFE FORM
• REGENERATION PROCESSES
• SITE CHARACTERISTICS
• SUCCESSIONAL STATUS
• SEASONAL DEVELOPMENT

GENERAL BOTANICAL CHARACTERISTICS:

The leaves are alternate [70,285], 1 to 3 inches long [37,70,127,129,197,284,285], and 0.5 to 2 inches (1.5-5 cm) wide [70,82]. The inflorescence of snowbrush ceanothus is less than 5 inches (12 cm) long [70,127], and branched with many flowers [70,154,197]. The inflorescence is borne on axillary and terminal peduncles [70]. Fruit is shallowly 3-lobed [37,70,109,127,197,285], 0.12 to 0.16 inch (3-4 mm) thick [70,127,285], 0.27 inch (6 mm) across [197], and sticky [70,127]. Each lobe contains a single seed [197]. Seeds are about 0.1 inch (2.8 mm) long, 0.1 inch (2.3 mm) wide, and 0.08 inch (2.0 mm) thick [109].

Snowbrush ceanothus forms large, dense colonies [70,121,240]. Thickets may be up to 33 feet (10 m) wide and are often dense and impenetrable [121,261]. In general, the number of snowbrush ceanothus plants in an area decreases with age [303]. Though stands of snowbrush ceanothus may begin to deteriorate after 15 years [175,303], the natural life span of snowbrush ceanothus is greater than 25 years [94,175], and 50-year-old plants have been observed [59,63].

RAUNKIAER [220] LIFE FORM:

REGENERATION PROCESSES:

Breeding system: No information

Pollination: | Snowbrush Ceanothus No information

Seed production: | Snowbrush Ceanothus Snowbrush ceanothus produces abundant seed crops [240]. It 1st produces seed at about 3 to 6 years of age [63,263], and continues producing until past age 20 [263]. Sprouts can produce prolific seed crops 8 years after top-kill [63]. Snowbrush ceanothus in Oregon produced up to 100,000 seeds per acre (250,000 seeds/hectare) [109].

Seed dispersal: When Ceanothus seeds ripen, they are forcibly ejected from the pods [63,144]. The heavy snowbrush ceanothus seeds generally stay where they fall, gradually filtering into the duff and soil unless they are carried off by small animals [63,75,144,149,243,271,295]. 

Seed banking: Snowbrush ceanothus seed is stored in the soil [40,148,154] for up to 200 years [154], and can regenerate from seed stored in the soil for up to "several centuries" [21,63,91,109,143]. In British Columbia, germination of soil-stored seed occurred following fire on sites where snowbrush ceanothus had been excluded at least 200 years [293]. Counts made on tree stumps indicated that the intermission between 2 generations of snowbrush ceanothus might be as long as 575 years [301,303]. Snowbrush ceanothus contributed 25% of the seeds found in soil samples taken from central Idaho Douglas-fir and grand fir habitat types [149]. Snowbrush ceanothus seeds are less successfully stored in wet soils [245].

Germination: Snowbrush ceanothus has a very hard, impermeable seedcoat that must be cracked, abraded, or exposed to heat in order for germination to occur [79,109,123,144,148,163,197,293,303]. Though exposure to heat is most effective in promoting germination, other disturbance (e.g. timber harvest) may stimulate snowbrush ceanothus germination by abrading the seedcoat [303]. Germination is improved by stratification [109,197]. Heating or breaking the seed coat allows the seeds to imbibe water and swell, but germination is unlikely if seeds are not exposed to cold stratification [109,123,144,197,218,219]. The mechanism for fire-induced germination in snowbrush ceanothus is a heat-induced, irreversible cracking of the hylar fissure in the seedcoat, which allows water to enter the seed and physiological processes to begin [22,109]. Temperatures of 176 to 203 degrees Fahrenheit (80-95 ^oC) are optimal to break the seedcoat [109,163]. Snowbrush ceanothus seeds may also germinate without high temperatures (e.g. on unburned sites), but snowbrush ceanothus stands develop more rapidly and more completely following heat exposure (burned sites) [63,109,288]. In a study conducted in Douglas-fir and grand fir habitat types, snowbrush ceanothus seeds found in the soil were 91% viable [148].

Seedling establishment/growth: Although large numbers of seeds typically germinate after fire, snowbrush ceanothus may experience high early mortality [63]. In general, snowbrush ceanothus is a slow-growing species [301,303]. Height growth of seedlings is slow for 3-5 years and then is rapid until about 10 years when it begins to level off [63,189]. Zavitovski [303] found that after 5 years, snowbrush ceanothus may be less than 3 feet (1 m) tall, but doubles its height in the next 5 years. Then height growth slows, gaining only 1.5 feet (0.5 m) in the following 5 years [303]. A typical snowbrush ceanothus stand in Oregon or California reaches 2 to 8 feet after 10 years; stand height may sometimes decrease between age 15 and 50 as older stems die back [63].

Asexual regeneration: Snowbrush ceanothus sprouts from the root crown [138,139] following damage to stems and/or top removal [30,31,63,121,162,178,238]. Sprout growth of 20 to 25 inches (51-65 cm) after 1 year, and growth of 3 to 7 feet (1.0-2.1 m) after 5 years has been observed. The ability to sprout may be a function of age and vigor of the plant when it is damaged. In 1 Cascade Range study, the percentage of sprouting plants decreased from 100% for 5-year-old plants to 50% for 11-year-old plants [63]. However, vigorous sprouting followed the cutting of 35- to 50-year-old snowbrush ceanothus in the Sierra Nevada [59,63]. Snowbrush ceanothus may increase in density by layering. Layering results when stems are forced close to the ground, bringing them in contact with the soil and allowing the branches to root [31].

SITE CHARACTERISTICS:

Elevation: | Snowbrush Ceanothus Snowbrush ceanothus has a wide elevational distribution [240], extending from near sea level to high mountains [271]. It generally occurs at higher elevations on south-facing slopes than on north-facing slopes [5,14]. Elevation ranges for different areas of snowbrush ceanothus distribution are as follows:

Climate: | Snowbrush Ceanothus In the Pacific Northwest, winters are moderately cold and relatively wet, with precipitation generally occurring from November to May. Annual precipitation at sites with snowbrush ceanothus in this region has been reported at 18 to 23 inches (460-580 mm) [26,124]. Summers are warm and dry [26]. In California, annual precipitation may range from 40 to 60 inches (1020-1520 mm) [104,176]. In Montana and Idaho, annual precipitation ranges from 27 to 45 inches (690-1140 mm) [51,158]. In Utah, the moisture requirement of snowbrush ceanothus is 16 to 20 inches (410-510 mm) [209].

In Idaho, the growing season lasts from 70 to 90 days [51].  Snowbrush ceanothus has good winter hardiness, though it may be subject to winter dieback on exposed sites [121]. It is damaged by low temperatures if not protected by snow cover [162,252,261]. Conversely, if snowbrush ceanothus crowns are not covered by snow, they are susceptible to winterkill if a relatively warm period (reducing winter hardiness) is followed by a sudden severe drop in temperature [252]. 

Soils: | Snowbrush Ceanothus Growth of snowbrush ceanothus is fair on gravelly, sandy, and clay loam soils and poor on dense clays [80]. It grows well on sandy loams, loams, and clay loams [80,130,176,208] and on poorly developed, loose or unstable soils [14,26]. Soil depths range from shallow soils with numerous rock outcrops to deposits of unconsolidated material many feet deep [26]. Although snowbrush ceanothus grows in almost any soil, it grows best in medium- to coarse-textured, well-drained soils 20 to 60+ inches (51-152+ cm) deep [37,130,198,208,240,261]. Soil nutrient content is generally low [121,162]. A soil pH of 5.5 to 7.0 is often found on snowbrush ceanothus sites [37,261]. Snowbrush ceanothus has medium tolerance for acid soils [121,271], and neutral to moderately alkaline soils can also produce good growth [37]. Snowbrush ceanothus is moderately drought tolerant [121,261].

SUCCESSIONAL STATUS:

Snowbrush ceanothus is an early to mid-seral species [7,60,63,75,85,116,150,242,244,245,249,255,288]. It invades recently disturbed sites [1,58,63,68,74,99,118,121,292], particularly burned sites [52,75,85,116,140,240]. Snowbrush ceanothus is essentially absent in mature seral and old-growth stages, often becoming a stand component after fire [11,223,288]. In several Douglas-fir habitat types [11,91,102,256,304] and in ponderosa pine habitat types [6,272], snowbrush ceanothus is common in early seral stages (within 1-7 years) following disturbance. The Douglas-fir-snowbrush ceanothus community type is characteristic of habitats that have been recently (within the last 100 years) and repeatedly burned [93]. Snowbrush ceanothus also occurs in dense stands of montane chaparral following major disturbance [14], though it may be eliminated from the chaparral after 40 years [301]. For further information on postfire succession of snowbrush ceanothus, see "Plant Response to Fire" in the "Fire Effects" section of this summary.

Snowbrush ceanothus can be described as a seral dominant, becoming common after major disturbances, especially fire [12,18,148,162,163,194,229]. Seral shrubfields, of which snowbrush ceanothus is a major component, result from repeated disturbance [21,57,71,71,103,137,170,172,208]. Snowbrush ceanothus may dominate this seral vegetation [57,63,68,104,120,125,168,172,182,237,299,304] and retard succession [63,104].

Douglas-fir: Snowbrush ceanothus is generally considered an important early to mid-seral species in most Douglas-fir forests of the northern Rockies and Pacific Northwest. However, in some locations Douglas-fir forests are sufficiently open to allow snowbrush ceanothus to become a persistent, if not permanent, member of the community. It occurs as a climax dominant in some open Douglas-fir forests of southwestern Oregon and in eastern Montana habitat types on decomposed granitic substrates [63]. In Douglas-fir forests of the western Cascades, snowbrush ceanothus generally dominates the middle or tall shrub phase of succession from years 5 through 10 [115]. Here it replaces initial weedy annual, biennial, and short-statured perennial invaders [116]. Snowbrush ceanothus typically competes effectively with fireweed (Epilobium angustifolium) by postfire year 6 and can become dominant by year 9 [94]. Earlier increases in snowbrush ceanothus have also been noted, with this shrub dominating some shrubfields as soon as 4 or 5 growing seasons after fire [83]. Snowbrush ceanothus generally persists for 20 to 40 years in the Cascades [63], although some stands may become decadent 10 to 15 years after disturbance [63,301]. Stands 40 or more years of age generally have only scattered dead shrubs [301]. South slopes offer the greatest potential for development of snowbrush ceanothus-dominated brushfields in these Douglas-fir types [206]. Shrubs decline rapidly as shade levels increase, and in parts of the northern Rockies, shrubs may become senescent by year 10 [301].

Western hemlock-western redcedar: Snowbrush ceanothus can dominate western hemlock-western redcedar-grand fir forests of the northern Rockies within 2 or 3 years after fire [157].  Snowbrush ceanothus cover typically declines rapidly in western hemlock-western redcedar forests of northern Idaho [159,199].

Grand fir: Snowbrush ceanothus is an important component of the initial shrub sere that following disturbance in grand fir habitat types and can become established by the 1st year after disturbance [300]. In north-central Idaho, it is particularly abundant on north slopes at higher elevations and can become a dominant shrubfield species by year 12 [299]. These shrubfields decline rapidly as shade increases. However, long-lived snowbrush ceanothus communities are prevalent on rocky outcrops in grand fir forests of Oregon and Washington [92].

Ponderosa pine: Snowbrush ceanothus assumes a dual successional role in ponderosa pine and mixed-conifer forests of the Northwest. Where forests are relatively open, it can grow as a long-lived seral shrub or climax dominant, but where densely forested stands develop, snowbrush ceanothus declines rapidly as it is overtopped. Snowbrush ceanothus and bitterbrush occur as understory dominants in open ponderosa pine forests of south-central Oregon [92]. In an Oregon ponderosa pine-white fir forest, snowbrush ceanothus was only dominant on sites where the mean fire interval was 15 years or less over the past 250 years, and it was almost absent where the interval was greater than 20 years [181,182]. Snowbrush ceanothus also grows as a climax species in some open ponderosa pine woodlands on the east side of the Cascades [63].

In mixed-conifer forests of Oregon, snowbrush ceanothus and other tall shrubs become dominant within 14 years after timber harvest but begin to decline within 20 years [150].

SEASONAL DEVELOPMENT:

Related categories for SPECIES: Ceanothus velutinus | Snowbrush Ceanothus