• IMMEDIATE FIRE EFFECT ON PLANT
• DISCUSSION AND QUALIFICATION OF FIRE EFFECT
• PLANT RESPONSE TO FIRE
• DISCUSSION AND QUALIFICATION OF PLANT RESPONSE
• FIRE MANAGEMENT CONSIDERATIONS

IMMEDIATE FIRE EFFECT ON PLANT:

DISCUSSION AND QUALIFICATION OF FIRE EFFECT:

PLANT RESPONSE TO FIRE:

Seedling Density: A flush of snowbrush ceanothus seedlings appeared in quaking aspen and quaking aspen/mixed conifer stands the 1st year after the Idaho prescribed fire. The seedling density decreased substantially by the 2nd postfire year; a much smaller decrease occurred in subsequent years. The average number of snowbrush ceanothus seedlings/ha in 3 different stands over 4 postfire years is presented below [43]:

In Idaho, Lyon [165] found 4,000 snowbrush ceanothus seedlings/1,000 ft² 1 year after an August prescribed fire. By the 2nd postfire year, over 40% of the seedlings had died, and by the 7th postfire year, only 20% of the original seedlings were still alive [165]. Seedling densities following fire are not uniform, and a study in a Douglas-fir stand in Oregon found snowbrush ceanothus densities ranging from 200 seedlings/ha to 30,000 seedlings/ha [190]. Weatherspoon [282] reported up to 410,000 snowbrush ceanothus seedlings/hectare following a moderate-consumption prescribed fire in a white fir forest in California. In an Oregon Douglas-fir forest, Gratkowski [109] found that although snowbrush ceanothus seedlings emerged on both logged/unburned and logged/burned sites, seedlings were far more numerous on burned sites.

Fire Severity: Higher densities of snowbrush ceanothus may be related to increased fire severity [115,140,239,243]. Dense stands of snowbrush ceanothus often develop following a severe burn, as seeds stored in the soil are stimulated to germinate [40,41,116,154,163,217,234,240,250]. In northeastern Oregon, snowbrush ceanothus cover increased from 3% to as much as 32% 5 years following a severe burn [140]. Snowbrush ceanothus may dominate a site within 2 to 11 years [41,43,75,239,253,254]. Following a severe fire in a western larch-Douglas-fir forest in western Montana, snowbrush ceanothus formed a nearly closed shrub layer with 94% cover by the 13th postfire year [254,257]. Another severe fire in a Douglas-fir forest in Washington resulted in 10% snowbrush ceanothus cover by the 4th postfire year, increasing from 1% prior to the fire [266].

Height Growth: Snowbrush ceanothus height growth after fire is variable and may increase with the severity of the burn [101]. Snowbrush ceanothus seedlings can be expected to grow 3 to 5 feet tall within 3 postfire years in the Payette National Forest, Idaho [81]. Following a prescribed burn in Idaho, snowbrush ceanothus plants reached 2.4 feet tall by 7 postfire years [165]. However, on another site in Idaho, snowbrush ceanothus plants were only 2.8 inches (7 cm) tall after 1 year and only 2.6 feet (0.8 m) 12 years following broadcast burning [300].

DISCUSSION AND QUALIFICATION OF PLANT RESPONSE:

Fire severity: Though some authors report that snowbrush ceanothus establishment from seed is greatest following severe burns and lowest following low-severity burns [81,101], Gratkowksi [109] found that snowbrush ceanothus seedlings were far more abundant on "lightly" burned sites than on "severely" burned sites. Weatherspoon [281] found that greater snowbrush ceanothus seedling development occurred in areas of moderate burn depth or severity than in either unburned areas or areas of high burn depth. Moderate-severity fire removes the litter layer, sufficiently scarifying and leaving most snowbrush ceanothus seeds close enough to the postfire surface to permit emergence. Severe fire, on the other hand, results in lethal temperatures at a soil depth where most of the seed bank is located. Though creating a zone of scarification below that depth, much of the snowbrush ceanothus seed bank is consumed by the fire, leaving fewer seeds to germinate [281]. Following a prescribed fire in a white fir forest in California that burned to a depth of 4 inches (10 cm) in the soil, 94% of snowbrush ceanothus seeds were killed, with no viable seeds remaining above the 1.5-inch (4-cm) depth [282].

FIRE MANAGEMENT CONSIDERATIONS:

Slash Disposal: Snowbrush ceanothus commonly establishes on sites that have been broadcast burned following harvesting activities, and can establish by the 1st year after disturbance [54,109,223,300]. Burned sites are more likely to have substantial snowbrush ceanothus in the successional community than unburned sites [199]. In the western redcedar-western hemlock zone of northern Idaho, the frequency, crown cover, and relative importance of snowbrush ceanothus were much greater in broadcast burned areas than in either undisturbed or logged, unburned areas [198]. Maximum cover was attained 3 to 5 years after timber harvest associated with subsequent slash burns in western hemlock forests of north-central Idaho. Where timber harvest was not followed by postharvest burns, cover increased much more slowly, and maximum values were not reached until 15 to 25 years after disturbance [159]. Snowbrush ceanothus also responded to broadcast burning following harvest in ponderosa pine stands in Mt. Hood National Forest, Oregon [228]. Broadcast burning results in a greater number of snowbrush ceanothus seedlings than piling and burning slash [109], though the occurrence of snowbrush ceanothus also increases on sites that have been slash-burned rather than not burned [251].

Snowbrush ceanothus may dominate early seral stages following clearcut and severe broadcast burning activities in grand fir and Douglas-fir habitat types [101,110,250,300], as well as sites in the western hemlock zone that have been logged and lightly or heavily burned [117]. Seven years following a prescribed fire in a Douglas-fir forest in Idaho, snowbrush ceanothus density increased from 0.1 to 56.4 per 1,000 square feet, and percent canopy cover increased from 0.02 to 10% [165]. In another study, however, snowbrush ceanothus cover on clearcut, broadcast burned Douglas-fir sites in Oregon did not increase substantially until 15 years after treatment, with cover values dropping again by postfire year 20 [232].

Fire Severity: The duration and magnitude of snowbrush ceanothus dominance generally increase with the severity of disturbance [117,155]. Following the Waterfalls Canyon Fire, a severe burn in Wyoming, snowbrush ceanothus remained abundant for more than 40 postfire years [18]. Fourteen to 23 years following a clearcut and "hot" broadcast burn treatment in a Douglas-fir forest, percent cover of snowbrush ceanothus ranged from 4 to 85%, increasing from the original 0% [12]. In a study of clearcut and broadcast burned grand fir sites, snowbrush ceanothus disappeared by 23 years after treatment [300]. Lafferty [155] found that the highest canopy cover increase of snowbrush ceanothus on sites in western Montana occurred on severely burned (vs. lightly burned), south-facing sites. In the western redcedar-western hemlock zone of northern Idaho, snowbrush ceanothus occurred more frequently and with greater percent cover on sites that had been burned than on sites that were either undisturbed or logged and not burned. Sites that were broadcast burned had more snowbrush ceanothus than sites that were slash-piled and burned, and multiple broadcast burns resulted in the highest snowbrush ceanothus values [199]. In a Douglas-fir forest on the H. J. Andrews Experimental Forest, percent cover of snowbrush ceanothus increased 2 years after clearcutting with no burning, clearcutting with light burning, and clearcutting with severe burning. The greatest increase in percent cover followed the light burn treatment [83]. On another Douglas-fir site in Oregon, snowbrush ceanothus percent cover steadily increased for 5 years following slash burning in clearcuts, from 0.3% to 7.5%. After logging but prior to burning, no increase of snowbrush ceanothus percent cover was observed [84]. Morris [194,195] found that snowbrush ceanothus grew on harvested sites following slash burning, but was much more scarce on unburned sites in Douglas-fir communities of Oregon.

Wildlife Implications: Dense canopies of snowbrush ceanothus generally result from severe burns, and will deter both livestock and erosion; light canopies generated by a low-severity burn can provide shelter for Douglas-fir seedlings [242,244,246,247,248]. In western Montana, long-term propagation of snowbrush ceanothus for elk winter range may be best accomplished through fall burning, both to stimulate seed germination and reduce impacts of concentrated browsing [169]. However, Noste [205] found that survival of snowbrush ceanothus was higher on spring-burned that on fall-burned sites (100% survival versus 40%).

Nutrient Content: During the 1st growing season following prescribed burning of seral shrubfields (Douglas-fir climax) in British Columbia, nitrogen concentration and phosphorus concentration of snowbrush ceanothus leaves increased, though the levels returned to preburn concentrations by the 2nd growing season. Copper concentrations in snowbrush ceanothus leaves and stems decreased following burning [78]. The following table summarizes snowbrush ceanothus plant information and nitrogen accretion of a snowbrush ceanothus stand developing on a Douglas-fir clearcut and slash-burn site in Oregon [298]:

As snowbrush ceanothus biomass increased with age, nitrogen concentration decreased due to the higher proportion of woody material relative to leaf tissue. Net accretion of nitrogen by snowbrush ceanothus fixation was 1,110 pounds per acre (1,261 kg/ha) over the 15 years of the study [298].

Related categories for SPECIES: Ceanothus velutinus | Snowbrush Ceanothus