• 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:

Scouler willow increases dramatically following a variety of burn intensities, especially on relatively moist sites [195]. Basal area after 3 years may exceed that on unburned sites [253]. Dramatic increases in volume occur over the first 15 years postfire [239]. Resprout height growth may be dramatic, reaching up to 10 feet (3 m) after the first growing season [46,131,259]. Within 3 years after burning, plant crowns can average over 11 feet (3.4 m) in height [131]. Following a prescribed summer burn in Idaho, nearly 80% of height growth of Scouler willow over a 7-year period was attained within 2 growing seasons [140]. Following a summer wildfire in northern Idaho, Scouler willow reached peak cover values within 8 years [240]. 

Scouler willow plants that experience severe canopy mortality apparently concentrate their nutrients into vigorous new growth more than plants which experience only light canopy mortality. Analysis of aboveground plant part mortality classes from controlled burns in Idaho revealed that Scouler willow plants which experience top-kill exhibit the most vigorous regrowth. Twig growth (length and weight) of Scouler willow following fire was 3 to 4 times greater on plants with greater than 50% canopy mortality than on plants with less than 50% canopy mortality [183].

Seeding: Scouler willow also has the potential to regenerate from off-site seed sources [30,31,46,86,91,103,172,222,226,239,247,258], and can establish in moist mineral soil postfire [30,31,66,76,222,226]. Sowing Scouler willow seeds on different severity burns in upland black spruce sites in Alaska showed that germination occurred only on moderately (organic layers partially consumed) and severely (ash layer present, organic material in soil consumed or nearly so to mineral soil) burned seedbeds. Severely burned sites had the best germination percentages and represented the only burn severity class where Scouler willow seedlings survived past 3 years [267]. Scouler willow establishes quickly, but the rate of cover development or increase is slow [237,238,240].

Germinating seed originating from off-site plants often raises Scouler willow frequency far above what would be expected from on-site surviving plants [140,145,240]. Stickney [240] observed that after a stand-replacing wildfire in northern Idaho, Scouler willow seedlings made up the majority of the shrub component of the vegetation. The importance of seedlings in the postfire community was similarly observed by Lyon [140]. He recorded the postfire density of Scouler willow plants for 7 years, summarized below (density = # of plants >18 inches (46 cm) tall per 1,000 ft²):

DISCUSSION AND QUALIFICATION OF PLANT RESPONSE:

FIRE MANAGEMENT CONSIDERATIONS:

On sites in northern Idaho, Scouler willow had substantially higher cover on a 30-year-old burn than after any intensive silvicultural treatment (ranging from thinning to clearcut), with no presence in the control [104]. However, after 30 to 40 years of fire exclusion in ponderosa pine forests, Scouler willow presence increased [22]. Logging and fire suppression allowed vigorous development of Scouler willow in a Douglas-fir/ponderosa pine community [87]. 

Prescribed fire enhances vigorous regrowth and germination of Scouler willow, and it is effective in increasing biomass [24]. In the cedar-hemlock zone of Idaho, it generally produces the most cover of any shrub species on broadcast burned areas. Cover and frequency of Scouler willow is substantially higher on broadcast burns than on areas not broadcast burned, as are the mean height values [171]. Total shrub volume of Scouler willow in Douglas-fir stands increased from 15 to 80% 2 years postfire [139]. Mean canopy coverage of Scouler willow  increased significantly (p<0.01) following selective logging and low intensity broadcast burning (intensity ~ 127 kcal/m/s) [12]. In the 1st year following burning, Scouler willow may produce up to 28 times as many sprouts as the previous year [136,162]. Scouler willow may grow significantly wider and taller (p<0.05) after fall burning than after spring burning [136]. However, fall burning removes the following winter's food supply for animals, while spring burns have substantial regrowth by summer [130]. After stand mechanical treatment and understory burning, Scouler willow was reduced by 9% from mechanical damage and an additional 16% from fire. The surviving plants were substantially more vigorous post-treatment [15,16]. While modest Scouler willow mortality may result after overstory removal and prescribed fire, the percentage of high vigor plants increases; in one study the amount of vigorous plants increased from 15% at pretreatment to 70% post treatment [23]. In northern Idaho, burning at 5-year intervals did not  result in decreased vigor [135]. Scouler willow was not markedly affected by burning until it suffered deep charring of the root crown. The following table presents the change in Scouler willow population characteristics in response to different treatments (% change is relative to pretreatment conditions) [23]:

Shelterwood cuts combined with prescribed burning in a ponderosa pine resulted in modest Scouler willow mortality; plants remaining in the harvest only and burned treatments had higher vigor than those in the control [19,23].

A summary of Scouler willow's response to different types of disturbance is presented below [228]:

Related categories for SPECIES: Salix scouleriana | Scouler Willow