Fuel consumption varied with season, prescription, and site. Fuel reduction was generally least with early spring, moderate-consumption fires, although the late-fall, moderate-consumption fire reduced fuels least at Quincy. There were no significant differences between fire treatments in total amount of fuels consumed at the Quincy site. (See Table 2 for details.)

Among sites, open physiognomy promoted fuel drying, which increased fuel reduction during burning. The Quincy site was most open, so fuels were usually drier than on the other sites. In contrast, although the early spring fire on the Blodgett site was the last of the 3 early spring fires, fuel reduction was least on the Blodgett site. A dense canopy, level terrain, and high elevation all contributed to increased fuel moisture levels at Blodgett compared to other sites. Low percent duff moisture content was highly correlated (R²=5.1, P<0.001) with duff consumption. The authors credited duff moisture as the best predictor of fuel consumption [6].

Minimizing fireline intensity reduces risk of a crown fire. Fireline intensity was not correlated with either duff moisture content (R²=0) or duff consumption (R²=0.02). It was apparently related to weather variables (relative humidity and wind speed), flammability of vegetation, slope and aspect, fine fuel moisture, and burn pattern. The authors stated that "fireline intensity was related to the skill and expertise of the person doing the actual burning". Fireline intensity was highest in the late spring, high-consumption fires at all sites [6].

Shrubs― Prescribed fires resulted in significant increases in shrub mortality (including shrubby hardwoods) compared to unburned controls [3]. Shrub mortality on the unburned control was <2%, while mortality on burned sites ranged from 21% to 88% (see Table 2 and Table 5).

Species response― Among all shrub species studied, whitethorn ceanothus and giant chinquapin were most resistant to fire mortality, and manzanitas were most susceptible. Lignotubers and root crowns of whitethorn ceanothus and giant chinquapin, respectively, were more deeply buried compared to other shrubs, and Kauffman [7] attributed their higher survival to this protection. Some tanoaks had lignotubers located in the duff layer, and such tanoaks showed high mortality after high-consumption fires [7].

Fuels― Composition and biomass of fuel loads affected shrub mortality. Sites with highest fuel biomass and thickest duff layers (Challenge and Blodgett) had higher mortality than Quincy, the site with the lowest fuel biomass and thinnest duff layer (see Table 2). Additionally, greater amounts of fuels were consumed at Challenge and Blodgett [7]. As a result, shrub mortality was significantly greater (P<0.05) in postfire year 2 at Challenge and Blodgett compared to Quincy in all treatments except on the early spring, moderate-consumption burn. The authors suggested that high flame temperatures at the shrub root crowns caused high shrub mortality at Challenge and Blodgett [5,6].

Kauffman and Martin [3] suggest that differences in soil moisture, along with season of burning, may partially explain significant differences in mortality for California black oak shrubs in response to spring fires at Quincy. Although duff consumption was similar for early and late spring fires (77-79%), soil moisture content during the early spring fire (x=20.3%) was nearly twice soil moisture content during the late spring fire (x=11.0%). Soils with greater moisture content may have lower temperatures while burning, thereby lowering California black oak mortality [3].

Fire season― Season of burning probably modified the ability of shrubs to sprout after fire. Fires set before the growing season began (early spring, moderate-consumption burns) resulted in least shrub mortality across all study sites [7]. Early fall, high-consumption and late spring, high-consumption burns resulted in highest mortality for small California black oaks and tanoaks. Across sites, high-consumption fires caused greatest shrub mortality. At Quincy, the late spring, high-consumption fire, which corresponded with periods of rapid aboveground growth, caused significantly greater shrub mortality compared to early spring, moderate-consumption fire even though there were no significant differences in the percent and amount (t/ha) of duff consumed [6]. However, all fire treatments resulted in significantly (P<0.05) higher mortality than the control, with the smallest hardwood shrubs showing highest rates of mortality [5]. At Quincy, there were no significant differences in fuel reduction between early and late spring fires (77.3% and 77.4%, respectively); however, California black oak mortality was 24% greater in the late spring treatment (P<0.10) [3,7]. Shrub mortality was least after the early spring fires, which were conducted prior to initiation of spring growth [3].

Size classes― Hardwood survivorship tended to increase with increasing plant size. Survivorship was analyzed by size class for shrubby California black oaks and tanoaks. Size classes and size class survivorship by fire season are shown in Table 4. The trend of best survivorship for the largest shrubs was most evident in late fall and early spring, moderate-consumption fires. After late fall, moderate-consumption fire at Challenge, for example, 71% of tanoaks in the largest size class (>200 g dry weight biomass) survived, while only 11% in the smallest size class (<26 g dry weight biomass) survived [3]. Comparing survivorship of California black oak at Quincy, the population at Quincy showed greatest survivorship across fire treatments. Quincy had the greatest number of large California black oaks. Blodgett had the smallest California black oaks, and among study sites, California black oak showed least survivorship at Blodgett [7].

Prescribed burning altered size class distribution of California black oak and tanoak. For shrubby hardwoods in the smallest size class, survivorship was low regardless of burn treatment. At Blodgett, for example, heat flux of even the low-consumption fires was sufficient to kill the smallest California black oaks. The smallest size class was composed of germinants and seedlings with meristematic root crowns still in the organic soil horizon. Before prescribed burning, most hardwoods were in the 2 smallest size classes. Differential mortality in small size classes resulted in a more uniform distribution of individuals among size classes after the fire. For the largest size class (around 5 kg aboveground dry weight), described as "subarboreal", mortality increased as consumption of the organic horizon increased. At Blodgett, all California black oaks in the largest size class survived the early spring fire, while only 14% of the largest California black oaks survived the early fall fire. At Challenge, 83% of the largest tanoaks survived the early spring fire, while only 45% survived the early fall fire [3].

Individual hardwoods may take longer to resume growth after top-kill than smaller shrubs. On all sites, 14% of shrubs that failed to sprout in postfire year 1 sprouted in postfire year 2. The majority of shrubs that first sprouted in postfire year 2 were California black oaks [7].

Shrubs and shrubby hardwood survivorship after prescribed fires is shown in Tables 3 and 4 below [3]:

Hardwood trees― All tree-sized California black oaks and tanoaks survived fire, and many produced root crown sprouts even though they were not top-killed [3]. A few large California black oaks that survived the fires had toppled by postfire year 2 [7]. No further information was given for tree-sized hardwoods.

Conifers― Density of conifers <2 m in height decreased significantly after all fire treatments at all sites. Incense-cedar showed greatest mortality among conifers, with mortalities near 100% on some plots. Incense-cedar was "all but eliminated" from the understory by all fire treatments [7]. Ponderosa pine, Douglas-fir, and sugar pine saplings (3-8 cm DBH) showed low mortalities. Many burned sites had 1,200 or more conifer saplings/ha. No conifers >20 cm DBH were killed by any fire treatment [4]. Ponderosa pines on all 3 study sites experienced "many attacks" by red turpentine beetles after spring, high-consumption burns, but the attacks had not caused any ponderosa pine mortality as of postfire year 3 [7].

Density and frequency of shrubs, shrubby hardwoods, and conifers on fire treatments and the unburned control are shown in Tables 5 and 6 [4,7].

Table 5: Density.pdf

Table 6: Frequency.pdf

Sprouting response: In all treatments, >80% of shrubs were top-killed; in most treatments, >90% of shrubs were top-killed. Species sprouting from root crowns tended to support a larger number of sprouts/plant compared to species sprouting from lignotubers. Giant chinquapin root crowns, for example, often supported 100 to 300 sprouts/root crown in postfire year 2. Ceanothus species also supported many sprouts. At Blodgett, mean number of whitethorn ceanothus basal stems ranged from 5 to 8 stems/root crown before fire and from 22 to 37 stems/root crown in postfire year 2. Generally for all sprouting species, large plants produced more sprouts than small plants. Postfire growth rate was generally fastest after moderate-consumption fires; however, Kauffman [7] emphasized that it is difficult to predict the effects of fire season on postfire growth of sprouting species. Much depends upon individual species response and the size class of individual burned plants. Postfire growth rates are shown in Table 7.

Tanoak was the dominant shrub at Challenge before the fires. Prefire cover was estimated at 9% to 15%. During 3 years of postfire study, tanoak cover was significantly reduced (P≤0.05) to less than 2% in all fire treatments. Tanoak cover on unburned plots increased to 18.1% to 27.8% during that time. Tanoak, California black oak, and giant chinquapin showed increasing ability to sprout with increasing size. Exceptions occurred when lignotubers or root crowns of very large individuals grew in the organic soil layer: fire usually killed such trees [7].

Comparing plant response to fuel consumption at postfire year 1, all sprouting species had lower rates of sprout growth in high-consumption fires. Tanoak and California black oak had highest sprouting growth rates after early spring, moderate-consumption fires. Whitethorn ceanothus and giant chinquapin had highest rates of sprout growth after late fall, moderate-consumption fires. Sprout growth of tanoak, California black oak, and whitethorn ceanothus was lowest after late spring, high-consumption fires. The growing season was well underway by late spring, which may account for this slow growth rate [7].

Some California black oaks, tanoaks, and Pacific dogwoods produced epicormic sprouts in response to burning [7]. This response was not quantified.

Sierra mountain misery is a shrub of particular concern on burned timber sites because it sprouts from roots crowns and deeply buried roots, so fire seldom kills it. It often forms continuous mats that interfere greatly with growth of young conifers. The experimental fires significantly reduced Sierra mountain misery density for all treatments except the early spring, moderate-consumption fires. Late spring, high-consumption fires reduced Sierra mountain misery most effectively, with reductions of 89% and 64% on the Blodgett and Challenge sites, respectively. Sierra mountain misery was not present at Quincy [4]. Sierra mountain misery only established from sprouts after fire [7]. See Table 5 and Table 6 for further information.

Changes in sprouting shrub physiognomy: Prescribed burning resulted in significant decreases in mean shrub basal diameter, height, crown volume, cover, and aboveground biomass. There were significant increases in the number of stems/plant. Shrubby California black oak and tanoak generally had more sprouts/root crown after fire compared to their prefire sprout counts. The ceanothus species (deerbrush and whitethorn ceanothus) usually produced many more sprouts/root crown after fire compared to prefire counts. For all shrubs, number of sprouting stems was related to prefire shrub size, with large shrubs producing a greater number of sprouts, with larger biomasses, compared to small shrubs. Evergreen species such as tanoak partitioned more aboveground biomass in leaves (37-41% of total aboveground biomass) compared to deciduous species like California black oak (12-17% total aboveground biomass). Four shrubs were selected for intensive studies. Response of these sprouting shrubs to the experimental fires was as follows [3]:

Postfire shrub seedling establishment: Ceanothus and Manzanita spp. seedlings were most abundant after fire treatments compared to other shrub species. Greenleaf manzanita, whiteleaf manzanita, whitethorn ceanothus, and deerbrush have persistent seed banks with seeds that require fire or other heat scarification to germinate. Pale serviceberry, Pacific madrone, Sierra mountain misery, Sierra gooseberry, pine rose, and thimbleberry also have persistent seed banks, but their nonrefractory seeds do not require heat scarification to germinate. Whitethorn ceanothus and whiteleaf manzanita seedlings were most common on burn treatments at Blodgett; deerbrush and whiteleaf manzanita seedlings most common at Challenge; and deerbrush, greenleaf manzanita, and prostrate ceanothus most common at Quincy. Of the species with nonrefractory seeds, only Sierra gooseberry seedlings were common after fire treatments. Sierra gooseberry was not present on Challenge and Quincy study sites before the fires, but was abundant on all 3 study sites after burning treatments [7]. Most ceanothus and manzanita species require heat scarification followed by overwinter stratification to germinate, so spring fires did not promote their seedling establishment on any of the study sites in postfire year 1. However, ceanothus and manzanita seedling establishment commenced on spring-burned plots in postfire year 2. For fall fire treatments, most ceanothus and manzanita germinants arose from the duff-mineral soil interface or just below the mineral soil surface the following spring [4,7]. Few seedlings were counted on study plots before the fires. After the fires, there was a general trend of denser seedling establishment after fall fires than after spring fires [7]. Whitethorn ceanothus seedling density was greatest on the late fall, moderate-consumption Blodgett fires. At Quincy, whiteleaf manzanita seedling density was 15 times greater on fall burns compared to spring burns. Greenleaf manzanita mostly emerged from seed cached by animals before fire treatments. After fire treatments, rodents dug up many seed caches with greenleaf manzanita emergents and consumed the new plants. Some greenleaf manzanita seedlings established from undisturbed caches, but rodent browsing and rodent digging disturbance caused high mortality for greenleaf manzanita seedlings [7]. Densities for ceanothus and manzanita seedlings that were selected for intensive counts are shown below [4].