Research Project Summary: Prescribed fire effects on canyon live oak and invertebrates in a southern California forest



RESEARCH PROJECT SUMMARY CITATION:
Smith, Jane Kapler, compiler. 2008. Research Project Summary: Prescribed fire effects on canyon live oak and invertebrates in a southern California forest. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/ [].

Sources: Unless otherwise indicated, the information in this Research Project Summary comes from the following papers:

Narog, Marcia Gay. 1991. Invertebrate responses to the effects of thinning and understory burning in a canyon live oak (Quercus chrysolepis) forest in the San Bernardino mountains, California. San Bernardino, CA: California State University, San Bernardino. 50 p. Thesis. [5].

Narog, Maria G.; Paysen, Timothy E. 1994. Multiple-use management of canyon live oak forests using thinning and prescribed burning. Proceedings, 15th annual forest vegetation management conference; 1994 January 25-27; Redding, CA. Redding, CA: Forest Vegetation Management Conference: 154-160. [6].

Narog, Marcia G.; Wilson, Ruth C.; Paysen, Timothy E. 1993. Invertebrate responses to thinning and understory burning in a canyon live oak forest. In: ICFVM, Proceedings of the international conference on forest vegetation management. Auburn, AL: Auburn University School of Forestry Report No. 1: 209-213. [4].

Paysen, Timothy E.; Narog, Marcia G. 1990. Selective mortality with prescribed fire in canyon live oak. In: Krammes, J. S., technical coordinator. Effects of fire management of southwestern natural resources: Proceedings of the symposium; 1988 November 15-17; Tucson, AZ. Gen. Tech. Rep. RM-191. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station: 241-243. [7].

Paysen, Timothy E.; Narog, Marcia G. 1993. Tree mortality 6 years after burning a thinned Quercus chrysolepis stand. Canadian Journal of Forest Research. 23(10): 2236-2241. [8].

SPECIES INCLUDED IN THE SUMMARY:
Common names are used throughout this summary. For a complete list of the common and scientific names of species discussed in this summary and for links to FEIS species reviews, see the Appendix.

STUDY LOCATION:
The research was conducted on a north-facing slope on Skinner Ridge, 1,500 m in elevation, in the San Bernardino National Forest, southern California [5].

SITE DESCRIPTION:
Study sites are generally north facing, with slopes up to 35 degrees. Soils are in the Winthrop family (sandyskeletal, mixed mesic Entic Haploxerolls). Soil surface cover varies from organic matter 1 m deep to gravel. Some large rock outcroppings occur within the area [8].

The study was initiated at the beginning of a 7-year drought (1984-1990) [8].

PREFIRE PLANT COMMUNITY:
The study was conducted in a canyon live oak forest. Stand structure was closed, dominated by single- and multistemmed canyon live oak, with occasional conifers and some hardwoods. The authors estimated that canyon live oak established after fire approximately 100 years earlier. Before treatment, stand density was 3,100 trees/ha, overstory height averaged 8.2 m, tree DBH averaged 16.5 cm, and basal area was 54 m²/ha [8].

Based on the description provided in Narog [5], vegetation on the study site could be classified in the following plant community and probably historically experienced the fire regime described below:

Fire regime information on the vegetation community studied in this Research Project Summary. Fire regime characteristics are taken from the LANDFIRE Rapid Assessment Vegetation Model [3]. This vegetation model was developed by local experts using available literature as documented in the PDF file linked from the Potential Natural Vegetation Group listed below.
Vegetation Community (Potential Natural Vegetation Group) Fire severity* Fire regime characteristics
Percent of fires Mean interval (years)
Mixed evergreen-bigcone Douglas-fir (southern coastal) Replacement 29% 250
Mixed 71% 100
*Fire Severities:
Replacement=Any fire that causes greater than 75% top removal of a vegetation-fuel type, resulting in general replacement of existing vegetation; may or may not cause a lethal effect on the plants.
Mixed=Any fire burning more than 5% of an area that does not qualify as a replacement, surface, or low-severity fire; includes mosaic and other fires that are intermediate in effects [1,2].

PLANT PHENOLOGY:
Burning occurred in November, while most plants were probably dormant [5].

FIRE SEASON/SEVERITY CLASSIFICATION:
Fall/Low to moderate severity

FIRE DESCRIPTION:
Treatments consisted of control, thin-only (to approximately 50% of pretreatment basal area), and thin-plus-burn [7]. Thinning began in 1984 and was completed in spring 1985. Prescribed burning was conducted on 5 and 7 November 1985 [8].

Abundance of ground-level invertebrates was measured for 30-day periods in winter (November/December) from 1983 through 1986. These measurements covered 2 prefire years (1983 and 1984), conditions in the first month after prescribed burns (1985), and conditions 1 year after prescribed burning (1986) [4]. Many ground-level invertebrate species in canyon live oak forests are inactive during winter, but the species collected were considered representative of the native invertebrate community [5].

Fire management objectives:

Fire prescription and behavior: Slash greater than 5 cm in diameter was removed before burning. Fuels consisted of "light slash" and oak leaf litter [8], which was "generally heavy" [4]. Fine fuel moistures averaged around 10%; duff moisture was slightly greater [8]:

Fuel moistures at time of burning [8]

Fuel Layer Mean % Moisture (SD)
Twigs 9.3 (1.0)
Leaves on ground 7.9 (1.4)
Top litter 9.3 (0.9)
Middle litter 16.4 (13.8)
Lower litter 14.1 (13.5)

Prescribed burning was conducted when wind speed averaged less than 10 miles/hour. Due to danger of fire spread from Santa Ana winds, burned areas were saturated with water immediately after burning [8].

Weather conditions at time of burns and fire behavior [8]

Relative humidity 26-35%
Wind speed 8-16 km/hr
Flame height <1.5 m
Flame length 10 cm to 2 m

Firing proceeded from top to bottom of plots in an "inverse chevron" formation, which concentrated heat near the center of plots [8]. Flames did not reach the canopy, so no crowning occurred [7]. Because of fuel discontinuity, fire carried poorly on portions of some plots [8].

FIRE EFFECTS ON BIOTIC COMMUNITY:
Canyon live oak: No mortality of canyon live oak was observed in untreated plots, and only one tree died in thin-only plots. In thin-burn plots, the firing technique drew heat toward the center, where most canopy foliage was killed [8]. In the first postfire year, mean live canopy cover in thin-burn plots was 24%; by postfire year 3, it had recovered to 47% [7]. Bark damage from the fires was "generally light", although some trees had charred bark all the way around the bole. Most large trees survived burning [8], but several died on the plot with the steepest slope and deepest fuels, probably due to long fire residence time around the bases of the trees [7].

Canyon live oak mortality in thin-burn treatments was measured 2 and 6 years after burning. Nearly half of small trees died in the first 2 postfire years, and a much smaller proportion (6%) of larger trees died; mortality in both size classes had increased 4% to 5% by postfire year 6 [8]:

Proportion of dead trees in two diameter (DBH) classes 2 and 6 years after thinning and burning [8]

DBH class

% dead after 2 years

% dead after 6 years

<15 cm 41.3 46.5
≥15 cm 6.0 10.1
Total 22.8 25.5

The following descriptors were useful for discriminating live from dead trees in postfire year 6 [8]:

Parameters distinguishing live from dead canyon live oak 6 years after thinning and burning [8]

Parameter

Mean live (SD) Mean dead (SD)
Tree height (m) 10.3 (3.6) 7.6 (2.8)
Bark area charred below maximum scorch height (%) 26.0 (20.9) 54.6 (20.5)
Maximum proportion of bole circumference scorched (%) 51.5 (40.5) 86.9 (29.3)
Estimated proportion of scorched bole with cambial death* (%) 3.7 (12.3) 28.1 (29.3)
*Measured by cambial separation, indicated by hollow sound when tree bark is tapped.

In the first 6 postfire years, trees in control plots increased in diameter at about half the rate of trees in treated plots. Average diameter increase on control plots after 6 years was 0.44 cm. Diameter increase on thin-only plots averaged 0.82 cm; on thin-burn plots, diameter increase in surviving trees averaged 0.98 cm [6].

Ground-level invertebrates: Invertebrate abundance fluctuated substantially from year to year. Populations of most orders declined from 1983 to 1984 and were lowest in 1985, regardless of treatment. Narog [5] attribute these population declines to effects of cold temperatures and drought.

Abundance* of ground-level invertebrates collected in 4 winters in a canyon live oak forest. Data from control and treatments are combined [4].
  Invertebrate order
Sample time Year Noninsect** Beetles (Coleoptera) Grasshoppers, crickets (Orthoptera) Bees, wasps (Hymenoptera) Flies (Diptera) Springtails (Collembola)
pretreatment 1 1983 1,439 3,323 137 57 360 12,009
Pretreatment 2 1984 814 1,166 45 37 887 9,763
1 month after fire 1985 487 399 129 335 144 1,074
1 year after fire 1986 773 604 89 126 141 8,044
*Number collected in 15 pitfall traps within each of 9 plots, trapped for 30 days in November and/or December of each year.
**Noninsects included Arachnida, Chilopoda, Isopoda, and Annelida.

Invertebrate populations showed little sensitivity to treatments, including prescribed fire (see figures below). Abundance was lowest one month after the prescribed burns, regardless of treatment. A year later, abundance had increased for all treatments, although recovery in thin-burn areas was less than that in control and thinned areas. Treatments apparently did not affect species richness [5].

Invertebrate abundance (A) and species richness (B) on pitfall trap sites (adapted from Table 10 in [5])

Species in 3 insect families were selected for in-depth analysis of population trends:

FIRE MANAGEMENT IMPLICATIONS:
Fire management objectives: During the 6 years following treatments, canyon live oak in both thin-only and thin-burn treatments showed increased diameter growth, indicating stable or increased productivity relative to controls [6].

Thinning and fall prescribed burning produced a shaded fuel break, with high mortality in small trees and minimal mortality of canyon live oak >15 cm DBH. Approximately 95% of surface fuels were consumed by burning, so the thin-burn treatment reduced fire hazard [8].

Other fire management information: The authors comment that fire-caused mortality of canyon live oak in this study was "minimal" compared to mortality usually caused by wildfires. Logging slash may enhance potential heat release over that in unlogged stands, but thinning may also reduce the heat convection around tree boles that is likely to damage large trees in unthinned stands [8].

In southern California, canyon live oak forests are common between chaparral and higher-elevation forests, so they are often focal points in fire management programs, forming the "defining line" between urban areas and wildlands [6]. Results of this study suggest that thinning and burning canyon live oak stands can increase growth [6] and reduce fire hazard [6,8].

In this study, ground-level invertebrate populations appeared little affected by low- to moderate-severity prescribed fire. The relatively small plots (30 × 40 m) and patchy quality of burns may have improved invertebrate population resilience because of reservoir populations within burns and short migration distances from adjacent areas. The authors recommend further research to investigate sensitivity of ground-level invertebrates to fire [4].

Because the study occurred during a 7-year drought [8], results may not reflect potential treatment effects under more mesic climatic conditions.
SPECIES INCLUDED IN THE SUMMARY:
This Research Project Summary contains fire effects and/or fire response information on the following species. For further information, follow the highlighted links to the FEIS review of canyon live oak.

Appendix

Common name (if given) Scientific name

Plant Species

canyon live oak Quercus chrysolepis

Invertebrate Orders, Families, and Species

beetles Coleoptera
     ground beetles/tiger beetles      Carabidae
            Pterostichus spp.
springtails Collembola
       Entomobryidae
            Tomerus flavescens
flies Diptera
bees, wasps Hymenoptera
grasshoppers, crickets Orthoptera
     leaf-rolling grasshoppers      Gryllacrididae
            Ceutophilus spp.
            Gammarotetix spp.
            Pristoceutophilus pacificus

REFERENCES:


1. Hann, Wendel; Havlina, Doug; Shlisky, Ayn; [and others]. 2005. Interagency fire regime condition class guidebook. Version 1.2, [Online]. In: Interagency fire regime condition class website. U.S. Department of Agriculture, Forest Service; U.S. Department of the Interior; The Nature Conservancy; Systems for Environmental Management (Producer). Variously paginated [+ appendices]. Available: http://www.frcc.gov/docs/1.2.2.2/Complete_Guidebook_V1.2.pdf [2007, May 23]. [66734]
2. LANDFIRE Rapid Assessment. 2005. Reference condition modeling manual (Version 2.1), [Online]. In: LANDFIRE. Cooperative Agreement 04-CA-11132543-189. Boulder, CO: The Nature Conservancy; U.S. Department of Agriculture, Forest Service; U.S. Department of the Interior (Producers). 72 p. Available: http://www.landfire.gov/downloadfile.php?file=RA_Modeling_Manual_v2_1.pdf [2007, May 24]. [66741]
3. LANDFIRE Rapid Assessment. 2007. Rapid assessment reference condition models, [Online]. In: LANDFIRE. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Lab; U.S. Geological Survey; The Nature Conservancy (Producers). Available: http://www.landfire.gov/models_EW.php [2008, April 18] [66533]
4. Narog, Marcia G.; Wilson, Ruth C.; Paysen, Timothy E. 1993. Invertebrate responses to thinning and understory burning in a canyon live oak forest. In: ICFVM, Proceedings of the international conference on forest vegetation management. Auburn, AL: Auburn University School of Forestry Report No. 1: 209-213. [68690]
5. Narog, Marcia Gay. 1991. Invertebrate responses to the effects of thinning and understory burning in a canyon live oak (Quercus chrysolepis) forest in the San Bernardino mountains, California. San Bernardino, CA: California State University, San Bernardino. 50 p. Thesis. [69718]
6. Narog, Maria G.; Paysen, Timothy E. 1994. Multiple-use management of canyon live oak forests using thinning and prescribed burning. Proceedings, 15th annual forest vegetation management conference; 1994 January 25-27; Redding, CA. Redding, CA: Forest Vegetation Management Conference: 154-160. [68696]
7. Paysen, Timothy E.; Narog, Marcia G. 1990. Selective mortality with prescribed fire in canyon live oak. In: Krammes, J. S., technical coordinator. Effects of fire management of southwestern natural resources: Proceedings of the symposium; 1988 November 15-17; Tucson, AZ. Gen. Tech. Rep. RM-191. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Forest and Range Experiment Station: 241-243. [11297]
8. Paysen, Timothy E.; Narog, Marcia G. 1993. Tree mortality 6 years after burning a thinned Quercus chrysolepis stand. Canadian Journal of Forest Research. 23(10): 2236-2241. [22734]

FEIS Home Page