Effects of understory fire on cavity-nesting birds in Arizona pine forests
Smith, Jane Kapler, comp. 2008. Research Project Summary: Effects of understory fire on cavity-nesting birds in Arizona pine forests. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: https://research.fs.usda.gov/feis/fire-studies/horton-and-mannan-2008
Source
Unless otherwise indicated, the information in this Research Project Summary comes from the following paper:
- Horton, Scott P.; Mannan, R. William. 1988. Effects of prescribed fire on snags and cavity-nesting birds in southeastern Arizona pine forests. Wildlife Society Bulletin. 16: 37-44 [2].
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.
The study was conducted in the Santa Catalina Mountains on the Coronado National Forest, southeastern Arizona.
Site Description
Elevation at the 3 study sites ranged from 2,075 to 2,410 m. Two sites were in southwest-draining canyons, and the third was on a west-facing mountainside. Area of the study sites ranged from 22 to 45 ha.
Before treatment, Arizona pine snags constituted 62% of snags and showed more evidence of use by cavity-nesting birds than snags of other species; Arizona pine snags contained 94% of cavities and 82% of active nests. Arizona pine snags >15 cm DBH are referred to in this Summary as "large snags", and those <15 cm DBH are referred to as "small snags".
Small snags in unburned stands showed little evidence of decay and contained no cavities. Most large snags in unburned stands showed some evidence of decay:
| Decay class | Number of snags/ha* | Description of decay class | ||
|---|---|---|---|---|
| Limbs | Sapwood | Bark cover (%) | ||
| I | <0.1 | Foliage still on twigs | Sound | 100 |
| II | 4.0 | Fine twigs remaining | Sound to rotting | 75-100 |
| III | 1.9 | Secondary branches remaining | Intact to rotting | 25-85 |
| IV | 3.0 | Branch stubs remaining | Some sloughed | 10-50 |
| V | 2.5 | None | Much sloughed | 0-50 |
| VI | 0.5 | Secondary branches remaining | Sound to rotting | <10 |
| *Average of density in control stands and prefire treatment stands | ||||
Densities of cavity-nesting birds before treatment are shown below with posttreatment data (see Fire Effects on Cavity-nesting Birds). In unburned stands, cavity nesters generally preferred snags >50 cm DBH in decay classes II or III, although nest-tree preferences varied for the 8 most common species:
| Bird species | Preferred size of large snag (cm DBH) | Preferred decay class |
|---|---|---|
| House wren | no preference | no preference |
| Mountain chickadee | >30 | II |
| Pygmy nuthatch | >50 | III |
| Violet-green swallow | 15 to <30 | III |
| Western bluebird | no preference | III |
| Woodpecker species** | >50 | II |
*Preferences shown in this table are all statistically significant (P<0.10), except for mountain chickadee (for which all 5 nests occurred in the same size and decay class) **Data were combined for 3 species: acorn woodpecker, hairy woodpecker, and northern flicker | ||
In the 65 years prior to this study, no wildfires in the study area were larger than 2 ha. The authors note that, prior to the 20th century, fires were probably frequent and extensive in southwestern ponderosa pine forests (including Arizona pine), burning every 5 to 12 years [2]. A recent synthesis of fire regime information for southwestern ponderosa pine forests [4] provides this description of the historical fire regime. See the LANDFIRE Biophysical Settings section for additional information about historical fire regimes in this community.
Plant Phenology
Plant phenology was not described in the study. The November fires probably occurred after tree growth had ceased, and the May burn probably occurred while trees were growing.
Fire Season/Severity Classification
Fall/Low
Spring/Low
Fire Management Objectives
Study sites were underburned to improve regeneration and growth of Arizona pines by exposing mineral soil and reducing density of small trees, and to reduce fuels as follows:
| Woody fuel size class | Planned % reduction in fuel load |
|---|---|
| <0.6 cm diameter | 70 |
| 0.6-7.6 cm diameter | 55 |
| >7.6 cm diameter | 25 |
Research Objectives
This study compared 3 characteristics of Arizona pine forests before and after prescribed fire: number and characteristics of Arizona pine snags, availability of snags used by cavity-nesting birds, and breeding populations of cavity-nesting birds.
Fires were broadcast underburns that backed downslope and into the wind. Two stands were burned in mid-November 1984; the third was burned in early May 1985. Burns were conducted within the prescribed weather conditions listed below, and fire behavior generally stayed within the prescribed limits.
| Air temperature | 4 to 24 °C |
| Relative Humidity | 25% to 40% |
| Wind speed | 1-16 km/hr |
| Flame height | 0.3-1.0 m |
| Flame length | 0.3-1.2 m |
| Rate of spread | 40-120 m/hr |
Fire Effects on Snags
Fire effects on Arizona pine snags were measured the first summer after prescribed burning (summer 1985). Treatments reduced both large and small snags by about 50%. Density of the kind of snags generally preferred by cavity nesters (>50 cm DBH in decay classes II or III) were reduced from 1.5 to 1.0 snags/ha. Snags with greater decay were significantly (P<0.001) more vulnerable to fire damage; 73% of snags in decay class IV burned down or were reduced more than 50% in height, in comparison with less than 20% of snags in decay classes II and VI. Snags >30 cm DBH were more likely to burn than smaller snags, probably because larger snags had more advanced decay. Snags with large amounts of undecayed twigs, branches, and sloughed bark at the base ignited more easily than those with less fuel or mostly decayed fuel at the base. Few large snags were created by the burns, but small snags increased 20-fold:
| Size class | Prefire density (number/ha) | Postfire density (number/ha) | ||
|---|---|---|---|---|
| Burned* | Created** | Total after fire | ||
| Large (>15 cm DBH) | 11.1 | 5.5 | 0.5 | 6.1 |
| Small (<15 cm DBH) | 10.9 | 6 | 216.1 | 221 |
*Burned down, were reduced >50% in height, or had most of sapwood burned away **Killed by prescribed burns | ||||
Fire Effects on Cavity-Nesting Birds
Cavity-nesting birds were surveyed the first breeding season after prescribed burning (May-July 1985). Only 3 species showed significant (P<0.10) differences in density between burned and unburned sites (which included both control sites and preburn treatment sites): Mountain chickadee density was greater, and northern flicker and violet-green swallow densities decreased. The authors attributed the differences to changes in prey populations, shifts in foraging areas after burning, or both.
| Species | Unburned (control) sites | Burned sites | ||
|---|---|---|---|---|
| 1984 | 1985 | 1984 (prefire) | 1985 (breeding season after treatments) | |
| Acorn woodpecker | 1.1 | 1.5 | 4.1 | 2.8 |
| Ash-throated flycatcher | — | — | P* | — |
| Bridled titmouse | P | P | P | P |
| Bewick's wren | P | P | P | P |
| Brown creeper | 5.8 | 7.3 | 9.8 | 7.9 |
| Cordilleran flycatcher (western flycatcher) | 62.4 | 48 | 39.2 | 67 |
| Dusky-capped flycatcher | P | P | P | P |
| Eastern bluebird | P | — | — | — |
| Hairy woodpecker | 0.7 | 0.8 | 0.8 | 1 |
| House wren | 53.2 | 91.8 | 15 | 46.2 |
| Mountain chickadee | 7.2 | 7 | 5.6 | 12.2** |
| Northern flicker | 1.7 | 2.3 | 2.6 | 2.1** |
| Pygmy nuthatch | 26.2 | 15.8 | 24.4 | 14.2 |
| Violet-green swallow | 31.7 | 34 | 37.4 | 17.6** |
| Western bluebird | 11.3 | 6.1 | 12.5 | 6.2 |
| White-breasted nuthatch | 4.4 | 2.9 | 7 | 4.2 |
*P=present at low density. Blank cell indicates not present. **Significantly different from density on unburned sites (P<0.10) | ||||
Management objectives for the burns, to improve regeneration and growth of Arizona pines and reduce woody fuels, were met.
The authors recommend that protection of large snags (by constructing fuel breaks around the trees) be considered before conducting prescribed underburns in forests where large snags have been reduced by logging. It is most important to protect snags >50 cm DBH in decay classes II and III, which can provide nest sites for most cavity-nesting birds, and snags in decay class I, which may provide nest sites in the future.
| Biophysical Setting | Mean Fire Interval (years) | Fire Severity Percent (%) | ||||||
|---|---|---|---|---|---|---|---|---|
| Code | Fire Regime Group | Low | Mixed | Replacement | All | Low | Mixed | Replacement |
| Series 10520 - Southern Rocky Mountain Mesic Montane Mixed Conifer Forest and Woodland | ||||||||
| 10520_15 | I-C | 72 | 90 | 186 | 33 | 45 | 37 | 18 |
| Summary | ||||||||
| Minimum | 72 | 90 | 186 | 33 | 45 | 37 | 18 | |
| Maximum | 72 | 90 | 186 | 33 | 45 | 37 | 18 | |
| Mean | 72 | 90 | 186 | 33 | 45 | 37 | 18 | |
| Median | 72 | 90 | 186 | 33 | 45 | 37 | 18 | |
| Percentage of fires in 3 fire severity classes, derived from LANDFIRE succession modeling. Replacement-severity fires cause >75% kill or top-kill of the upper canopy layer; mixed-severity fires cause 26%-75%; low-severity fires cause <26%. | ||||||||
| LANDFIRE. 2020. Biophysical settings models and descriptions, [Online]. Washington, DC: U.S. Department of Agriculture, Forest Service; U.S. Department of the Interior; U.S. Geological Survey; Arlington, VA: The Nature Conservancy, (Producers). Available: https://www.landfirereview.org/search.php [96496] | ||||||||
Table A1: Common and scientific names of species mentioned in this summary.
| Common name | Scientific name |
|---|---|
| Trees | |
| Arizona pine | Pinus arizonica |
| Birds | |
| Bridled titmouse | Baeolophus wollweberi (Parus wollweberi)* |
| Brown creeper | Certhia americana |
| Northern flicker | Colaptes auratus |
| Cordilleran flycatcher (western flycatcher) | Empidonax occidentalis (Empidonax difficilis) |
| Acorn woodpecker | Melanerpes formicivorus |
| Ash-throated flycatcher | Myiarchus cinerascens |
| Dusky-capped flycatcher | Myiarchus tuberculifer |
| Hairy woodpecker | Picoides villosus |
| Mountain chickadee | Poecile gambeli (Parus gambeli) |
| Eastern bluebird | Sialia sialis |
| Western bluebird | Sialia mexicana |
| White-breasted nuthatch | Sitta carolinensis |
| Pygmy nuthatch | Sitta pygmaea |
| Violet-green swallow | Tachycineta thalassina |
| Bewick's wren | Thryomanes bewickii |
| House wren | Troglodytes aedon |
| *For species that have undergone scientific name changes, names in parentheses are those used in the research paper. | |
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. Horton, Scott P.; Mannan, R. William. 1988. Effects of prescribed fire on snags and cavity-nesting birds in southeastern Arizona pine forests. Wildlife Society Bulletin. 16: 37-44. [5549]
3. 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]