Effects of prescribed fire on winter assemblages of birds in ponderosa pine forests of northern Arizona.
For many forests, including ponderosa pine (Pinus ponderosa) forests in northern Arizona, fire was a natural disturbance of the system until fire-suppression efforts began in the early 20th century. Frequent, low-intensity fires were part of the ecology and evolutionary history of ponderosa pine forests (cooper, 1960; Covington and Moore, 1994; Swetnam and Baisan, 1996; Moir et al., 1997). Managers are attempting alternative forest-management strategies that include using prescribed burns in an effort to return fire to the landscape. As such, it will be important to understand effects of these treatments on birds wintering in areas where managers are using this tool.
A few studies have examined effects of wildfire on wintering birds in coniferous forests (Blake, 1982; Kreisel and Stein, 1999; Bock and Block, 2005; Covert-Bratland et al., 2006). Prescribed fire could have different effects on wintering birds than wildfire, yet only one study has examined effects of prescribed fire on wintering birds in a coniferous forest (King et al., 1998). Therefore, we compared assemblages of wintering birds in ponderosa pine forests recently treated by prescribed fire with untreated controls to determine whether prescribed fire affects composition and abundances of species during the first few winters following prescribed treatments.
Materials and Methods--Study Area--We located study sites in the Coconino and Kaibab national forests in northern Arizona, as part of the Birds and Burns Network. Ponderosa pine was the dominant overstory species on both study sites, with Gambel oak (Quercus gambelii) contributing to the canopy on study units in Coconino National Forest. Pinyon pine (Pinus edulis), one-seed juniper (Juniperus monosperma), and alligator juniper (J. deppeana) occurred on control units in Kaibab National Forest, but contributed little to the canopy. Alligator juniper was on both units in Coconino National Forest. Open patches of grassland on both sites were dominated by bunchgrasses, including Arizona fescue (Festuca arizonica) and blue gramma (Bouteloua gracilis). Topography on the study site in Coconino National Forest varied from flat to steep hills, with elevations of 2,070-2,160 m. The study site in Kaibab National Forest was flat, with elevations of 2,100-2,300 m.
Each study site in the forests had a burned treatment unit paired with control unit(s) of similar structure (Table 1). We chose treatment units in consultation with district fire managers on each forest. We then placed control units in representative areas with similar structure within 1 km of the treatment unit where no management (e.g., thinning or prescribed burn) was planned. It was not possible to randomize location of each treatment unit; however, we made efforts to ensure all sampling occurred at randomly placed stations within units. We used a systematic random-sampling design for placement of point-count stations. We randomized placement of the first point, assigning remaining points using a Geographical Information System algorithm (Dickson, 2006).
Personnel of the United States Forest Service administered prescribed fires during autumn 2003 on the treatment unit in Coconino National Forest and on the treatment unit in Kaibab National Forest during autumn 2003 and spring 2004 (Table 2). Fire prescriptions were characterized as broadcast burns with expected behaviors of fire to be low-to-moderate intensity (Dickson, 2006). Fires were heterogeneous in nature, ranging from areas not burned to areas with burns severe enough to kill trees. We measured maximum height of char on bole, percentage of circumference of bole that was charred at the base, and percentage of needles scorched, because these are measures of fire that fire managers can incorporate into fire prescriptions. Average ([+ or -] SE) maximum height of char on bole for burn units was 1.2 m [+ or -] 0.04. Average percentage circumference of bole that was charred at the base was 65.0 [+ or -] 0.81 and average percentage of needles scorched was 6.6 [+ or -] 0.39. Measurements for individual burn units are included in Table 2. Nevertheless, these values represent low-severity fire that had little post-treatment effect on structure of the forest.
Field Methods--We conducted point counts in winter (Reynolds et al., 1980) at 170 point-count stations in northern Arizona during the first 2 winters following treatments. The study site in Coconino National Forest had 40 point-count stations each in burn and control units. The study site in Kaibab National Forest had 40 point-count stations in the burn unit and 50 point-count stations between two control units. each station was ca. 300 m apart and [greater than or equal to] 200 m from edges of units. At each station, we recorded number of individuals and distance to each individual for all birds observed during a 5-min survey period. Point counts began [less than or equal to] 30 min of sunrise and concluded within 5 h. We did not count in windy (i.e., >28 km/h) or wet (more than a light snow) conditions. We visited all stations eight times (4/season) between mid-October and mid-March, 2004-2006, with a single observer per visit.
We assigned all species detected within 100 m of a point-count station to one of four foraging groups (foraging group must include >1 species). We also recorded incidental observations (i.e., observed in a unit but not within 100 m of any point-count station). Foraging groups included seed-eating, bark-foraging/ sapsucking, gleaning insectivores, and generalists (see Table 3 for species-specific assignments to groups).
Statistical Analyses--We used a similarity index and a test of rank order of abundance to describe patterns in assemblages of wintering birds. We used an uncorrected index of abundance because we were examining patterns of abundance and not proposing actual estimates of abundance. We investigated similarity in assemblages of wintering birds between treatments (pooling across years) and years (pooling across treatments) using the Sorenson similarity index, C = 2j/(a + b); where j = number of species common to both treatment units or years, a = total number of species detected in burn units or year 1, and b = total number of species detected in control units or year 2 (Magurran, 1988). The similarity index equals a number between 0 and 1, with higher values representing greater similarity.
We used rank order of abundance to represent structure of assemblages for each year and treatment. We ranked species in order of abundance, based on number of individual detections. We calculated Spearman's rank-order correlation coefficient (Spearman's p; Conover, 1999) using SPSS 15.0 for Windows (SPSS, inc., Chicago, Illinois). A higher value of spearman's p represents a higher correlation in rank order of species between treatments and years. For example, Spearman's p = 1.00 will have species ranked in the same order for each treatment or year.
Results--We detected 39 species of birds during winters of 2004-2006 (Table 3). Nine species comprised 81% of observations. In descending order, these were dark-eyed junco (Junco hyemalis), pygmy nuthatch (Sitta pygmaea), western bluebird (Sialia mexicana), white-breasted nuthatch (Sitta carolinensis), mountain chickadee (Poecile gambeli), ruby-crowned kinglet (Regulus calendula), Steller's jay (Cyanocitta stelleri), hairy woodpecker (Picoides villosus), and brown creeper (Certhia americana). All of these species, except for ruby-crowned kinglet, are year-round residents of ponderosa pine forests in northern Arizona.
Assemblages were similar in composition and structure among years and between treatments. Using the Sorenson similarity index (C)to examine all non-incidental species detected during point counts, similarity between treatments and years was C = 0.85. We detected similar patterns when examining individual foraging groups. Seed-eating birds had C = 1.00 between treatments and C = 0.80 among years. Gleaning insectivores had C = 0.95 between treatments and C = 0.89 among years. Bark-foraging/sapsucking birds had C = 0.89 for both treatment and year. Generalists had C = 0.85 between years, however, C = 0.66 between treatments because we detected two species, pinyon jay (Gymnorhinus cyanocephalus) and American crow (Corvus brachyrhynchos), in control units only.
We also examined how rank order of abundance of species in each treatment differed among years for all non-incidental species. in burn units, Spearman's p = 0.69 (P < 0.01). Spearman's p = 0.70 (P < 0.01) in control units. Because there was no yearly difference, we combined years for a Spearman's p = 0.83 (P < 0.01) correlation between treatments. individual foraging groups differed among years in each treatment. Seed-eating birds had Spearman's p = 0.50 (P = 0.67) among years in burn units and Spearman's p = 1.00 in control units. This group had Spearman's p = 0.50 (P = 0.67) between treatments for both years combined. Generalists had Spearman's p = 1.00 in burn units and control units among years, and Spearman's p = 0.63 (P = 0.37) between treatments. Gleaning insectivores had Spearman's p = 0.47 (P = 0.17) in burn units, Spearman's p = 0.28 (P = 0.43) in control units, yet Spearman's p = 0.91 (P < 0.01) between treatments. Bark-foraging/sapsucking birds had Spearman's p = 0.95 (P < 0.01) in the burn units, Spearman's p = 0.96 (P < 0.01) in the control units, and Spearman's p = 0.92 (P < 0.01) between treatments.
We also compared composition and structure of assemblages of birds between burn units to determine whether intensity of fire had an effect. The Sorenson similarity index was C = 0.78 between burn units and Spearman's p = 0.79 (P < 0.01). order of abundance for individual foraging groups in each burn unit were all correlated (bark-foraging/sapsucking--Spearman's p = 0.97 (P < 0.01); gleaning insectivore--Spearman's p = 0.76 (P = 0.03); generalist--Spearman's p = 1.00) except seed-eating, which had Spearman's p = 0.50 (P = 0.67).
Discussion--Assemblages of birds in northern Arizona were similar in composition and structure among treatments and years during the first 2 winters following low-intensity prescribed fire. Differences in assemblages of wintering birds might depend on type of fire, i.e., whether wildfire (high-intensity) or prescribed fire (low-to-moderate intensity). Blake (1982) compared assemblages of wintering birds in areas burned by wildfire and unburned areas in northern Arizona. in his study, hairy woodpeckers were more common in burned areas. our results were the same although our prescribed fires were lower intensity than many wildfires. Blake (1982) also reported that species that search crevices in bark for insects, such as nuthatches, were more common in unburned sites in winter; however, nuthatches had similar abundances in burned and unburned areas in our study. This pattern could be the result of low-intensity prescribed fire not altering structure of forest stands as much as high-intensity wildfire.
Number of species detected in undisturbed sites in ponderosa pine forests during winter varies between studies. our study and Bock and Block (2005) detected a similar number of species wintering in unburned areas (31 and 26, respectively). However, Haldeman et al. (1973) recorded only 18 species wintering in undisturbed sites in ponderosa pine forests of northern Arizona. Pygmy nuthatch was the most common species reported by Haldeman et al. (1973) and the second-most common species behind dark-eyed juncos in our study. However, common species were generally the same for each study, including mountain chickadee, pygmy and white-breasted nuthatch, dark-eyed junco, western bluebird, hairy woodpecker, northern flicker, and Steller's jay.
Of 39 species we detected, 25 were common between treatment and years (Table 3). However, some species were only present in 1 year or treatment. For example, violet-green swallows (Tachycineta thalassina) had returned from migration before counts ended the first year. We had 13 species only detected in one treatment (five in control, eight in burn). These species were represented mostly by raptors (three), owls (three), and corvids (three). Of these, only pinyon jays were detected more than twice (Table 3). Therefore, less-abundant species may be present in only one treatment, producing diversity while maintaining composition and structure of assemblages. As such, creating a mosaic of burned and unburned areas will enhance species diversity in ponderosa pine forests.
Although there was some variability among foraging groups, assemblages of birds were similar between unburned areas and areas treated with prescribed fire, between each burn unit, and among years during winters initially following prescribed fire. Therefore, managers that use low-severity prescribed fires in ponderosa pine forests of northern Arizona might not be altering structure of the forest enough to impact assemblages of wintering birds during the first few years following prescribed fire.
We thank V. Saab, B. Dickson, S. Vojta, N. Gwinn, C. Breece, N. Breece, S. Hurteau, K. Bratland, S. Stollery, P. Beier, P. Fule, T. Sisk, D. Huebner, and the wildlife lab group in the Northern Arizona University School of Forestry for assistance and constructive advice in different aspects of this project.
Submitted 14 December 2007. Accepted 14 May 2009. Associate Editor was Michael S. Husak.
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THERESA L. POPE * AND WILLIAM M. BLOCK
United States Forest Service Rocky Mountain Research Station, 2500 South Pine Knoll Drive, Flagstaff, AZ 86001 Present address of TLP: Department of Wildlife and Fisheries Sciences, Texas A&M University, 210 Nagle Hall, College Station, TX 77843-2258
* Correspondent: email@example.com
TABLE 1--Description of study units in the Birds and Burns Network of the Coconino and Kaibab national forests, Arizona, including treatment (burn and control), area (ha), number of trees surveyed, average ([+ or -]SE) diameter at breast height (cm), and average ([+ or -]SE) height of tree (m). Kaibab National Forest Diameter at Height of breast height tree Treatment Area n x [+ or -] SE x [+ or -] SE Burn 369 758 33.7 [+ or -] 0.5 13.7 [+ or -] 0.2 Control 487 872 33.3 [+ or -] 0.4 11.3 [+ or -] 0.1 Coconino National Forest Diameter at Height of breast height tree Treatment Area n x [+ or -] SE x [+ or -] SE Burn 405 1940 23.1 [+ or -] 0.2 12.7 [+ or -] 0.1 Control 404 1567 24.5 [+ or -] 0.3 10.9 [+ or -] 0.1 TABLE 2--Measurements of fire activity from prescribed fires on each burn unit and burn units combined on the Coconino and Kaibab national forests, Arizona. National Maximum height of forest Dates burned char on bole (m) Kaibab 27 October 2003 2.6 [+ or -] 0.11 6 November 2003 25 March 2004 Coconino 15 September 2003 0.7 [+ or -] 0.02 18 September 2003 19 September 2003 Combined -- 1.2 [+ or -] 0.04 National Percentage of forest Dates burned needles scorched Kaibab 27 October 2003 17.6 [+ or -] 1.05 6 November 2003 25 March 2004 Coconino 15 September 2003 2.3 [+ or -] 0.29 18 September 2003 19 September 2003 Combined -- 6.6 [+ or -] 0.39 National Percentage of forest Dates burned bole charred Kaibab 27 October 2003 85.8 [+ or -] 1.01 6 November 2003 25 March 2004 Coconino 15 September 2003 56.9 [+ or -] 1.00 18 September 2003 19 September 2003 Combined -- 65.0 [+ or -] 0.81 TABLE 3--Species detected during point counts from mid-October to mid-March 2004--2006, including incidental species (i) only detected beyond 100-m radius of point-count stations. Species, scientific name, foraging group, number of detections, percentage of total detections, year(s) detected, and treatment(s) detected are listed. Incidental species and those that are the only representative of their foraging group were not assigned to foraging groups analyzed in rank order of abundance. Common name Taxon Foraging group Bald eagle Haliaeetus leucocephalus -- Northern goshawk Accipiter gentiles -- Red-tailed hawk Buteo jamaicensis -- Swainson's hawk Buteo swainsoni -- Wild turkey Meleagris gallopavo -- Mourning dove Zenaida macroura -- long-eared owl Asio otus -- Great horned owl Bubo virginianus -- Northern pygmy-owl Glaucidium gnoma -- Northern flicker Colaptes auratus Bark-foraging/ sapsucking Williamson's sapsucker Sphyrapicus Bark-foraging/ thyroideus sapsucking Red-naped sapsucker Sphyrapicus nuchalis Bark-foraging/ sapsucking Downy woodpecker Picoides pubescens Bark-foraging/ sapsucking Hairy woodpecker Picoides villosus Bark-foraging/ sapsucking Three-toed woodpecker Picoides tridactylus Bark-foraging/ sapsucking Steller's jay Cyanocitta stelleri Generalist Clark's nutcracker Nucifraga columbiana -- Pinyon jay Gymnorhinus cyanocephalus Generalist American crow Corvus brachyrhynchos Generalist Common raven Corvus corax Generalist Violet-green swallow Tachycineta thalassina -- Mountain chickadee Poecile gambeli Gleaning insectivore Bushtit Psaltriparus minimus Gleaning insectivore Brown creeper Certhia americana Bark-foraging/ sapsucking White-breasted nuthatch Sitta carolinensis Bark-foraging/ sapsucking Red-breasted nuthatch Sitta canadensis Bark-foraging/ sapsucking Pygmy nuthatch Sitta pygmaea Bark-foraging/ sapsucking Golden-crowned kinglet Regulus satrapa Gleaning insectivore Ruby-crowned kinglet Regulus calendula Gleaning insectivore Western bluebird Sialia mexicana Gleaning insectivore Mountain bluebird Sialia currucoides Gleaning insectivore Townsend's solitaire Myadestes townsendi Gleaning insectivore American robin Turdus migratorius Gleaning insectivore Yellow-rumped warbler Dendroica coronata Gleaning insectivore Olive warbler Peucedramus taeniatus Gleaning insectivore Dark-eyed junco Junco hyemalis Seed-eating Cassin's finch Carpodacus cassinii -- Red crossbill Loxia curvirostra Seed-eating Pine siskin Carduelis pinus Seed-eating Percentage Number of of total detections detections Year(s) Common name (within 100 m) (n = 4,639) detected Bald eagle i -- Both Northern goshawk i -- 1 Red-tailed hawk 2 0.04 Both Swainson's hawk i -- 1 Wild turkey 3 0.06 Both Mourning dove 1 0.02 2 long-eared owl 1 0.02 2 Great horned owl 1 0.02 1 Northern pygmy-owl 1 0.02 1 Northern flicker 62 1.34 Both Williamson's sapsucker 11 0.24 Both Red-naped sapsucker 7 0.15 Both Downy woodpecker 2 0.04 1 Hairy woodpecker 160 3.45 Both Three-toed woodpecker 9 0.19 Both Steller's jay 176 3.79 Both Clark's nutcracker i -- 2 Pinyon jay 28 0.60 Both American crow 2 0.04 Both Common raven 50 1.08 Both Violet-green swallow 8 0.17 1 Mountain chickadee 405 8.73 Both Bushtit 78 1.68 Both Brown creeper 133 2.87 Both White-breasted nuthatch 406 8.75 Both Red-breasted nuthatch 2 0.04 2 Pygmy nuthatch 678 14.62 Both Golden-crowned kinglet 34 0.73 Both Ruby-crowned kinglet 220 4.74 Both Western bluebird 508 10.95 Both Mountain bluebird 1 0.02 1 Townsend's solitaire 10 0.22 Both American robin 84 1.81 1 Yellow-rumped warbler 32 0.69 Both Olive warbler 16 0.34 Both Dark-eyed junco 1,065 22.96 Both Cassin's finch i -- Both Red crossbill 38 0.82 Both Pine siskin 32 0.69 Both Treatment(s) Common name detected Bald eagle Control only Northern goshawk Burn only Red-tailed hawk Both Swainson's hawk Burn only Wild turkey Both Mourning dove Burn only long-eared owl Control only Great horned owl Burn only Northern pygmy-owl Burn only Northern flicker Both Williamson's sapsucker Both Red-naped sapsucker Both Downy woodpecker Burn only Hairy woodpecker Both Three-toed woodpecker Both Steller's jay Both Clark's nutcracker Burn only Pinyon jay Control only American crow Control only Common raven Both Violet-green swallow Both Mountain chickadee Both Bushtit Both Brown creeper Both White-breasted nuthatch Both Red-breasted nuthatch Burn only Pygmy nuthatch Both Golden-crowned kinglet Both Ruby-crowned kinglet Both Western bluebird Both Mountain bluebird Control only Townsend's solitaire Both American robin Both Yellow-rumped warbler Both Olive warbler Both Dark-eyed junco Both Cassin's finch Both Red crossbill Both Pine siskin Both
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|Author:||Pope, Theresa L.; Block, William M.|
|Date:||Mar 1, 2010|
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