Understory recovery after low- and high-intensity fires in northern Idaho ponderosa pine forests

INTRODUCTORY:

RESEARCH PROJECT SUMMARY CITATION: :
Gucker, Corey L. 2005. Understory recovery after low- and high-intensity fires in northern Idaho ponderosa pine forests. 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/ [].

RESEARCH PROJECT SUMMARY REFERENCES:
Armour, Charles D.; Bunting, Stephen C.; Neuenschwander, Leon F. 1984. Fire intensity effects on the understory in ponderosa pine forests. Journal of Range Management. 37(1): 44-48.

Armour, Charles D.; Bunting, Stephen C.; Neuenschwander, Leon F. (n.d.). The effect of fire intensity on understory vegetational development. Unpublished report on file with: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory, Missoula, MT. 17 p.

STUDY LOCATION:
The study area was on the Coeur d'Alene Indian Reservation in Benewah County, Idaho [1,3].

SITE DESCRIPTION:
This study occurs in the following vegetation classifications:

FRES20 Douglas-fir [5]
FRES21 Ponderosa pine
K011 Western ponderosa forest [6]
K012 Douglas-fir forest
SAF210 Interior Douglas-fir [4]
SAF237 Interior ponderosa pine

Burned sites occurred on gentle slopes (0% to 30%) at elevations of about 880 m. Average annual precipitation is 560 mm, the majority of which falls from October through March. Soils are fine silts, and study sites received approximately 10 cm of ash from the Mount St. Helens volcanic eruption in May of 1981, which occurred prior to the 2nd postfire vegetation sampling [1,3].

PREFIRE PLANT COMMUNITY:
Sites were within the Douglas-fir/ninebark (Pseudotsuga menziesii/Physocarpus malvaceus) potential natural vegetation type; however, the overstory dominant was early seral ponderosa pine (Pinus ponderosa). The basal area of ponderosa pine before burning was 37.48 m²/ha. The most common shrub was common snowberry (Symphoricarpos albus), but baldhip rose (Rosa gymnocarpa), chokecherry (Prunus virginiana), and oceanspray (Holodiscus discolor) were also typical. Pinegrass (Calamagrostis rubescens) dominated the understory vegetation, where bluegrass (Poa spp.) and blue wildrye (Elymus glaucus) were also important. Typical forbs on the study sites were northern bedstraw (Galium boreale), Virginia strawberry (Fragaria virginiana), western yarrow (Achillea millefolium), and twin clover (Trifolium latifolium) [1,2,3].

The estimated mean fire return interval is 22 years in this area. However, sites had not burned for 44 to 62 years, and sites had not been grazed by livestock for more than 30 years. Some selective logging (removal of 11% to 35% of canopy) occurred in the study area. Sites were logged 3 times in approximately 30 years. The last logging disturbance was in 1977 [1,2].

Burned and unburned sites had similar stand structures, land use histories, species compositions, and species abundances prior to burning. Sites were located within 25 km of each other [1].

PLANT PHENOLOGY
Phenology of the prefire vegetation was not described.

FIRE SEASON/SEVERITY CLASSIFICATION:
High- and low-intensity prescription fires were ignited in 1978:

Fall/High intensity
Fall/Low intensity

FIRE DESCRIPTION:
Researchers designed this study to compare early postfire vegetation recovery on sites burned with different intensities in ponderosa pine communities of the Douglas-fir-ninebark habitat type.

The average fuel load on burned sites was 58,200 kg/ha, nearly half of which was duff [3]. Depth of duff was 1.3 cm on high-intensity sites, 4.0 cm on low-intensity sites, and 6.6 cm on unburned sites. Three replicated high- and low-intensity fires were sampled. High- and low-intensity fires had significantly different (p<0.05) fireline intensities. Energy produced by high-intensity fires was between 30 to 3,034 kcal/m/s and averaged 781 kcal/m/s; energy released on low-intensity fires averaged 127 kcal/m/s and ranged from 25 to 194 kcal/m/s. Significantly (p value not reported) more duff was consumed on the high-intensity fire sites (80%) than on low-intensity fire sites (40%). Flame lengths averaged 0.9 m and ranged from 0.1 to 1.7 m on both sites. On average, duff smoldered longer on high-intensity sites than on low-intensity sites.

FIRE EFFECTS ON PLANT COMMUNITY:
Researchers measured frequency and cover on burned and unburned sites for 3 consecutive posttreatment years. Shrub canopy estimates came from line intercept sampling using five 10-m transects in macroplots (15×15 m). Herbaceous cover and frequency came from 10 microplots (20×50 cm) read at the edge of the shrub transects.

Graminoid coverage was significantly (p<0.1) lower on high-intensity burned sites than on unburned sites. Forbs coverage was greatest on low-intensity burned sites, and researchers noted that increases in forb coverage on burned sites were significantly greater than on unburned sites for all 3 postfire years. Shrub coverage was not significantly different between treatments. Canopy coverage (%) was:

  Unburned Low intensity High intensity
Shrubs 31 23 27
Forbs 17 25 20
Graminoids 20 ~19 11

When researchers assessed individual species coverages, they found significant (p<0.1) differences between at least 2 treatments for 5 shrub, 3 perennial graminoid, 8 perennial forb, and 4 annual species. These species are identified in the table below. Most of the species with significant coverage differences between treatments showed significant differences in frequency as well.

Fire-sensitive species: Columbia brome, baldhip rose, and ninebark had significantly greater coverage on unburned sites than on either burned site.

Species sensitive to high-intensity fires: The coverage of Oregon-grape (Berberis repens), field woodrush (Luzula campestris), Wood's rose (R. woodsii), and Virginia strawberry was significantly lower on high-intensity burned sites than on low-intensity burned or unburned sites.

Fire adapted species: Coverage was highest on low-intensity burned sites for Scouler willow (Salix scouleriana), Jessica's aster (Aster jessicae), old man's whiskers (Geum triflorum), slender cinquefoil (Potentilla gracilis), and American vetch (Vicia americana). Spreading dogbane (Apocynum androsaemifolium), thistle (Cirsium spp.), fireweed (Chamerion angustifolium), maiden blue-eyed Mary (Collinsia parviflora), tiny trumpet (Collomia linearis), tall annual willowherb (E. paniculatum), and prickly lettuce (Lactuca serriola) were most common on high-intensity burned sites. The researchers also noted that redstem ceanothus (Ceanothus sanguineus) seedlings occurred only on sites burned with high intensities.

The following table provides the percent cover in unburned, low-intensity, and high-intensity treatments. Coverages are averaged over 3 postfire years of data collection.

Common name Scientific name Unburned Low intensity High intensity
Shrubs

cover (%)
Saskatoon serviceberry Amelanchier alnifolia 0.5a 0.2a 0.1a
Oregon-grape* Berberis repens 1.1a 1.2a 0b
redstem ceanothus Ceanothus sanguineus 0.2a 0.1a 0.8a
Douglas hawthorn Crataegus douglasii 1a 0a 0.2a
oceanspray Holodiscus discolor 3.9a 1a 2.7a
ninebark* Physocarpus malvaceus 2a 0b 0.4b
bitter cherry Prunus emarginata 0a 0a 0.1a
chokecherry Prunus virginiana 3.7a 5a 2.1a
baldhip rose* Rosa gymnocarpa 3.1a 0.6b 0.9b
Nootka rose Rosa nutkana 0.5a 0.1a 0.2a
Wood's rose* Rosa woodsii 0.8a 0.7a 0.2b
Scouler willow* Salix scouleriana 0.1b 1.1a 0b
white spirea Spiraea betulifolia 0.6a 1.8a 2.1a
common snowberry Symphoricarpos albus 17.3a 14.3a 20.4a
trailing snowberry Symphoricarpos hesperius 0a 0a 1a
Perennial graminoids
Columbia brome* Bromus vulgaris 0.7a 0.3b 0.3b
pinegrass Calamagrostis rubescens 29.1a 27.8a 16.1a
blue wildrye Elymus glaucus 2.7a 1.7a 1.2a
rough fescue* Festuca altaica 0b 0.6a 0.2ab
Idaho fescue Festuca idahoensis 1.9a 1a 0.4a
field woodrush* Luzula campestris 0.5a 0.4a 0.1b
bluegrass Poa spp. 2.8a 2.1a 1.8a
bluebunch wheatgrass Pseudoroegneria spicata ssp. spicata 1.4a 2.1a 0.8a
Perennial forbs
western yarrow Achillea millefolium 1a 1.3a 0.5a
Piper's anemone Anemone piperi 0a 0.1a 0.1a
spreading dogbane* Apocynum androsaemifolium 0b 0b 1a
largeleaf sandwort Arenaria macrophylla 1.3a 2.1a 0.6a
Jessica's aster* Aster jessicae 0.3b 2.2a 1b
fireweed* Chamerion angustifolium 0b 0.3b 1.2a
thistle* Cirsium spp. 0.1b 0.1b 0.4a
Virginia strawberry* Fragaria virginiana 2.9ab 3.4a 1.6b
northern bedstraw Galium boreale 2.7a 3.5a 1.9a
sticky purple geranium Geranium viscosissimum 0.9a 1.7a 1.1a
old man's whiskers* Geum triflorum 0.3b 0.8a 0.1b
white hawkweed Hieracium albiflorum 0.7a 0.8a 0.4a
pinewoods sweetpea Lathyrus bijugatus 0.7a 0.4a 0.6a
nineleaf biscuitroot Lomatium triternatum 0.4a 0.4a 0.4a
lupine Lupinus spp. 0.1a 0.6a 0.4a
sweetcicely Osmorhiza berteroi 0.1a 0.2a 0.2a
beardtongue Penstemon spp. 0.5a 0.2a 0a
sticky cinquefoil Potentilla glandulosa 0.4a 0.4a 0a
slender cinquefoil* Potentilla gracilis 1.4ab 2.2a 0.8b
western bracken fern Pteridium aquilinum 1.3a 2.3a 2.5a
Canada goldenrod Solidago canadensis 0.5a 1.1a 0.1a
starwort Stellaria spp. 0.6a 0.6a 1.2a
common dandelion Taraxacum officinale 0.1a 0.1a 0.2a
twin clover Trifolium latifolium 1.9a 1.2a 2.3a
American vetch* Vicia americana 0.1b 0.7a 0.1b
Annuals
Japanese brome Bromus japonicus 0.1a 0.1a 0.1a
maiden blue-eyed Mary* Collinsia parviflora 0.1b 0.1b 0.4a
tiny trumpet* Collomia linearis 0.2b 0.4b 0.9a
tall annual willowherb* Epilobium paniculatum 0.1b 0.2b 1.3a
sweet fennel Foeniculum vulgare 0.2a 0.3a 0.4a
prickly lettuce* Lactuca serriola 0b 0.1b 0.8a
*Species with a significant change in coverage between at least 2 treatments.

The following table provides the percent frequency in unburned, low-intensity, and high-intensity treatments. Frequencies are averaged over 3 postfire years of data collection [1,2].

Common name Scientific name Unburned Low intensity High intensity
Shrub

frequency (%)
Oregon-grape* Berberis repens 8.6ab 11.1a 0.2b
Perennial graminoids
Columbia brome* Bromus vulgaris 15.5a 7.7b 4.6b
pinegrass Calamagrostis rubescens 44a 48.1a 25.7a
blue wildrye Elymus glaucus 46.1a 36.4a 24.4a
rough fescue Festuca altaica 24.8a 20.4a 10.8a
Idaho fescue Festuca idahoensis 0.6a 5.3a 2.1a
field woodrush* Luzula campestris 14.5a 11.6a 2b
bluegrass Poa spp. 29a 29.3a 22.2a
bluebunch wheatgrass Pseudoroegneria spicata ssp. spicata 25.7a 30.4a 11.8a
Perennial forbs
western yarrow Achillea millefolium 28.2a 28.3a 12.1a
Piper's anemone Anemone piperi 1.9a 3.3a 1.5a
spreading dogbane* Apocynum androsaemifolium 0.7b 0.1b 9.2a
largeleaf sandwort Arenaria macrophylla 11a 16.8a 3.9a
Jessica's aster* Aster jessicae 3.9b 22.2a 7.6b
fireweed* Chamerion angustifolium 0.2b 2.7ab 7.6a
thistle* Cirsium spp. 1b 2.8b 8.7a
Virginia strawberry* Fragaria virginiana 47.6a 53.6a 24.2b
northern bedstraw Galium boreale 24.4a 25.3a 13a
sticky purple geranium Geranium viscosissimum 12.7a 17.9a 11.3a
old man's whiskers* Geum triflorum 4.2b 11.8a 2.3b
white hawkweed Hieracium albiflorum 2.7a 3.7a 1.9a
pinewoods sweetpea Lathyrus bijugatus 13.9a 11a 12a
nineleaf biscuitroot Lomatium triternatum 4.5a 3.6a 3.6a
lupine Lupinus spp. 1.4a 6.9a 5.4a
sweetcicely Osmorhiza berteroi 2.7a 5.6a 4.8a
beardtongue Penstemon spp. 6.2a 3.3a 1.2a
sticky cinquefoil Potentilla glandulosa 5.6a 5.1a 0.6a
slender cinquefoil* Potentilla gracilis 20.2c 31.6a 10.2b
western bracken fern Pteridium aquilinum 6.5a 8.9a 8.7a
Canada goldenrod Solidago canadensis 3.2a 6.2a 0.9a
starwort Stellaria spp. 4.4a 5.9a 11.7a
common dandelion Taraxacum officinale 3.6a 3.3a 4.3a
twin clover Trifolium latifolium 25.5a 18.4a 20.1a
American vetch* Vicia americana 1.2b 11.1a 2.1b
Annuals
Japanese brome Bromus japonicus 3.6a 1.6a 2.6a
maiden blue-eyed Mary* Collinsia parviflora 3b 2.3b 11.5a
tiny trumpet* Collomia linearis 6.8b 11.3b 22.9a
tall annual willowherb* Epilobium paniculatum 2.4b 5.9b 27.3a
sweet fennel Foeniculum vulgare 5a 7.8a 8.7a
prickly lettuce* Lactuca serriola 1.2b 2.7b 17.5a
*Species with a significant change in coverage between at least 2 treatments.

FIRE MANAGEMENT IMPLICATIONS:
Comparisons between unburned sites, low-intensity fires, and high-intensity fires in this ponderosa pine-dominated community indicate that a majority of the species coverages and frequencies are unchanged regardless of burn treatment. Also, a majority of species that were impacted by the fires showed increased coverage and/or frequency on low-intensity and/or high-intensity sites. The substantial decrease in graminoid coverage and small increase in forb coverage on high-intensity burned sites would likely affect native ungulate and livestock grazing management.

Understory recovery after low- and high-intensity fires in northern Idaho ponderosa pine forests: REFERENCES

1. Armour, Charles D.; Bunting, Stephen C.; Neuenschwander, Leon F. 1984. Fire intensity effects on the understory in ponderosa pine forests. Journal of Range Management. 37(1): 44-48. [6618]
2. Armour, Charles D.; Bunting, Stephen C.; Neuenschwander, Leon F. [n.d.]. The effect of fire intensity on understory vegetational development. Unpublished report on file with: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory, Missoula, MT. 17 p. [30855]
3. Bakken, Stephen. 1981. Predictions of fire behavior, fuel reduction, and tree damage from understory prescribed burning in the Douglas-fir/ninebark habitat type of northern Idaho. Moscow, ID: University of Idaho. 137 p. Thesis. [43780]
4. Eyre, F. H., ed. 1980. Forest cover types of the United States and Canada. Washington, DC: Society of American Foresters. 148 p. [905]
5. Garrison, George A.; Bjugstad, Ardell J.; Duncan, Don A.; Lewis, Mont E.; Smith, Dixie R. 1977. Vegetation and environmental features of forest and range ecosystems. Agric. Handb. 475. Washington, DC: U.S. Department of Agriculture, Forest Service. 68 p. [998]
6. Kuchler, A. W. 1964. United States [Potential natural vegetation of the conterminous United States]. Special Publication No. 36. New York: American Geographical Society. 1:3,168,000; colored. [3455]

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