Research Project Summary: Early postfire response of Georgian Table Mountain pine stands burned under prescription at varying intensities



RESEARCH PROJECT SUMMARY CITATION:
Reeves, Sonja L., compiler. 2007. Research Project Summary: Early postfire response of Georgian Table Mountain pine stands burned under prescription at varying intensities. 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:

Waldrop, T. A.; Mohr, H. H.; Brose, P. H. 2006. Early dynamics of table mountain pine stands following stand-replacement prescribed fires of varying intensity. In: K. F. Connor. Proceedings of the 13th Biennial Southern Silvicultural Research Conference; February 28-March 4, 2005, Memphis, TN. General Technical Report SRS-92. USDA Forest Service, Southern Research Station, Asheville, NC: 471-474 [5].

Waldrop, Thomas A.; Brose, Patrick H. 1999. A comparison of fire intensity levels for stand replacement of table mountain pine (Pinus pungens Lamb.). Forest Ecology and Management. 113: 155-166 [4].

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 related FEIS species reviews, see the Appendix.

STUDY LOCATION:
Study sites were located in the War Woman Wildlife Management Area of the Tallulah Ranger District of the Chattahoochee National Forest, Georgia.

SITE DESCRIPTION:
Study areas occur on sharp ridgetops and steep slopes with northeastern or southwestern aspects. Soils are moderately deep, somewhat excessively drained, and are very strongly acidic to strongly acidic. The elevations of the 3 study sites were 885 m, 915 m, and 1,100 m.

PREFIRE PLANT COMMUNITY:
Prior to burning, mean basal area of overstory trees in the study stands was 30.3 m/ha. Hardwoods made up 21.3 m of this total, and pines (almost all were Table Mountain pine) the remaining 8.9 m/ha. Chestnut oak, with 9.2 m/ha basal area, was the predominant hardwood. Few overstory trees were more than 41 cm DBH and only 2 were over 15 m tall. The shrub layer consisted almost entirely of mountain-laurel, ranging in density from "very thick" to completely absent.

Study sites occur in the following plant communities and probably historically experienced one of the fire regimes 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, local data, and/or expert opinion 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)
Table Mountain-pitch pine Replacement 5% 100
Mixed 3% 160
Surface or low 92% 5
Appalachian oak forest (dry-mesic) Replacement 6% 220
Mixed 15% 90
Surface or low 79% 17
*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.
Surface or low=Any fire that causes less than 25% upper layer replacement and/or removal in a vegetation-fuel class but burns 5% or more of the area [1,2].

PLANT PHENOLOGY:
Phenology of the vegetation before the spring burn was not described.

FIRE SEASON/INTENSITY CLASSIFICATION:
Spring/low, medium, and high intensity.

FIRE DESCRIPTION:
Prescribed burning was conducted on April 4, 1997. The burn unit was fired by helicopter using a plastic sphere dispenser beginning at 1030 hours. Relative humidity was 51% at the time the fire started, dropped to a low of 27% at 1220 hours, and increased to 32% at 1600 hours. Temperatures ranged from 15 C at 0830 hours to 21 C at 1345 hours. Eye-level wind speeds ranged from 3 to 13 km/h from the south and southwest. Moisture content was 8% for the duff and 6% for the litter layer at the time the fire started. Fire intensity was generally high, with crowning in portions of the upper ridges and torching occurring intermittently along the ridge. Other areas burned with high-intensity flames, but crowning was not observed.

Three months after burning, the entire burn unit was surveyed to study the range of fire intensities. Fire intensities were classified as low, medium-low, medium-high, and high and distinguished by mean bark char height, height of tallest tree killed, and bark char height as a percentage of total tree height. Higher percentage of prefire mountain-laurel (a ladder fuel) cover led to higher intensity fires (see table below).

Mean values of discriminating variables by fire intensity category
Fire intensity Mean bark char height (m) Height of largest dead tree (m) Bark char as a percent of tree height Prefire percent cover of mountain-laurel
Low 1.8 10.1 14.3 26.2
Medium-low 2.0 14.9 18.8 29.6
Medium-high 6.6 16.4 44.3 41.1
High 12.2 14.9 87.0 85.9

FIRE EFFECTS ON PLANT COMMUNITY:
Postfire effects reported were surveyed on 60 plots following the 1st (1997) and 6th (2002) growing seasons.

All areas burned at sufficient temperatures to open serotinous cones. Pine and hardwood basal area decreased after burning at all fire intensities, moreso on high- than low-intensity plots. Low-intensity fire had little effect on pine basal area but decreased hardwood basal area by nearly 25%.

Basal area (m/ha) of pines and hardwoods before and after the first postfire growing season

Fire intensity

Pine basal area Hardwood basal area
Before burning After burning Before burning After burning
Low 6.2a* 5.9b 22.1a 16.8b
Medium-low 10.9a 6.0b 23.6a 5.1a
Medium-high 7.9a 1.1a 15.5a 0.5a
High 6.6a 0.0a 20.4a 1.0a
*Means followed by the same letter within a column are not statistically different at the 0.05 level

Overstory mortality increased for several years after burning, even in areas burned at low intensities. By the end of the 6th growing season, basal area of all surviving trees ranged from 0 m/ha in the high-intensity plots to 0.5 m/ha in the low-intensity plots.

Postfire pine seedling density ranged from 1,396 to 9,130 stems/acre. Unexpectedly, the lowest pine seedling densities were in plots burned at the highest intensity levels, possibly because high-intensity fire consumed cones or killed the seeds. The table below provides regeneration data for Table Mountain pine and pitch pine.

Regeneration (seedlings/acre) of pines by fire intensity level, after the 1st and 6th growing seasons
Year Fire intensity Table Mountain pine Pitch pine
1997 Low 5,608 0
1997 Medium-low 9,130 0
1997 Medium-high 3,650 0
1997 High 1,396 0
 
2002 Low 2,640 3,116
2002 Medium-low 4,533 2,258
2002 Medium-high 2,578 2,702
2002 High 2,486 2,194

Competition from hardwoods and shrubs that sprouted after fire may inhibit the development of a pine-dominated stand. There were no significant differences in the number of hardwood sprouts/acre by fire intensity category for any species after the first growing season. By 2002, mountain-laurel sprouts were exceptionally dense in plots burned at medium-high and high intensities. Sprouts of all other species were dense but not significantly different in number among fire intensity levels. Competition did not seem to greatly impact pine survival, even though sprout densities were high. Regeneration of hardwoods and shrubs is described in the table below.

Regeneration (sprouts/acre) of predominant hardwood and shrub species by fire intensity level, after the 1st and 6th growing seasons
Year Fire intensity Black tupelo Oaks* Sassafras Other hardwoods Shrubs
1997 Low 6,473 1,894 192 1,076 378
1997 Medium-low 6,631 3,477 3,835 1,187 800
1997 Medium-high 6,155 2,477 759 1,375 3,030
1997 High 4,617 3,164 1,968 3,019 5,417
 
2002 Low 6,951 3,375 3,803 7,260 14,229
2002 Medium-low 6,626 4,619 1,671 7,058 12,724
2002 Medium-high 10,775 7,241 3,976 8,989 69,008
2002 High 9,063 11,853 6,902 8,569 81,033
*Includes chestnut oak and scarlet oak

Table Mountain pine survival can be hindered if the seedling roots cannot penetrate the duff left after fire. Duff depths varied significantly (P=0.05) among plots burned at different intensity levels, and there was no distinct relationship between duff depth and fire intensity. Height and rooting characteristics for Table Mountain pine seedlings are provided in the table below.

Height and rooting characteristics of Table Mountain pine seedlings by fire intensity category, after the 1st postfire growing season
Fire intensity Postfire forest floor depth (cm) Seedling height (cm) Total root length (cm) Length of root in soil (cm) Percentage of seedlings with roots in the soil
Low 5.3ab* 6.9a 9.4a 4.6a 71.1a
Medium-low 3.8a 8.6b 10.4a 6.4b 94.6b
Medium-high 7.6b 7.1a 10.2a 3.6a 63.0
High 6.6b 7.4a 9.7a 4.3a 56.1a
*Means followed by the same letter within a column are not significantly different at the 0.05 level

Pine regeneration and hardwood and shrub sprouts were measured following the 6th growing season after burning. Hardwood sprouts overtopped pines regardless of fire intensity level. Hardwoods were approximately 2.4 m tall, Table Mountain pines were 1.2 to 1.5 m tall, and pitch pines were 0.9 to 1.2 m tall. Table Mountain pine overtopped shrubs. Even though hardwoods overtop the pines, they are not expected to eliminate the pines completely, since pines are numerous and are continuing to receive overhead sunlight.

FIRE MANAGEMENT IMPLICATIONS:
This study provided valuable information on the types of fire needed to create conditions for successful regeneration of Table Mountain pine. In the first publication, overstory mortality was thought to occur only on plots where flames reached into the crowns of both hardwoods and pines. Fires of all intensities killed essentially all overstory trees, but mortality was not immediate and occurred over a 3- to 6-year period. Regardless of fire intensity, pine regeneration was abundant in all study plots after 6 years. Fires of all intensities resulted in heavy hardwood competition. Shrub density was very high, especially in areas where shrub density was high before burning. Pines remain overtopped by hardwoods, but are expected to survive and may eventually outgrow the hardwoods.

Observations made the 6th growing season after fire suggest that lower intensity fires, such as those with flame heights of 1.8 to 2.4 m, can be just as successful as the previously recommended medium-high flames at regenerating Table Mountain pine stands. These fires would be safer, easier to accomplish, and can be achieved during an even larger burning window than medium-high or high-intensity fires.


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 reviews for those species.

Appendix

Common name Scientific name
mountain-laurel Kalmia latifolia
black tupelo Nyssa sylvatica
Table Mountain pine Pinus pungens
chestnut oak Quercus prinus
scarlet oak Quercus coccinea
sassafras Sassafras albidum

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. 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 [66533]
4. Waldrop, Thomas A.; Brose, Patrick H. 1999. A comparison of fire intensity levels for stand replacement of Table Mountain pine (Pinus pungens Lamb.). Forest Ecology and Management. 113: 155-166. [29450]
5. Waldrop, Thomas A.; Mohr, Helen H.; Brose, Patrick H. 2006. Early dynamics of Table Mountain pine stands following stand-replacement prescribed fires of varying intensity. In: Conner, Kristina F., ed. Proceedings of the 13th biennial southern silvicultural research conference; 2005 February 28 - March 4; Memphis, TN. Gen. Tech. Rep. SRS-92. Asheville, NC: U.S. Department of Agriculture, Forest Service, Southern Research Station: 471-474. [66295]

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