• CASE NAME
• REFERENCE(S)
• FIRE CASE STUDY AUTHORSHIP
• SEASON/SEVERITY CLASSIFICATION
• STUDY LOCATION
• PREFIRE VEGETATIVE COMMUNITY
• TARGET SPECIES PHENOLOGICAL STATE
• SITE DESCRIPTION
• FIRE DESCRIPTION
• FIRE EFFECTS ON TARGET SPECIES
• FIRE MANAGEMENT IMPLICATIONS

CASE NAME:

REFERENCE(S):
Harrington, Michael G. 1982 [221]
Harrington, Michael G. 1985 [94]

FIRE CASE STUDY AUTHORSHIP:
Tirmenstein, D. (1988, February).

SEASON/SEVERITY CLASSIFICATION:
Fall 1977/fire severities not reported
Spring 1978
Summer 1978
Fall 1979
Spring 1980
Summer 1980

STUDY LOCATION:
The study was conducted on 2.5-acre (1 ha) plots within the San Juan National Forest in southwestern Colorado.

PREFIRE VEGETATIVE COMMUNITY:
The study site consisted of a multiple-aged Rocky Mountain ponderosa pine overstory averaging 300 trees and 124 square feet (11.5 m²) basal area per acre. There was a dense Gambel oak (Quercus gambelii) understory. Herbaceous and other shrubby understory vegetation was sparse.  The majority of Rocky Mountain ponderosa pine (75%) occurred as trees in the 4- to 11-inch (10-28 cm) d.b.h. class. In forest openings, Gambel oak reached heights of 15 feet (4.8 m) with 4-inch (10 cm) basal diameters. The majority of Gambel oak was less than 4 feet (1.2 m) tall and 2 inches (5 cm) in basal diameter.

TARGET SPECIES PHENOLOGICAL STATE:

Spring	Summer	Fall
full leaf stage	2nd growth period	dormant, near peak root carbohydrate levels

SITE DESCRIPTION:
Burned areas were located on a south aspect with less than 5% slope at 7,600 feet (2,316 m). Average annual precipitation in Mancos, Colorado, 5 miles southwest of the study site is 17 inches (430 mm), with the least amount of precipitation occurring in June and the greatest amount in August. Fire has not occurred since 1877. Before 1877 fire intervals were 1 to 16 years with an average of 6 years.  

FIRE DESCRIPTION:
Initial burn:

	Fall	Spring	Summer
Temperature (°F)	56-63	65-79	72-77
Humidity (%)	32-41	14-41	21-37
Wind speed (mph)	2-5	1-6	1-5
Moisture (%)
Litter layer	7.2	5.4	6.0
Fermentation layer	11.8	6.9	7.5
Humus layer	18.9	11.5	9.2
Spread rate (ft/min)	6	8	5
Flame length (ft)	3.0	3.5	3.5

2nd burn:

	Fall	Spring	Summer
Temperature (°F)	48-53	77-83	68-72
Humidity (%)	25-30	19-24	20-27
Wind speed (mph)	1-3	2-7	2-6
Moisture (%)
Litter layer	13.1	3.6	4.5
Fermentation layer	---	---	---
Humus layer	26.2	5.8	9.2
Spread rate (ft/min)	3	10	6
Flame length (ft)	1.0	3.5	3.0

Fuels were dry during the 2nd spring burn, resulting in rapid-fire spread that consumed 35% of the forest floor fuels. Nearly all the new litter was consumed, along with 10% of the residual fuels. The summer burn consumed 17% of the forest floor, 70% of which was new litter.  

FIRE EFFECTS ON TARGET SPECIES:
Single-burn treatments resulted in 100 to 150% increases in Gambel oak density and a 10 to 40% increase in frequency. Cover of Gambel oak was only reduced temporarily. Reductions 1 year after the initial burns were as follows:

Oak d.b.h (in)	Reduction (%)	Reduction numbers (stems/200 ft2)
1/4-1	80	2.6-13.7
1-2	70	0.7-2.2
> 2	50	0.4-0.8

Overall cover of Gambel oak was reduced 20 to 35% 1 year after the initial burn. Cover of fall and spring burn plots equaled those of control plots 2 years after the burn.

Consecutive fall and spring burns resulted in slight increases in Gambel oak sprouts with successive summer burns reducing Gambel oak density by 20%, frequency by 16%, and cover by 12%. Gambel oak frequencies after the twice-burn spring and fall treatments increased 10% by postfire year 4. Cover of the twice-burned plats was reduced, particularly on the summer treatment. However, all treatments had slight Gambel oak cover increases by postfire year 4.

FIRE MANAGEMENT IMPLICATIONS:
Single burns in any season are unlikely to remove Gambel oak from ponderosa pine understories. However, results of this study suggest consecutive summer burns reduce Gambel oak populations. Gambel oak burned during the summer regrowth period, when carbohydrate levels are reduced, is unable to sprout and accumulate carbohydrates before fall dormancy. Successive burns in this period can place additional stress on Gambel oak. Spring burns generally allow good recovery prior to dormancy. Similarly, fall burns after carbohydrate reserves are accumulated have little effect on Gambel oak.

The deep-rooted Gambel oak can compete effectively with ponderosa pine for available water and nutrients. When Gambel oak sprouts prolifically after fire or other disturbance, it is capable of inhibiting ponderosa pine regeneration. Consecutive burns in ponderosa pine-Gambel oak stands could, in time, favor the growth and regeneration of pine.

Related categories for SPECIES: Quercus gambelii | Gambel Oak