Prescribed Burning

Prescribed Fire for Woody Plant Management

Prescribed fire is a historic land management tool dating back to the American Indians, who used it to promote green grass for buffalo. The practice controls encroachment of woody plants such as juniper and mesquite and improves soil health by creating plant diversity. A third benefit is the removal of dead plant growth which can fuel wildfires. Prescribed fire is very effective in managing seedling trees and shrubs. The smaller or more immature encroaching brush, the more successful the prescribed fire will be in suppressing or killing invasive trees and shrubs. Fire is effective at suppressing resprouting brush such as: redberry juniper and mesquite. However, prescribed fire will kill non re-sprouting brush like: Ashe juniper, Eastern red cedar, pricklypear, etc..

Figure 1. A small, immature redberry juniper seedling was suppressed due to a summer, growing-season prescribed fire. However, the larger trees in the background were left unaffected by the prescribed fire.

Figure 2. Eastern Redcedar seedling before (right) and following (left) prescribed fire.

Tree seedling size and age killed by prescribed fire

Tree Species

Top Killed by Low Intensity Fire

Top Killed by High Intensity Fire

Mechanical or Chemical Control Needed

Source

Ashe Juniper
<2ft tall
2-6ft tall
6+ ft tall
Dalrymple 1969
Blackjack Oak
<1.5in diameter at 4.5ft height (DBH)
1.5-3.5in diameter at 4.5ft height (DBH)
>3.5in diameter at 4.5ft height (DBH)
Johnson and Risser 1975
Easter Red Cedar
<4ft tall
4-8ft tall
8ft or taller
Owensby et al. 1973
Honey Mesquite
<6mo old
<1.5 to 3yr old
>3yr old
Wright et al. 1976
Live Oak
very small seedlings
<3in diameter at 4.5ft height (DBH)
>12in diameter at 4.5ft height (DBH)
Huffman and Blanchard 1991
Davison and Bratton 1988
Post Oak
<2.5in diameter at 4.5ft height (DBH)
2.5-6in diameter at 4.5ft height (DBH)
6+ in diameter at 4.5ft height (DBH)
Ferguson 1961
Redberry Juniper
<20in
<3ft
>3ft
Steuter and Carlton 1983

Invasive Resprouting Trees and Shrubs Commonly Found Throughout the Great Plains

  • Mesquite
  • Honey locust
  • Black locust
  • Redberry juniper
  • Sumac
  • Dogwood
  • Post Oak
  • Winged elm
  • Salt cedar
  • Huisache

Invasive Non-resprouting Trees and Shrubs Commonly Found Throughout the Great Plains

  • Ashe juniper
  • Eastern redcedar

Prescribed fire can control non-resprouting trees like Ashe juniper or Eastern redcedar that are 6-ft. tall or smaller under average burning conditions. The following are prescribed fire conditions that will be effective in managing non-sprouting trees and shrubs that are within the target height:

  1. Air temp: 60-80
  2. Relative humidity 30-50%
  3. Wind speed: 5-10mph
  4. Fine fuel load: 2000lbs+/acre

Source: Eastern Redcedar Control and Management – Best Management Practices to Restore Oklahoma’s Ecosystems (factsheet NREM 2876)

Figure 3. Relationships between shrub height class (m) and probability of mortality following extreme fire treatments in the Edwards Plateau of West-Central Texas.

Larger Tree Control

Larger trees and shrubs that are older, more mature, and typically taller than 6-ft can be managed with prescribed fire, but usually more than the initial fire treatment is required or intense fire effects.  Higher levels of mortality of adult resprouting plants have been observed for some species when exposed to high-intensity fires (Brad-stock & Myerscough 1988; Adie et al. 2011). Anthropogenic constraints on fire behavior may be masking the theoretical potential of fire as an agent of vegetation change (Twidwell et al. 2016a). Extreme fire is a technical term that has been used commonly in the US wildland fire community since the 1950s (Potter & Werth 2011) to describe atypical behavior in high intensity fires that lead to blow-ups, fire storms, fire whirls and other forms of erratic fire behavior. A single extreme fire in drought in the Edwards Plateau of Texas resulted in shrub densities that were 35 –55% lower than shrub densities in control treatments (not burned).  Densities of resprouters were lower 3-years after applying extreme fire because mortality of established individuals exceeded recruitment of new individuals for multiple brush species, whereas recruitment exceeded mortality in non-burned plots, despite drought conditions.  A single extreme fire in drought resulted in shrub densities that were 35 –55% lower than shrub densities in control treatments (not burned, no herbicide) also subject to drought conditions, and the magnitudes of change were remarkably consistent at both sites (Fig. 2). Densities of resprouters were lower 3 years after applying extreme fire because mortality of established individuals exceeded recruitment of new individuals for multiple species, whereas recruitment exceeded mortality in control plots, despite drought conditions.

The following are prescribed fire conditions that constitute extreme:

  1. Air temperature: 80 - 100+F
  2. Relative humidity: 10-20%
  3. Wind speed: 10-20mph
  4. Fine fuel load: 1500lbs+/acre

Figure 4. A mature Redberry juniper tree burns during a summer prescribed burn in the Edwards Plateau in West Central Texas.

Another option to achieve intense fire effects is to accumulate more fuel prior to burning. Consistent and heavy fine fuel loads will ensure appropriate amounts of consumption. Accumulated fuel loads will also increase the potential for fire to climb into ladder fuels that are adjacent to tree canopies. Achieving consumption and scorch height goals and objectives can be done in two ways. One option is to defer grazing before burning in order to accumulate increased fine fuel. The more arid the environment, the longer the deferment period in order to achieve appropriate fine fuel loads. Another option is to change livestock grazing patterns to accumulate more fuels in certain areas of the pasture. Patch burning can be an effective tool to achieve a heterogeneous landscape that optimizes plant species diversity.

Prescribed fire for livestock production

Prescribed fire in the spring helps plants start growth earlier and summer and fall prescribed fire helps plants continue growth later in the fall. This extends the season of palatable, high quality forage and reduces the amount of winter protein supplementation livestock producers need to feed.

Prescribed fire is an effective method to change animal grazing patterns in a pasture. Areas far from water and areas with moderate slopes are normally avoided by most cattle. When these areas are burned cattle can spend up to 70% of their time on the recently burned patches.