Prescribed 

Burning as a

Restoration Tool

Robert R. Blank, Soil Scientist

USDA, Agricultural Research Service

Background

As fire ecology research matures,

interactions among fire, smoke,

seeds, plant growth, and soil have

been revealed to be exceedingly

complex, often perplexing. A sampling of recent research emphasizes

this complexity. Germination of

Nicotiana attenuata after wildfire is

controlled by both smoke-derived

cues (+) and destruction of inhibitory

signals in unburned litter (-) (Preston and Baldwin, 1999). Firenutrient interactions influence

quality and quantity of browse

(Rundel P W, et. al, 1980). Charcoal from forest fires reduces phytotoxic compounds; effect may last

100 years (Zackrisson, et al, 1996).

Picogram amounts of unknown

compound in smoke separated by

gas chromatography stimulates germination of Nicotiana attenuate

(Baldwin et al., 1994). Oxides of

nitrogen in smog stimulate germination of particular chaparral

species. These compounds are also

found in smoke from burning vegetation. Smog may untimely cue

germination and alter species composition (Keeley and Fotheringham,

1997). Compared to the control,

seeds of several range grasses treated

with smoke from burning sagebrush

grew faster and had greater plant

mass (Blank and Young, 1998). 

Our research unit has been investigating the ecological consequence of

fire in sagebrush ecosystems, particularly interactions involving soil

chemistry, the soil seedbank, and

the effects of smoke on seeds.

Most recently, in cooperation with

Dr. Jeanne Chamber of the USDAForest Service, we have investigated

the utility of prescribed burning in

ecosystem restoration of degraded

riparian ecosystem of central Nevada. 

Fire Ecology and 

Interactions Important

in Restoration

Nutrient Release and

Enzyme Activities 

Human experience and research has

shown that fire fosters the release of

soil nutrients. The source of these

nutrients is from pyrolysis of soil

organic matter and organic debris

and alteration of the clay complex.

As a result, plant available N, Ca,

Mg, S, K, and many micronutrients

generally increase after a fire. Our

prescribed fire research in sagebrush

encroached riparian ecosystem of

central Nevada has confirmed past

studies. Pertinent to prescribed

burning in heterogeneous environments, such as sagebrush communities, is the effect of microsite on the

quantity of nutrients released as

shown in the following graphs. This

microsite effect is largely a combination of differential fire temperatures

(greater fuel load in sagebrush fosters higher temperatures for longer

periods of time) and pre-fire

microsite differences in quantity of

plant litter and soil organic matter

(sagebrush subcanopies are nutrient

islands).

Soil enzyme activities have become

important indicators of ecosystem

health for they are positively correlated to nutrient release from organic

matter. Recent research has shown

that fire greatly reduces enzyme

activity because enzymes, being

proteins, are denatured at temperatures greater than about 60C.

The prescribed burns in central

Nevada significantly reduced

enzyme activities of urease and

phosphatase as shown in the following graph. Surprisingly, enzyme activities decreased at depths of 10-20

cm where temperatures are not

appreciably affected by fire.

Germination Cues

In fire prone ecosystems, such as the

chaparral of coastal California, the

germination of many species is cued

synchronous to wildfires. Recent

research has shown that, for certain

seeds, this cueing is due to particular

chemical compound(s) in the smoke

and charred wood. The chemical(s)

cause an impermeable membrane in

the seed coat to become permeable

and signal the embryo to germinate.

We have experimented with the

effect of smoke and previously heated

soil on the germination of several

range grasses. Soil was heated in the

muffle furnace at various temperatures to mimic fire and various seeds

were planted in the soil. Many

species exhibited mildly elevated

germination as shown below.

Thurber’s needlegrass had far higher

germination when planted in previously heated soil, but almost no

germination when exposed to sagebrush smoke. We have not explored

the effect of smoke and heated soil

on any forb as of yet. The observation that particular forbs significantly

increase after wildfire in the sagebrush steppe suggests the possibility

of germination cueing.

Negative Cueing

Litter from particular species can

retard or prevent the germination of

many seeds. Sagebrush litter has

been shown to elicit this response

and thus has been tagged allelopathic.

Resent research, however, suggests

that in certain cases, allelopathy

may in fact be negative cueing.

Apparently certain seeds have

evolved a two-way fail-safe dormancy

system. In order to germinate both

NO. 56 DATE 11/02/01

Range

Fire
positive cueing (smoke) and

destruction of negative cues (some

unknown compound in shrub litter)

are required.

Sagebrush Smoke and 

Heated Soil Extract: Effect

of Plant Growth

We studied the influence of seeds

treated with either sagebrush smoke

or an aqueous extract of soil heated

to 350C on plant growth. Compared to the control, an aqueous

extract of heated soil did not have a

stimulatory effect on aboveground

or below ground mass. To our surprise, however, plants from seeds of

particular species exposed to sagebrush smoke, grew faster, grew

taller, and gained more total mass

than control plants as shown in the

following figures. We are not sure of

the mechanism. Perhaps smoke acts

as a microbiocide. Possibly smoke

attenuates certain enzyme systems

affecting plant growth. We have for

the last three years attempted to

duplicate these greenhouse results in

the field, but establishment trials

have failed either due to lack of

timely precipitation or below normal

spring temperatures.

Effect of Smoke Type

We are presently conducting experiments to test the effect of sagebrush

smoke and cheatgrass smoke on

seed germination and seedling

growth. These are preliminary

results, but the growth of Basin

Wildrye seems to be suppressed

when pre-exposed to cheatgrass

smoke as shown in the following

figure. Although somewhat premature, these experiments suggest that

there may be different seed/fire

interactions between sagebrush

dominated burns versus cheatgrass

dominated burns. If this is the case,

which ongoing experiments will clarify, it suggests that the ecological consequences of cheatgrass invasion will

be more pernicious and convoluted

than previously appreciated. 

Conclusion

Prescribed burning will elicit a host

of ecological interactions potentially

important in restoration, including

release from plant competition,

greater access to light and water,

nutrient enrichment, germination

cueing, destruction of germination

retardants, and effects of smoke on

plant growth. Seeds in the soil seedbank not exposed to lethal heat and

seeds sown after the fire will be

influenced by these interactions.

Restoration will be further influenced by timing of prescribed burn

and preburn conditions such as fuel

load and heterogeneity of fuel load,

species composition, soil water content and the nature of the soil seedbank and the time of the burn.

With such inexorable complexity

can predictions be made regarding

the potential success of restoration

following prescribed burning?

Small-scale experiments such as we

have undertaken in central Nevada

will greatly assist in the planning of

future large-scale restoration. 

Citations

Baldwin, Ian T.; Staszak_Kozinski,

Lynn; Davidson, Robert. 1994. Up

in Smoke: Smoke-derived germination cues for post-fire annual,. Nicotiana attenuata Torr Ex. Watson. J.

of Chem. Ecol. 20(9):2345-2371.

Blank, RR and Young, JA. 1998.

Heated substrate and smoke:

Influence on seed emergence and

plant growth J. Range Manage.

51:577-583.

Keeley, J. E.; Fotheringham, C. J.

1997. Trace gas emissions and

smoke induced seed germination.

Science, 276(5316):1248-1250.

Rundel, P W; Parsons, D J, 1980.

Nutrient Changes in 2 Chaparral

Shrubs along a fire induced age

gradient, Amer. J. Bot. 67 (1) pp.

51-58.

Preston, CS and Baldwin, IT. 1999.

Positive and negative signals regulate germination in the post-fire

annual, Nicotiana attenuata. Ecol.

80:481 494.

Zackrisson, O.; Nilsson, M._C.;

Wardle, D.A. 1996. Key ecological

function of charcoal from wildfire

in the Boreal forest. Oikos,

77(1):10-19.

Range

Resource Notes are intended to be early

announcements of technical and informational topics for

Bureau of Land Management personnel and some of their customers.

Information in this Resource Note is based on the opinion and

experience of the author and has not been peer-reviewed. Conclusions

and opinions expressed herein do not

necessarily represent those of BLM. Use of trade names does not

imply U.S. Government endorsement of commercial products.

If you have received a copy of or found out about Resource

Notes in an indirect way and would like to be included in future

mailings, please send the following:

NAME, TITLE, MAILING ADDRESS and a list of the two or three

subject areas that you are most interested in or that most directly

relate to your job. Send this information to Phil Dittberner, BLM,

RS-140, P.O. Box 25047, Denver, CO. 80225-0047 or

phil_dittberner@blm.gov or FAX 303-236-3508.

If you would like to prepare a Resource Note for

distribution, or you have an idea and author in mind for a good

Resource Note, please contact Phil Dittberner at

303-236-1833, FAX 303-236-3508 or phil_dittberner@blm.gov with

the topic and the name of writer, including an address, phone

number, and e-mail address.

Thank you for your interest in Resource NoteS.

www.blm.gov/nstc/resourcenotes/resnotes.html