Fire effects on nitrogen dynamics - University of Idaho...rate: mg N / kg dry soil * d Pool: N produced – N taken up soil N concentration: mg N / kg dry soil Ammonium (NH 4 +) The

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Fire effects on nitrogen dynamics

Kirsten Stephan

Glacier NPPhoto: K. Stephan

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1. N is critical nutrient in forests and streams(Vitousek and Howarth 1991, Grimm and Fisher 1986)

Why?

2. Fire has profound influence on N dynamics

Wildfire ↔ Prescribed burns

Why is the study of fire effects on N dynamics important?

2. Fire effects: Apparent paradox: net N loss versus increase in ‘available’ N

How do wildfires and prescribed burns compare in their effects on N cycling?

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Examples from Stephan et al.

Moscow

HallSouth Fork

Danskin Cr.

Canyon Cr.

ParksSixbit

Squaw Cr.

Wildfires: August 2003 (except Danskin Cr. 2002)

Spring Rx: April/May 2004

Elevation range: 1100- 2200 m

Overstory: Pseudotsuga menziesiiPinus ponderosa

Watershed size: 78 ha (min: 8, max: 512)

Streams: intermittent- small (1st order) perennial

Study areas

Some of the examples shown are from my own research (together with A. Koyama and K. Kavanagh).Data collected for N concentration (and isotopic) analyses in 2004, 2005 and 2006: mineral soil, plant foliage, stream water, aquatic moss.

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•Nitrogen cycleMicrobes as drivers of the N cycle

•Immediate fire effects: effects of combustion on N in VegetationForest floor Mineral soil

•Short term post-fire effects on N concentrations inSoil VegetationStreams

•Long term post-fire effects on ecosystem N cycling

Outline

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Litter

Organic NAmmonifi-cation by fungi & bacteria

Nitrification bynitrifying bacteria

Nitrogen in atmosphere (N2)

Denitrificationby denitrifying bacteria

N-Fixer

N-fixingsoil bacteria

Plants

Nitrate (NO3-)Ammonium (NH4

+)

Assimilation

LeachingLeaching

Litter, PON

N fixer:Cyanobacteria

Algae, moss, biofilm

Organic N

Ammonium (NH4+) Nitrate (NO3

-)

AIR

SOIL

WATER

Nitrogen is the only soil nutrient not generated by rock weathering.Therefore its main source is recycling from decomposing organic matter.Microbes play a key role in the decomposition of organic matter and therefore in N cycling. Nitrogen cycling within streams is as complex as on the land, but this is often ignored by terrestrial ecologists interested in the leaching of soil ammonium and nitrate.Generally, very little nitrogen is leached from the land. This changes with disturbance.

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Organic N


+)

Microbial immobilization of NMicrobial release of N

C source of high quality(glucose, starch, cellulose)

• fuels microbial growth → high N demand→ N retention & uptake of inorganic N

from soil ⇓

Very low NH4+/NO3

- concentration in soil

C source of low quality(lignins, polyphenol-protein)

• no net microbial population growth → low N demand → release of inorganic N from substrate

being decomposed⇓

Accumulation of NH4+ in soil

Ammonifiers=heterotrophs

Microbes as generators and sinks of inorganic N

N release or immobilization by heterotrophic microbes (e.g. ammonifiers): -depends on C:N ratio of substrate and microbial demand of N-Microbial demand depends on quality of C source, i.e. how much energy microbes gain by breaking C-C bonds- spatially and temporally variable in the soil

Nitrification can be autotrophic or heterotrophic.The conversion of ammonium into nitrate is autotrophic, i.e. C is not used as energy source, but instead ammonium is. Therefore, autotrophic nitrifiers release nitrate whenever substrate (ammonium) is present. Some of the ammonium will be retained for nitrifier population growth.Heterotrophic nitrification is also possible, that is the direct conversion of organic N to nitrate. This process is not depicted in the diagrams.

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Nitrogen pools versus fluxes

Organic N

Nitrate (NO3-)

Pools are big if inorganic N production >> N uptake

Pools are small if little N productionOR

high N production & high N uptake(Stark and Hart 1997)

Flux:•N production •N uptakerate: mg N / kg dry soil * d

Pool:N produced – N taken upsoil N concentration: mg N / kg dry soil

Ammonium (NH4+)

The distinction between N pools and fluxes is important.Pool sizes are easy to measure but their interpretation is limited because both production and uptake rates determine pool size.Rates are difficult to measure.

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Immediate fire effects

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+ O2 → CO2 + H2O + N2

alanineH2N-CH-COOH

|CH3

Oxidation of organic compounds during combustion:(glowing combustion ~650 °C, flaming combustion (wood) 1100 °C)

N loss is proportional to fuel consumption

Immediate fire effectsN loss from vegetation

•<2,000- >300,000 kg/ ha fuel consumed (grass-shrub-woody vegetation)• N loss: 11-1000 kg N/ ha (Raison et al 1985)

• ca. 5 kg N lost per 1000 kg fuel consumed (Fisher and Binkley 2000)• 50 cm (20’’) DBH Douglas-fir contains 2.3 kg N (above ground)

Example

During combustion organic matter is oxidized.Under complete oxidation, organic matter is converted mainly to carbon dioxide, water, and di-nitrogen gas.N and C contents in organic matter are within fairly constrained range, hence, N and C losses are proportional to fuel consumption.

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Immediate fire effectsN loss from forest floor and organic matter of mineral soil

Down Wood (1-1000 h fuels):~6300 kg/ha ⇒ 6.3 kg N/ ha

Litter: ~ 500 kg/ha ⇒ 5 kg N/ ha

Duff:~ 3400 kg/ha ⇒ 51 kg N/ ha

Mineral soil (0-10 cm): ~700,000 kg/ha ⇒ 1400 kg N/ ha

• Oxidation of organic compounds during combustion• Pyrolysis: chemical decomposition of organic materials by

heating in the absence of oxygen [R-NH2 → NH3 ↑ (ammonia)]• Vaporization (volatilization) during heating: change of phase

w/out chemical change [NO3- ↑ (80 °C), AA ↑ (200 °C), NH3 ↑ (-33 °C)]

Koyama & Stephan unpublished data

Litter Organic N

Example

There are other forms of N loss even without direct combustion of organic material.

In example: N content in fuel and mineral soil. N loss from forest floor is proportional to combustion.There is a large N store in mineral soil. N loss from organic matter in mineral soil is rare but has been found (1/3 lost: Grier 1975).

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Immediate fire effectsIncrease in soil N concentration

NH4+ formation by protonation (+ H+) of NH3 in mineral soil

(and deposition of NH4+ from litter (Covington & Sackett 1992))

Mineral soil T atsurface : > 700 °C2-3 cm: 200 °C 15-30 cm: normal

Nitrate (NO3-)

Ammonium (NH4+)

(From Kovacic et al. 1986 )

Time after fire (d)

No increase in NO3-

conc. because

•Not formed by heat

•vaporization of NO3-

(>80 °C)

Time after fire (d)

Increase in NH4+ conc.

is function of

•amount of organic matter present (N source)

•soil/ litter temperature (N conversion)

Ammonia (NH3) release by pyrolysis of organic matter (>100°C)

Example

Ammonium concentration in the soil increases immediately after the fire due to physicochemical process.

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Immediate fire effectsSoil microbes

• T > 127 °C sterilize the soil • Temperatures > 50-70 °C kill non-spore forming fungi, protozoa and some

bacteria

Nitrifiers: killed at 53-58 °C (thin walled cells)Ammonifiers: some have thick walls or spores, survive at 100 °C

Immediate soil ammonium pool increase is not microbially mediated but due to physicochemical breakdown of organic N

Examplesoil temperatures during fire Scrub: on surface 200 °C; 5 cm: 100 °C; 10 cm: 60 °CLongleaf pine: 3-6 mm depth: 52 °C, 2.5 cm: 40 °C (Raison 1979)

Because microbes are killed or substantially reduced in numbers the immediate increase in NH4+ is a purely physicochemical process (i.e. lack of microbial N breakdown (mineralization) to contribute to NH4

+ pool but also lack of microbial N uptake (immobilization) to diminish abundant NH4

+ pool).

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Canyon Cr. Fire, Lowman RDPhoto K. Stephan

Short-Term Post-Fire Effects

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Short term post-fire effects on soil

Increased ammonium and nitrate concentrations in the soil1 month - ~5 years

Nitrate (NO3-)

Ammonium (NH4+)

Litter

Organic N

Plants


+)

1. Reduced plant N uptake

2. Increase in microbial activity(due to change in moisture, temperature, pH)

3. Reduced microbial N uptake(due to C limitation)

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Ash

Three processes could explain short term post-fire increase soil N concentrations,proportional contribution of each process is not known yet.

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Short term post-fire increase in soil N 1. Reduced N uptake by plants

Hall Fire, Payette NF, Council IDPhoto K. Stephan

Plants


+)

It is quite plausible that soil N pools increase when plants don’t take up any N because they have been killed by the fire.

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Short term post-fire increase in soil N 2. Increase in microbial activity:

soil temperature and soil moisture

Soil temperature increases- Higher absorption of solar energy by dark surface

Soil moisture increases- Reduced interception and transpiration losses from removed vegetation

Soil temperature decreases- Higher heat loss due to lack of insulation

Soil moisture decreases- Higher soil temperature reduces water viscosity and allows percolation

through the soil profile- Higher evaporation from warm (unshaded, dark) soil surface- Hydrophobicity reduced infiltration

Microbial activity depends on external factors, such as soil moisture and temperature.Increase in amplitude of soil temperature and soil moisture variability:Temperature: higher during the day, colder at nightMoisture: higher in wet season (spring), lower in dry season (summer)

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Increased soil temperature & moisture→Increases microbial activity and activity of extracellular enzymes

Short term increase in post-fire soil N 2. Increases in microbial activity:

Soil temperature and soil moisture

Organic N


+)

Increased rates of decomposition of residual organic matter (ammonification)

Increased nitrification (NO3- -production)

due to ample (NH4+) substrate supply

Increased microbial activity and activity of extracellular enzymes due to -higher diffusion rates, -lower cell plasma viscosity, -presence of water as diffusion medium and reactantas a consequence of higher soil temperature and moisture.

Short term increase in post-fire soil N due to microbial activity only possible if microbial numbers recover post-fire: Recovery of ammonifiers is quick (1 wk), often surpassing pre-burn numbers (for limited time)Recovery of nitrifiers is more gradual (weeks-months), depending on heat intensity, soil moisture and inoculation opportunity

Change in microbial community composition?

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pH increases after fire• due to consumption of H+ and • concurrent release of base cations (K+, Mg+, etc.)

during combustion of organic compounds

Example:pH in central Idaho Rocky Mountain soils:Unburned soils: ~6 ↔ Burned soils: ~6.7(Koyama & Stephan unpublished data)

higher pH raises solubility of organic N

nitrification occurs at pH>5Nitrate (NO3-)Ammonium (NH4

+)

Organic N

Short term increase in post-fire soil N 2. Increases in microbial activity:

pH

Low pH response to fire: strongly buffered soils at pH >6.5 or <4.5Strongest pH response to fire: soils with pH between 4.5 and 6.5

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Short term increase in post-fire soil N Role of ash as organic N source

• Contains between 0.15-1.88 % N depending on - fuel type (wood vs. foliage)- ash type (grey: more mineral, black: more OM remains due toinhibited combustion)

[e.g. grey wood ash : 0.15 % N, 3.5 % P, 1.2 % K, 24 % Ca, 2.5 % Mg](Raison et al. 1985)

• N form in ash: 0.1 % NO3-, 2.2 % NH4

+, 97.7 % organic N (Grogan et al. 2000)

Litter

Organic N


+)

Ash Examples: N input by ashcited in Grogan et al. 2000-89 kg N/ ha California bishop pine forest-66 kg N/ ha South African coastal shrub fynbosh-21 kg N/ ha California chaparral-23 kg N/ ha Washington conifer stand

Ash does not only alter microbial activity via increased pH but it also contains significant amounts of N itself.Which aspect of ash is most important?: influence on pH (which affects nitrifier activity and solubility of soil organic N) or direct source of decomposable organic N?Presence of ash had substantial influence on aboveground biomass of regenerating vegetation: aboveground biomass after the first growing season post-fire in a bishop pine forest in CA was 3 time higher in plots with ash than in plots with ash removed.

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Ash contributes to landscape scale heterogeneity

Ash redistribution post-fire by wind and water⇒ major factor in heterogeneity of soil N availability

and hence to vegetation patchiness in fire-prone ecosystemsGrogan et al. 2000

Danskin Cr., Boise NF Photos A. Koyama

Surface ash is rapidly displaced by wind and rain and tends to accumulate in local hollows, on leeward side of stumps/fallen trees, and downslope in ravines.

The photo shows how ash is blown around about a month after the fire (and before the onset of rain).

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After fire: • easily decomposable C pool

(e.g. root exudates, fine roots) is depleted quickly

+ no ready C replenishment, i.e. no new litter input yet!

• Decomposition of low quality C-source→ microbial growth slows → low internal N demand → release of NH4

+

→ accumulates in soil

Short term increase in post-fire soil N 3. Reduced microbial uptake of N

Litter

Organic N

Plants


+)

Microbial activity also depends on the availability of quality decomposable substrate.Low substrate quality results in low N demand for microbial population growth and thus a net release of NH4+ from decomposing substrate. This will be measurable as increased N pool sizes.

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Example: Short term effect on NH4+ concentration in soil

Wildfires

Spring Burns

Fire

Burn

Stephan et al. unpubl. data

0

20

40

60

80

100

120

J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A

mg

NH

4+ -N k

g-1 d

ry s

oil Burned

Unburned

0

20

40

60

80

100

120


mg

NH

4+ -N k

g-1 d

ry s

oil

BurnedUnburned

2003 2004 2005 2006

***

*

no data

Arrow: denotes time of fireAsterisk (*) denoted statistically significant difference between burned and unburned fire sites

Ammonium concentrations: •Wildfire: increased for 1st post-fire season •Prescribed burn (spring): increased for 1 month post-fire

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Example: Short term effect on NO3- concentration in soil

Wildfires

Spring Burns

-5

0

5

10

15

20

25


mg

NO

3- -N

kg-

1 dr

y so

il BurnedUnburned

-5

0

5

10

15

20

25


mg

NO

3- -N k

g-1 d

ry s

oil Burned

Unburned

*** * * * *

** * * *

no data

(*** )

2003 2004 2005 2006

Severe RX


Arrow: denotes time of fireAsterisk (*) denoted statistically significant difference between burned and unburned fire sites

Nitrate concentrations:•Wildfire: increased at 2-3(+?) years•Prescribed burn: increased 1 season (low intensity spring burns), 2(+?) y (when including one intense spring burn)

Literature: Choromanska & DeLuca 2001: increase 1 y with spring prescribed burn in MT (1 site only, i.e. pseudoreplication)

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0

0.5

1

1.5

2

2.5

3

Carex geyeri Physocarpusmalvaceus

Symphoricarposalbus

Spiraeabetulifolia

Folia

r N c

onc.

(%) p

er D

w

Unburned Burned

Example: Short term post-fire effects on N in vegetation

Increase of N concentrations in foliage of surviving or resprouting plants

Wildfire: 2 (+?) y ↔ Rx: 1 y

Squaw Cr. 2004 2005

* * * *


Quick understory recovery post fireGraph: N concentrations in understory foliage 1 y post fire (wildfire only)Species on x-axis: Carex geyeri (elk sedge), Physocarpus malvaceus (ninebark), Symphoricarpus albus (snowberry), Spiraea betulifolia (spiraea)

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Fire effects on stream N

Streamwater inorganic N concentrations increase


+)

LeachingLeaching

Litter, PON Algae, moss, biofilm

Organic N


-)

Generally, streamwater inorganic N concentrations increase short term post-fire-mainly assumed to be a result of leaching from hillside-studies of fire effects on aquatic N cycling lacking

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Effect Immediate Short term

Ammonium 60-fold increase 3-20 fold increase 1st spring run offNH4

+ (dissolved NH3 of smoke)

Nitrate no change increase 1- 3 spring run offsNO3

-

Fire effects on streamwater inorganic N concentrations

(Hauer and Spencer 1998, Flathead NF & Glacier NP)

Long term

? decrease in N concentrations below pre-burn leveldue to sequestration into growing forest

(Minshall 1989)

Nitrate (NO3-)

Ammonium (NH4+)

Increase in streamwater N concentrations is most noticeable in small streams because of the tight linkage to the uplands in small watersheds.

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0

200

400

600

800

1000

1200

1400

J ASONDJ FMAMJ J ASONDJ FMAMJ JASONDJ FMAMJ J AS

2003 2004 2005 2006μ

g N

O3- -N

l-1

BurnedUnburned

Spring Burns

0

200

400

600

800

1000

1200

1400

J ASONDJ F MAMJ J ASONDJ FMAMJ J ASONDJ FMAMJ J AS

2003 2004 2005 2006

μg

NO

3- -N l-1

BurnedUnburned

*** ***** ****

Example: Short term effects on streamwater N

Wildfires

?

Nitrate (NO3-)


Short term post- fire streamwater ammonium (NH4+) concentrations were not

altered by fire: ~ 15 microgram N/ l

Strong effect of wildfire on streamwater nitrate concentrations but none with spring prescribed burns.Dashed line in wildfire graph: spring run-off missed in 2004, peak concentrations therefore unknown.

Maximum allowed nitrate concentration in drinking water is 1000 microgram N/ l.

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Example: Short term post-fire effects on N in moss

0

0.5

1

1.5

2

2.5

3

3.5

4

2004 2005 2006

Mos

s %

N in

AFD

M

Unburned BurnedP = 0.04 P = 0.01 P = 0.08

Litter, PON

Organic N


-)

Algae, moss, biofilm


Graph in slide is for 4 wildfires only With wildfires moss N concentrations are increased. Rx had no influence on N concentration in moss (no effect on streamwater in the first place).

Moss is not “aquatic” in the strict sense, it grows on rocks that are submerged in the spring.

Moss as bioindicators? Studies in France and Germany that moss are used as monitors for heavy metal mobilization in acidified streams.

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Long-Term Post-Fire Effects

Clear Cr., Lowman RDPhoto K. Stephan

Summary short term:Increased N pools in soil and waterand increased N concentrations in terrestrial vegetation and in-stream moss-> increased uptake by autotrophs is an important N retention mechanism

Long term post-fire fire effects are little studied.

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Long term post-fire effects on ecosystem

Example (Grier 1975)

907 kg N/ ha lost (forest floor + mineral soil) during severe wildfire in WA

Ecosystem N inputs/ outputs

+ Atmospheric N deposition rate of 1.5 kg/ha/y

+ N2-fixation- N-fixing soil bacteria: <0.1-1.4 kg/ha/y- Symbiotic N fixation of legumes: 1 kg/ha/y (low legume density)

5-10 kg/ha/y (high legume densityalder: 50-150 kg/ha/y

ceanothus: 0-110 kg/ha/ylichens: 3.5 kg/ha/y

- N leaching losses 0.6 kg/ha/y (Vanderbilt et al. 2003)

Example (Giessen et al. in prep.)Douglas-fir forest of western Cascades: 200 y till combusted N is replaced

Eventually the N lost through combustion will be restored, through N fixation and deposition- if fire interval is long enough.

“Fire exclusion has been shown to reduce the number of N-fixers (Newland andDeLuca, 2000) and it is likely that historic timber harvest further reduced total soil N reserves.” from MacKenzie et al. 2006

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time since fire

Immediate & short term effects fire return

interval

Fires occur at natural fire interval Fire suppressed

But what happens to the N cycling processes within the soil/plant system during the long term post-fire recovery of forest?Two scenarios: fires occur at natural fire return interval or fires suppressed

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MacKenzie et al. 2006: Chronosequence in western Montana

Long term post-fire effects on soil

Microbial numbers constantbut decrease in microbial activity

Phenolic compounds- secondary metabolites of plants- byproduct of microbial decomposition of lignin

⇓•Allelopathic interference with microbes•N uptake by microbes for breakdown of phenols as C source

•phenolic sorption of N

Decrease in N production rate and pool size

Y- axis: N adsorbed to ion exchange resins placed in the soil; this represents a mix of N production rate and pool size

Decrease in microbial activity has been inferred from slower decomposition of experimentally placed cotton strips (cellulose) and tongue depressors (lignin+ cellulose)

Lower microbial activity due to phenols?It is possible that N availability is modified by soil organic matter quality which is mediated by plant community composition: low soil N availability leads to plants with low quality litter (higher contents of secondary plant metabolites, low N content) which in turn leads to slow decomposition and low soil N

Decrease in N production rate/ pool size not linear and differs for ammonium and nitrate. Why?Ammonium decrease: plant uptake & initially sustained high nitrate productionNitrate decrease: sigmoidal curve with inflection point at 40-70 y. Role of Charcoal !?!

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DeLuca et al. 2006

Long term post-fire effects on soil

Charcoal increases soil nitrate concentration

Charcoal stimulates microbial nitrate production

Charcoal also has potential to absorb phenols

Mechanism not clear

Role of charcoal in soil nitrate concentrations-Adding charcoal to soil (89 y since last fire) almost doubled nitrate concentration in a 14 d incubation experiment-Adding a phenol-rich extract of kinnikinnick (Arctostaphylos uva-ursi) resulted in low nitrate concentrations-Adding extract and charcoal could offset the effect of the extract.Charcoal loses its absorptive capabilities after ca 100 y (Zackrisson et al., Oikos1996)

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time since fire

fire returninterval

Immediate & short term effects

Fires occur at natural fire interval Fire suppressedN availability mediated by plant community/ succession

N availability mediated by fire

MacKenzie et al. (2006): Steep decline in soil nitrate concentrations coincides with fire return interval of 50 y at the study site.Disturbance maintains high nitrate availability during the historic fire return interval; potentially mediated by charcoal.Fire suppression: charcoal loses ‘activity’, processes associated with late successional stage (e.g. accumulation of phenols in soil) determine (slow) N cycling rates and (low) productivity.

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Summary

• N dynamics are very complex

• Ultimate goal: understand mechanisms at all temporal and spatial scales – Predictions of fire effects on ecosystem N cycling– Informed management decisions

• Fire alters many aspects of N dynamics

–Immediate, short term, long term–Local, watershed ecosystem–Consequences vs. mechanisms

Fire alters many aspects of N dynamics: not all equally well studied-Short term & local post-fire effects fairly well studied for terrestrial part of the ecosystem:

-Net ecosystem N loss but immediate / short term increase in inorganic (plant-available) N in soi

-Post-fire soil N is retained in regenerating vegetation and leaches to streams-Despite in-stream retention of N still export from watershed

-Mechanisms that lead to observed effects are less well studiede.g. microbial processes no well studied, because methods are time intensive and

involved, large spatial heterogeneity in soil in general); instead, net effects are studied (e.g. soil and streamwater N concentrations) that have limited -long term effects little studied so far-lack of integrating land and water

Management decisions: evaluate ecological trade-offs between: suppression, rehabilitation, wildland fire use, prescribed burning

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“The focus of the Healthy Forest Initiative in the US has been on fuel loading and not on N cycling and microbial activity, both of which are equally important components of secondary succession and healthy forests.”

MacKenzie et al. 2006

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ReferencesChoromanska, U. and T. H. DeLuca (2001). “Prescribed fire alters the impact of wildfire on soil biochemical properties in a ponderosa

pine forest.” Soil Science Society of America Journal 65: 232-238.Covington, W. W. and S. S. Sackett (1992). “Soil mineral nitrogen changes following prescribed burning in ponderosa pine.” Forest

Ecology and Management 54: 175-191.DeLuca, T. H. and K. L. Zouhar (2000). “Effects of selection harvest and prescribed fire on the soil nitrogen status of ponderosa pine

forests.” Forest Ecology and Management 138: 263-271.DeLuca, T. H., M. D. MacKenzie, M. J. Gundale, and W. E. Holben. 2006. Wildfire-produced charcoal directly influences nitrogen cycling

in ponderosa pine forests. Soil Science Society of America Journal 70: 448-453.Fisher, R. F. and D. Binkley (2000). Ecology and management of forest soils. New York, Wiley.Grimm, N. B. and S. G. Fisher (1986). “Nitrogen limitation in a Sonoran Desert stream.” Journal of the North American Benthological

Society 5(1): 2-15.Grogan, P., T. D. Bruns, et al. (2000). “Fire effects on ecosystem nitrogen cycling in a Californian bishop pine forest.” Oecologia 122:

537-544.Hauer, F. R. and C. N. Spencer (1998). “Phosphorous and nitrogen dynamics in streams associated with wildfire: a study of

intermediate and longterm effects.” International Journal of Wildland Fire 8(4): 183-198.Kovacic, D. A., D. M. Swift, et al. (1986). “Immediate effects of prescribed burning on mineral soil nitrogen in ponderosa pine of New

Mexico.” Soil Science 141(1): 71-75. DeLuca, T. H., M. D. MacKenzie, M. J. Gundale, and W. E. Holben. 2006. Wildfire-produced charcoal directly influences nitrogen cycling in ponderosa pine forests. Soil Science Society of America Journal 70: 448-453.

MacKenzie, M. D., T. H. DeLuca, and A. Sala. 2006. Fire exclusion and nitrogen mineralization in low elevation forests of western Montana. Soil Biology & Biochemistry 38: 952-961.

Minshall, G. W., J. T. Brock, et al. (1989). “Wildfires and Yellowstone's stream ecosystems.” BioScience 39(10): 707-715.Pardo, L. H., H. F. Hemond, J. P. Montoya, T. J. Fahey, and T. G. Siccama. 2002. Response of the natural abundance of 15N in forest

soils and foliage to high nitrate loss following clear-cutting. Canadian Journal of Forest Resources 32: 1126-1136.Raison, R. J. (1979). “Modification of the soil environment by vegetation fires, with particular reference to nitrogen transformations: a

review.” Plant Soil 51: 73-108.Raison, R. J., P. K. Khana, et al. (1985). “Mechanisms of element transfer to the atmosphere during vegetation fires.” Canadian Journal

of Forest Research 15: 132-140.Stark, J. M., and S. C. Hart. 1997. High rates of nitrification and nitrate turnover in undisturbed coniferous forests. Nature 385: 61-64.Vitousek, P. M. and R. W. Howarth (1991). “Nitrogen limitation on land and in the sea: how can it occur?” Biogeochemistry 13(87-115).Wright, R. J. and S. C. Hart (1997). “Nitrogen and phosphorous status ina ponderosa pine forest after 20 years of interval burning.”

Ecoscience 4(4): 526-533.

Documents

Fire effects on nitrogen dynamics - University of Idaho...rate: mg N / kg dry soil * d Pool: N produced – N taken up soil N concentration: mg N / kg dry soil Ammonium (NH 4 +) The