Leigh Hunt_Modelling above- and below-ground carbon dynamics of different fire regimes in extensive grazing systems in northern Australia
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Leigh Hunt_Modelling above- and below-ground carbon dynamics of different fire regimes in extensive grazing systems in northern Australia
- 1. Fire and carbon dynamics in grazed rangelands of northern Australia Leigh Hunt, Adam Liedloff and Robert Eager 20th February 2013 CSIRO SUSTAINABLE AGRICULTURE FLAGSHIP
- 2. What this talk is about Can land managers increase aboveground carbon stocks through improved fire management? Two approaches: • Experimental (field) studies • Modelling 2 | Fire and carbon | Hunt, Liedloff and Eager
- 3. Key questions vs. ? • Can a change in fire regime increase carbon stocks? • What fire regime can increase carbon stocks? • How much additional carbon can be stored in the landscape? • Is there likely to be an effect on livestock production? 3 | Fire and carbon | Hunt, Liedloff and Eager
- 4. Kidman Springs fire experiment Savanna grassland-open shrubland Open eucalypt savanna woodland on grey Vertosol soil on red Calcarosol soil Trees/Shrubs: Terminalia, Bauhinia Eucalyptus, Hakea, Carissa Perennial grasses: Heteropogon, Dichanthium Chrysopogon, Dichanthium + Enneapogon, Brachyachne Annual rainfall ≈ 680 mm; grazed at 5 cattle/sq. km 4 | Fire and carbon | Hunt, Liedloff and Eager
- 5. Experimental details 2.6 ha plots Three fire frequencies • every 2, 4 or 6 years (and no fire) Two times of fire • early or late dry season Two randomised blocks per vegetation type Determined biomass in • grass • litter May 2011 • coarse woody debris (twigs) (18 years) • heavy ground fuels (logs) • trees and shrub and converted to carbon 5 | Fire and carbon | Hunt, Liedloff and Eager
- 6. Aboveground carbon – open woodland 24 Fire freq P=0.01 Fire season P>0.05 No effect of fire season 20 Freq x season P=0.023 Variable effect of fire frequency 16 Exclosure = 16.2 t C/ha Carbon (t/ha) 12 Grass 8 Litter Coarse woody debris 4 Heavy ground fuels Shrub Tree 0 Early 2 Early 4 Early 6 Late 2 Late 4 Late 6 Not burnt Open Eucalypt woodland 6 | Fire and carbon | Hunt, Liedloff and Eager
- 7. Aboveground carbon – grassland/shrubland 24 Fire freq P>0.05 Fire season P>0.05 No effect of fire 20 Freq x season P>0.05 frequency or intensity on C stock 16 Exclosure = 5.0 t C/ha Carbon (t/ha) 12 Grass 8 Litter Coarse woody debris 4 Heavy ground fuels Shrub Tree 0 Early 2 Early 4 Early 6 Late 2 Late 4 Late 6 Not burnt Open grassland/shrubland 7 | Fire and carbon | Hunt, Liedloff and Eager
- 8. Carbon trajectory – Eucalypt woodland Past to future Total C Soil C (30 cm) Aboveground C Pastoralism starts Fire experiment starts 8 | Fire and carbon | Hunt, Liedloff and Eager
- 9. Current carbon stock* (t/ha) *includes aboveground carbon and root carbon but not soil carbon 9 | Fire and carbon | Hunt, Liedloff and Eager
- 10. If fire excluded Change in carbon stock* (t/ha) over 50 years *includes aboveground carbon and root carbon but not soil carbon 10 | Fire and carbon | Hunt, Liedloff and Eager
- 11. Conclusions • Changing fire management has a relatively small effect on carbon stocks (per unit area) • Reducing fire can increase C, but many areas already have a low fire frequency • Changing the vegetation state (e.g. increase woody density) may be the key to getting a measurable effect on carbon stocks • Increasing carbon stocks may be the expense of pasture and livestock production 11 | Fire and carbon | Hunt, Liedloff and Eager
- 12. Thank you • Aust. Centre Ecological Analysis & Synthesis • Robyn Cowley • Dept of Agriculture, Fisheries & Forestry • Tony Moran • Qld Dept of Agriculture, Fisheries & Forestry • Alison Haines •Aust. Collaborative Rangeland Information System • Dionne Walsh • NT Department of Resources • John Carter • Casey Collier • Bill Parton • Jodie Ward • Gary Bastin • Beverley Henry Contact: Leigh Hunt CSIRO Ecosystem Sciences Darwin T (08) 8944 8485 e Leigh.Hunt@csiro.au SUSTAINABLE AGRICULTURE & CLIMATE ADAPTION FLAGSHIPS
Notas do Editor
- Talk relating to fire and carbon dynamics in the extensive grazed rangelands of northern Australia – circumstances with savanna burning in the ungrazed areas of the Top End are somewhat differentFire is a useful tool for vegetation management in the grazed rangelands: Management of tree:grass balance Management of patch grazing Promotion of pasture growth by removing moribund pasture build-upIn recent times there has been interest in whether changing fire management may be able to increase carbon storage in the landscape so that managers can take advantage of the Carbon Farming Initiative
- I report results from :field studies at a long-term fire experiment at the Victoria River Research Station (Kidman Springs) modelling at the local (i.e. the fire plots) and regional scales.
- Many producers consider that fire has a negative relationship on livestock production through, for example, reducing pasture availability in the short term.They therefore actively suppress/exclude fire so fire frequency is generally low.But this can lead to a build up of woody plants, which itself can present management problems – suppressing pasture growth and making mustering more difficult.There is uncertainty about the relationship between increasing carbon and livestock production, and many suspect that managing for increased carbon will have a negative effect on their livestock enterprise.Therefore there are several key questions to be considered in thinking about the possibility of increasing carbon stocks.Can changing the fire regime increase carbon stocks and what regime is needed?How much additional carbon can be stored and is there likely to be an effect on livestock production?I will mainly address the first three questions.I do not consider emissions in this analysis.
- Since fire suppression can lead to an increase in woody plants, the NT Govt established a fire experiment at Kidman Springs in 1993 to explore the use of fire to manage woody increase and determine the optimum regime under pastoral management.Conducted on two land types – Vertosol and Calcarosol with characteristic veg. – savanna grassland-open shrubland and an open Eucalypt savanna woodland.Annual rainfall and grazing at typical regional stocking rates
- The experimental design and details What we did
- Error bars are the SD of total aboveground C Total aboveground carbon stock is between 6 and 20 t C/ha, with a mean around 11 t C/ha. Trees are the largest carbon stock. There was no effect of fire season. Overall fire frequency was significant but there was no consistent trend in C with fire frequency. For early fires there was a significant difference only between early 2 and early 4. For late fires, late 6 was sig. greater, but this treatment was not burnt for 10 years due to an error in applying the experimental fires. There is possible confounding due to inherent site differences – no data available on initial C stocks.In comparison, AGC on an unburnt, ungrazed exclosure established 30 years ago was 16 t C/haDiane Allen (QLD) found no significant difference in soil carbon amongst treatments
- Clearly less C than the woodland site because of a lack of trees. Mean of 3.8 t C/ha, so about 7 t C/ha less than the woodland site.No effect of fire frequency or season on AGC.Early 4 had one plot with many more trees, producing the greater C stock.In comparison, AGC on a 30 year unburnt, ungrazed exclosure was 5 t C/ha.No effect on soil C.To get a better understanding of the likely long-term consequences of these fire regimes we modelled the effects using the Century model.
- This presents the modelled results for selected fire regimes at the woodland site. A lot on this slide so will go through it in detail. Cool fire every five years to simulate Aboriginal fire regime before pastoral settlement, hot fire every ten after pastoral settlement (wildfire) with continuous grazing, then experimental fire regimes. Should point out that for modelling in general there are very limited data available for model parameterisation and validation – in terms of soil characteristics and carbon stocks. Estimating soil carbon well (compared to actual data) but underestimating aboveground carbon slightly.The model suggests there was a build-up of C following pastoral development – associated with reduced fire frequency and increased woodiness.Subsequently, a late fire every four years (recommended to manage woody species) may have reduced total carbon stocks by about 3-4 t/ha to the present day, with a continuing slow decline over the next few decades under this regime. The soil carbon stock (the largest carbon pool) reflects the general trend in aboveground carbon, but the shifts are substantially more subdued. Both early and late 2-yearly fires (late fires not shown) reduce aboveground and soil carbon stocks more rapidly than 4-yearly fires, while both early (not shown) and late 6-yearly fires have a negligible effect on carbon stocks. Also suggests that under more frequent fire C is still declining. Appears that less frequent fire (or excluding fire) is the way to increase carbon stocks, but this will be associated with an increase in woodiness.The magnitude of change is not large.
- What about for other locations?We extended our analysis to a regional level across northern Australia using the Flames model. This is current carbon stock (AGC and root carbon - excludes soil C) modelled under current fire and grazing regimes for he dominant soils/land types in each IBRA region. White areas not modelled. We have less confidence in the output for the more arid, treeless areas. Greater C stocks associated with the Brigalow and mulga lands. The results are strongly driven by soil water availability and capacity to grow trees.
- This is the change in C stock over 50 years if fire is completely excluded (which we appreciate is somewhat unrealistic). Generally quite small increases (if any) in C stocks are predicted for most regions. Red regions have no increase. The differences amongst regions largely reflect differences in current fire frequency – with those with a high fire frequency having greater potential to increase C stocks with the cessation of fire. Not surprising really!
- This work is of a preliminary nature, so I wouldn’t say the results are definitive. Part of the reason for the small effect of fire is that the trees don’t burn and the grass layer recovers the following wet season. Carbon stocks may be approaching their peak in many areas that currently have low fire frequency Multiplying up small gains over a whole property might amount to a worthwhile carbon increase, but verifying the small increments per land area will be challenging.