Seasonal Fire Effects on Seed Banks in a Semiarid Grassland

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Seasonal Fire Effects on Seed Banks in a
Semi-arid Grassland

• Sevilleta NWR LTER
• CJ Jewell

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FIRE

• Effects of Fire
• release of nutrients
• breakdown of hydrophobic plant litter
• breakdown of dormancy
• removal of inhibiting chemicals
• Impact on plant communities varies among seasons
  and across sites

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Seed Bank

• Belowground plant community
• Dispersed seeds
• germinate immediately
• die
• remain dormant
• Transient seeds
• Persistent seeds
• Seed bank
• Benefits of seed dormancy
• (Fenner Thompson, 2005)

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Why are seed banks important?

• Species diversity
• Biodiversity
• Genetic diversity
• Food sources
• Environmental stimuli

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How Fire affects Seed Banks

• Fire triggers seed germination and seedling
  recruitment by the
• Removal of vegetation
• Intense temperatures recorded in the soil

6
Fire Seasonality

• Dominant vegetation is perennial grasses
• grow in the summer
• dormant in fall and winter
• More seeds available during spring/summer
• Abundance decreases in autumn/winter

Blue Grama
Black Grama
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What do we know or not know about fire and seed
banks?

• Sevilleta studies
• Establishment ecology of Creosote
• Recruitment studies from seed banks
• Seedling establishment after removal of dominant
  species
• How fire affects vegetation and insect diversity

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Overall Questions

• 1) What is the composition and size of the seed
  banks in the fall, summer, and control burn
  plots?
• 2) Does the seasonality of fire affect seed bank
  size and content?
• 3) How does fire affect seedling germination in
  the field?

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Hypotheses

• Fire will cause an overall decrease in the size
  and species diversity in the seed bank
• The summer burn plots will have a greater amount
  of viable seeds and species richness compared to
  the fall burn plots

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Experimental Site Burn Plots

• Sevilleta NWR/LTER
• McKenzie Flats, 2.8 miles south of Black Butte
  gate
• 34 21 33.0 N 106 41 25.9 W
• Vegetation dominated by the grasses blue grama
  (Bouteloua eriopoda), and black grama (Bouteloua
  gracilis).

Pictures provided by Laura Calabrese
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Site Layout
C5
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Collecting Soil Samples
40m transect with flags every 2m Collected 20
10cm (length) x 10cm (width) x 2cm (depth)
samples per plot Total of 20 samples from 6 plots
120 soil samples
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Methods

• 3 Treatments X 2 Plots per Treatment X 20 soil
  samples per plot 120 samples
• Randomly selected 15 soil samples per plot
• 90 soil samples used 30 per treatment
• Randomly distributed selected samples in the
  Sevilleta Lath House

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Growing Seedlings!

• 90 26.7cm x 53.3cm flats in Sev Lath House
• Soil mixture contains half Metromix 360 and half
  sandbox sand
• Spread soil sample over mixture
• Watered daily

• Marked and counted new seedlings weekly
• Recorded if monocot or dicot

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Monocots vs Dicots

• Monocots
• Embryo as one cotyledon
• Flower parts in 3s
• Parallel Veination
• Grasses-no secondary growth

• Dicots
• Embryo has two cotyledons
• Flower parts in 4s or 5s
• Reticulated/Branched Veination
• Woody species-secondary growth

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Comparison of seed bank size between treatments

• SAS
• Wald Chi-Squared11.7953
• P0.0027
• DF2

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Comparison of seed bank content between treatments

• SAS
• Monocots
• Wald Chi-Square9.7042
• p value0.0078
• DF2
• Dicots
• Wald Chi-Square0.242
• p value0.8860
• DF2

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Burn Plot Seedlings

• 9 sample areas from each of the 6 plots54 areas
• A 30cm X 30cm niner was used to count number of
  naturally germinating seedlings in each sample
  area
• Specific species were identified when possible

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Seedlings Found
Assp- Asclepias speciosa, native, Herb, Perennial
Dapu7 - Dasyochloa pulchella, native, Grass,
Perennial

• Plpa2- Plantago patagonica, native, Herb, Annual

Gusa2- Gutierrezia sarothrae, native, Shrub,
Perennial
Chsp- Chloracantha spinosa, native, Herb,
Perennial
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Fire effects on seedling germination in the field

• SAS
• Wald Chi-Square11.6579
• P0.0029
• DF2

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Fire effects on seedling germination in the field

• SAS
• Monocot
• Wald Chi-Squared12.1415
• P0.0023
• DF2

• Dicot
• Wald Chi-Squared5.8969
• P0.0524
• DF2

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Conclusions

• Fires negatively affect the seed bank in the
  short term
• Semi-arid grasslands are not adapted to fire
• Monocots and dicots are equally affected by
  seasonal fire
• After a summer burn, there is more space
  available for newly released seeds, so more can
  germinate right away
• Species found in the field are a fair
  representation of what may be found in the seed
  bank, but not an absolute reference

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Limitations of Experiment

• Limited sample size
• Lath house conditions
• Time since burns

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Future Research

• Long term effects of fire
• Flotation method to mechanically find the seeds
  in soil samples (30 extra samples)
• Assess spring seed bank
• Assess how fire affects the seed bank and
  vegetation of shrublands and woodlands on the
  Sevilleta

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Acknowledgements

• Sevilleta NWR LTER
• UNM
• Jennifer Johnson
• Diane Marshall
• Tim Lowrey
• Terri Koontz
• All Sev 2008 REUs
• Especially
• Damon Lowrey
• Molly Ladd
• And everyone who helped me water!!

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Questions?
Lath House seedlings at the end of the rainbow!