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

Seasonal Fire Effects on Seed Banks in a Semi-arid Grassland. Sevilleta NWR LTER CJ Jewell. FIRE. Effects of Fire: release of nutrients breakdown of hydrophobic plant litter breakdown of dormancy removal of inhibiting chemicals

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

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  1. Seasonal Fire Effects on Seed Banks in a Semi-arid Grassland Sevilleta NWR LTER CJ Jewell

  2. 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

  3. 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)

  4. Why are seed banks important? • Species diversity • Biodiversity • Genetic diversity • Food sources • Environmental stimuli

  5. 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

  7. 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

  8. 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?

  9. 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

  10. 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

  11. Site Layout Sp1 Su4 F3 F5 C2 Sp2 F2 Sp5 C1 C3 Su5 Sp4 C5 Su1 Su3 Sp3 F1 Su2 C4 F4

  12. Collecting Soil Samples 40m 10m 10m 2m 40m 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 60m

  13. 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

  14. 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

  15. Monocots vsDicots • 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

  16. Comparison of seed bank size between treatments • SAS • Wald Chi-Squared=11.7953 • P=0.0027 • DF=2

  17. Comparison of seed bank content between treatments • SAS • Monocots • Wald Chi-Square=9.7042 • p value=0.0078 • DF=2 • Dicots • Wald Chi-Square=0.242 • p value=0.8860 • DF=2

  18. Burn Plot Seedlings • 9 sample areas from each of the 6 plots=54 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

  19. Seedlings Found • Plpa2- Plantagopatagonica, native, Herb, Annual Assp- Asclepias speciosa, native, Herb, Perennial Dapu7 - Dasyochloa pulchella, native, Grass, Perennial Gusa2- Gutierrezia sarothrae, native, Shrub, Perennial Chsp- Chloracantha spinosa, native, Herb, Perennial

  20. Fire effects on seedling germination in the field • SAS • Wald Chi-Square=11.6579 • P=0.0029 • DF=2

  21. Fire effects on seedling germination in the field • SAS • Monocot • Wald Chi-Squared=12.1415 • P=0.0023 • DF=2 • Dicot • Wald Chi-Squared=5.8969 • P=0.0524 • DF=2

  22. 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

  23. Limitations of Experiment • Limited sample size • Lath house conditions • Time since burns

  24. 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

  25. 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!!

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

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