seasonal fire effects on seed banks in a semi-arid grassland

Sevilleta NWR LTERCJ Jewell

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

Belowground plant community Dispersed seeds

germinate immediately die remain dormant

Transient seeds Persistent seeds

Seed bank Benefits of seed dormancy

(Fenner & Thompson, 2005)

Species diversity Biodiversity Genetic diversity Food sources Environmental stimuli

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

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 GramaBlack Grama

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

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?

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

Pictures provided by Laura Calabrese

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).

C5

10m

10m

40m

60m

2m

40m

40m transect with flags every 2mCollected 20 10cm (length) x 10cm (width) x 2cm (depth) samples per plotTotal of 20 samples from 6 plots = 120 soil samples

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

•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

•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

SAS Wald Chi-Squared=11.7953 P=0.0027 DF=2

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

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

Plpa2- Plantago patagonica, native, Herb, Annual

Dapu7 - Dasyochloa pulchella, native, Grass, Perennial

Gusa2- Gutierrezia sarothrae, native, Shrub, Perennial

Chsp- Chloracantha spinosa, native, Herb, Perennial

Assp- Asclepias speciosa, native, Herb, Perennial

SAS Wald Chi-

Square=11.6579 P=0.0029 DF=2

•SAS•Monocot

•Wald Chi-Squared=12.1415 •P=0.0023•DF=2

•Dicot•Wald Chi-Squared=5.8969• P=0.0524•DF=2

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

Limited sample size Lath house conditions Time since burns

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

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!!

Lath House seedlings at the end of

the rainbow!