Plant Response to Microhabitat Changes Following Hurricane Disturbance II: The Soil Seedbank

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Plant Response to Microhabitat Changes
Following Hurricane Disturbance II The Soil
Seedbank

• L.E. Gorham, B.D. Keeland,
• G. Weisbrich, C.J. Wells,
• and S. Mopper

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Hurricane Andrew
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Initial Observations

• Uprooted Trees left Mounds and associated
  Depressions
• Mounds or Tree Trunks were the only Exposed
  Substrate during Flooding
• Vegetation on Mounds Differed from Vegetation on
  Undisturbed Soil
• Depressions Generally Lacked Vegetation

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Terminology

• Seedbank
• Seeds stored in a dormant state forming a living
  bank in or on the soil
• Seed Rain or Fall
• The dispersal of seed into and out of a unit of
  habitat
• Seed Source
• The origin of vegetative propagules
• Seed Sink
• A unit of area with a disproportionately high
  amount of seeds

J.L Harper 1977
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Objectives

• 1994 Study Objectives
• Compare seed germination from mound, depression,
  and undisturbed microhabitats.
• Determine the effects of different hydrologic
  regimes on seed germination.

• 1998 Study Objectives
• Compare the changes in seedbank from mound,
  depression, and undisturbed microhabitat from
  1994 to 1998.

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The Southern Atchafalaya Basin
Study Sites
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1994 Field Methods Soil Sampling Technique
20 randomly selected mounds from each site
Mound samples
Control samples
Depression samples
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Greenhouse Methods

• Cold storage for five weeks
• Divide soil of each bag
• equally into three flats
• Each treatment gets a flat
• Flooded
• Moist
• Dry
• Follow germination for two
• months

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Statistical Methods

• Three-way full factorial fixed effect ANOVA on
  germination events (mean diversity) by site,
  microhabitat, treatment
• Categorical Model on species composition by
  microhabitat

No statisticians were harmed during the
statistical analyses
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Results
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Results
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Results

• Species Diversity
• Mounds gt Control
• Mitreola petiolata
• Control gt Mounds (Site B)
• Boehmeria cylindrica
• Control gt Depressions (Site A)
• Aster vimineous

• Plant Abundance
• Depressions gt Controls (Site A)
• Mikania scandens
• Samolus parviflorus
• Total plant abundance
• Controls gt Mounds Depressions (Site A)
• Aster vimineous

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Conclusions from 1994 Study

• Depressions
• Serve as seed sink
• Flooding and organic matter accumulation limits
  seed germination

• Undisturbed
• The Status Quo

• Mounds
• Provide microsite variation for seed collection
  and germination

Microsite variation resulting from Hurricane
Andrew provided habitat for a greater Species
diversity and abundance. Hydrology following the
hurricane resulted in differential germination
opportunities in the various microhabitats
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1998 Field Methods Soil Sampling Technique
20 randomly selected mounds from each site
Mound samples
Control samples
Depression samples
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Greenhouse Methods

• Cold storage for five weeks
• Divide soil of each bag
• equally, but only fill one flat
• Flats are exposed to moist
• conditions
• Follow germination for two
• months

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Statistical Methods

• Two-way ANOVA on germination events (mean
  diversity) by microhabitat time

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Results
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Conclusions from 1998 Study

• By the sixth growing season, plant diversity and
  abundance had increased significantly, but the
  microsite affect on the seedbank was no longer
  evident.
• These results support the findings from the
  vegetation study where fewer significant
  differences in species diversity and abundance
  were observed among microsites.
• Further reductions in plant diversity and
  abundance may be expected as the amount of
  sunlight reaching the forest floor is reduced as
  a result of canopy closure.

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Questions