Dispersal of bottomland hardwood forest species during oldfield succession

1
Dispersal of bottomland hardwood forest species
during old-field succession

• L. L. Battaglia1, D. W. Pritchett2 P. R.
  Minchin1
• 1Department of Plant Biology, Southern Illinois
  University
• 2Department of Biology, University of Louisiana
  at Monroe

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Loss of BLH Forest

• agriculture, hydrologic modification, logging,
  development
• fragmentation and degradation
• 78 decline in LMAV (MacDonald et al. 1978)
• 50 loss of the 6,554,000 ha in Louisiana
  (Turner Craig 1980 Dahl 1990)

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Distribution of Bottomland Forest in LMAV
LITTLE ROCK
MEMPHIS
VICKSBURG
BATON ROUGE
Source The Nature Conservancy 1992
NEW ORLEANS
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Study Site

• northeast Louisiana (LMAV)
• Ouachita Wildlife Management Area
• disked and abandoned in 1984
• 3.2 ha (200 m X 160 m)
• elevation, precipitation, and flooding from Bayou
  Lafourche control hydrology

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Relative Basal Area
Total Basal Area 0.71 m2 ha-1
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Fraxinus pennsylvanicaDensity vs Distance from
Seed Source
Battaglia et al. 2002
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Spatial Distributions of Saplingswind vs.
bird-dispersed
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Distribution of Saplings in Baccharis
halimifolia patches
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Objectives

• characterize patterns of seed rain in a
  early-successional bottomland hardwood forest
• determine the effects of distance to forest edge
  on dispersal
• test the effects of proximity to shrub patches on
  dispersal

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Seed Traps
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Field Methods Part 1

• seed traps at 10 meter intervals along 3 N-S
  transects
• traps emptied every 6 weeks
• began July 2002
• fruits of woody species identified and counted

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Density of Dispersed Seeds
n 1123
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Fraxinus pennsylvanica Seed Rain
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Fraxinus pennsylvanica Seed Rain
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Crataegus viridis Fruit Rain

• 5 seeds/pome

16
Ilex decidua Fruit Rain

• 4-7 seeds/drupe

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Seed Rain of Heavy-Seeded Species
Carya aquatica
Quercus nigra
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Results Part 1

• wind-dispersed Fraxinus pennsylvanica had highest
  seed rain
• distance decay
• reproductively mature tree in interior of field
• patchy dispersal of bird-dispersed Ilex decidua
  and Crataegus viridis
• heavy-seeded Carya aquatica and Quercus spp.
  restricted to forest edges

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Field Methods Part 2

• Baccharis halimifolia patches
• seed traps
• inside patch
• edge of patch
• outside patch
• traps emptied every 6 weeks, starting May 2003
• fruits of woody species identified and counted

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Fraxinus Seed Rain in Baccharis halimifolia
patches
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Results Part 2

• 20 Ilex decidua and 204 Fraxinus pennsylvanica
  seeds found
• no difference in dispersal of F. pennsylvanica
  among positions in and around saltbush patches
• decline in seed rain with distance from forest
  edge
• suggests lower seedling establishment under B.
  halimifolia shrubs

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Conclusions

• gaps between Fraxinus trees should begin to
  fill in as early colonists provide local seed
  sources
• Baccharis halimifolia is not limiting dispersal
  but appears to inhibit seedling establishment of
  Fraxinus
• mode of dispersal influences spatial patterns of
  regeneration

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Acknowledgements

• Louisiana Wildlife Fisheries
• Ouachita Wildlife Management Area staff