Forest Floor Invasion Results BIO 205F, 2003

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Forest Floor Invasion ResultsBIO 205F, 2003

• Objectives
• To determine whether plant species from the
  natural forest floor will reestablish if the
  invading ornamental Vinca species is removed.
• To determine how Vinca cover changes the
  environment below it in order to understand why
  the vegetation coming up through Vinca cover
  differs from that in natural forest floor
  quadrats.
• To mark the edge of the invading Vinca front to
  allow a future measurement of the rate of
  movement of this front.
• To help produce an estimate of the amount of
  annual variation in conditions on the forest
  floor, against which invasion-related changes can
  be evaluated.

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How does Vinca cover change the soil environment
below it?
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Dollar-size temperature loggers were buried 1 cm
underground in the centre of quadrats. They
recorded temperature every 8 minutes and stored a
full year of records. The following slide
illustrates the seasonal pattern in average daily
soil temperature from one of the quadrats. The
slide after that compares the temperature in a
quadrat from which Vinca was removed, to that
underneath the undisturbed Vinca just 2m away.
Temperature logger and a loonie at approximately
the same scale
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Notice that soil temperature seldom gets below
-5C even though average winter air temperatures
frequently dip below -10.
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Vinca cover slows soil heating in spring and
slows heat loss in the fall
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Does Vinca invasion change the organic or
moisture content of the soil?
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Soil moisture content and and percent organic
matter are higher in the river site (V1) than in
V2, but averaged across both sites, soil
characteristics do not differ significantly among
treatments (error bars are 1 standard error).
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How do the plant communities in Vinca, Removal,
and Natural Forest Floor quadrats compare now,
two years after Vinca removal?
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Removal quadrats now have as much cover as the
natural forest floor.
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Plant species richness in removal quadrats varies
between the two sites, but after averaging across
sites, richness is not significantly affected by
treatments.
Although neither our richness nor plant cover
values differ significantly between removal and
natural sites, our measurements are are made at a
time of year when most forest floor species have
entered their seasonal dormancy and are not
visually apparent. We need to conduct late
spring or early summer censuses.
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Woody stem densities this year did not differ
significantly between treatments. In two
previous years Vinca quadrats had woody stem
densities only 1/4 of those on the natural forest
floor. Is this a real change, or could we just
be changing our criteria about whats a countable
woody stem? We need to further control our
technique in future years to answer this question.
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Summary

• Vinca cover makes the soil cooler in spring and
  warmer in fall. Since many forest floor plants
  accomplish most of their annual growth in the
  spring before the canopy leafs out and reduces
  light intensity, the temperature effect could be
  important.
• Vinca cover didnt seem to affect soil moisture
  or organic matter levels in the fall (based on
  two years of measurements), but the effects on
  temperature suggest that there could be effects
  on moisture at other times of year. Either the
  high Vinca density could reduce soil water
  through transpiration, or it could increase
  moisture through shading the soil surface from
  direct sun. More measurements are needed.
• Based on the our crude and relatively
  uninformative fall measurements of plant kinds,
  Vinca removal quadrats after two years seem
  similar to the natural forest floor.
• This years measurements throw into doubt our
  previous finding that establishment of young
  trees is inhibited by Vinca.