Forest Floor Invasion ResultsBIO 205F, 2003

Objectives:1. To determine whether plant species from the natural

forest floor will reestablish if the invading ornamental Vinca species is removed.

2. 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.

3. To mark the edge of the invading Vinca front to allow a future measurement of the rate of movement of this front.

4. 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.

How does Vinca cover change the soil environment below it?

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

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

River Site: Removal quadrat minus Vinca quadrat temperature

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)Removal quadrat is warmer in summer and early fall,

and gains heat much more quickly in early spring

Vinca quadrat holds heat longer into fall and early winter.

Does Vinca invasion change the organic or moisture content of

the soil?

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?

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.

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V1 V2 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.

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 what’s a countable woody stem? We need to further control our technique in future years to answer this question.

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Summary1. 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.

2. Vinca cover didn’t 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.

3. 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.

4. This year’s measurements throw into doubt our previous finding that establishment of young trees is inhibited by Vinca.