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Alien Plants
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The effect of alien plant species on native plant richness
and community composition in urban
mid-age Sugar Maple (Acer saccharum) dominated forests
in London, Ontario
Page 3 of 9
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Results:
Influence of Site Size
Overall, vascular plant species richness
varied among the sites. Larger sites had higher numbers of vascular plant
species (Fig. 2, p=0.024, R2=0.49). Similarly, native
species richness increased with increasing area of the site (Fig. 3, p=0.014,
R2=0.55). Larger, and hence, richer sites also had higher richness of species
encountered in quadrats (Fig. 4). Therefore, site richness was significantly
(p<0.01) reflected in total richness from quadrats. The greater numbers of
species in larger sites, were being effectively represented in the quadrats.
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Figure 2. Effect of site area on total site plant
species richness. |
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Figure 3. Effect of area on total site native plant
species richness. NS indicates a non-significant relationship. |
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Figure 4. Relationship between total site species
richness and total quadrat species richness. |
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| Effect of Alien Species Richness on Native Species Richness |
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| A regression of alien plant richness on native richness was not significant
(Fig. 5, p=0.34). However, since this was analyzed using total native richness
and total alien richness, another test was done to see if the relationship was
affected by differences in site area (Fig. 6). No relationship was found between
the size of the site and the ratio of alien to native species (p=0.85, R2<0.00). |
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Figure 5. Total native species richness against total
alien species richness at each site. |
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Figure 6. Effect of site area on mean alien : native
species richness ratio in the quadrats.
NS indicates a non-significant relationship. |
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| A one-way ANOVA of native richness in quadrats with or without alien species
showed (Fig. 7) a small but highly significant difference, with more native
species in quadrats with no aliens (p<0.001). Therefore, at the quadrat
level, the presence of an alien species was associated with reduced native
richness. However, when native species richness was tested against the number of
alien species in quadrats containing alien species (Fig. 8), native species
richness was found to increase significantly with increasing with alien
richness. However, the test was highly unbalanced, with only 2 of 200 quadrats
containing three alien species. |
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Figure 7. Mean native species richness in quadrats with
alien plant species present or absent in the quadrat with 95% confidence
intervals. Different letters indicate a significant difference in means. |
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Figure 8. Mean native species richness in the presence
of varying numbers of alien plant species within the same quadrat with 95%
confidence intervals. Different letters indicate a significant difference
in means. |
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Copyright © Peter Moc
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