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A field test of the degree of coevolution between red alder and Frankia populations

University of British Columbia

A cross inoculation experiment was set up to examine the degree of coevolution between red alder (Alnus rubra Bong.) and Frankia populations and to test the competitive ability of red dlAer/Frankia combinations under different field conditions. Seedlings from high and low elevation populations from three watersheds in southwestern B. C. were inoculated with Frankia from the parent tree populations and planted into three high and three low elevation planting sites in the U.B.C.M.K. Research Forest. Seedlings were also inoculated with Frankia from trees near the planting sites. To examine the effect of neighbours on plant growth, each combination was planted with and without red alder neighbours. There was a significant interaction between planting elevation, parent and Frankia source. On low elevation sites, the final yield of plants inoculated with Frankia from their parent's elevation was half that of plants inoculated with Frankia from the opposite elevation. There was also an inverse relationship between yield and the proportion of fixed nitrogen in leaves for the different dldex/Frankia combinations. On high elevation sites, final yield was 3.6 times lower and nitrogen fixation levels were two times higher than on the low elevation sites. On these sites, plants inoculated with Frankia from their parents grew significantly more than plants inoculated with Frankia from any novel source. These data suggest that Frankia can evolve to a less mutualistic state and that expression of this effect depends on environmental conditions. It is predicted that less mutualistic Frankia will evolve in situations where the relationship with the host is likely to break down. The presence of neighbours reduced the growth of plants by half but had no effect on the interaction between plmt/Frankia combinations. There was no significant difference in plant yield when plants had neighbours from different parent elevations. In terms of productivity, total harvested plant mass per site ranged from 22,000 to 302 grams. Competitive intensity did not vary across sites, except that on the lowest productivity site, where no competitive effect was detectable, plants with neighbours were 44 % larger than plants without neighbours. On all other sites, the mass of plants with neighbours, relative to the mass of plants without neighbours, decreased over the course of the experiment. The plants in this experiment were attacked by woolly alder sawfly, Eriocampa ovata (L.). The sawflies attacked the fastest growing individuals on low elevation sites, resulting in decreased growth in late summer, 1993. This made observed differences between treatments conservative estimates of potential differences. The only exception to this pattern was that plants with neighbours had a higher degree of herbivore damage than plants without neighbours, confounding the effects of competition and herbivory.

Thesis/Dissertation

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2009-02-19

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http://hdl.handle.net/2429/4791

Forestry

University of British Columbia

UBCV

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