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Elevation
All elevations are given in relation to the average elevation of
the natural marsh at the particular site, lie Grande or Kerlavos. At
lie Grande the average elevation of the Juncus marsh on the southwest
side of the bridge was the reference datum. This average elevation is
tied to a white mark on the rock wall of the bridge for which
Mademoiselle Odile Guerin, who has worked on the lie Grande project,
has elevation tied to a national datum. The average elevation is also
tied to the concrete foundation of the bridge itself. At Kerlavos the
average elevation of the marsh is tied to a bench mark at an electric
station tower ca . 0.5 km from the study site. Based on relating water
levels at the two sites, the Juncus marsh at lie Grande is about 0.1 m
above the elevation of the natural marsh at Kerlavos.
At lie Grande we planted Juncus , Puccinellia , Spartina and
Triglochin over a range of elevation from 0.8 m below to 0.3 m above
the average elevation of the natural Juncus marsh. Juncus transplants
did not survive at elevations below that of the natural Juncus marsh
and best survival occurred at 0.3 m above that of the natural Juncus
marsh. Puccinellia transplants did not survive at elevations of 0.7 m
below that of the natural Juncus marsh and survival was less than 10%
at elevations of 0.5 m below that of the natural Juncus marsh. The
best growth and survival of Puccinellia transplants was achieved in the
range of elevation between 0.1 m below and 0.3 m above that of the
natural Juncus marsh. Spartina transplants survived at the lowest
elevations of all species tested. Although Spartina transplants
survived at elevations of 0.8 m below that of the natural Juncus marsh,
growth was best at 0.3 m below that of the natural Juncus marsh.
Survival and growth of Triglochin was generally poor but its elevation
response was similar to that of Puccinellia with no survival at
elevations of 0.7 m below that of the natural Juncus marsh.
At Kerlavos experimental plantings of Puccinellia and Triglochin
were established over a range of elevation from 0.5 m below to 0.1 m
below that of the natural marsh. The best survival and growth of these
Puccinellia transplants occurred at 0.2 m below that of the natural
marsh. Transplants at 0.4 m below the elevation of the natural marsh
did very poorly. Triglochin transplants responded in a similar manner.
Halimione was planted at elevations from 0.1 m below to 0.3 m
above that of the natural marsh at lie Grande. Survival and growth of
these transplants were best at about 0.3 m above the elevation of the
natural marsh, but survival was good throughout the range of elevations
planted. At Kerlavos, Halimione was planted from 0.4 m below to 0.2 m
below the elevation of the natural marsh. Survival and growth was best
in the upper half of this elevation range.
Plantings in General
About 9,700 transplants have been planted at lie grande and about
1,800 others at Kerlavos over the period May 1979 through May 1981
(Table 2). Although half of these transplants were those of
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