Náttúrufræðingurinn - 1992, Blaðsíða 30

Whittaker, R.H. 1975. Communities and
ecosystems. Macmillan Publishing Co.,
Inc., New York. 385 bls.
SUMMARY
Effect of willow (Salix) on the
establishment of birch
(Betula pubescens) from seeds
by
Sigurður H. Magnússon
and Borgþór Magnússon
Agricultural Research Institute
Keldnaholt
112 REYKJA VÍK
Iceland
In recent years experiments to introduce
birch (Betula pubescens) by seeding into
areas under reclamation have been carried
out in Southern Iceland. Most of these ar-
eas, which have lost their former top-soil
and vegetation, are sparsely vegetated
witli self-established willow species (Salix
callicarpaea, S. lanata, S. phylicifolia and
S. herbacea) and other early colonizers of
barren areas. In one of these experiments
it was noted that birch seedlings growing
in the immediate vicinity of willow plants
were considerably larger in size and of
healthier appearance than seedlings of the
same age distanced further away from the
willow. In order to investigate this rela-
tionship in a greater detail a special study
was carricd out at one experimental site
where willow plants are relatively abun-
dant.
Contparisons were made of the size of
birch seedlings in relation to their distance
front the nearest willow plant. The experi-
mental plots had received the following
treatments: a) seeding in fall, b) seeding
in spring, c) seeding in fall, fertilized the
following spring, d) seeding in spring,
coated seeds. Measurements of seedlings
which germinated during the suntmers of
1989 and 1990 were made in the autumn of
1990.
A similar pattern of size distribution of
birch seedlings was found for all treat-
ments (Fig. 3 and 4). The seedlings within
70 cm of willow plants were larger than
those distanced further away from them.
This growth pattern was already establish-
ed at the end of one growing season when
seedlings near the willow had on the aver-
age more than 1.7 times wider crown than
seedlings further away. After two growing
seasons the birch seedlings close to the
willow plants had at least two times wider
crown than seedlings growing further
away from the willow.
The enhanced growth of birch seedlings
near the willow plants can amongst other
things be related to shelter, improved nu-
trient status of the soil and development
of mycorrhiza. In the paper it is argued,
however, that mycorrhizal infection was
the main reason for the improved growth
of birch seedlings near the willow. At the
study site fruitbodies of the i'ungal species
Laccaria laccata were very common
around willow plants in the area of en-
hanced birch growth. Fruitbodies of In-
ocybe, Galerina, Hebelonui, Cortinarius
and Psilocyhe were also found near the
willow. Examination of the roots of the
willow plants and the birch seedlings next
to them revealed that they were all infect-
ed with mycorrhiza.
This relationship between willow plants
and birch seedlings does not appear to
have been previously described. The rela-
tionship may be of considerable intpor-
tance in the colonization and establish-
ment of birch in riew areas and in plant
succession, in particular in areas of low
soil fertility. Further studies are needed
on this relationship, especially on the role
played by ntycorrhiza.
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