Skógræktarritið - 15.05.2001, Side 166

Three types of dry to mesic
secondary birch forest succes-
sion zones were defined: (i)
Seminatural vegetation without
trees but with a scattered bush-
vegetation. This zone is still
influenced by some domestic
grazing, (ii) young forest, 10 to 40
years old, (iii) old forest of the
age 40 to 70 years. Within these
succession zones the number of
vascular plant species were
noted for two plot sizes:
(a) 4 m2 (small-plots) and (b)
between 1.2 and 4.3 ha (large-
plots) in a nested design. Totally
27 large-plots were sampled,
9 within each succession zones,
and 5 small-plots randomised
within each large-plot, giving a
totai of 135 small-plots.
Number of vascular plant
species within a small-plot is
defined as a-diversity (Whittaker
1972). -y-diversity is defined as
the number of vascular plants
found within a iarge-plot. The
amount of change or turnover of
species between small-plots is
defined as (3-diversity (Wilson
and Shmida 1984).
Results
Differences with regard to plant
species diversity between the
three succession zones depended
on the spatial scale studied. On a
large spatial scale i.e. looking at
the 7-diversity, there were signifi-
cant differences between the
three succession zones (Table 1).
A total species pool of 253 vascu-
Seminatural Young birch Old birch
vegetation forest forest
Figure I. Arithmetic average of annu-
als and biennials in 27 large-plots,
9 from each succession zone.
Confidence intervals at a<0.05.
lar plants was found in the plots,
and most plants were found
around all three summer farm
clusters (58.1%), whereas 17.79%
and 24.11% were found around
two and one summer farm cluster
respectively. Comparison on a
small spatial scale shows that the
a-diversity was lower in the old
forest than in the two other suc-
cession zones. Of these, young
forest had the highest a-diversity,
but not significant higher than for
seminatural vegetation.
The distribution of different
functional plant groups also var-
ied between the three succession
zones. Annuals and biennials
were clearly favoured in the sem-
inatural vegetation (Figure 1).
Other functional plant groups
favoured in this zone compared
with the other two zones, were
alpine plants, lowland thermo-
philous plants and antropoch-
ores (Bryn 2000).
Table I. Arithmetic averages and confidence intervals (a<0.051 for three variables
and significant differences for one-way ANOVA and Tukey HSD post hoc test
(P<0.0l). Tests were performed in SPSS 10.0.
Seminatural vegetation Young birch forest Old birch forest
Area in m2 (large-plots) 3174 ± 361 2654 ± 405 2917 ±277
y-diversity 113.7 ±8,5' 85.4 ±5.4' 63.9 ± 10.1*
a-diversity 20.622 ± 2,288 21.889 ± 1.704 17.356 ± 1.499'
* = signíficantly different from the other groups.
Discussion
The activities connected to sum-
mer farming created an open
landscape and seminatural vege-
tation types with characteristic
physiognomy and species compo-
sition. The clearing of birch
forests resulted in an almost tree-
less landscape even several kilo-
meters from the summer farm
locality and several hundred verti-
cal meters. In Grimsdalen the
actual forest-limit was suppressed
300 vertical meters. Also in the
municipality of Lærdal, West-
Norway, the forest-limit was sup-
pressed about 329 vertical meters
around summerfarms (Ve 1940),
and in 0ystre Slidre municipality,
Oppland county, almost 25% of
the areas below the potential for-
est-limit was cleared because of
summer farming (Axelsen 1975).
In Nes municipality, Buskerud
county, the forest was not sup-
pressed more than about 150 ver-
tical meters, but the tree-less area
covered several square kilometers
around the summer farm villages
(Rukke 1996).
In the 19th century, when the
population pressure was consid-
erable and the summer farming
was at its height, Norwegian sci-
entists claimed that the utiliza-
tion was too intensive and the
pressure on the vegetation criti-
cal (lensenius 1872). They point-
ed out that the production was
lowered due to too intensive
grazing, and that summer farm-
ing was delaying the develop-
ment of agriculture in Norway.
Today the birch forest is re-
capturing large subalpine areas
previously used for summer
farming in Norway. In Grimsdal-
en the area of birch forest has
increased by approximately 60%
since 1930 until 1997. ln Budal,
Sor-Trondelag county, approxi-
mately 60% of the area that was
covered with seminatural vegeta-
tion in 1963 now consist of early
164
SKÓGRÆKTARRITIÐ 2001 l.tbl.