Raisduottar
belongs to the hotspot area of Fennoscandian
arctic-alpine biodiversity, streching from Duortnosjávri (Totneträsk) in
Swedish Lapland to Áltafávli (Indre
Altafjord) in
Numbers of lime-dependent arctic-alpine species
in different Atlas Florae Europae grids; according to
the situation in 2003, when the mapping was done for 20% of vascular plants.
(Even if lime-rich areas only cover 1-2% of the mountain/tundra landscape, they
stand for most of the biodiversity in Fennoscandia); Raisduottar is one of the
three hottest spots, along with the Gilbesjávri
(Kilpisjärvi, 1) and Duortnosjávri (Torneträsk, 3) areas
Geology and
climate contribute. Dolomite (red in the below scheme) is
most prevalent in the bottom of the Scandinavian mountain formation, and is
thus exposed along the eastern edge of the mountain chain and around “windows”
(granite outcrops). The arid climate along the edge counteracts leaching and
helps to keep pH in the neutral range. Moreover, reindeer aggregate to lime rich areas (grassy) – impact??
We conducted a preliminary study, utilizing gradients
in reindeer densities caused by differences in grazing policies between
Finland, Sweden and Norway and by the exclusion of reindeer from the dolomite
rich Malla in NW Finnish Lapland. All work was done
in areas where the dolomite cliffs get exposed (either along the east edge of
the mountain chain or around “granite windows” within the mountain chain). Main
result: local species diversity indifferent to grazing but the abundance of
arctic-alpine rarities correlates positively with grazing intensity (Olofsson
& Oksanen 2005). Correlations, however, have always alternative
explanations – finding correlations is just the start
for experiments.
In Norway, migration is mandatory; to help to
keep the reindeer within legal summer ranges, the Sámi of Norway have built
hundreds of kilometres of reindeer fence
across the mountain– tundra landscape in the north. One of these fences – the
red line in the figure below - goes
right across the hottest part of the Raisduottar
hot spot, creating a sharp contrast of grazing intensity – strong grazing
pressure in the summer range, and practically non-grazed “dead angles” (the
area surrounded by a blue line). The reason: when reindeer are allowed to enter
the autumn range after marking in the corral (the red circle) they rapidly move
southwards towards the mushroom rich inland heaths within the angle limited by
the blue arrows; hence especially the area to the east of the corral has been
very little grazed since the 1960’s. (In spring the reindeer cross the area on
broad front as the fence is then snow covered but only graze on the most
exposed ridges, the rest is inaccessible)
Þ long
term experiment already done. On the west side of the corral the situation is
more complicated as a part of the area is now used as a calming down ground after
marking to ensure that the does do not move southwards so fast that their
calves would risk being left behind.
The impact of
the contrasting treatments is especially striking in relatively nutrient-poor habitats, where the
grazed (left, front) is dominated by unpalatable dwarf shrubs, while palatable grasses and forbs prevail on the intensely
grazed summer range (right, back), where productivity is higher, soils are warmer, and nutrient circulation is
rapid. (Olofsson
et al. 2001, 2004,
Olofsson
& Oksanen, L. 2002; see also Zimov et al. 1995,
Am. Nat. 146:765-794). It may indeed seem strange that unpalatable
plants prevail in a lightly grazed area, while palatable plants prevail in the
area with intense grazing pressure. However, light grazing is more selective
than heavy grazing, making defensive investments more profitable for plants.
Moreover, nutrient availability is dramatically higher on the intensely grazed
side, which increases the marginal costs of chemical defense, thus favoring
resilient plants (see
Oksanen, L. 1990. Predation, herbivory and plant strategies along gradients of
primary productivity. - pp. 445-473 in: D. Tilman
and J. Grace,
eds. Perspectives on plant competition. Academic Press).
In nutrient-rich habitats, herbaceous plants prevail on both sides, but the
vegetation is still very different (non-grazed = left; intensely grazed =
right) – where do rare species flourish?
We are studying
this right now, using various methods (line transects, transplantations,
seeding experiments, short-term manipulations of grazing intensity). The
results are still preliminary but an interesting paradox is emerging. Sheer
censuses indicate that the majority of the rarities are grazing-favored, whereas the results of transplantations and short-term
grazer exclusion experiments are ambiguous or indicate that the most rarities
are negatively influenced by grazing.
The likely
reason for the apparent paradox is different kinds of grazing impacts operate
in entirely different time scales; the negative impacts are direct and rapid,
the positive impacts are indirect and slow. An example is provided by Viola biflora (not
a rare species, but one we have studied in different contexts). In our previous
experiment, which lasted for 10 years, we found that this species is strongly favored by exclusion of grazers (left panel, from Moen and Oksanen 1998, Oikos
82: 333-346). On Raisduottar, however, where the involuntary “fence
experiment” has lasted for 40 years, this species is among the ones that has
most pronounced gained from intense grazing; its yellow flowers decorate the
summer range (right panel, right side), while it is practically absent on the
other side of the fence (right panel, left side). This indeed depends on the
nutrient pool; if the bedrock is sufficiently nutrient rich, V. biflora
abounds on both sides of the fence, but its habitat amplitude is wider in areas
where reindeer keep nutrients in rapid circulation.
Even the tall herb meadows in the non-grazed areas
(previous page, left) are, in fact, products
of past grazing. In the absence of reindeer, such sites would be occupied
by willows, with the tall herbs just as a minor component of the community.
However, willows are grazing sensitive and disappear from areas preferred by
reindeer. Tall herbs are fairly grazing-sensitive, too, but survive at low
densities and quickly take over when grazing ceases. Once the tall herbs have
become dominants, they easily exclude willow seedlings as willow seeds are tiny
and provide no resources for the seedlings. During the 40 grazing-free years,
willows have thus got foothold only in disturbed sites (around power line
posts, along the access road, in eroding river banks and on gravel bars in
braided streams). In all other sites, the tall herbs have stood their ground,
indicating that history counts on the
tundra.
The
project is going on; please recall that the above results are preliminary.
Like all
arctic-alpine projects, the work on Raisduottar requires a team with a good working spirit, willing to live in a remote place
under primitive conditions (only Sámi tepees available as accommodation in this
area). I have indeed had the advantage of having such teams – below the 2004
work group collecting Saxifraga oppositifolia for
transplantation experiments.
…and indeed, the
team must thrive in the outback, as my students and collaborators have done –
coffee break on the tundra
