The arctic forest-tundra ecotone (FTE) represents a
major transition zone between contrasting ecosystems,
which can be strongly affected by climatic
and biotic factors. Expected northward
expansion and encroachment on arctic tundra in
response to climate warming may be counteracted
by natural and anthropogenic processes such as
defoliating insect outbreaks and grazing/browsing
regimes. Such natural and anthropogenic changes
in land cover can substantially affect FTE
dynamics, alter ground albedo (index of the
amount of solar energy reflected back into the
atmosphere) and provide important feedbacks into
the climate system. We took advantage of a naturally
occurring contrast between reindeer grazing
regimes in a border region between northern
Finland and Norway which was recently defoliated
by an outbreak of the geometrid moth. We
examined ecosystem-wide contrasts between
potentially year-round (but mainly summer)
grazed (YRG) regions in Finland and mainly
winter grazed (WG) regions in Norway. We also
used a remotely sensed vegetation index and albedo
to quantify effects on local energy balance
and potential climate feedbacks. Although differences
in soil characteristics and ground vegetation
cover were small, we found dramatic differences
in the tree layer component of the ecosystem.
Regeneration of mountain birch stands appears to
have been severely hampered in the YRG regime,
by limiting regeneration from basal shoots and
reestablishment of individual trees from saplings.
This has led to a more open forest structure and a
significant 5% increase in spring albedo in the
summer grazed compared to the winter grazed
regions. This supports recent suggestions that
ecosystem processes in the Arctic can significantly
influence the climate system, and that such processes
must be taken into account when developing
climate change scenarios and adaptation
strategies.
Key words: Arctic vegetation; climate change;
insect defoliation; grazing; climate feedback; reindeer
husbandry.
