International Polar Year 2007–2008 - WMO

300
IPY 20 07–20 08
2.9-4. Field sites
established in 1967
on Disko Island, West
Greenland, were revisited
in 2009 as part
of the BTF project to
repeat measurements
of plant performance
and plant community
composition in order
to detect changes
over four decades.
(Photo: T.V. Callaghan)
aspen trees (Van Bogaett et al., 2010a; Rundqvist
et al., in press) and increases in the growth of some
shrub species. Repeated photography over 100
years has been used to document changes in tree
line location, birch forest growth and aspen stand
growth. Also, dendrochronology has been used to
identify disturbances to the birch forest caused by
periodic outbreaks of geometrid moths that are
currently expanding their northern ranges (Post et
al., 2009) and herbivory of aspen by moose. A picture
emerges in which disturbance to birch caused by its
invertebrate herbivore facilitates invasion by aspen
that is subsequently controlled by moose browsing
(Van Bogaert et al., 2010a, 2010b). Thus the effects
of climate on vegetation growth in this region are
complex and at least partly result form indirect effects
via the population dynamics of herbivores. At tree line
near Kharp in northwest Siberia, IPY-GOA studies have
shown that alder shrubs are expanding vigorously
in fire-disturbed areas and seedling establishment is
occurring primarily in areas with disturbed mineral
soils, particularly non-sorted circles. Analysis of NDVI
trends using three Landsat images (1985, 1995 and
1999) near Toolik Lake in Alaska shows that the higher
spatial-resolution Landsat-derived greenness trends
match those derived from the AVHRR GIMMS data
and that increased greenness is strongest in disturbed
areas, such as road-side tracks, and sites with warmer
soils and abundant moisture such as south-facing
water tracks, wetlands and areas with warmer soils,
such as moist non-acid tundras (Munger, 2007).
At the most detailed level of observation, the GOA
team used methods developed for the International
Tundra Experiment (ITEX) to monitor changes
between 1990 and 2008 in the species composition
and structure of the vegetation in 150 plots near Toolik
Lake, Alaska (Gould and Mercado, 2008). Average
plant canopy height at each point has increased by
a factor of three; shrub cover and graminoid cover
also increased, whereas moss cover has decreased.
These observations are concomitant with direct
warming manipulations carried out within ITEX. At
the same level of detail, observations on the species
composition of fellfield and herb slope sites in West
Greenland under the PTF project over a period of
42 years showed general reductions in biodiversity
although some new species were recorded. Phenology
of flowering increased by up to six weeks (as recorded
for Zackenberg, North-east Greenland; Høya et al.,
2008) although the performance (size, reproductive
capacity and population density) of the targeted grass
species remained identical after 42 years (Callaghan
et al., in prep). Detailed inventories of species over a
30-year period in sub-Arctic Sweden showed changes