The upper mountain forest and tree response
to climate change in south Siberian Mountains
Vyacheslav
y
I. Kharuk,, and K. Jon Ranson
Forest Monitoring Lab,
Sukachev Institute of Forest,
Krasnoyarsk, Russia
NASA’s Goddard Space Flight Center
Greenbelt, MD 20771
Siberia is the zone of most pronounced observed and
predicted climate change
Tree response to climate change is primarily
expected in the areas where temperature and
precipitation limits growth, e.g., in alpine foresttundra ecotone.
The area of investigation
Is the upper elevation forests and
forest-tundra ecotone of
Altai - Sayan Mountain country.
This is the southern border of
Siberian taiga and
Mongolian steppes and deserts
The purpose of this report is to address the
following questions:
1. How has tree line changed during the last millennium?
2. How does forest response to climate variables depend on
topography?
3. How do the main tree species (Larix sibirica and Pinus
sibirica) respond to climate change?
Study was based on in situ measurements within
elevation transects,
time series of satellite data and forest maps,
dendrochronology data,
and DEM.
The study parameters were
apical and radial increments,
tree natality/mortality,
tree physiognomy,
regeneration abundance
and age structure.
The study area is a zone of
Siberian larch and
Siberian pine contact.
These species differ in precipitation sensitivity.
Larch can survive at semi desert level of
precipitation (~ 250 mm/yr), whereas Siberian pine is
precipitation sensitive
sensitive, and has optimal growth with
precipitation level >1000 mm/yr.
Life span of Larix sibirica and Siberian pine within
study area is 600 -700 yr and 400 - 500 yr,
respectively.
Results
I. The tree line evolution
Several tree lines were defined and georeferenced.
1. The historical tree line
(i.e., highest tree line during last millennium)
was marked by subfossil trees.
2. Refugee tree line
The maximal tree retreat during Little Ice Age
was marked by old-growth trees (A>300yr).
This “refugee line” is ~70 m lower
in comparison with historical line.
3. A current tree line
4. Regeneration line
Notably that majority of regeneration appeared mainly during the last 2-3
decades.
Siberian pine regeneration
age structure and heights
distribution.
1 – number of viable
seedlings,
2 – dead and dying
samples;
3 – regeneration height.
Tree line evolution during last millennium
Tree mortality was observed during Little Ice Age. The new tree
establishment wave Appeared at the end of the 19th century.
Since 19th century trees
were
“diffusing” into tundra
area
A mean rate of tree line migration into the alpine
tundra during the last century was about
1.0 m/yr;
past three decades of warming increased
migration rate to 2.5 m/yr.
In the beginning of 21st century tree line surpassed
its historical record by 20 m; regeneration line
surpassed it by about 80-100 m
Siberian pine and larch now survive
at elevations up to 150 m higher
in comparison with the maximum
tree line retreat during Little Ice
Period.
Warming (+1.2ºC) was observed mainly during the
winter .
Winter temperatures increase promotes
regeneration recruitment by reducing stem and
needles desiccation and snow abrasion.
II. Changes in tree physiognomy
(prostrate vs. arboreal )
A wide-spread transformation
of krummholz into arboreal
forms has been observed.
The beginning of this process
occurred in the mid 1980s.
These changes in
tree morphology
coincide with
similar events on
the western end of
Eurasia,
in Swedish Scandia
(Kullman, 2007).
This indicates the
Eurasian scale of
the phenomena,
caused some
temperature
threshold “trigger”
effect.
III. Climate-driven forest response and
topography
3000
Areaa increment (ha)
100
Year
2002
90
80
1983
2500
70
1960
2000
60
1500
40
50
30
1000
Areaa increment (%)
3500
20
500
10
0
0
18001900
19002000
2000- 21002100 2200
Elevation (m)
22002300
23002400
The forest area increment dependence on elevation. 1 – total area
increment (ha) (2002 vs 1960 yr); 2, 3 – area increment in percents (2002 vs
1960 yr and 2002 vs 1983 yr, respectively).
25
Slope (º)
20
15
10
1960
1983
2002
Terrain
5
0
18001900
19002000
2000- 2100- 22002100
2200
2300
Elevation (m)
23002400
24002500
The dependence of “slope steepness medians” on elevation. Plotted values are
median steepness values for forested slopes over a range of elevations for 1960,
1983, and 2002. For comparison the median slope value for all terrain in the
study area (i.e. forested and non-forested) is shown.
Elevation (m)
1900-2000
2100-2200
2300-2400
350
Areea increment (%)
300
250
200
150
100
50
0
0
5
10
15
20
25
30
35
Slope (º)
Forest area increment dependence on slope steepness (2002 vs. 1960 yrs.).
Winds impact at least as
important
as temperature for tree
survival
at upper limit due to
desiccation and snow
abrasion
Distribution of forests with respect to azimuth. The radius-vector shows the
dominant direction of forest distribution. Areas of forest for a given year are
proportional to the areas within the boundaries.
Winds forms a “flag-like”
flag like
crown shape, and
caused minimal radial
increment on the windward side
Winter winds in concert with temperature are
forming tree line boundary.
On the wind-protected areas trees grow 100200 m higher.
In the “cross-fire” zone
of upper tree limit
regeneration is located
in the wind-protected sites
IV. Larch vs Siberian pine reaction to
climate change
Larch surpasses Siberian pine in arid zone,
whereas with
precipitation increase
Siberian pine gets
competitive
advantages
Larch surpasses Siberian pine
in its cold and wind resistance,
and is growing arboreal where pine is still prostrate
…whereas Siberian pine
response to warming is
stronger, than larch
(as tree increment
dynamics showed).
Dynamics of apical and radial increments of Siberian pine and larch.
Siberian pine: 1 –- apical increment, 2 -- radial increment.
Larch: 4 –- radial increment.
3, 5 –- pre-warming period.
With temperature and precipitation increase
Siberian pine is increasing its proportion within
upper elevation belt.
It is notable that similar changes are predicted in the
European Alps: increasing proportion of Pinus cembra
(which is, like P. sibirica, is a five-needle pine)
vs. L. decidua at higher altitudes (Bugmann et al, 2005).
Conclusions
1. A temperature increase of 1Сº allows regeneration
to occupy areas 10-- 40 m higher in elevation.
Winter temperatures increase is essential for
regeneration recruitment.
2. A mean rate of tree line migration into the alpine
tundra during the last century was about 1.0 m/yr.
Past three decades of warming increased
migration rate to 2.5 m/yr.
3. Siberian pine and larch trees now survive at
elevations up to 150 m higher in comparison with
the maximum observed tree line retreat during the
last millennium, and surpass the upper historical
line up to 80-100 m.
4. Forest response to warming strongly depends on
elevation, azimuth, and slope steepness.
Warming promotes tree migration to areas less
protected from winter desiccation and snow
abrasion.
5. A warming climate provides competitive
advantages to Siberian pine in comparison with
larch in areas with sufficient precipitation.
Increased Siberian pine proportion, as well as tree
growth and migration into alpine will also decrease
albedo, which may increase warming at the regional
level.
6. Climate-induced forest response
significantly modified the spatial patterns of
high elevation forests in southern Siberia
during the last four decades.
Thank you!