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Summary
Climate
has
a
large
impact
on
the
occurrence,
growth
and
development
of
plant
species.
In
case
of
global
climate
change,
most
animal
species
will
be
able
to
survive
by
moving
to
more
suitable
areas.
However,
most
plants
are
not
able
to
do
so
and
as
a
consequence
have
to
apply
various
adaptation
and
survival
strategies
and
produce
seeds.
Dispersed
seeds
may
reach
the
more
suitable
areas
and
after
germination,
may
settle
as
a
start
for
a
new
population.
This
study
focusses
on
two
areas
with
very
different
climates,
in
the
south
in
the
Netherlands
with
a
moderate
maritime
climate
and
in
the
north
on
the
island
of
Spitsbergen,
part
of
the
Svalbard
archipelago
with
an
Arctic
climate.
Both
areas
have
faced
an
annual
average
temperature
increase
of
1.2
oC
respectively
1.4
oC
since
the
last
century
and
this
warming
continued
during
the
first
decade
of
the
present
century.
By
the
end
of
the
21th
century,
a
global
temperature
increase
that
will
vary
from
1.8
oC
–
6.4
oC
is
expected
(e.g.
IPCC
2007).
Related
to
increased
temperatures
are
increased
cloud
formation
and
the
amount
of
precipitation
that
has
increased
up
to
14%
regionally
in
northwest
Europe.
Thanks
to
a
dense
network
of
observers
in
many
European
countries,
a
number
of
data
on
the
occurrence
and
the
phenology
of
plant
species
in
response
to
global
climate
change
have
been
collected
(e.g.
Parmesan
2006,
Root
et
al.
2003).
The
analysis
of
this
data
showed
that
the
on‐going
global
climate
change
(warming)
resulted
in
a
northward
shift
up
to
over
6
km
per
decade
of
many
species
in
Europe,
reaching
new
areas
north
of
their
previous
range
and
leaving
earlier
populated
southern
areas
(longitudinal
shifts).
Similarly,
species
moved
upward
from
valleys
to
more
uphill
areas
(altitudinal
shifts),
up
to
over
6
m
per
decade.
In
addition
to
these
range
shifts,
the
phenology
of
flowering
and
leaf
unfolding
as
studied
in
phenological
gardens
across
a
large
geographical
area
has
shown
advanced
phenology
for
many
plant
species,
ranging
from
1.5
over
3
days
per
decade.
Up
till
now
the
methods
used
to
determine
occurrences
and
phenology
of
species
are
mainly
descriptive
and
observed
changes
are
correlated
with
environmental
factors,
thus
limiting
a
more
causal
interpretation
of
range
shifts
and
phenological
events.
This
applies
to
one
of
the
European
dwarf
shrub
species,
Crowberry
(Empetrum
nigrum)
that
was
subjected
to
manipulated
environmental
conditions
since
2005.
This
heathland
dwarf
shrub
species
is
distributed
within
the
cool
and
humid
Boreal‐(sub)Arctic
and
Atlantic
biomes
in
Europe.The
more
southern
occurrences
of
Crowberry
in
Germany,
the
Netherlands
and
Great
Britain
tend
to
decrease
since
the
fifties
of
the
last
century,
while
occurrences
north
at
Spitsbergen
are
increasing.
Thus,
Crowberry
seems
to
demonstrate
responsiveness
to
climate
changes
both
at
the
southern
and
northern
range
margins.
By
manipulating
three
climate
factors
at
these
range
margins,
simulating
global
climate
change,
we
intend
to
increase
our
knowledge
in
the
mechanisms
underpinning
these
shifts
and
including
our
knowledge
of
phenology
and
fruit
production.
By
doing
so
we
aimed
to
gather
experimental
evidence
to
confirm
or
to
falsify
our
hypotheses
concerning
the
observed
range
shifts
and
the
altered
phenology.
These
field
experiments,
both
at
the
southern
and
northern
range
margin
of
Crowberry,
are
to
our
knowledge
the
first
to
increase
our
knowledge
of
the
species’
ecological
responses
to
climate
change.
The
temperature
was
manipulated
with
open
top
chambers
(OTCs)
(Figures
2‐2,
2‐4)
from
2005‐
2010
and
at
the
southern
range
margin
this
resulted
in
an
average
increase
of
air
temperature
of
2.0
oC
during
summer
and
an
average
annual
increase
of
1.2
oC.
On
Spitsbergen
the
increase
was
1.7
o
C
during
the
summer
period.
These
results
simulate
the
observed
and
expected
climate
change
in
the
course
of
this
century
in
a
realistic
way.
Ambient
precipitation
was
doubled
(2006‐2010),
based
on
the
increased
precipitation
measured
since
the
fifties
of
the
20th
century.
Also
Crowberry
was
subjected
to
increased
cloudiness
(2007‐2009)
by
reducing
the
amount
of
incoming
sunlight
(Figure
2‐5),
reaching
the
plant’s
leaf
surface
We
based
this
reduction
on
the
observed
increased
cloudiness
(global
dimming;
e.g.
Stanhill
2005).
Year‐round,
plants
were
subjected
to
these
manipulations,
thus
ensuring
that
plants
were
experiencing
at
least
several
year
cycles
to
altered
conditions.
At
the
southern
range
margin,
we
expected
direct
responses
resulting
in
decreased
vitality
and
increased
vitality
north.
We
also
subjected
the
co‐occurring
dwarf
shrubs
Heather
(Calluna
vulgaris)
and
Cross‐leaved
heather
(Erica
tetralix)
to
experimentally
simulated
global
change
with
the
intention
to
compare
ecological
responses
and
to
consider
possible
interactions
between
the
three
species
studied.
At
the
southern
range
margin,
compared
to
data
valued
at
100%
from
control
plots
and
in
contrast
to
our
expectation,
increased
temperatures
caused
increased
shoot
growth,
increased
biomass,
advanced
flowering
and
an
extended
growing
season
of
Crowberry,
both
in
spring
and
autumn.
The
berries
developed
in
OTCs
also
demonstrated
a
larger
diameter
and
increased
weight.
Shoots
of
Heather
increased
by
+
79%,
of
Cross‐leaved
heather
by
+
69%
and
those
of
Crowberry
by
+
200%
(Table
5‐9,
Chapter
5).
Doubled
precipitation
(Chapter
6)
caused
shoots
–
the
only
parameters
studied
‐
of
Crowberry
to
increase
by
+
108%,
of
Cross‐leaved
heather
by
+
80%
and
of
Heather
by
+
66%.
The
manipulated
increased
cloudiness
resulted
in
significantly
longer
shoots
of
Crowberry
with
more,
longer
and
thinner
leaves,
while
leaf
weight
decreased.
Stem
diameter
did,
in
contrast
to
our
expectations,
not
change.
The
shoots
of
Crowberry
increased
by
+
98%,
of
Heather
by
+
27%
and
of
Cross‐leaved
heather
by
+
20%.
Both
Heather
and
Cross‐leaved
heather
were
expected
to
respond
positively
to
the
manipulated
environmental
conditions.
Heather,
with
a
continental
distribution,
profited
most
of
the
warming
by
increased
shoot
length,
but
also
by
the
extension
of
the
growing
season
by
14
weeks
(Figure
5‐5)
and
an
increased
shoot
growth
rate
(Table
5‐2).
The
increased
shoot
length
(+
80%)
of
Cross‐leaved
heather
in
response
to
doubled
precipitation
expressed
the
species’
preference
for
moist
Atlantic
growing
conditions
(Table
1‐7).
On
Spitsbergen,
at
the
northern
range
margin
of
Empetrum,
increased
temperature
in
OTCs
caused,
according
to
our
expectations
increased
growth,
increased
berry
occurrences
with
significant
increased
diameter
and
weight.
However,
air
warming
by
OTCs
did
not
cause
the
expected
increase
of
the
growing
season
but
increased
accumulated
heat
(Growing
Degree
Day‐value)
was
observed.
Similarly,
this
increased
growing
season
intensity
has
been
reported
by
Weijers
(2012)
and
Weijers
et
al.
(2013b)
with
OTCs
in
the
high
Arctic.
In
Chapter
8
of
this
thesis,
the
results
of
our
field
experiments
with
manipulated
climate
factors
on
Crowberry,
Heather
and
Cross‐leaved
heather
have
been
evaluated
and
discussed.
We
concluded
that
the
response
of
Crowberry
to
manipulated
warming
does
not
provide
conclusive
evidence
for
the
observed
northward
shift
at
the
southern
range
margin.
The
positive
response
of
the
dwarf
shrub
species
to
increased
precipitation
was
attributed
to
water
limitation
in
the
dry
dune
research
area
while
responses
to
increased
cloudiness
indicated
that
Crowberry
(more
than
Heather
and
Cross‐leaved
heather)
is
able
to
withstand
a
certain
amount
of
shade,
explaining
its
occurrence
in
the
understorey
of
wooded
areas.
In
summary,
the
ecological
responses
found
do
not
readily
explain
the
observed
northward
shift
at
the
southern
range
margin.
However,
for
the
direct
responses
to
temperature
manipulation
at
the
northern
range
margin
we
concluded
that
these
are
in
line
with
the
increased
occurrences
of
Empetrum
nigrum
on
Spitsbergen.