Global Change Abstracts The Swiss Contribution - SCNAT

Global Change Abstracts – The Swiss Contribution | Terrestrial Ecosystems 89
deeper than 30 cm since abandonment of waste
application about 50 years ago. The total amount
of BC in the Witzwil profiles ranged from 3.2 to 7.5
kg BC m(-2), with 21 to 69 percent of it stemming
from below the former ploughing depth. Under
the premise of negligible rates of BC consumption
since abandonment of waste application, minimum
BC transport rates in these peats are 0.6 to
1.2 cm a(-1). The high mobility of BC might be explained
by high macropore volumes in combination
with occasional water saturation. By means
of DSC peak temperatures, different types of BC
could be distinguished, with deeper horizons containing
BC of higher thermal stability. Application
of combustion residues likely involved a mixture
of various BC types, of which thermally more
stable ones, most likely soots, were preferentially
transported downwards.
Biogeosciences, 2007, V4, N3, pp 425-432.
08.1-140
Tree species diversity affects canopy leaf temperatures
in a mature temperate forest
Leuzinger S, Körner C
Switzerland
Forestry , Biodiversity , Plant Sciences , Ecology
Forest canopies play a major role in biosphereatmosphere
interaction. Their actual temperature
may deviate substantially from ambient atmospheric
conditions as reported by weather stations.
While there is a long tradition of false-colour imagery,
new digital technologies in combination
with IR transmission lenses and autocalibration
routines permit unprecedented insight into the
actual temperature regimes in canopies. We report
canopy leaf temperature distribution over
space and time assessed over a 35 m tall mixed
deciduous forest in NW Switzerland by means of
a construction crane and a high resolution thermal
camera. At an air temperature of 25 degrees
C, conifers (Picea abies, Pinus sylverstris and Larix
decidua) and deciduous broad-leaved trees with
exceptionally high transpiration (Quercus petraea)
or very open, low density canopies (Prunus
avium) exhibited mean canopy leaf temperatures
close to air temperature (0.3-2.7 K above ambient)
and the maximum amplitude within a given
crown reached 69 K. In contrast, broad-leaved deciduous
species with dense canopies (Fagus sylvatica,
Carpinus betulus and Tilia platyphyllos)
were 4.5-5 K warmer than air temperature and
showed within canopy temperature amplitudes of
10-12 K. Calculated leaf boundary resistance was
clearly lower for conifers (3-24 m s(-1)) than for
broad-leaved trees (33-64 m s(-1)). The study illustrates
that mean leaf temperatures in forest trees
are not adequately explained by either stomatal
conductance or leaf dimensions, but strongly depend
on canopy architecture (leaf area density,
branching habits) in combination with leaf traits.
Aerodynamic leaf and canopy characteristics lead
to strongly enhanced vapour pressure gradients
(evaporative forcing) and leaf temperatures vary
enormously over short distances, calling for statistical
temperature models (frequency distribution)
rather than the use of means in any flux calculations.
The presence/absence of certain tree taxa
plays a key role in forest surface temperature.
Agricultural and Forest Meteorology, 2007, V146,
N1-2, SEP 11, pp 29-37.
08.1-141
Water savings in mature deciduous forest
trees under elevated CO 2
Leuzinger S, Körner C
Switzerland
Forestry , Plant Sciences , Biodiversity , Ecology
Stomatal conductance of plants exposed to elevated
CO 2 is often reduced. Whether this leads
to water savings in tall forest-trees under future
CO 2 concentrations is largely unknown but could
have significant implications for climate and hydrology.
We used three different sets of measurements
(sap flow, soil moisture and canopy temperature)
to quantify potential water savings under
elevated CO 2 in a ca. 35 m tall, ca. 100 years old
mixed deciduous forest. Part of the forest canopy
was exposed to 540 ppm CO 2 during daylight
hours using free air CO 2 enrichment (FACE) and
the Swiss Canopy Crane (SCC) . Across species and
a wide range of weather conditions, sap flow was
reduced by 14% in trees subjected to elevated CO 2,
yielding ca. 10% reduction in evapotranspiration.
This signal is likely to diminish as atmospheric
feedback through reduced moistening of the air
comes into play at landscape scale. Vapour pressure
deficit (VPD)-sap flow response curves show
that the CO 2 effect is greatest at low VPD, and that
sap flow saturation tends to occur at lower VPD
in CO 2-treated trees. Matching stomatal response
data, the CO 2 effect was largely produced by Carpinus
and Fagus, with Quercus contributing little.
In line with these findings, soil moisture at 10
cm depth decreased at a slower rate under high-
CO 2 trees than under control trees during rainless
periods, with a reversal of this trend during
prolonged drought when CO 2-treated trees take
advantage from initial water savings. High-resolution
thermal images taken at different heights
above the forest canopy did detect reduced water
loss through altered energy balance only at < 5 m
distance (0.44 K leaf warming of CO 2- treated Fa-