Climate extremes will cause forest changes

Date:
June 25, 2020
Source:
University of Wu"rzburg
Summary:
No year has been as hot and dry as 2018 since climate records began.

Central European forests showed severe signs of drought
stress. Mortality of trees triggered in 2018 will continue for
several years.



FULL STORY ========================================================================== Until now, 2003 was considered as the driest and hottest year since
the beginning of instrumental climate recording. This record can now
be considered obsolete: "The past five years were among the warmest in
Central Europe since record, and 2018 was the most extreme one," says
Professor Bernhard Schuldt from Julius-Maximilians-Universita"t (JMU)
Wu"rzburg in Bavaria, Germany.


==========================================================================
The average temperature from April to October 2018 was on average 3.3
degrees Celsius above the long-term average and 1.2 degrees higher than
in 2003, Schuldt and a research team report in the journal Basic and
Applied Ecology.

This had dramatic consequences for the forests in Germany, Austria
and Switzerland.

Water transport through the wood collapses "At such temperatures,
our Central European vegetation reaches its limits," says the JMU
professor. Together with other researchers from Germany and Switzerland,
the plant ecologist was able to confirm with physiological measurements:
When it is too hot, the tree simply loses too much water via its
surface. As a result, the negative tension in the wood's conducting
tissue becomes too steep, which ultimately leads to hydraulic failure interrupting the water transport.

Already during the course of the summer, severe drought-related stress
symptoms were observed in most ecologically and economically important
tree species, including widespread leaf discoloration and premature
lead shedding.

Spruce and beech trees most affected Moreover, unexpectedly strong drought-legacy effects were detected in 2019: many broad-leaved trees
did not unfold their leaves -- they had died. Others that survived the
2018 event where not able to withstand the following drought in 2019, or
became increasingly susceptible to infestation with bark beetles or fungi.



========================================================================== "Spruce was most severely affected, mainly because this mountainous
species has been planted outside its natural habitat in Central Europe," explains Schuldt.

"Unexpected was, however, the extent to which beech trees were
affected. Here in Northern Bavaria, I have seen several stands with
complete dieback, especially on sites with shallow soil." Until this
event, beech has been considered as "future tree species," even though
its drought tolerance has been controversially discussed since the hot
drought in 2003.

This year's climatic condition in spring again started too warm and
too dry.

"Now in June 2020 we have fortunately received high amounts of rainfall,"
the Wu"rzburg professor is pleased to report. This has mitigated the
situation, but the water deficit in the deeper soil layers has certainly
not been recharged.

Therefore, he assumes that affected trees will continue to die-off in
the coming years due to legacy effects.

Mixed forests with drought-stress resistant tree species are needed
So what should one do? "I think that extreme drought and heat events
will become more frequent in near future due to climate change," says
the JMU scientist. At least locally, forests will therefore have to
be restructured.

Mixed forests with tree species that are as drought-resistant as possible
are needed. "However, we still have to identify what species combination
is best suited, also from an ecological and economic perspective. This is
going to take some time." Monitoring forests with Earth observation data
More data are needed to manage this forest conversion as good as possible.

"Although damages to our forests are obvious, it is difficult to quantify
them at high temporal and spatial resolution." Therefore, remote
monitoring systems are needed to support ground-based measures. Remotely
sensed airborne or satellite earth observation data with high temporal
and spatial resolution will enable us to track individual tree dieback
and provide these data to the scientific community. "In the US, such
systems are operating in given regions, but they are currently lacking
for Central Europe. We will not be able to monitor forest health from
the ground at larger scales."

========================================================================== Story Source: Materials provided by University_of_Wu"rzburg. Original
written by Robert Emmerich. Note: Content may be edited for style
and length.


========================================================================== Journal Reference:
1. Bernhard Schuldt, Allan Buras, Matthias Arend, Yann Vitasse, Carl
Beierkuhnlein, Alexander Damm, Mana Gharun, Thorsten E.E. Grams,
Markus Hauck, Peter Hajek, Henrik Hartmann, Erika Hiltbrunner,
Gu"nter Hoch, Meisha Holloway-Phillips, Christian Ko"rner, Elena
Larysch, Torben Lu"bbe, Daniel B. Nelson, Anja Rammig, Andreas
Rigling, Laura Rose, Nadine K. Ruehr, Katja Schumann, Frank Weiser,
Christiane Werner, Thomas Wohlgemuth, Christian S. Zang, Ansgar
Kahmen. A first assessment of the impact of the extreme 2018 summer
drought on Central European forests.

Basic and Applied Ecology, 2020; 45: 86 DOI:
10.1016/j.baae.2020.04.003 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/06/200625115913.htm

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