The document discusses the impacts of drought on forest ecosystems, highlighting an increase in tree mortality linked to climate change. It outlines objectives such as understanding forest mortality patterns and defining ecological drought, while detailing the formation of a dead wood collective comprised of various experts. The document also emphasizes the development of databases and frameworks for assessing drought impacts and plant responses, aiming to enhance knowledge of species resilience and drought tolerance traits.

1. Drought impacts on ecosystems
Dead wood group – Forest mortality and Australian
terrestrial carbon stores
Patrick Mitchell – CSIRO Ecosystem Sciences

2. Background
Recent reviews suggest an increase in the frequency and
scale of mortality events and implicate temperature
increases as amplifying stress on tree species

3. Background
Recent reviews suggest an increase in the frequency and
scale of mortality events and implicate temperature
increases as amplifying stress on tree species
Forest
dieback
and
mortality
Energy
Budget
Carbon
budget
Wood
quality
Water
budget
Biodiversity
Biomass
production

4. Group objectives
•Understand patterns in forest mortality across a
diverse range of ecosystems
•Define ecological drought in a way that facilitates
comparison of responses across ecosystems and
biomes
•Determine the relationship between plant water
relations, drought tolerance traits and climate
through the compilation of existing data.

5. Dead wood collective -who are we?
Group comprised:
-Physiologists: water
relations, hydraulics, C
dynamics
-Ecologists: invasives,
recruitment and
restoration
-Modellers: process-
based, carbon
accounting/dynamics
-Industry reps: forest C
accounting

6. Forest mortality database: if a tree falls
in woods...
-Living database based on
lit survey of known tree
die-off events associated
with drought
-Provides data on basic
attributes of site and
event
-Data tends to be biased,
incomplete and patchy
-Develop a mortality
niche (Mitchell et al. Ecol.
and Evol. 2014)

7. Data synthesis: towards an ecologically
relevant definition of drought
-Apply a risk-based framework to define drought
impacts on ecosystems
-Assess exposure using a probabilistic approach
-Quantify key features of ecosystem resistance
and resilience to drought

8. Data synthesis:
- Involves a broad
assessment of drought to
include processes such as
recruitment, productivity
and canopy
collapse/mortality
- Develop approach to
merge exposure and
sensitivity to predict species
and ecosystem responses
- Example: Using ecological
transformations we can
estimate droughts that may
exceed these physiological
thresholds
Probability of occurrence
i) Recruitment failure – 18 %
ii) Cessation of productivity – 8 %
iii) Canopy collapse – 2 %

9. Data synthesis and analysis:
Drought tolerance traits
-What traits are
important? Develop a
conceptual model of plant
responses to drought
-Assemble trait database
for plant water relations of
Aust. spp. and utilise
existing
-What traits and important
thresholds can we use to
understand species
bioclimatic limits?
Recovery / non-
recovery
time
leaf
lethal
hydraulic
isolation
Capacitance phase
Stomatal phase
Is P50 this
threshold?
0 500 1000 1500 2000 2500
-16-14-12-10-8-6-4-2
Gymnosperms
MAP (mm)
P50MPa
Wooddensitygcm
3

< 0.45
0.45 - 0.60
0.60 - 0.75
> 0.75
Angiosperms
MAP (mm)
P50MPa
Wooddensitygcm
3

< 0.45
0.45 - 0.60
0.60 - 0.75
> 0.75
0 500 1000 1500 2000 2500
MAP (mm)
P50MPa

10. What we learned from our working
group
-Event database: key outcome was establishing
approaches to characterise event-based data and
how to use them
-Data synthesis: this component produced some
novel and testable frameworks and approaches to
broaden our understanding of drought and forests
-Trait database: take a step back and see how the
system behaves and see if we are asking the right
questions and using the right trait data