Drought impacts on ecosystems

Dead wood group – Forest mortality and Australian terrestrial carbon stores

Patrick Mitchell – CSIRO Ecosystem Sciences

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

BackgroundRecent 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

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.

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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

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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)

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Data synthesis: towards an ecologically relevant definition of drought

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-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

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

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Probability of occurrence i) Recruitment failure – 18 %ii) Cessation of productivity – 8 %iii) Canopy collapse – 2 %

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?

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Recovery / non-recovery

time

Yleaf

Ylethal

Yhydraulic

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

MP

a

Wooddensitygcm 3

< 0.450.45 - 0.600.60 - 0.75> 0.75

Angiosperms

MAP (mm)P

50

MP

a

Wooddensitygcm 3

< 0.450.45 - 0.600.60 - 0.75> 0.75

0 500 1000 1500 2000 2500

MAP (mm)

P50

M

Pa

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

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