Seminar presented to the Hawkesbury Institute for the Environment's weekly seminar series on 28 October 2015. Topics include a global database of plant biomass and allometry, leaf area index at the EucFACE, and canopy greenness as measured with phenocams.

1. Biomass partitioning, leaf area index, and
canopy greenness:
the Good, the BAAD and the Ugly
HIE, 28 October 2015
Remko Duursma
(and many collaborators)

2. Why are we obsessed with the Earth’s carbon balance?
Source: IPCC
Climate warming is proportional to cumulative CO2 emissions

3. Source: IPCC
Why are we obsessed with the Earth’s carbon balance?
A large fraction of CO2 emissions is sequestered by the land sink

4. But difficult to predict the change in carbon sequestration with climate change
Global vegetation models are used for these predictions.
Friend et al. 2014 (PNAS)
Large
uncertainty!
Very large disagreement between models in the residence time of carbon in ecosystems

5. Global vegetation models make different assumptions about most processes
Medlyn et al. 2015 (Nature Climate Change)

6. Improving representation of residence time
• The residence time will depend in part on the partitioning of carbon to
long-lived stems vs. short-lived foliage
• Leaves turn over quickly, enter the soil carbon cycle where most of the
carbon is released back to the atmosphere
• Woody biomass persist for many years.
• For biomass allocation, current-generation GVMs are highly simplified and
based on very sparse input data or often 'best guesses‘
• We need data

7. Will Cornwell (Twitter, 10 June 2014; @will_cornwell)
Another problem is the huge diversity in plants, and lack of data on most species

8. Plant functional types: simple classification to avoid species-level data
Ca. 45% of the world’s plant species are woody (Fitzjohn et al. 2014)
DeciduousEvergreen
Angiosperm Gymnosperm

9. Global distribution of four major woody plant functional types
Based on data from ESA Climate Change Initiative Land Cover project
(http://www.esa-landcover-cci.org/)

10. But the major PFTs have much overlap in climate space

11. BioScience

12. Gary Hincks
Angiosperms evolved later, are far more diverse than gymnosperms
(copyrighted image)

13. Functional significance of the angiosperm / gymnosperm divide
• Angiosperms differ from gymnosperms in water transport vessel anatomy
(both in stems and in leaves)
• This has consequences for water relations (drought tolerance) and is also
reflected in wood density
Based on data by Zanne et al. 2009 & TRY Categorical Plant Traits

14. Enquist & Niklas 2002 (Science)
Gymnosperms have more foliage biomass than angiosperms
(Although these figures hide this difference very well)
• But, surprisingly, we don’t know whether leaf area differs between PFTs
• Leaf area is relevant because it drives light interception and thus photosynthesis

15. “… some gymnosperms attain a higher productivity than co-occurring angiosperm
trees by accumulating several cohorts of leaves with a higher total leaf area.”
1989

16. Based on data from Wright et al. 2004 (Nature; GlopNET)
Plant functional types differ strongly in leaf mass per area (LMA)
0.25-0.75 quantiles
• In turn, LMA correlates with leaf lifespan, and thus residence
time of foliage.
Can lower leaf mass in deciduous angiosperms be compensated by LMA?

17. Questions
• How does biomass partitioning (leaf vs.
stem) differ between
• Angiosperms vs. Gymnosperms
• Deciduous vs. Evergreen
• Does higher leaf mass per area (LMA) lead
to higher plant leaf mass, or lower leaf
area?
• Does biomass partitioning depend on
climate (mean annual rainfall, mean annual
temperature)?

18. The Biomass and Allometry Database (BAAD)
• data from published and unpublished sources, containing biomass and
size metrics for woody plants
• Authors were contacted directly, and were asked for raw data + metadata
• Individual plants, destructive harvest (not from allometric estimates)
Raw data
 Manipulate data (if needed)
 Extract variables included in BAAD (and assign unified variable names)
 Add new data (e.g. latitude, longitude, species)
 Store metadata (methods for data collection)
 Store study contacts
Clean data • Repeat for each separate study
• Combine all clean datasets
• Post-process (calculate derived
variables, check species names
against databases, etc.)
BAAD
See also our post on https://ropensci.org/blog/

19. See also our post on https://ropensci.org/blog/
Data are available without restrictions (CC0 License)

20. BAAD in numbers
20950 individual woody plants
176 published or unpublished studies
674 species from 120 taxonomic families
Height range from <1cm to 112m,
weight from <1g to >300t.

21. Falster et al. 2015 (Ecology)

22. MAP and MAT of studies in BAAD compared to global land cover
Duursma & Falster in revision

23. Komiyama et al. 2002, 2003

27. Komiyama et al., Japan

28. Ribeiro et al. 2011

29. Australia
Canada
Spain
Malaysia

30. Congo Estonia
Spain Argentina

31. Also : N content, wood density by component (limited)

32. Different scaling for leaf and woody biomass with plant height
Duursma & Falster in revision
Sequioa
sempervirens
Eucalyptus
regnans

33. Terminology
• We here considered aboveground biomass only
(Analysis of root data showed no differences between PFTs)
Leaf Mass Fraction (LMF) = leaf mass / aboveground biomass
Leaf Area Ratio (LAR) = leaf area / aboveground biomass
Leaf Mass per Area (LMA) = leaf mass / leaf area

34. Least-square means
Leaf mass fraction : proportional to leaf mass per area across PFTs
PFTs have similar
leaf area per unit
biomass
 Leaf area ratio does not differ between PFTs
Duursma & Falster in revision

35. Pipe model: every leaf is connected to a unit
sapwood which supplies water to the leaves
When pipes die, they turn into heartwood,
which stays on the plant
When leaves die, they fall off
So we expect leaf / stem ratio to decline over
time, as plants grow in size
Valentine 1988 (AnnBot)
Why does the leaf mass fraction decrease as plants grow?

36. • LMF and LAR are strongly dependent
on plant height
• Leaf mass fraction can be further
decomposed into
where AS is basal stem area
• Similar to LMF, foliage biomass per
unit stem area was proportional to
LMA
• These variables are only very weakly
dependent on plant height

37. Weak and inconsistent effects of climate
• Either by biome (boreal, temperate, tropical) or mean
annual precipitation and mean annual temperature
Duursma & Falster in revision

38. Conclusions
• Three plant functional types differ strongly in leaf mass supported at a
total aboveground biomass or basal stem area
• At given plant height, LMF was proportional to LMA across PFTs
• This also to some extent across species, although there is much
variation within PFTs not accounted for
• As a result, leaf area ratio was not different between PFTs
• No clear effects of climate on biomass partitioning
• These results can be used to constrain biomass partitioning estimates in
global vegetation models, which routinely predict differences between
PFTs

39. But what about leaf area of plant communities?
Leaf area index (LAI) :
amount of leaf area per unit
ground area.
LAI = stocking * tree leaf area
(stocking: number of trees per
unit ground area)
Based on data compiled by Luyssaert et al. 2007

40. n = 943, ‘Natural’ vegetation only. Based on data by Iio et al. 2013
Evergreen gymnosperms have higher LAI than evergreen angiosperms

41. But low LAI in evergreen angiosperms seems largely driven by Eucalyptus!
‘Natural’ vegetation only. Based on data by Iio et al. 2013

42. Leaf area index at the EucFACE : response to elevated CO2 and/or soil water?
• Low LAI for Eucalyptus suggests a response to CO2 is possible
• CO2 enhances photosynthesis, we could expect increased leaf growth?
Review of Free-Air CO2 Enrichment (FACE) sites by Norby & Zak 2011

43. Models largely also predict a positive response to CO2
Model simulations at the EucFACE, over 12 years with variable rainfall
Based on simulation data by Medlyn et al. in revision (Application of ecosystem models to EucFACE)
(%)
Largely because increased productivity leads to more leaf growth

44. EucFACE
• Six 'rings' of 25m diameter
• 3 at ambient [CO2], 3 at ambient + 150ppm
• 'Fully' instrumented
• Supersite nearby
• Eucalyptus tereticornis

46. High variability in rainfall : frequent water limitation

47. LAI estimates via canopy transmittance
Monsi and Saeki 1953
Very long history of estimating LAI based on measurements of light intensity
(The slope of this
relationship is the
‘extinction coefficient’)

48. • 3 sensors below the canopy, one above, each ring.
• PAR is logged every minute since October 2012.
Almost 40 million readings of PAR to date.

49. Measurements of light above and below the canopy
PAR = photosynthetically active radiation
Sunny
Time (hours)
PPFDmolm
2
s
1
0 4 8 12 16 20 24
0500100015002000
Cloudy
Time (hours)
PPFDmolm
2
s
1
0 4 8 12 16 20 240200400600800
PAR
PAR

50. Canopy transmittance : ratio of below / above canopy PAR
Sunny
Time (hours)
TransmittancePPFDbelowPPFDabove
0 4 8 12 16 20 24
0.00.20.40.60.81.0
Cloudy
Time (hours)
TransmittancePPFDbelowPPFDabove
0 4 8 12 16 20 240.00.20.40.60.81.0
‘SunShine’ sensor tells us how cloudy it is (‘fraction diffuse radiation’)

51. LAI from canopy transmittance reveals high temporal and among-ring variability

52. An uninvited guest : psyllids are affecting leaf area dynamics
Cardiaspina sp. Photos: Aidan Hall
Hall et al. 2015
Gherlenda et al. submitted
LerpPsyllid

53. Duursma et al. accepted, GlobChangeBiol
No effect of CO2 on LAI at the EucFACE

54. Why is there no effect of elevated CO2 on LAI at the EucFACE?
1. Leaf growth may not be limited by availability of carbon
• Water limitation
• Nutrient limitations
2. Extra carbon from increased photosynthesis may be allocated elsewhere
• Roots? Storage?
3. It’s the statistics, dummy : not detecting a difference is no evidence for
absence of a difference

55. Least-square means : fitted LAI at a common pre-treatment basal area
Confidence intervals are very small : we could pick up a difference of 6% in
LAI between treatments
Duursma et al. accepted, GlobChangeBiol

56. 'Flat canopy' photos (canopy cover photography)
ca. 30 degrees
• Automated tresholding (blue channel)
• Ca. 21 photos per ring, ca. monthly, when
cloudy
Teresa Gimeno, Matthias Boer

57. Good correspondence between independent methods
Photography-based method also showed no response to elevated CO2
LAIfromcanopytransmittance
Duursma et al. accepted, GlobChangeBiol

58. EucFACE: no effect of elevated CO2 on LAI
Eucalyptus
Norby & Zak 2011 + EucFACE

59. Leaf growth observed

60. 19 Dec 2013 6 Jan 2014
maps.nearmap.com

61. 𝑑𝐿𝐴𝐼
𝑑𝑡
= Leaf production – Leaf shedding

62. Litter production and dynamics of leaf area index
Litter production shows interesting dynamics:
when new leaves are growing, old leaves are shed
MonthlynetchangeinLAI
Monthly litter production
Duursma et al. accepted, GlobChangeBiol

63. So we now how much leaf area there is, but what does it look like?
Is all leaf area functional all of the time?

65. The cameras are programmed to take six photos of each ring, 3 times a day
So far, more than 25,000 photos have been taken since Nov . 2014

66. Canopy greenness
‘Green chromatic coordinate’ (GCC) = R / (R + G + B)
Has been used extensively to study phenology of deciduous canopies
Useful for ‘evergreen’ Eucalyptus canopies?
Richardson et al. 2009 (Ecol. App.)

67. Link to Video
Nov. 2014 Jan. 2015
Sep. 2015 Oct. 2015

69. Ring 3
Duursma, unpublished

70. Ring 6, sunny days

71. The Good : Leaf area index at the EucFACE can be measured accurately with
canopy transmittance, and we can confidently conclude no response to CO2
The BAAD: a global Biomass And Allometry Database reveals consistent patterns
among major woody plant functional types.
… but these do not easily translate to patterns in leaf area index.
The Ugly: Canopy greenness as measured by automated cameras reveals when the
canopy is ugly, but analysis will be difficult

72. Acknowledgments
Biomass And Allometry Database:
Daniel Falster, Masae Ishihara, Diego R. Barneche, Rich G. FitzJohn,
Angelica Vårhammar, and 86 data contributors
EucFACE
Teresa Gimeno, Matthias Boer, Kristine Crous, Mark Tjoelker, David
Ellsworth, Steven Wohl, Vinod Kumar, Craig McNamara, Craig
Barton, Andrew Gherlenda, Jeff Powell
Other
Belinda Medlyn, Martin De Kauwe
www.remkoduursma.com