Changes in leaf functional traits of rainforest canopy trees associated with an El Nino event in Borneo

M. H. Nunes, S. Both, B. Bongalov, C. Brelsford, S. Khoury, D. F. R. P. Burslem, C. Philipson, N. Majalap, T. Riutta, D. A. Coomes (Lead / Corresponding author), M. E. J. Cutler (Lead / Corresponding author)

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Abstract

El Nino events generate periods of relatively low precipitation, low cloud cover and high temperature over the rainforests of Southeast Asia, but their impact on tree physiology remains poorly understood. Here we use remote sensing and functional trait approaches - commonly used to understand plant acclimation to environmental fluctuations - to evaluate rainforest responses to an El Nino event at a site in northern Borneo. Spaceborne measurements (i.e. normalised difference vegetation index calculated from Moderate Resolution Imaging Spectroradiometer data) show the rainforest canopy greened throughout 2015, coinciding with a strengthening of the El Nino event in Sabah, Malaysia, then lost greenness in early 2016, when the El Nino was at its peak. Leaf chemical and structural traits measured for mature leaves of 65 species (104 branches from 99 tree canopies), during and after this El Nino event revealed that chlorophyll and carotenoid concentrations were 35% higher in mid 2015 than in mid 2016. Foliar concentrations of the nutrients N, P, K and Mg did not vary, suggesting the mineralisation and transportation processes were unaffected by the El Nino event. Leaves contained more phenolics, tannins and cellulose but less Ca and lignin during the El Nino event, with concentration shifts varying strongly among species. These changes in functional traits were also apparent in hyperspectral reflectance data collected using a field spectrometer, particularly in the shortwave infrared region. Leaf-level acclimation and leaf turnover could have driven the trait changes observed. We argue that trees were not water limited in the initial phase of the El Nino event, and responded by flushing new leaves, seen in the canopy greening trend and higher pigment concentrations (associated with young leaves); we argue that high evaporative demand and depleted soil water eventually caused leaves to drop in 2016. However, further studies are needed to confirm these ideas. Time-series of vegetation dynamics obtained from space can only be understood if changes in functional traits, as well as the quantity of leaves in canopies, are monitored on the ground.

Original languageEnglish
Article number085005
Pages (from-to)1-13
Number of pages13
JournalEnvironmental Research Letters
Volume14
Issue number8
DOIs
Publication statusPublished - 29 Jul 2019

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El Nino-Southern Oscillation
Borneo
rainforest
El Nino
canopy
Tannins
Physiology
Chlorophyll
Lignin
Pigments
Nutrients
Spectrometers
Water
Time series
Remote sensing
Cellulose
Infrared radiation
Soils
Imaging techniques
Acclimatization

Keywords

  • El Nino
  • ground-based reflectance
  • leaf greening
  • leaf trait dynamics
  • tropical forests

Cite this

Nunes, M. H. ; Both, S. ; Bongalov, B. ; Brelsford, C. ; Khoury, S. ; Burslem, D. F. R. P. ; Philipson, C. ; Majalap, N. ; Riutta, T. ; Coomes, D. A. ; Cutler, M. E. J. / Changes in leaf functional traits of rainforest canopy trees associated with an El Nino event in Borneo. In: Environmental Research Letters. 2019 ; Vol. 14, No. 8. pp. 1-13.
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abstract = "El Nino events generate periods of relatively low precipitation, low cloud cover and high temperature over the rainforests of Southeast Asia, but their impact on tree physiology remains poorly understood. Here we use remote sensing and functional trait approaches - commonly used to understand plant acclimation to environmental fluctuations - to evaluate rainforest responses to an El Nino event at a site in northern Borneo. Spaceborne measurements (i.e. normalised difference vegetation index calculated from Moderate Resolution Imaging Spectroradiometer data) show the rainforest canopy greened throughout 2015, coinciding with a strengthening of the El Nino event in Sabah, Malaysia, then lost greenness in early 2016, when the El Nino was at its peak. Leaf chemical and structural traits measured for mature leaves of 65 species (104 branches from 99 tree canopies), during and after this El Nino event revealed that chlorophyll and carotenoid concentrations were 35{\%} higher in mid 2015 than in mid 2016. Foliar concentrations of the nutrients N, P, K and Mg did not vary, suggesting the mineralisation and transportation processes were unaffected by the El Nino event. Leaves contained more phenolics, tannins and cellulose but less Ca and lignin during the El Nino event, with concentration shifts varying strongly among species. These changes in functional traits were also apparent in hyperspectral reflectance data collected using a field spectrometer, particularly in the shortwave infrared region. Leaf-level acclimation and leaf turnover could have driven the trait changes observed. We argue that trees were not water limited in the initial phase of the El Nino event, and responded by flushing new leaves, seen in the canopy greening trend and higher pigment concentrations (associated with young leaves); we argue that high evaporative demand and depleted soil water eventually caused leaves to drop in 2016. However, further studies are needed to confirm these ideas. Time-series of vegetation dynamics obtained from space can only be understood if changes in functional traits, as well as the quantity of leaves in canopies, are monitored on the ground.",
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Nunes, MH, Both, S, Bongalov, B, Brelsford, C, Khoury, S, Burslem, DFRP, Philipson, C, Majalap, N, Riutta, T, Coomes, DA & Cutler, MEJ 2019, 'Changes in leaf functional traits of rainforest canopy trees associated with an El Nino event in Borneo', Environmental Research Letters, vol. 14, no. 8, 085005, pp. 1-13. https://doi.org/10.1088/1748-9326/ab2eae

Changes in leaf functional traits of rainforest canopy trees associated with an El Nino event in Borneo. / Nunes, M. H.; Both, S.; Bongalov, B.; Brelsford, C.; Khoury, S.; Burslem, D. F. R. P.; Philipson, C.; Majalap, N.; Riutta, T.; Coomes, D. A. (Lead / Corresponding author); Cutler, M. E. J. (Lead / Corresponding author).

In: Environmental Research Letters, Vol. 14, No. 8, 085005, 29.07.2019, p. 1-13.

Research output: Contribution to journalArticle

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AU - Nunes, M. H.

AU - Both, S.

AU - Bongalov, B.

AU - Brelsford, C.

AU - Khoury, S.

AU - Burslem, D. F. R. P.

AU - Philipson, C.

AU - Majalap, N.

AU - Riutta, T.

AU - Coomes, D. A.

AU - Cutler, M. E. J.

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AB - El Nino events generate periods of relatively low precipitation, low cloud cover and high temperature over the rainforests of Southeast Asia, but their impact on tree physiology remains poorly understood. Here we use remote sensing and functional trait approaches - commonly used to understand plant acclimation to environmental fluctuations - to evaluate rainforest responses to an El Nino event at a site in northern Borneo. Spaceborne measurements (i.e. normalised difference vegetation index calculated from Moderate Resolution Imaging Spectroradiometer data) show the rainforest canopy greened throughout 2015, coinciding with a strengthening of the El Nino event in Sabah, Malaysia, then lost greenness in early 2016, when the El Nino was at its peak. Leaf chemical and structural traits measured for mature leaves of 65 species (104 branches from 99 tree canopies), during and after this El Nino event revealed that chlorophyll and carotenoid concentrations were 35% higher in mid 2015 than in mid 2016. Foliar concentrations of the nutrients N, P, K and Mg did not vary, suggesting the mineralisation and transportation processes were unaffected by the El Nino event. Leaves contained more phenolics, tannins and cellulose but less Ca and lignin during the El Nino event, with concentration shifts varying strongly among species. These changes in functional traits were also apparent in hyperspectral reflectance data collected using a field spectrometer, particularly in the shortwave infrared region. Leaf-level acclimation and leaf turnover could have driven the trait changes observed. We argue that trees were not water limited in the initial phase of the El Nino event, and responded by flushing new leaves, seen in the canopy greening trend and higher pigment concentrations (associated with young leaves); we argue that high evaporative demand and depleted soil water eventually caused leaves to drop in 2016. However, further studies are needed to confirm these ideas. Time-series of vegetation dynamics obtained from space can only be understood if changes in functional traits, as well as the quantity of leaves in canopies, are monitored on the ground.

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KW - ground-based reflectance

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