Imaging spectroscopy reveals the effects of topography and logging on the leaf chemistry of tropical forest canopy trees

Tom Swinfield, Sabine Both, Terhi Riutta, Boris Bongalov, Dafydd Elias, Noreen Majalap-Lee, Nicholas Ostle, Martin Svátek, Jakub Kvasnica, David Milodowski, Tommaso Jucker, Robert M Ewers, Yi Zhang, David Johnson, Yit Arn Teh, David F R P Burslem, Yadvinder Malhi, David Coomes*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

22 Citations (Scopus)
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Abstract

Logging, pervasive across the lowland tropics, affects millions of hectares of forest, yet its influence on nutrient cycling remains poorly understood. One hypothesis is that logging influences phosphorus (P) cycling, because this scarce nutrient is removed in extracted timber and eroded soil, leading to shifts in ecosystem functioning and community composition. However, testing this is challenging because P varies within landscapes as a function of geology, topography and climate. Superimposed upon these trends are compositional changes in logged forests, with species with more acquisitive traits, characterized by higher foliar P concentrations, more dominant. It is difficult to resolve these patterns using traditional field approaches alone. Here, we use airborne light detection and ranging-guided hyperspectral imagery to map foliar nutrient (i.e. P, nitrogen [N]) concentrations, calibrated using field measured traits, over 400 km2 of northeastern Borneo, including a landscape-level disturbance gradient spanning old-growth to repeatedly logged forests. The maps reveal that canopy foliar P and N concentrations decrease with elevation. These relationships were not identified using traditional field measurements of leaf and soil nutrients. After controlling for topography, canopy foliar nutrient concentrations were lower in logged forest than in old-growth areas, reflecting decreased nutrient availability. However, foliar nutrient concentrations and specific leaf area were greatest in relatively short patches in logged areas, reflecting a shift in composition to pioneer species with acquisitive traits. N:P ratio increased in logged forest, suggesting reduced soil P availability through disturbance. Through the first landscape scale assessment of how functional leaf traits change in response to logging, we find that differences from old-growth forest become more pronounced as logged forests increase in stature over time, suggesting exacerbated phosphorus limitation as forests recover.

Original languageEnglish
Pages (from-to)989-1002
Number of pages14
JournalGlobal Change Biology
Volume26
Issue number2
Early online date17 Dec 2019
DOIs
Publication statusPublished - 1 Feb 2020

Bibliographical note

We gratefully acknowledge the Sabah Biodiversity Council, the Maliau Basin and Danum Valley Management Committees, the Institute for Tropical Biology and Conservation at the University of Malaysia, Sabah, and the Sabah Forestry Department, South East Asia Rainforest Research Partnership, Yayasan Sabah, Benta Wawasan, the State Secretary, Sabah Chief Minister's Departments, Sabah Biodiversity Centre and the Economic Planning Unit for their support, access to the field site and for permission to carry out fieldwork in Sabah. This work was funded through NERC's Human Modified Tropical Forests research programme (grant number NE/K016377/1 awarded to the BALI consortium) and by the Sime Darby Foundation. MS and JK were funded through a grant from the Ministry of Education, Youth and Sports of the Czech Republic (grant number: INTER‐TRANSFER LTT17017). DAC was supported by an international travel grant from the Leverhulme Trust. DAC and TS were supported by the Frank Jackson Trust. We are grateful to NERC's Airborne Research Facility and Data Analysis Node for conducting the airborne survey and preprocessing the data. We thank Dr. Reuben Nilus who facilitated research in Sabah, and Laura Kruitbos, Unding Jami and the many field assistants who contributed to logistics and data collection. We thank Greg Asner for helpful discussions with DAC while at the Carnegie lab, five anonymous reviewers and Dr Toby Jackson for their highly relevant and constructive input.

Keywords

  • imaging spectroscopy
  • leaf traits
  • logging
  • nutrient availability
  • phosphorus
  • specific leaf area
  • topography
  • tropical forest

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