The impact of logging on vertical canopy structure across a gradient of tropical forest degradation intensity in Borneo

David T. Milodowski* (Corresponding Author), David A. Coomes, Tom Swinfield, Tommaso Jucker, Terhi Riutta, Yadvinder Malhi, Martin Svátek, Jakub Kvasnica, David F.R.P. Burslem, Robert M. Ewers, Yit Arn Teh, Mathew Williams

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

32 Citations (Scopus)

Abstract

Forest degradation through logging is pervasive throughout the world's tropical forests, leading to changes in the three-dimensional canopy structure that have profound consequences for wildlife, microclimate and ecosystem functioning. Quantifying these structural changes is fundamental to understanding the impact of degradation, but is challenging in dense, structurally complex forest canopies. We exploited discrete-return airborne LiDAR surveys across a gradient of logging intensity in Sabah, Malaysian Borneo, and assessed how selective logging had affected canopy structure (Plant Area Index, PAI, and its vertical distribution within the canopy). LiDAR products compared well to independent, analogue models of canopy structure produced from detailed ground-based inventories undertaken in forest plots, demonstrating the potential for airborne LiDAR to quantify the structural impacts of forest degradation at landscape scale, even in some of the world's tallest and most structurally complex tropical forests. Plant Area Index estimates across the plot network exhibited a strong linear relationship with stem basal area (R2 = 0.95). After at least 11–14 years of recovery, PAI was ~28% lower in moderately logged plots and ~52% lower in heavily logged plots than that in old-growth forest plots. These reductions in PAI were associated with near-complete lack of trees >30-m tall, which had not been fully compensated for by increasing plant area lower in the canopy. This structural change drives a marked reduction in the diversity of canopy environments, with the deep, dark understorey conditions characteristic of old-growth forests far less prevalent in logged sites. Full canopy recovery is likely to take decades. Synthesis and applications. Effective management and restoration of tropical forests requires detailed monitoring of the forest and its environment. We demonstrate that airborne LiDAR can effectively map the canopy architecture of the complex tropical forests of Borneo, capturing the three-dimensional impact of degradation on canopy structure at landscape scales, therefore facilitating efforts to restore and conserve these ecosystems.

Original languageEnglish
Pages (from-to)1764-1775
Number of pages12
JournalJournal of Applied Ecology
Volume58
Issue number8
Early online date1 Jun 2021
DOIs
Publication statusPublished - 1 Aug 2021

Bibliographical note

Funding Information:
D.T.M., M.W.: UK NERC (NE/K016458/1, NE/M017389/1) and NCEO; T.J.: UK NERC (NE/S01537X/1); T.S.: Frank Jackson Foundation; Y.M.: ERC (GEM-TRAIT; Grant 321131); M.S.: INGO II (LG15051); J.K.: IGA (LDF_VP_2016040). Thanks to: Sime Darby Foundation to the SAFE Project; Yayasan Sabah; Maliau Basin and Danum Valley Management Committees; NERC Airborne Remote Sensing Facility; NERC Data Analysis Node; Rostin Jantan; SAFE Carbon Team; Danum 50-ha plot team; Laura Kruitbos, Unding Jami, Alexander Karolus, Ryan Gray and Reuben Nilus. Finally, we are very grateful for the comments from the Associate Editor and two anonymous reviewers.

Publisher Copyright:
© 2021 British Ecological Society

Data Availability Statement

Source code (python) is available to via GitHub: https://github.com/DTMilodows ki/LiDAR_canopy_structure_JAppEcol. The data are available via the SAFE archive: https://doi.org/10.5281/ze-nodo.4572775 (Milodowski et al., 2021).

Supporting Information:
Additional supporting information may be found online in the Supporting Information section.

Keywords

  • Borneo
  • canopy structure
  • degradation
  • leaf area index
  • LiDAR
  • logging
  • tropical rainforest

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