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

Abstract

1. 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.2. 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).3. 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. 4. Plant Area Index estimates across the plot network exhibited a strong linear relationship with stem basal area (R 2 = 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. | 1765Journal of Applied Ecology MILODOWSKI et aL.

Reduced deforestation and degradation in Indigenous Lands pan-tropically

“…A myriad of other factors that we were unable to quantify in our analysis also contribute to losses in forest integrity across tropical moist forests 37 . These include alteration of microclimates, proliferation of lianas, and the cascading ecological effects resulting from selective logging, road edges, and reduced populations of large-bodied vertebrates 38,39 . The complexities of monitoring forest degradation using remote sensing not withstanding 40 , our finding that short term tree cover loss is reduced relative to non-protected areas and comparably with PAs is encouraging, since 45% of short-term degradation leads to deforestation, particularly in Southeast Africa and Southeast Asia 24 .…”

The shape of trees: Reimagining forest ecology in three dimensions with remote sensing

“…For instance, total gap fraction and gap size frequency distributions have been shown to closely reflect tree mortality rates and reliably detect the effects of selective logging in tropical forests (Dalagnol et al, 2021; Kent et al, 2015; Reis et al, 2021; Wedeux & Coomes, 2015). Beyond gaps, the impacts of logging and habitat fragmentation can also be seen in dramatic changes in the vertical distribution and density of foliage and woody biomass captured by LiDAR (Milodowski et al, 2021), and the spatial and temporal extent of structural change due to habitat fragmentation. A combination of airborne LiDAR and hyperspectral imaging in Borneo has shown that above‐ground carbon stocks are >20% lower in the first 100 m from a forest edge, and that these changes are linked to declines in canopy height and shifts in foliar traits related to light capture, growth and longevity such as leaf mass per area and phosphorus content (Ordway & Asner, 2020).…”

Quantifying Tropical Forest Disturbances Using Canopy Structural Traits Derived from Terrestrial Laser Scanning

“…Long-term experiments, such as the Stability of Altered Forest Ecosystem (SAFE) project (Ewers et al, 2011), have substantially contributed to our understanding of how deforestation, forest fragmentation, and logging modify the functioning of tropical forests. Numerous studies have been conducted to understand the effects of logging on forest structure (Milodowski et al, 2021;Pfeifer et al, 2015), primary productivity (Riutta et al, 2018), biodiversity (Struebig et al, 2013), and biomass (Jucker et al, 2018).…”

“…Approaches aimed at collecting three-dimensional (3D) information such as Synthetic Aperture Radar (SAR) (Treuhaft and Siqueira, 2000), and Light Detection and Ranging (LiDAR) can provide a more detailed description of the forest structure (Dubayah and Drake, 2000). Airborne Laser Scanning (ALS) collects 3D data from above the canopy and has been widely used to quantify forest biomass and carbon (Asner et al, 2018;Coomes et al, 2017;Ellis et al, 2016;Jucker et al, 2018), and to identify disturbances caused by selective logging (Andersen et al, 2014;Ellis et al, 2016;Milodowski et al, 2021). However, despite considerable progress offered by ALS system in assessing forest disturbance (Jucker et al, 2018;Kent et al, 2015) the occlusion in dense vegetation using ALS data makes it difficult to detect fine structural details of the forest understory.…”