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Trees adjust their architecture to acclimate to various external stressors, which regulates ecological functions that are needed for growth, reproduction, and survival. Human activities, however, are fragmenting natural habitats apace and could affect tree architecture and allometry, but quantitative assessments remain lacking. Here, we leverage ground surveys of terrestrial LiDAR in Central Amazonia to comprehensively assess forest edge effects on tree architecture and allometry, and their associated impacts on the forest biomass 40 years after fragmentation. We found that young trees colonising the forest fragments have thicker branches and architectural traits that maximise light capture, and can produce 50% more wood than their counterparts of similar stem size and height in interior forests. Large trees that have survived disturbances arising from forest fragmentation are able to acclimate and maintain their wood production, but damages that reduce tree height near the edges can lead to a 30% decline of their woody volume. Despite the large wood production of colonising trees, changes in tree architecture lead to a net loss of 6.6 Mg ha-1 of the forest aboveground biomass, which account for 20% of all edge-related aboveground biomass losses of fragmented Amazonian forests (34.3 Mg ha-1). Our findings show a strong influence of edge effects on tree architecture and allometry, and reveal an additional unaccounted factor that exacerbates carbon losses in fragmented forests.

Forest disturbances can reduce the potential of ecosystems to provide resources and services. Despite the urgent need to understand the effects of logging on tropical ecosystems, the quantification of disturbances arising from selective logging remains a challenge. Here, we used canopy-three-dimensional information retrieved from Terrestrial Laser Scanner (TLS) measurements to investigate the impacts of logging on key structural traits relevant to forest functioning. We addressed the following questions: 1) Which canopy structural traits were mostly affected by logging? 2) Can remotely-sensed canopy structural traits be used to quantify forest distur-bances? Fourteen canopy structural traits were applied as input to machine learning models, which were trained to quantify the intensity of logging disturbance. The plots were located in Malaysian Borneo, over a gradient of logging intensity, ranging from forest not recently disturbed by logging, to forest at the early stage of recovery following logging. Our results showed that using the Random Forest regression approach, the Plant Area Index (PAI) between 0 m -5 m aboveground, Relative Height at 50 %, and metrics describing plant allocation in the middle-higher canopy layer were the strongest predictors of disturbance. In particular, PAI between 35 m and 40 m explained 12 % to 19 % of the structural variability between plots, followed by the relative height at 50 %, (10.5 % -18.6 %), and the foliage height diversity (7.5 % -16.9 %). The approach presented in this study allowed a spatially explicitly characterization of disturbances, providing a novel approach for quantifying and monitoring the integrity of tropical forests. Our results indicate that canopy structural traits can provide a robust indication of disturbances, with strong potential to be applied at regional or global scales. The data used in this study are openly available and we encourage other researchers to use them as a benchmark data set to test larger scale approaches based on satellite and airborne platforms.

Repeat airborne LiDAR data provides a unique opportunity to study tree mortality at the landscape scale. We use maps of canopy height derived from repeat LiDAR (two or more scans collected a few years apart) to detect changes in forest structure. Visually, the most obvious changes are caused by large treefall events, which are difficult to study using field plots due to their rarity. While repeat LiDAR data provides exciting new possibilities, validation is a challenge, since we cannot easily determine how many trees have died and we may miss trees which are dead but still standing. I will discuss our progress so far, studying large-tree mortality rates across multiple countries and forest types.

The measurement of whole lung mechanics forms the basis of diagnostic measurements for many respiratory diseases. Despite this, there are currently no quantitative methods to link alterations in pulmonary microstructures to measurements of whole lung function. The normal decline in the lung’s microstructure that occurs with age is virtually indistinguishable from early disease on imaging or standard lung function measurements, leading to frequent misdiagnosis in the elderly. Accurate characterisation of lung mechanics across spatial scales has the potential to assist distinguishing age from pathology, which would benefit patients across a range of medical conditions and procedures. While computational modelling promises to be a useful tool for improving our understanding of lung mechanics, there is currently no unified structure-function computational model that explains how age-dependent structural changes translate to decline in whole lung function. This paper presents novel instrumentation and imaging techniques for measurements of intact ex vivo lung tissue mechanics. We seek to address problems of weak parameterisation that existing models suffer from, due to lack of reliable measurements. To begin addressing this issue, we have developed a full-field stereoscopic imaging system for tracking surface deformation of the rat lung during pressure-controlled ventilation. This study presents a pipeline for the reconstruction and tracking of the intact left lobe of a rat lung during inflation, ex vivo. Model-based 3D reconstruction of the lungs enabled the 3D shape of a surface patch of the imaged lung to be determined. The 3D reconstruction and tracking of the fresh lung surface patch in this study was completed with three cameras across 21 pressure steps, encompassing a total pressure change from 2069 Pa to 2386 Pa. This approach shows that reconstructing intact ex vivo fresh lungs, with no additional surface markers, is feasible.

Wind is a key disturbance agent in forests worldwide, but the interaction between wind and trees is poorly understood in natural forests. Wind damage leads to the formation of canopy gaps, which drive structural and compositional changes in the forest. Trees also adapt to their local wind regime in the absence of any damage, a process known as thigmomorphogenesis. This process alters local height-diameter allometries and so influences forest carbon stocks. Previous work on the wind-tree interaction has focussed on conifer plantations due to their economic importance and the relative simplicity of these systems. In this thesis I use terrestrial laser scanning to map the 3D architecture of broadleaf trees and so simulates their response to wind loading using finite element analysis. I also use field techniques developed in the forestry industry to directly measure the response of broadleaf trees to the wind. I found that the simulations performed well against field data for trees in Wytham Woods, UK, but that they failed to predict the field data from Danum Valley, Malaysia. This is likely due to the more complex topography and canopy structure in the tropical site. In Wytham Woods, I found that the critical wind speed, a measure of wind damage risk, was related to tree species, growth rate and architecture. I also found an interesting link between critical wind speed and the timing of autumn leaf phenology, although this requires further investigation. In Danum Valley I found that understory trees approach their gravitational limits to height in their struggle to reach the canopy but that gravitational risk factors decrease with tree height. In contrast, I found that wind risk factors increased with tree height meaning that tall trees are likely to be mechanically limited by wind. I also found that the natural frequencies of broadleaf trees do not follow the same simple pattern as those of conifers, a difference which is accounted for by tree architecture. Overall, this thesis emphasises the role of wind damage risk in forest ecology and the importance of tree architecture in determining the response to wind loading for broadleaf trees.

When retired Harvard professor Nathan Glazer died Jan. 19 at 95, descriptive sociology lost its last great practitioner.