Novel insights into Mediterranean forest structure using high-resolution remote sensing

Tree crown morphology and arrangement in three-dimensional space is a key driver of forest dynamics, determining not only the competitiveness of an individual but also the competitive effect exerted on neighbouring trees. Many theoretical frameworks aim to predict crown morphology from first principles and assumptions of Euclidean form and ultimately infer whole forest stand structure and dynamics but paucity in data has limited vigorous testing. Tree crowns are also not rigid in form and due to their sessile nature, must morphologically adapt to immediate abiotic and biotic surroundings to enhance survival. The characterisation of tree structure has been limited by the simplicity and associated error of traditional crown measurements. This project uses Terrestrial Laser Scanning data collected from a water limited Mediterranean forest community in Spain to highlight methodological opportunities presented by TLS in understanding forest structure and also the various developments required to extract ecologically meaningful metrics from these data. It then applies these novel metrics to answer questions about how tree crowns scale with size, the effects of competition and how plasticity in shape and arrangement interacts with light capture at the individual and plot scales. Modification to existing code as well as bespoke development were required to segment and calculate individual metrics from trees in this forest type. Accurate measures of crown morphology highlighted allometric scaling deviations from theoretical predictions and intra-specific differences in response to competition, calculated using more representative neighbourhood metrics. Inter-specific differences in crown plasticity and significant effects of size (height) were also evident, along with trade-offs between morphological plasticity and crown size. Light capture was positively affected by plasticity with inter-specific differences highlighting various biomass allocations strategies species undertake to acquire light. At the plot scale, mixed-genus plots intercepted less direct light and were structurally more complex rather than more volume filling.