Large trees are vital for the functioning of tropical forests. They house a wide range of organisms, making them true biodiversity hotspots and play a key role in forest biomass storage.The Life On Trees (LOT) project is a research program in which all eukaryotic organisms on individual trees are surveyed, including plants, fungi, animals and protists. One of the goals of the research program is to explore the link between the distribution of the occurring organisms and the tree architecture of those large trees. To accurately quantify the structure of such trees and investigate the interplay between the tree and its surroundings, terrestrial laser scanning is currently used as a state-of-the-art technology. Terrestrial laser scanning (TLS) generally uses a laser scanner to scan trees from multiple viewpoints from the ground. In dense tropical forests, the tree canopy often reaches a height of 50 m or more. Due to the large distance between the scanner and the tree crown, even the best laser scanners have difficulty getting a clear view of the top of the canopy. For those large, colossal trees, data is limited and suffers a lot of occlusion. Since all scans are taken from the ground, data on the upperpart of branches is nonexistent. To assess this limitation of TLS, we explore how much additional 3D information is gained from the tree structure by collecting 3D scans inside the tree crown. With the aid of professional climbers, we lifted a RIEGL vz-400 laser scanner into a Dussia tree in Rio Abiseo National park located in the Peruvian Amazon. The selected tree is quite spectacular, it reaches a height of 50 m and a width of 45 m, and is covered with vegetation including many orchids and epiphytes hosting a wide variety of life forms. The first results of this project will be presented, focusing on the tree architecture with its impressive volume and branch length, and the benefits and challenges of scanning inside the tree crown.
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Introduction: Basic data on biodiversity, such as the variety of life forms coexisting on a single tree, are still lacking and prevent a full understanding of the complexity of interactions among organisms in a tropical rainforest. Filling this gap has recently become more achievable thanks to advances in canopy access methods and genetic tools. Objective: The main aims of the research program Life On Trees (LOT) are to generate baseline knowledge about the number of species a single tropical tree can support and to understand how these communities of organisms are assembled. Methods: Our first project is performed in one of the most biologically diverse regions: the Peruvian Amazon, in the Rio Abiseo National Park. We focus our sampling on a spectacular Dussia tree (Fabaceae), which is 50 m high and 45 m wide and covered with epiphytes. For safety reasons, the sampling is carried out by professional climbers, guided by experts of the different eukaryotic groups studied (plants, fungi, animals, protists). In order to better understand the contribution of different tree components (bark, leaves, fruits, flowers, dead wood) to overall tree biodiversity, we assign observations into communities based on height zone or microhabitat and examine similarities and nestedness in the composition of these communities. The complex architecture of the tree is studied using terrestrial LiDAR and the location of samples is recorded using a high precision differential GPS receiver (dGNSS). The collected specimens will be determined by classical taxonomy and genetic methods (DNA metabarcoding). An online tracking system for those specimens sent to taxonomists for identification, as well as a central database system, are already under development. Results: The first results of the LOT-Peru project from April-May 2022 and of the preliminary tests conducted in October 2021 will be presented. Implications: The scope of this program is not only scientific. Using the simple example of a large tree, we can reach out to the public and explain difficult concepts, such as what biodiversity is and how it is generated and sustained. In addition, the tree is a strong symbol that has an emotional impact. We hope that this program will build awareness about the impacts of deforestation, and conversely the value of conservation, by showing foresters, city dwellers or villagers that when a tree is cut down, a whole range of biodiversity disappears.
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