Understanding tree architecture, form and function in the tropics

Lead Research Organisation: University of Oxford
Department Name: Geography - SoGE

Abstract

The basic shape and branching structure of a tree can be distinctive and characteristic, yet there exists no consistent dataset quantifying how tree form varies across species and how it is related to other functional traits of a tree. Understanding the variation in structure and form of trees is important in order to link tree physiology to tree performance, scale fluxes of water and carbon within and among trees, and understand constraints on tree growth and mortality. These topics hold great importance in the field of ecosystem science, especially in light of current and future changes to climate. It is surprising, therefore, that tree structure and form are currently neglected areas of study. There are two primary reasons for this neglect: 1) it is difficult and time-consuming to quantify tree structure in-situ and 2) there is a lack of theory that explicitly links tree form parameters with physiological function.

Recent developments in technology and theory now enable us to overcome these limitations. In this proposal we aim to use new ground-based 3D terrestrial laser scanning technologies (TLS) in combination with recently developed theoretical frameworks to measure and compare tree architecture. We focus on the tropics, since (i) they host the vast majority of broadleaf tree diversity and play a disproportionate role in global and regional carbon and water fluxes, and (ii) the high species diversity of tropical forests (typically 100-250 tree species per hectare) means we can sample a large number of species under almost identical climate and soil conditions, making it more likely to detect overall tendencies in tree form response to environment that are not dominated by the peculiarity of a particular species.

Specifically, we will employ TLS to collect highly-detailed 3D structural information from mature rainforest trees spanning contrasting environments ranging from cloud forests to wet rainforests to dry savanna, and contrasting biogeographical histories from the cloud forests of the Andes through legume-dominated forests of Amazonia and Africa, through the dipterocarp-dominated tall forests of Borneo, to the ancient rainforest flora of Australia. All field sites are locations where we have already collected information of the leaf and wood traits of a number of tropical trees. We plan to achieve three goals: i) definition of quantitative classes of tree form using advanced imaging and computational techniques, ii) development of an understanding of the degree of covariance between tree form and tree leaf and wood functional traits, and the degree of phylogenetic constraint and plasticity in tree form, iii) testing and refinement of metabolic-scaling based approaches to scaling fluxes and productivity of tropical tree communities.
Over the course of three years our team will:
1) Create a database of branch- and canopy-level trait data collected from our field campaigns.
2) Use variation in branching architecture and canopy structure traits to define a suite of branching and canopy traits that allow for the classification of tree form.
3) Assess the scaling of tree form traits within trees and integrate the scaling of tree-form into a mechanistic plant scaling framework.
4) Explore the link between tree-form traits and leaf and wood traits to determine a whole-tree integrated economics spectrum.

In doing so, we hope to acquire a mechanistic understanding of the relationship between tree form, function, phylogeny and environment over a large spatial scale. We expect to find that behind the dazzling variety of shapes and forms found in trees hides a remarkably similar architecture based on fundamental, shared principles.

Planned Impact

We summarise impact across three main groups:

1) Tropical Junior Researchers:
We have a strong track record in involving local researchers and students in our field work, and encouraging them to use data collection to publish dissertations, and local and international papers. Many tropical countries still have only a few scientists with the skills and confidence to publish papers in international standard journals. Within this project we will run explicitly funded training workshops at the start of field campaigns in Peru, Brazil, Ghana and Malaysia, and will invite a student from each of these countries to spend one month in the UK working on data analysis and interpretation. Through our ongoing commitment to tropical research, we have a long-term record of building capacity with partner institutes, assisting students to find graduate positions in a variety of countries and giving them ready access to data and assistance with analysis.
In 2013 we published a special issue of the journal Plant Ecology and Diversity focused on Amazon-Andes ecosystem ecology where there were 12 papers with Peruvian, Bolivian and Brazilian student first authors. We worked closely with the South American students through training workshops and parallel writing on Google Docs, to build their confidence in writing in concise scientific English. We anticipate similar publications with our African and Malaysian students in coming years, and will assist and mentor them through this process.

2) Schools and the general public seeking to understand and be motivated by modern tropical forest science:
3D images of trees and forests are instantly appealing to schoolchildren and adults, and offer an entryway to explain concepts such as branching, fractals and architectural design. There is a thirst in sectors of the UK and wider public for access to the latest science, and a need to motivate schoolchildren about the excitement and importance of environmental science. Tropical forests are seen as particularly important and exciting, but their remoteness means that few have the chance to directly experience them and understand the work that scientists do there. Using Pathways to Impact funding on a recent NERC grant (focussed on African forests and on the Andes transect), we have just developed an innovative Geoweb Portal that brings together data, imagery and stories from our global network of ecosystem ecology sites (40+ sites, in Peru, Brazil, Bolivia, Chile, UK, Ghana, Gabon and Malaysia; (gem.tropicalforests.ox.ac.uk). Innovative aspects of the site include a "plots social network" where students in different regions (e.g. Peru and Ghana) can communicate with each other about techniques, science and questions, and a "public questions forum" where members of the public can pose questions that are answered by researchers and students. The whole Portal is designed in a form where it is easy for researchers and students to upload information, text and imagery. We have requested funds to support development of a part of this website dedicated to explanation of our tree architecture science, and to prepare materials and displays for the Royal Society Summer Exhibition and other public events.

3) The scientific community engaged in understanding tropical forest ecology and function, and its sensitivity to environmental change:
The scientific beneficiaries have been outlined in the academic beneficiaries section.