Why do trees in different tropical forests grow at different rates? Why do some trees within a site grow faster than others? At first impression, It seems a reasonable assumption that the 'visible productivity' (e.g. wood production and canopy litterfall) is somehow related to how much carbon and energy the forest or the individual tree captures from photosynthesis, the Gross Primary Productivity (GPP); this assumption is implicit in much of the forest ecology literature, as well as in many biosphere models. When we see explanations as why forests are increasing growth rates in response to global change, or increased productivity after disturbance, we tend to frame these explanations in the context of increased photosynthesis (either because of increased abiotic drivers - e.g. increased light or carbon dioxide, or because of increased photosyntheric capacity, e.g leaf nitrogen content) However, our recent work in Amazonia has indicated that the site-to-site variability in net primary productivity (NPP) in lowland rainforests is not related to how much carbon and energy the forest captures through photosynthesis, but much more determined by how much of that captured carbon used by plants for their internal metabolism (Malhi et al., submitted to Nature), the autotrophic respiration, Ra. This tentative finding has consequences for much of tropical forest research, and global change vegetation models. Moreover, our early results suggest that disturbance is the main determinant of how much an ecosystem allocates to autotrophic respiration, with less autotrophic respiration in disturbed systems. We would now like to explore this topic further in five ways: (i) by exploring in greater detail the spatial and temporal variation of autotrophic respiration; (ii) by greatly increasing the number of sites investigated; (iii) by assessing the extent to which results from Amazonia are generalisable in another biogeographical realm, namely equatorial Africa; (iv) by explicitly exploring how disturbance affects carbon use and allocation by tracking these before and after selective logging; (v) by exploring how much interspecific variation in NPP is determined by autotrophic respiration. The underlying hypotheses we are exploring are that (i) there is no significant site-to-site variation in the GPP of moist tropical lowland forests (within Africa and in comparison to Amazonia), despite variation is soil properties, climate and tree species composition; (ii) there is substantial site-to-site variation in net primary productivity (NPP), and this is mainly driven by shifts in carbon use efficiency (CUE, the proportion of photosynthetic carbon converted to biomass), and (iii) forest CUE increases substantially after disturbance (logging) and subsequently declines over time, and (iv) this shift is driven by differing plastic variation in CUE within surviving individuals, rather than by community replacement. In the process, we will pioneer comprehensive carbon cycle assessment in intact and disturbed African tropical forests, replicated across two contrasting countries, Ghana (West Africa) and Gabon (Central Africa). Our sampling strategy will encompass plots in (i) wet primary forests (2 countries x 2 plots), (ii) moist primary forests (2 countries x 2 plots),(iii) tracking sites before, during and after logging disturbance (2 countries x 2 plots), and (iv) plots recovering from logging disturbance 10, 15 and 20 years ago (2 countries x 2 plots). At all sites we will collect 2.0-2.5 years of data. Our project will provide substantial scientific capacity building in Ghana and Gabon,we will train and utilise 6 student field researchers (3 full time, 3 part-time) in each country, and hold wider-reach training workshops in carbon cycle science in each country at the start and end of the project. this event.

Incoming solar irradiance ultimately governs the amount of energy within the Earth's system. Our understanding of how solar irradiance is modulated by the Earth's orbital pathway underpins our understanding of long-term (>10,000 year) global climate and vegetation change through the geological record. However, there is no independent long-term record empirical record of solar irradiance on timescales >10,000 years. Our proposal is designed to generate the first record of solar irradiance change at the Earth's surface by applying cutting-edge organic geochemical techniques to a unique tropical record of past vegetation change. Current understanding of solar flux is based upon changes observed in cosmogenic isotopes (10Be and 14C); however, the temporal range over which these techniques can be applied is limited by the half-lives of the respective isotopes. Recent advances in our understanding of pollen/spore chemical composition indicate that a signature of maximum Ultra Violet-B (UV-B) radiation exposure during growth is locked-in, and preserved, within the sporopollenin chemical structure [1]. As UV-B is directly proportional to total incoming solar irradiance this offers an opportunity to extract a long-term record of solar irradiance flux from the fossil pollen/spore record. During the Quaternary period (last 2.6 million years) orbital forcing has been identified as particularly important in relation to climate and vegetation change associated with glacial-interglacial cycles [2]. However, due to a paucity of appropriate study sites our understanding of terrestrial vegetation change over multiple glacial-interglacial cycles remains limited. New fossil pollen/spore data from a continuous c. 1 million year sedimentary record recovered from Lake Bosumtwi (Ghana), recovered by the International Continental Scientific Drilling Program, provides the first terrestrial record of vegetation change in Africa during this period [3]. The Lake Bosumtwi study site offers an ideal opportunity to assess how solar insolation, climate and vegetation have changed through time because it is well placed to record changes in the global climate system (Inter Tropical Convergence Zone, monsoon) and vegetation (shifts between forest and savannah biome are observed in the fossil pollen record). We will use Fourier Transformed Infra-Red spectroscopy to analyse the chemical structure of c. 15,000 pollen/spores extracted from 500 different depths (ages) in the Lake Bosumtwi sediment record over the last 500,000 years. By characterizing past change in solar irradiance at the Earth's surface and comparing chemical change with existing model and vegetation data we will provide new insights into the pattern of change. The independent record of solar irradiance will allow climate and vegetation change inferences to be decoupled within the fossil record. Therefore, we will have the potential to determine leads and lags (causality) within the Earth's system, e.g. how do shifts in climate systems related to vegetation change. The research team have all the requisite skills and experience to deliver the proposal: Gosling (PI OU) has worked on past environmental change in the tropics for 12 years and has worked on Lake Bosumtwi sediments since 2007; Lomax (PI Univ. Nottingham) and Fraser (Res Co-I OU) are organic geochemists who have pioneered research into pollen/spore chemical composition change and its preservation in the geological record. The Centre for Earth, Planetary, Space & Astronomical Research (The OU) will provide the required facilities and research environment. REFS: [1] Lomax, B.H. et al., Plant spore walls as a record of long-term changes in ultraviolet-B radiation. Nature Geosci., 2008. 1: 592-596. [2] Hays, J.D. et al., Variations in the Earth's orbit: Pacemaker of the ice ages. Science, 1976. 194: 1121-1132. [3] Koeberl, C., et al., The 2004 ICDP Bosumtwi Crater Drilling Project. Meteorit. Planet. Sci., 2007. 42: 483-511.

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.

Forests are a critical component of the global carbon cycle because they take carbon dioxide out of the atmosphere through photosynthesis, and store the carbon in wood and soil. All living things in forests also produce carbon dioxide through respiration as an inevitable consequence of sustaining themselves and growing. At present, forests take in more carbon dioxide than they release, helping to reduce the amount of carbon dioxide present in the atmosphere, but this 'free gift' from forests is not guaranteed to continue at its current rate indefinitely under climate change. As well as the carbon cycle, forests are also crucial in the water cycle as trees pump water from the soil into the atmosphere. Leaves are the key part of the plant that regulates the exchange of gases (water, carbon dioxide) with the atmosphere. The pores in the leaf surface (stomata) are important for water loss and temperature control as well as the entry of carbon dioxide. Leaves exposed to direct sunlight can be more than ten degrees hotter than the air, even in temperate latitudes. Leaf temperature is important because many biological processes, including photosynthesis and respiration, are sensitive to temperature; very high temperatures can cause immediate and acute damage to leaves. Over the coming century, we expect carbon dioxide concentrations and air temperatures to continue to rise. When trees are grown in higher carbon dioxide concentrations, stomata close and limit water loss; this prevents the plant dehydrating but also reduces how much leaves can cool down. However, there is limited monitoring on forest canopy temperatures, and limiting understanding on how different species and forests in different climate zones are responding to climate change. This project will build a global network of researchers working to measure forest canopy temperatures using thermal infrared cameras, which will provide both greater understanding and also a crucial data resource for scientists in other disciplines to utilise. The network will ensure that the data collected by separate groups are comparable, and aid data processing and analysis by providing clear guidance and tools. This is will encourage other researchers to take up use of thermal infrared cameras, the analysis of which can be challenging. Our network will monitor canopy temperatures at fourteen sites in tropical and temperate forests and savannah, in UK, China, India, Australia, Brazil, Peru, Panama, USA, and Ghana. The sites in the UK and Peru will be newly established by this project. Ten sites already have established data collection, while the final two sites (Australia, Ghana) are in development. Having data collected using cameras will allow us to understand not only how forests in different locations are behaving, but also whether and how different species within sites respond. The long-term nature of the project means that seasonal variation will be included, and the forest response to extreme events such as heat waves and droughts will be quantified. Future work will establish in more detail how changes to canopy temperature link to changes in forest carbon and water cycling. Our work providing insight into the response of forest canopies to climate change will inform models produced to assess the impacts of greenhouse gas emissions on the planet, which are used to inform global climate change policies. Further, the current global emphasis on mitigating climate change through tree planting makes it crucial to assess how these trees will cope under future conditions.