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How will humid forests respond to increasing heat extremes?

Prof. Emanuel Gloor (SOG), Dr. David Galbraith (SoG), Dr. Sophie Fauset (SoG), Prof. Christine Foyer (SoB)

Project partner(s): Dr. Hartmut Boesch (National Center for Earth Observation (NCEO)) (Potential CASE); Prof. Ben Hur Marimon (Nova Xavantina, Brazil); Prof. Eric Cosio (Lima, Peru)

Contact email: e.gloor@leeds.ac.uk

Background

Tropical forests play a vital role in the Earth System, housing >50% of global plant biodiversity and regulating climate by virtue of their exchanges of carbon, water and energy with the atmosphere. They are also home to significant human populations, with approximately 50% of the global population projected to live in the tropics by 2050. The continued functioning of tropical forests is, however, critically dependent on the maintenance of favorable climatic conditions. There is growing concern that predicted higher temperatures in tropical regions may push tropical forests beyond their high temperature threshold, leading to large-scale changes in forest structure and function (Galbraith et al. 2010, Brienen et al. 2015). Temperatures are rapidly rising pan-tropically - e.g. the recent heat waves in India have substantially exceeded usual temperature levels, affecting on the order of 300 mio. people. The effect of high temperatures on forest vegetation is further exacerbated by drought and there is also a need to better understand the interactive effects of heat and drought on forest vegetation.

One approach to gain insight into heat effects on tropical forest vegetation is to use on-going warming and extreme events as a natural laboratory and harbinger of the consequences of future conditions. Thus key ecosystem state variables related to water/heat stress and key metrics of ecosystem functioning are continuously being recorded and the effects of heat peaks and waves can be observed in situ. A complimentary approach is to measure plant heat response under controlled warming conditions although it is unclear to what extent responses under controlled conditions compare with responses under natural conditions.

We are currently establishing two continuously observed forest sites in tropical South America, Nova Xavantina (Southern border of Amazon forests), and Tambopata (Western Amazon, wet but seasonal) based on a range of diagnostics measured partially from a tower overlooking tree canopies. If funding permits we will also equip a third site,  Jennaro Herrera (Western Amazon, wettest region of the Amazon). The Nova Xavantina site is particularly well suited to study heat effects because maximum daily temperatures are high and peak temperatures have increased rapidly over the past years. Between 2005 and 2014 (data from INMET, www.inmet.gov.br) they exceeded 40°C a total of 53 times. Xavantina is amongst the dry end of Amazonian forests, and generally experiences significant seasonal shortages in rainfall. These forests are characterized by Amazon species at their current thermal extreme and thus are a very good analogue for future conditions. The other two sites when combined with the Nova Xavantina site span a wetness and seasonality gradient ranging form seasonal and comparably dry humid forest to very wet and nearly non-seasonal humid forest (Jennaro Herrera) permitting a broader picture outlook.

Fig. 1  Comparison of daily peak temperatures at three sites in the Amazon over roughly the last decade and earlier decades based on meteorological data from INMET Brazil (Brazilian meteorological service).

Objectives

The general aim of this PhD project is to observe and understand responses of canopy level processes to ongoing heat peaks at Amazon forest sites during a phase of quite rapid warming.

The main focus is on observations of tree canopy status using cameras of phenology, heat radiation and fluorescence installed on purpose-built towers. A particular focus of the project will be on establishing the capability to measure canopy - and to some extent leaf level - fluorescence with other key parameters like soil hydraulic status, sap flow and tree diameter growth, also being measured. Fluorescence is a measure of leaf level stress of the canopy leaf photosystems as well as a diagnostic of photosynthetic activity and thus is related to tree productivity (e.g. Guanter et al. 2014). The instrument used for this purpose is a highly resolving spectrometer which will also permit to measure canopy chlorophyll content and various vegetation indices which will help understand tree responses on comparably short time-scales.

Fig. 2 Infrared image measuring temperature of plant leaves (from a recent test of field equipment at Leeds) (Courtesy R. Tiwari).

Fluorescence can also be measured from space and has led to interesting insights about main controls of Amazon humid forests (Guan et al. 2015). However  estimates of fluorescence from space based on different instruments and different satellite missions show considerable discrepancies. Thus on-ground data are important for 'ground-truthing' the satellite data. There is also an option to equip a drone with a highly resolving spectrometer as part of an ongoing joint Brazilian-UK project (BIO-RED), which will permit to scale from tower based data to a larger scale comparable with areas sensed by remote sensing instruments and thus strengthen comparisons with satellite data. The project is a collaboration with Dr. Boesch from Leicester University, head of NCEO (Divisional director of the National Center of Earth Observation) who will provide the expertise for this aspect of the project.

Finally there will likely also be an option for lab based leaf level fluorescence measurements under a range of controlled conditions (control of temperature and CO2 levels) in growth chambers at the laboratory of Christine Foyer at Leeds University. This last aspect will be centrally guided by Christine Foyer.

Potential for high impact outcome

The fate of tropical forests is of concern for many reasons including the global carbon cycle and future greenhouse gas levels, global biodiversity and regional lively-hoods. Research in this field is very often reported on in public media and scientific literature. Thus the project has the potential to lead to important 'high impact' results and insights.

Training

The student will be part of a team led jointly by Emanuel Gloor and David Galbraith at School of Geography Leeds, and will be co-led by Hartmut Boesch from NCEO & University of Leicester, a remote sensing specialist, and Christine Foyer from School of Biology, University of Leeds.

The student will gain expertise in forest functioning measurements at the 'plot scale' (~1ha) in the tropics. Some of the methods will be developed during the project and tested at University of Leeds.

The student will be involved in analysing and processing fairly large data streams using computer tools like Matlab and R.

Finally the student will gain knowledge about remote sensing of tropical vegetation functioning and state.

Student Profile

We seek an enthusiastic student interested in tropical forest ecology with a strong interest in quantitative methods and who enjoys working in a team.

CASE Partner

The National Center for Earth Observation (NCEO) represented by Dr. Hartmut Boesch plans to be a CASE partner for this project and contribute accordingly financially to this studentship. An important focus of NCEO is the global carbon cycle and solar induced fluorescence (SIF) is an important diagnostic for functioning and state of the land surface. This project will contribute to ground-truthing of this remote sensing quantity. The joint work with NCEO will also permit to link the results to a broader assessment of changes in and variation of the land component of the carbon cycle in the tropics.

References

Galbraith et al. (2010), Multiple mechanisms of Amazonian forest biomass losses in three dynamic global vegetation models under climate change, New Phyt. 187:645-65.

Brienen, Phillips, Feldpausch, Gloor, Galbraith et al. (2015) Long-term decline of the Amazon carbon sink, Nature 519, 344–348 doi:10.1038/nature14283

Guan, K. et al. (2015) Photosynthetic seasonality of global tropical forests con- strained by hydroclimate, Nature Geoscience, 8, 284-289.

Guanter, L. et al. (2014) Global and time-resolved monitoring of crop photo- synthesis with chlorophyll fluorescence, Proc. Nat. Acad. Sc. USA, E1327–E1333

Related undergraduate subjects:

  • Biology
  • Engineering
  • Environmental science
  • Physics