Remote Sensing and modelling of tropical forest physiology.

Supervisors : Dr. G.A. Blackburn, Dr. J.I. Pitman, Dr. M. Mulligan, Department of Geography, King's College London

The clear-felling of tropical forests and subsequent regeneration is dramatically changing nutrient and hydrological fluxes in large sectors of South America. A knowledge of the role of changing vegetation is therefore essential, particularly the variations in primary productivity and transpiration. This project aims to investigate the potential of remote sensing to provide information on these physiological processes, specifically by testing the hypotheses of Sellers (1985, 1987) which suggests that relationships exist between the reflectance properties of a vegetation canopy and the rates of photosynthesis and transpiration of that canopy.

However, to date, the testing of this hypothesis, using field-based experiments, has been limited to homogenous temperate vegetation and semi-arid communities (work currently underway at Kings). This project will investigate the validity of the hypothesis for the heterogenous, complex canopies of tropical forest. Ground-based physiological measurements will be made at test sites at La Planada and Rio Nambi and these will be compared with the multi-spectral response of these sites.

The hypothesis will be tested at a range of spatial scales, with physiological data being obtained for individuals and groups of plants using an Infra red gas analysis (IRGA) and more extensive areas of forest using eddy-flux correlation techniques. Similarly, spectral reflectance data will be collected using instruments supported above the canopy from tower and airborne platforms and imagery from fine and coarse resolution satellite sensors will be used. Sites will be used which exhibit a gradation in canopy cover (resulting from differing management regimes) and therefore encompass a wide variation in physiological rates. Furthermore, a number of sites will be used which have similar canopy cover but differ in terms of the spatial arrangements of individuals, vertical canopy structure, species composition and background reflectance properties.

Sellers, P.J. (1985) Canopy reflectance, photosynthesis and transpiration. International Journal of Remote Sensing, 6, 1335­1372.

Sellers, P.J. (1987) Canopy reflectance, photosynthesis and transpiration. II. The role of biophysics in the linearity of their interdependence. Remote Sensing of Environment, 21, 143-183.

Hogan KP, Smith AP, Araus JL, Saavedra A (1994) Ecotypic Differentiation Of Gas-Exchange Responses And Leaf Anatomy In A Tropical Forest Understory Shrub From Areas Of Contrasting Rainfall Regimes. Tree Physiology, 1994, Vol.14, No.7-9, Pp.819-831

Tinocoojanguren C, Pearcy RW (1993) Stomatal Dynamics And Its Importance To Carbon Gain In 2 Rain-Forest Piper-Species .1. Vpd Effects On The Transient Stomatal Response To Lightflecks. Oecologia, 1993, Vol.94, No.3, Pp.388-394