Title: Towards an understanding of the feedbacks between vegetation, carbon,
climate, and the growth of mountain belts
Supervisors: Simon Mudd (simon.m.mudd@ed.ac.uk), Richard Essery
(Richard.Essery@ed.ac.uk), Mathew Williams (mwilliam@stafmail.ed.ac.uk) and Philip
Wookey (Stirling; Philip.wookey@stir.ac.uk)
Project Background
Mountain belts feature strong feedbacks between climate, carbon cycling, vegetation, and
erosion. Erosion rates and uplift determine landform and topography; this topography then
influences the characteristics of the local climate such as temperature (via both the lapse
rate and the delivery of solar energy as modulated by slope aspect) and precipitation (as
influenced by orographic effects). Temperature and precipitation regulate both organic matter
decomposition and the growth of vegetation, which can affect runoff (by affecting
evapotraspiration and infiltration capacity of the soil). Erosion rates on hillslopes are
controlled by runoff and bioturbation (caused, in part, by vegetative turnover), and in rivers by
discharge (which is the integrated runoff over a drainage basin), thus closing the feedback
loop. While many studies have attempted to couple two of these landscape features (e.g.,
carbon cycling and vegetation, or climate and erosion), there has not been an attempt to
quantify the strength of the feedbacks using a fully integrative earth system model. In this
project the student will couple recognized models of the four landscape elements listed
above to explore the relative importance of these feedbacks within growing mountain belts
over timescales of tens of thousands to millions of years.
Techniques, approaches and work to be undertaken
The student will couple three to four widely used models of erosion, carbon cycling,
vegetation, and climate. A landscape evolution model will quantify erosion and topography in
an evolving mountain belt. This model will be driven by climate (since precipitation controls
erosion rates) and vegetation (since vegetation controls how susceptible the landscape is to
erosion). Climatic variables will then be downscaled using a model that takes into account
topography (because topographic gradients control precipitation and temperature) and
vegetation (vegetation affects the energy exchange between the atmosphere and the land
surface). Precipitation and temperature derived from the climate model, along with slope
aspect derived from the erosion model, will then be used to drive a carbon cycling and
vegetation model. Once the models are coupled, the integrative model will be used to test a
range of scientific questions. Some examples are: How sensitive is soil carbon storage to
uplift rates? What prevailing climate conditions will result in the strongest spatial variations in
vegetation? Does the change in vegetation in different prevailing climates result in a
quantifiable topographic signature?
Training element
The student should have some familiarity with numerical modelling (that is, experience with
either fortran, c, or c++) but additional instruction from the supervisory team will train the
student on use of a variety of modelling techniques. Each member of the supervisory team is
an expert in one of the components in the coupled landscape-climate system (Mudd: erosion;
Essery: climate; Williams: vegetation; Wookey: carbon cycling); the student will be
familiarized with of the total landscape system rather than an isolated component. The
student will learn how the biosphere, lithosphere, and atmosphere interact within a
quantitative framework.
Selected References:
Collins D.B.G., Bras R.L., Tucker G.E. 2004, Modeling the effects of vegetation-erosion
coupling on landscape evolution. Journal of Geophysical Research-Earth Surface (F3): Art.
No. F03004
Motavalli, P.P., C.A. Palm, W.J. Parton, E.T. Elliott, and S.D. Frey. 1994. Comparison of
laboratory and modeling simulation methods for estimating soil carbon pools in tropical forest
soils. Soil Biology & Biochemistry 26 :935-944.
Ojima, D.S., B.O.M. Dirks, E.P. Glenn, C.E. Owensby, and J.M.O. Scurlock. 1993.
Assessment of C budget for grasslands and drylands of the world. Water, Air, and Soil
Pollution 70 :95-109.
Roe, G.H. 2005. Orographic Precipitation, Annual Review of Earth and Planetary Sciences .
33 :645-671
Tucker G.E., 2004, Drainage basin sensitivity to tectonic and climatic forcing: Implications of
a stochastic model for the role of entrainment and erosion thresholds. Earth Surface
Processes and Landforms 29(2): 195-205.
Advertising Summary:
The project will quantify the feedbacks between vegetation, carbon cycling, climate, and
erosion in tectonically active mountain belts.
Links with SAGES themes: This project is designed to intimately mesh with the stated
objectives of the three scientific themes within SAGES. In all three themes a key aspect of
SAGES is to identify how the theme’s focus (landscape, carbon, and atmosphere) responds
to global change. As we highlight in the project background, landscape, carbon and
atmosphere are inextricably linked in tectonically active mountain belts. Despite this linkage,
the coupling of erosion, carbon, and climate has yet to be quantitatively explored at the
mountain belt scale; the purpose of this project is to addresses this fundamental gap in our
scientific understanding of feedbacks between the lithosphere, biosphere, and atmosphere.