Mudd, Simon

Mitchard, Edward

Milodowski, David Thomas

Natural Environment Research Council (NERC)

2017-02-28T13:49:16Z

2017-02-28T13:49:16Z

2016-06-27

The geomorphic and geochemical characteristics of landscapes impose a physical template on the establishment and development of ecosystems. Conversely, vegetation is a key geomorphic agent, actively involved both soil production and sediment transport. The evolution of hillslopes and the ecosystems that populate them, are thus intimately coupled; their co-dependence potentially has a profound impact on the way in which landscapes respond to environmental change. This thesis explores how rates of erosion, integrated over millennia, impact on the structural characteristics of the mixed conifer forest that presently mantles this landscape, the development of the underlying soils and emergence of bedrock. The focus for this investigation is the Feather River Region in the northern Sierra Nevada in California, a landscape characterised by a striking geomorphic gradient accompanied by spatial variations in erosion rate spanning over an order of magnitude, from 20 mm ka-1 to over 250 mm ka-1. Using LiDAR data to quantify forest structure, I demonstrate that increasing rates of erosion drive a reduction in canopy height and aboveground biomass. Subsequently, I exploit a novel method to map rock exposure, based on a metric of topographic roughness, to show that as erosion rates increase and soil thickness consequently decreases, the degree of bedrock exposed on hillsides increases. Importantly, this soil-bedrock transition is gradual, with rapidly eroding hillslopes frequently possessing a mosaic of bedrock outcrop and intermittent soil mantle. Both the ecological and geomorphic trends are shown to be impacted by the underlying bedrock, which provides an additional source of heterogeneity in the evolution of the Feather River landscape. The negative correlation between AGB and erosion rate has potential implications for soil production. Using a simple hillslope model I show that if this decrease in AGB is associated with a drop in biotic soil production, then feedbacks between soil thickness and biotic soil production are capable of generating a complex response to geomorphic forcing, such that hillslopes possess multiple stable states: for intermediate rates of erosion, equilibrium hillslopes may be either soil mantled or bedrock. Hillslope evolution in these simulations is path dependent; once exposed at the surface, significant patches of bedrock exposure may persist over a wide range of incision rates.

http://hdl.handle.net/1842/20438

en

The University of Edinburgh

Clubb, F., S. Mudd, and D. Milodowski (2015), Reply to comment by P. Passalacqua and E. Foufoula-Georgiou on “Objective extraction of channel heads from high-resolution topographic data,” Water Resour. Res., 51(2), 1377–1379, doi:10.1002/2014WR016603.

Clubb, F. J., S. M. Mudd, D. T. Milodowski, M. D. Hurst, and L. J. Slater (2014), Objective extraction of channel heads from high-resolution topographic data, Water Resour. Res., 50(5), 4283–4304, doi:10.1002/2013WR015167.

Gabet, E. J., S. M. Mudd, D. T. Milodowski, K. Yoo, M. D. Hurst, and A. Dosseto (2015), Local topography and erosion rate control regolith thickness along a ridgeline in the Sierra Nevada, California, Earth Surf. Process. Landf., 40, 1779–1790, doi:10.1002/esp.3754.

Grieve, S. W. D., S. M. Mudd, M. D. Hurst, and D. T. Milodowski (2016), A nondimensional framework for exploring the relief structure of landscapes, Earth Surf. Dyn. Discuss., 2016, 1–41, doi:10.5194/esurf-2015-53.

Milodowski, D. T., S. M. Mudd, and E. T. A. Mitchard (2015), Erosion rates as a potential bottom-up control of forest structural characteristics in the Sierra Nevada Mountains, Ecology, 96(1), 31–38, doi:10.1890/14-0649.1.

Milodowski, D. T., S. M. Mudd, and E. T. A. Mitchard (2015), Topographic roughness as a signature of the emergence of bedrock in eroding landscapes, Earth Surf. Dyn., 3(4), 483–499, doi:10.5194/esurf-3-483-2015.

Mudd, S. M., M. Attal, D. T. Milodowski, S. W. D. Grieve, and D. A. Valters (2014), A statistical framework to quantify spatial variation in channel gradients using the integral method of channel profile analysis, J. Geophys. Res. Earth Surf., 119(2), 2013JF002981, doi:10.1002/2013JF002981.

Attribution-NonCommercial-ShareAlike 4.0 International

http://creativecommons.org/licenses/by-nc-sa/4.0/

geomorphology

ecology

hillslope

soil

erosion

Erosion, vegetation and the evolution of hillslopes in upland landscapes

Thesis or Dissertation

Doctoral

PhD Doctor of Philosophy