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