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landscape and provide preferential pathways for transport of water, nutrients,
sediment, and propagules.
Figure 2.19
Profile of (A) filtered and transformed and (B) unprocessed ground-
penetrating radar data for a hilltop in the Hadsall Creek catchment in the Oregon Coast
Range. The locations of Douglas fir stumps within 1 m of the profile, and their diameters,
are shown in (A). (C) Soil depth estimated from the radar data. SOURCE: Roering et al.
(2010).
Changes in land use and climate can modify precipitation, runoff, and soil
moisture, favoring some species over others, leading to shifts in plant, animal, and
microbial composition. Examples include shifts from vegetated to bare soil during
periods of extended drought and establishment of water-intolerant species following
the drainage of wetland soils. These changes can, in turn, affect water and
biogeochemical cycling. For example, draining and drying of wetlands can increase
soil respiration and convert wetlands into a source of carbon, fueling further increases
in greenhouse gas emissions (Strack and Waddington, 2007). Feedbacks among
hydrological and geomorphological processes and biotic communities can allow some
species to live in otherwise unfavorable conditions (e.g., water-intolerant plants in
wetland environments) or the existence of alternative stable states (e.g., desert and
savanna; see Figure 2.20). Improved observations and models of soil moisture
variability and its feedbacks with landforms and ecosystems are needed to understand
the role of landscape and hydrological change in biodiversity, species invasions, and
shifts in plant functional types.
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