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coasts. Vegetation slows water flow, promotes sediment deposition, and inhibits
erosion. Sediment deposition, along with organic matter accumulation, supplies
nutrients and maintains the marsh platform at elevations beneficial for primary
biological production. These feedbacks result in rates of vertical marsh accretion
close to rates of contemporary sea-level rise, provided a sufficient supply of sediment
and undisturbed vegetation. The likely response of marshes to accelerated sea-level
rise is a complex eco-hydro-geomorphological question currently receiving
considerable attention.
In the context of a changing climate, it is particularly important to understand
why some regions of Earth's surface are relatively resilient to change, whereas others
are not. It is reasonable to assume that long-term trends of warming temperatures will
result in fundamental alterations to polar, glacial, and periglacial landscapes and
ecosystems, but at what point are these changes irreversible? More frequent climate
extremes are also among the expected manifestations of climate change. Drought, for
example, poses severe challenges with regard to food and water resources as well as
soil erosion. Yet there are regions of Earth that are able to support annual and
perennial plant growth despite low water availability. In these and other landscapes,
understanding the factors and processes governing landscape resilience, and in
particular the nature of feedbacks and thresholds in system response that may
fundamentally alter landscape and ecosystem characteristics, processes, and dynamics
are essential for forecasting and interpreting landscape change. Research
opportunities for such issues are found in the records of past environmental and
landscape change, in studies of contemporary processes, and in model simulations of
future scenarios.
Research at the intersections of geomorphology, hydrology, and ecology is
providing new insight into the mechanisms of landscape-ecosystem interactions and
co-evolution. For example, Roering et al. (2010) have brought an ecogeomorphic
perspective to questions related to rates of soil formation in forested landscapes. Soil
covers can only be maintained if rates of soil production equal or exceed rates of soil
erosion. Roering et al. found that large volumes of bedrock were incorporated into the
roots of large coniferous trees (>0.5 m diameter) overturned during storms in the
Oregon Coast Range. They suggest that the penetration of deep root systems into
bedrock is important in initiating soil formation processes (see Figure 2.19), which in
turn helps maintain the mineral-rich soils that support coniferous forest ecosystems in
temperate, active tectonic settings like the Pacific Northwest. In drier climates with
sparse vegetation, Owen et al. (2011) have shown that bedrock erosion becomes more
sensitive to precipitation.
The rapid growth in the field of ecohydrology is providing a theoretical
framework and new, testable hypotheses to explain complex ecosystem dynamics and
patterns (D'Odorico et al., 2010b). The dominant landscape control on most terrestrial
vegetation is soil moisture through its effects on transpiration and photosynthesis.
Soil moisture variations are regulated by external factors like topography and soil
composition, as well as feedbacks with vegetation, microbial communities, and
animal activities, including burrowing and grazing. Landforms and their associated
surface-water and groundwater flows also play essential roles in structuring biotic
communities. Stream networks, for example, enhance connectivity across the
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