(CRAM) For Wetlands User's Manual Version 5.0.2

California Rapid Assessment Method for Wetlands v. 5.0.2 – Chapter 4
4.3 Attribute 3: Physical Structure
Physical structure is defined as the spatial organization of living and non-living surfaces that
provide habitat for biota (Maddock 1999). For example, the distribution and abundance of
organisms in riverine systems are largely controlled by physical processes and the resulting
physical characteristics of habitats (e.g., Frissell et al. 1986). Metrics of the Physical Structure
attribute in CRAM therefore focus on physical conditions that are indicative of the capacity of a
wetland to support characteristic flora and fauna.
4.3.1 Structural Patch Richness
A. Definition: Patch richness is the number of different obvious types of physical surfaces or
features that may provide habitat for aquatic, wetland, or riparian species. This metric is
different from topographic complexity in that it addresses the number of different patch types,
whereas topographic complexity evaluates the spatial arrangement and interspersion of the types.
Physical patches can be natural or unnatural.
B. Rationale: The richness of physical, structural surfaces and features in a wetland reflects the
diversity of physical processes, such as energy dissipation, water storage, and groundwater
exchange, which strongly affect the potential ecological complexity of the wetland. The basic
assumption is that natural physical complexity promotes natural ecological complexity, which in
turn generally increases ecological functions, beneficial uses, and the overall condition of a
wetland. For each wetland type, there are visible patches of physical structure that typically
occur at multiple points along the hydrologic/moisture gradient. But not all patch types will
occur in all wetland types. Therefore, the rating is based on the percent of total expected patch
types for a given type of wetland.
C. Seasonality: This metric is not sensitive to seasonality.
D. Field Indicators: Prior to fieldwork, the imagery of the AA should be reviewed to survey
the major physical features or patch types present. The office work must be field-checked using
the Structural Patch Worksheet below, by noting the presence of each of the patch types
expected for a given wetland type, and calculating the percentage of expected patch types
actually found in the AA. Table 4.16 contains narratives for rating the Structural Patch Richness
Metric for each wetland type.
4.3.1.1 Patch Type Definitions for All Wetlands Except Vernal Pool Systems
Animal mounds and burrows. Many vertebrates make mounds or holes as a consequence of
their foraging, denning, predation, or other behaviors. The resulting soil disturbance
helps to redistribute soil nutrients and thus it influences plant species composition and
abundance. To be considered a patch type there should be evidence that a population
of burrowing animals has occupied the Assessment Area. A single burrow or mound
does not constitute a patch.
Bank slumps or undercut banks in channels or along shorelines. A bank slump is a portion of a
depressional, estuarine, or lacustrine bank that has broken free from the rest of the
bank but has not eroded away. Undercuts are areas along the bank or shoreline of a
wetland that have been excavated by waves or flowing water.
Cobble and boulders. Cobble and boulders are rocks of different size categories. The long axis
of cobble ranges from about 6 cm to about 25 cm. A boulder is any rock having a long
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