California Rapid Assessment Method for Wetlands - State Water ...

California Rapid Assessment Method for Wetlands v. 5.0.2 – Chapter 2
The PSR framework is a simple construct that can help organize the monitoring components of
adaptive management. It can be elaborated to better represent complex systems involving
interactions and nonlinear relations among stressors, states and management responses (e.g.,
Rissik et al. 2005) For the purposes of CRAM the PSR model is simply used to clarify that
CRAM is mainly intended to described state conditions of wetlands.
2.2.2 Rapid Assessment
CRAM embodies the basic assumption of most other rapid assessment methods that ecological
conditions vary predictably along gradients of stress, and that the conditions can be evaluated
based on a fixed set of observable indicators. CRAM metrics were built on this basic
assumption according to the following three criteria common to most wetland rapid assessment
methods (Fennessy et al. 2004):
the method should assess existing conditions (see Section 2.1 above), without regard for
past, planned, or anticipated future conditions;
the method should be truly rapid, meaning that it requires two people no more than
one half day of fieldwork plus one half day of subsequent data analysis to
complete; and
the method is a site assessment based on field conditions and does not depend largely
on inference from Level 1 data, existing reports, opinions of site managers, etc.
2.2.3 Forcing Functions, Stress, Buffer, and Condition
The condition of a wetland is determined by interactions among internal and external
hydrologic, biologic (biotic), and physical (abiotic) processes (Brinson, 1993). CRAM is based on
a series of assumptions about how these processes interact through space and over time. First,
CRAM assumes that the condition of a wetland is mainly determined by the quantities and
qualities of water and sediment (both mineral and organic) that are either processed on-site or
that are exchanged between the site and its immediate surroundings. Second, the supplies of
water and sediment are ultimately controlled by climate, geology, and land use. Third, geology
and climate govern natural disturbance, whereas land use accounts for anthropogenic stress.
Fourth, biota (especially vegetation) tend to mediate the effects of climate, geology, and land use
on the quantity and quality of water and sediment (Figure 2.1). For example, vegetation can
stabilize stream banks and hillsides, entrap sediment, filter pollutants, provide shade that lowers
temperatures, reduce winds, etc. Fifth, stress usually originates outside the wetland, in the
surrounding landscape or encompassing watershed. Sixth, buffers around the wetland can
intercept and otherwise mediate stress (Figure 2.2).
2.2.4 Condition, Ecological Service, and CRAM Scores
Three major assumptions govern how wetlands are scored using CRAM. First, it is assumed that
the societal value of a wetland (i.e., its ecological services) matters more than whatever intrinsic
value it might have in the absence of people. This assumption does not preclude the fact that the
support of biological diversity is a service to society. Second, it is assumed that the value
depends more on the diversity of services than the level of any one service. Third, it is assumed
that the diversity of services increases with structural complexity and size. CRAM therefore
favors large, structurally complex examples of each type of wetland.
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