Users of the California Wildlife-Habitat Relationships (CWHR) System are encouraged to collect information on special habitat elements when evaluating site-specific projects. We examined the level of disagreement between 12 pairs of individuals applying the information in A Guide to Wildlife Habitats of California to determine the presence or absence of 123 of these habitat elements on 182,0.25-ha plots. The level of individual disagreement, in parentheses, varied (P < 0.001) among the 7 major categories: physical (33%), live vegetation (30%), habitat edge (14%), vegetative diet (14%), animal diet (l0%), aquatic (5%), and man-made (0.4%). The level of disagreement also varied within subdivisions of the physical (P < 0.001), live vegetation (P < 0.001), and vegetative diet (P < 0.001) categories, but not in the subdivisions of the animal diet category (P > 0.25). Discrepancies were attributed to: (1) not detecting an element, (2) misidentifying plant species, (3) errors in size estimation, (4) uncertainty regarding the biology of organisms, (5) different interpretations of an element, (6) errors associated with the temporal period being sampled, (7) change in the status (present or absent) of elements due to environmental change between sampling events, and (8) errors in data entry. Using standard training procedures within planning units, measuring rather than estimating the size of elements where applicable, specifying a standard rate at which plots are sampled, and sampling at the time of year when the most important elements for species of concern are likely to be present, should substantially reduce individual differences in the detection of the special habitat elements described within A Guide to Wildlife Habitats of California.
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