Comparison of Coastal Wetland Vegetation Assessment Methods in Southern California

Vegetation surveys provide key information for evaluating functions within and across estuaries. However, survey methods and analyses are often highly variable, site-specific, and driven by monitoring program goals and objectives, making regional comparisons that include multiple programs difficult. This study compared multiple transect- and quadrat-based vegetation monitoring methods within eight southern California estuaries to assess variability and comparability among methods within programs and to provide recommendations for the development of regional and statewide coastal wetland monitoring programs. Using data from established monitoring programs with distinct, non-overlapping goals, vegetation percent cover, species richness, and community composition across five commonly used methods (line intercept, point contact, swath intercept, standard (visually assessed) quadrat, and laser quadrat) were compared. Of the seven vegetation cover comparisons made within programs (n = 2) and methods (n = 5), estimates did not vary by more than 7% on average, with the exception (12%) of the one newly restored and sparsely vegetated wetland included in the analysis. Similarly, plant community composition was not significantly different between methods. Whether the methods were comparable depended on three main factors: (1) method category (transect vs. quadrat), (2) the total amount of cover (high vs. low), and (3) the type of vegetation metrics (percent cover, species richness, and community composition). We also examined how survey decisions (e.g., bounding, plant state, nomenclature, binning) affected vegetation cover estimates within each monitoring program. Surprisingly, standardization across survey decisions was not key to the ability to compare within site estimates. However, it was critical for surveyors to first collect bounded vegetated and non-vegetated cover estimates (i.e., whether overall cover estimates can exceed 100%). When survey designs were similar (e.g., all transect-based and bounded), the data required less manipulation when combining and therefore had higher quality assurance than when survey designs varied (e.g. transect versus quadrat or bounded versus unbounded or combination). Review of method comparisons and survey decisions is reflected in a conceptual framework and led to six conclusions and recommendations for standardized, site-intensive vegetation monitoring that can inform broader recommendations for regional coastal wetland monitoring programs.

The online version contains supplementary material available at 10.1007/s12237-026-01779-2.