Puget Sound Marine Riparian Mapping

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• RCO's PRISM Project Search
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Cramer Fish Sciences and NOAA NWFSC are working to produce complete and regionally consistent spatial data layers mapping marine riparian forests by leveraging two approaches developed in previous studies mapping percent forest cover and contiguous marine riparian cover width for two data years (Hall et al. 2019; PSEMP NSWG 2019). Mapping of both datasets has been completed and will be made available online in Fall 2024.

The primary goal of this project is to support regional salmon recovery planning and evaluation by developing regionally consistent and up-to-date spatial data layers for tidally influenced and marine riparian habitats at the regional scale. To achieve this goal, we worked with salmon recovery agencies to develop spatial data products that leverage and integrate with existing habitat status and trends monitoring programs and metrics, address regional data gaps, and are readily accessible through online mapping applications to support restoration planning and evaluation of progress towards recovery at a regional scale. This project included two key objectives; (1) creating a consistent and up to date regional spatial database of tidal restriction and tidal wetland features, and (2) mapping marine riparian cover width for Puget Sound for two time steps. This page focuses on describing the efforts to map marine riparian habitat. More information about the tidal restriction mapping can be found on the Puget Sound Large River Delta Tidal Restriction and Wetland Mapping and the Puget Sound Tidal Restriction and Wetland Mapping pages.

Background

Riparian forests are critical for shade, bank stabilization, and providing sources of large wood and organic materials (Shreffler et al. 1994; Brennan & Culverwell 2004; Brennan et al. 2009). A significant amount of research, monitoring, and regulation has been focused on freshwater riparian forests, however marine riparian play a similar role in maintaining nearshore ecosystems that provide critical habitat to forage fish and juvenile salmonids and likewise the quality and size of marine riparian forests influences their function (Shreffler et al. 1994; Desbonnet et al. 1995; Brennan & Culverwell 2004). While natural variation exists in marine forest composition and condition between shoreforms, extensive shoreline development in Puget Sound has led to the loss and disconnection of marine riparian forests, resulting in reduced nearshore habitat function and quality (Thom et al. 1994; Johannessen and MacLennan 2007). Guidelines for marine riparian forest width recommend a buffer width of at least 200 feet for undeveloped shorelines and at least 100 feet for developed shorelines, which is required to maintain most ecological functions, such as sediment control, shade, and organic material inputs required and to maintain large wood inputs, respectively (Desbonnet et al. 1995; Brennan et al. 2009; PSEMP NSWG 2019). However, there is little data describing the current and historic marine riparian forest condition, thus limiting the ability to develop meaningful recovery goals and targets; to identify, evaluate, and prioritize restoration opportunities; and to evaluate progress towards recovery goals and targets over time. This project (PRISM 20-1941P) addressed this data gap by mapping marine riparian forests using two methods, developed in coordination with NOAA, PSP, and PSEMP, for the entire Puget Sound shoreline for two data years, represent a past and current condition (Hall et al. 2019; PSEMP NSWG 2019).

Project Goals and Objectives

• Summarize percent forested cover using a selected shoreline dataset to generate 0-100 ft and 0-200 ft buffers for 2013 and 2017.

• Segment a corrected shoreline with breaks based on contiguous forested cover width classes and shoreform types for 2009 and 2017.

• Summarize marine riparian extent and percent forested cover metrics by Lead Entity boundary, shoreform, and width classes for two time periods, evaluate trends, and compare methods to support regional habitat status and trends monitoring reporting.

Methods

Shoreline delineation
While numerous shoreline datasets exist, we needed a shoreline that described the start of marine riparian vegetation for both 2009 and 2017. As a result, the first step of our approach was the development of an updated shoreline layer at the Ordinary High-Water Mark (OHWM) - defined as a biological vegetation mark by Washington’s Shoreline Management Act (DOE, 2017). While delineation of OHWM is most accurate through field measurements, it isn’t possible at a regional scale due to funding and time constraints. Consequently, our method aimed to approximate OHWM identification using remotely sensed indicators. We utilized available LiDAR datasets in conjunction with aerial and oblique imagery to digitize the OHWM line. Using a 1-meter lidar Digital Terrain Model (DTM) hillshade, we identified elevation inflection points to ascertain the location of the shoreline and utilized National Agriculture Imagery Program (NAIP) aerial imagery in a color-infrared (CIR) configuration to differentiate vegetation from non-vegetation. Shoreline mapping was performed for two years, 2009 and 2017 to identify trends in the cover datasets. We selected 2009 because it is the earliest year of NAIP imagery with 4-bands, including near-infrared that allows configuration of aerial imagery into a CIR composite. We selected the 2017 aerial imagery to match the imagery year of a parallel effort to map the percent of forested cover using methods developed by Hall et al. (2019), which use the Washington Department of Fish and Wildlife Puget Sound High Resolution Land Cover (HRLC).

Width of contiguous forested cover

Example of forest width class measurement along No Appreciable Drift - Bedrock shoreform in oblique imagery (DOE 2018). Shoreline sections marked in red are classified as no forest due to the height at which forested cover begins. Shoreline sections marked in blue and purple are classified as 30-60 and 100-150 ft width classes, respectively, as a natural break in forested cover is present. The orange shoreline sections represent measurements of forested cover widths greater than 200 ft.

The contiguous marine forested cover metric was developed by NOAA NWFSC. The methods for delineating and calculating the width of contiguous forested marine riparian cover were based on the SHSTMP pilot study and the outcomes of the PSEMP NSWG workshop on marine riparian habitats (PSEMP NSWG 2019). In the pilot, the SHSTMP team completed mapping for the Puget Sound Straits and the Hood Canal using the 2017 NAIP imagery and DOE Oblique Shoreline Imagery (PSEMP NSWG 2019). This project updated and formalized the protocols and to map the entire Puget Sound shoreline using the updated protocols (Stefankiv & Beechie 2022).

After the shoreline was completed for a given year, the line network was segmented and attributed using the canopy height models and NAIP imagery to represent the width of forested cover at that segment. We selected width classes based on Shoreline Master Programs Handbook recommendations (e.g., 0-30 ft, 30-60 ft, 60-100 ft, 100-150 ft, 150-200 ft, and 200+ ft) .

Percent forested cover
The percent forested cover metric was developed in Hall et al. (2019). The previous protocol resulted in two datasets for 2013 high-resolution land cover, one representing the percent forested cover for the 0-100 ft ESRP Beach Strategies NGF shoreform polygons and one for the 0-200 ft polygons. In this mapping effort, we followed the same methods used in Hall et al. (2019), however, we buffered the shorelines developed from the contiguous marine riparian forested cover width dataset and the NGF polygon breaks as the baseline for mapping. We used the WDFW 2013 HRLC land cover and 2017 tree cover data to calculate percent forested cover and total forested area within each shoreform polygon.

An example of differences in mapping classifications between the percent forested cover and contiguous marine riparian forested cover datasets for 2017. Along the feeder bluff, the shoreline was mapped as having no forest cover due to the natural proximity break of over 10 vertical and horizontal feet from the top to the toe of the bluff, however the percent forest cover exceeded 40% for both the 0-100 and 0-200 foot buffers.

Data analysis

We compared the two datasets to evaluate differences in results, and strengths and weaknesses of each. For the overlapping mapping year, 2017, we compared how the percent forested cover metrics correlated to the width of contiguous marine riparian forest results. We also evaluated change in cover metrics between the two mapping years for each dataset (e.g., 2009 to 2017 for contiguous forested cover and 2013 to 2017 for percent forested cover) to examine if change detection was consistent between the two datasets.

Project status

Preliminary mapping has been completed and data will be made available on the project WDFW-CFS Review Webmap for local area expert review and feedback on accuracy and alignments. Access the WDFW-CFS Review map here.

Notes

• This project was funded as part of an ESRP/Learning Program (PRISM Project #20-1941)
• The project was contracted in 2021, regional review is currently underway and will conclude in August 2024. The final dataset and report reflecting the results of the review will be completed in December 2024.
• PRISM Project #20-1941 contract and documents

Please contact Jason Hall (jason.hall@fishsciences.net) with any questions regarding this project.

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