Name: Yellow-Cedar Decline 1986 to 2024 - Cumulative
Display Field: SeverityOverall
Type: Feature Layer
Geometry Type: esriGeometryPolygon
Description: <p>This dataset represents yellow-cedar decline mapped across Southeast Alaska since the 1986 through 2024 by aerial detection surveys and three remote sensing efforts in 2004, 2006, and 2020. Two cumulative decline datasets have been created from the same source data: this dataset displays the spatial extent of yellow-cedar decline in Alaska accounting for overlap in mapped decline through time, and a companion dataset with all years of data appended that is easily filterable but retains overlap between years of mapping (Yellow-Cedar Decline 1986 to 2024-Annual). Both datasets originate from the same source data and occupy the same spatial footprint with a total extent of about 728,000 acres.</p><p></p><p><strong>Survey Year Binomial Columns & Years Mapped</strong></p><p>The year of decline detection is identified in the field headings. For most years in the dataset, there is a single binomial column for each survey year (1 indicates the decline polygon was mapped in that year, 0 indicates it was not). Individual polygons may have been mapped more than once. The YearsMapped field sums the number of times an individual polygon was mapped, while the DetectionYears field lists the years in which decline was detected. During some survey years (1996, 1999, 2001, 2002), the spatial distribution of decline that was added to the cumulative decline layer produced that year exceeded the acreage mapped during that year's annual aerial survey, originating from continued efforts to digitize decline mapped during prior survey efforts. Decline added through these digitization efforts is identified in the fields 'YEARcumu' (short for cumulative) and appear alongside fields 'YEAR', denoting polygons added via aerial detection survey. The two photo interpretation mapping efforts correspond to the fields '2004PerilStraitPI' and '2006EdgecumbePI', while the remote sensing effort in 2020 corresponds to the field '2020RS'.</p><p></p><p>Yellow-cedar decline root freezing injury can take 10-15 years to kill individual trees and is progressive within affected forests; therefore, there is overlap in the impacted areas mapped over time. About one-quarter of the decline extent mapped from 1986 to 1987 and 1991 to 1994 was also captured through subsequent survey efforts. The lag between freezing injury and crown symptoms development, and the multi-year persistence of crown symptoms within affected trees and forests, makes it difficult to attribute mapped decline to specific weather events or years. There is a total extent of 728,000 acres of yellow-cedar decline in this dataset. This is slightly higher than the decline extent presented in the Forest Health Conditions in Alaska - 2024 report (718,500 acres) because of the inclusion of the photo interpretation efforts along Peril Strait and Mt. Edgecumbe.</p><p></p><p><strong>Survey Methods</strong></p><p>Aerial surveys in Alaska typically cover 10-15% of the forested area of the state each year. Aerial surveyors from the Alaska Division of Forestry & Fire Protection and USDA Forest Service - Forest Health Protection document insect, disease, and abiotic damage in the forest from about 1000 feet altitude using a digital mobile sketch-mapping tablet and software. This forest health dataset includes both polygon and point data. Points have a buffered area based on tree number. Initially, aerial surveys were conducted using paper 1:250,000 USGS quadrangle maps. In 1999, aerial surveys in Alaska transitioned to mapping with mobile tablets and software, called digital mobile sketch-mapping. Digital mobile sketch-mapping displays the plane’s location via GPS, allows observers to zoom to various scales, and generally improves the accuracy and resolution of polygon placement compared to paper mapping. During the periods 1986 to 1987 and 1991 to1994, decline data was digitized from paper aerial survey maps. The 363,000 acres mapped during this period include both active and older decline. Aerial surveys typically focus on actively damaged and dying trees, but there was a need to understand the full spatial extent of the problem while the cause was investigated and compared to broader landscape patterns. During the 2000s, decline mapping was almost entirely limited to actively dying trees with discolored tree crowns only.</p><p></p><p>Remote sensing efforts to map yellow-cedar decline include two mid-scale aerial photo interpretation efforts (25,388 acres along Peril Strait in 2004 and 9,057 acres on Mt. Edgecumbe on Kruzof Island in 2006). Details about the scale and methodology of photo interpretation mapping efforts are summarized in the report by P. Hennon and D. Wittwer: Evaluating key landscape features of a climate-induced forest decline (Project WC-EM-07-01). In: Potter, Kevin M.; Conkling, Barbara L., eds. 2013. Forest Health Monitoring: national status, trends, and analysis 2010. Gen. Tech. Rep. SRS-GTR-176. Asheville, NC: U.S. Department of Agriculture Forest Service, Southern Research Station. p117-122. The finer-scale polygons identified through photo interpretation were buffered 50 m to complement the scale of aerial survey. In 2020, decline was mapped on parts of Prince of Wales and Annette Islands using high-resolution satellite imagery (‘scan and sketch surveys’) due to the global pandemic. These details are recorded (method) and the methodology is summarized in Appendix 1 of the Forest Health Conditions in Alaska- 2020 report (FS-R10-FHP. 2020. Forest Health Conditions in Alaska 2020. Anchorage, AK. USDA-FS, Alaska Region. R10-PR-46. pp76).</p><p></p><p><strong>Decline Severity</strong></p><p>Decline severity was recorded with mapped decline starting in 2001. Severity has been assigned in different ways over time, initially based upon the number of trees per acre affected (rated low, medium, and high) and starting in 2014 based on the percentage of host trees affected (rated very light, light, moderate, severe, and very severe). This dataset has merged these types of severity assessments into a simplified low, moderate, high scale by lumping the very light and light ratings as low and the severe and very severe ratings as high. Since some polygons were mapped across multiple years, 'SeverityOverall' corresponds to the highest severity level recorded in that polygon. This is our first attempt to combine these systems, understanding that changes in methodology and variation in severity rankings among surveyors complicates interpretation.</p><p></p><p><strong>Decline Mask or Clip Using USGS National Land Cover Classes</strong></p><p>This cumulative yellow-cedar decline layer was clipped/restricted to areas occurring within upland forest and forested wetland cover classes in the USGS National Land Cover Database-modified dataset (modified by Frances Biles, Geographer, PNW Research Station USDA Forest Service for the 2016 Climate Adaptation Strategy for Yellow-Cedar in Alaska, PNW-GTR-917). This cover class refinement eliminates portions of mapped decline polygons that are unlikely to support yellow-cedar and reduces the total acreage of cumulative yellow-cedar decline by about 68,500 acres or 8.6%, and has been applied to cumulative yellow-cedar decline estimates published by the USDA-FS and partners over the past decade. The 2016 Climate Adaptation Strategy provides a detailed summary of yellow-cedar and yellow-cedar decline, as well as modeled projections of yellow-cedar habitat suitability into the 2050s and 2080s based on two key risk factors for decline development: snowpack and hydrology. Another significant refinement of the yellow-cedar decline cumulative layer occurred in 1996 that reduced the extent of decline by 120,000 acres, mostly by replacing very large polygons with smaller, carefully positioned polygons. The 1996 refinement was applied to mapped polygons that occurred prior to this effort such that the older errors were not reincorporated into the final dataset.</p><p><strong>Survey Year Binomial Columns: </strong>CDL1989, CDL1990, CDL80s_91to94, CDL1995, CDL1996, CDL1997, CDL1998, CDL1999, CDL2000, CDL2001, CDL2002, CDL2003, CDL2004, CDL2005, CDL2006, CDL2007, CDL2008, CDL2009, CDL2010, CDL2011, CDL2012, CDL2013, CDL2014, CDL2015, CDL2016, CDL2017, CDL2018, CDL2019, CDL2021, CDL2022, CDL2023, CDL2024, CDL1996cumu, CDL1999cumu, CDL2001cumu, CDL2002cumu, CDL2004PerilStraitPI, CDL2006EdgecumbePI, CDL2020RS</p><p><strong>YearsMapped:</strong> Sums the values in the survey year columns to quantify how many times a particular polygon was mapped</p><p><strong>Acres:</strong> International Survey Acres, Alaska Albers Equal Area Conic, NAD83</p><p><strong>SeverityOverall:</strong> Low, Moderate, High</p>
Copyright Text: USDA Forest Service and Alaska Division of Forestry & Fire Protection staff