Forests of the Susitna-Copper Unit, Alaska, 2020: Forest Inventory and Analysis Report

Abstract

This report provides detailed estimates and highlights key findings from U.S. Department of Agriculture, Forest Service, Forest Inventory and Analysis (FIA) data collected across its Alaska Susitna-Copper FIA unit in 2019 and 2020. The Susitna-Copper FIA unit encompasses much of the Susitna River and upper Copper River watersheds and is one of six FIA inventory units designed to measure the expansive boreal forests of Alaska. Estimates of forest area, volume, aboveground biomass, and ecosystem carbon are provided across land ownerships, forest types, and forest demographics throughout the unit. The Susitna-Copper FIA unit covers about 31.6 million acres, of which 9.1 million acres (29 percent) were considered forest land. As is typical in boreal forests, tree species diversity and average tree volume are extraordinarily low in the unit. The black spruce (Picea mariana (Mill.) Britton, Sterns & Poggenb.) forest type composed the most forest area, with white spruce (Picea glauca (Moench) Voss) and Alaska paper birch (Betula neoalaskana Sarg.) also covering a significant amount of area. Most of the forest land is managed by the State of Alaska, including most of the tree volume on 1.3 million acres of timberland in the unit. Unique to the FIA program measurement of boreal forests in its interior Alaska inventory, is the assessment of the nonvascular ground layer, collection of tree cores, and analysis of soil cores from each plot. Across the Susitna-Copper FIA unit, belowground carbon represented 70 percent of ecosystem carbon, compared to 17 percent for aboveground carbon in live trees. Vascular vegetation cover in forest understories was dominated by shrubs, though overall cover was relatively low at a mean of 20.67 percent. A significant spruce beetle (Dendroctonus rufipennis (Kirby)) outbreak in the Matanuska watershed coincided with FIA plot measurement in the Susitna-Copper FIA unit and is reflected in the number and volume of standing dead white and black spruce recorded, particularly in trees greater than 5 inches diameter at breast height. This report summarizes the status of forests in a region that has previously lacked a comprehensive inventory at such a scale.

A set of 57 supplemental online tables to accompany this report are available here.

Citation

Ellison, Sarah B.Z.; Kuegler, Olaf; Davis, Brett. 2026. Forests of the Susitna-Copper Unit, Alaska, 2020: Forest Inventory and Analysis Report. Gen. Tech. Rep. PNW-GTR-1037. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 60 p. https://doi.org/10.2737/pnw-gtr-1037.