Mature and old-growth forests contribute to large-scale conservation targets in the conterminous United States
The first spatially explicit assessment of Mature and old-growth (MOG) forests for the countermines United States based on three structural development measures—canopy height, canopy cover, and above-ground living biomass.
Study link: Frontiers in Forests & Global Change (2022)
Mature and old-growth (MOG) forests of the conterminous United States collectively support exceptional levels of biodiversity but have declined substantially from logging and development. National-scale proposals to protect 30 and 50% of all lands and waters are useful in assessing MOG conservation targets given the precarious status of these forests. This study presents the first coast to coast spatially explicit MOG assessment based on three structural development measures—canopy height, canopy cover, and above-ground living biomass to assess relative maturity.
MOG were displayed by major forest types (n = 22), land ownerships (federal, state, private, and tribal), and Gap Analysis Project (GAP) management status overlaid on the NatureServe’s Red-listed Ecosystems and species, above-ground living biomass, and drinking water source areas. MOG total ∼67.2 M ha (35.9%) of all forest structural classes and were scattered across 8 regions with most in western regions. All federal lands combined represented the greatest (35%) concentrations of MOG, ∼92% of which is on national forest lands with ∼9% on Bureau of Land Management (BLM) and ∼3% on national park lands (totals do not sum to 100% due to minor mapping errors in the datasets).
MOG on national forest lands supported the highest concentration of conservation values. However, national forests and BLM lands did not meet lower bound (30%) targets with only ∼24% of MOG (GAPs 1 and 2) having protection status. The vast majority (76%, 20.8 M ha) of MOG on federal lands, which store 10.64 Gt CO2, are vulnerable to logging (GAP 3). If federal MOG are logged over a decade, and half their carbon stock emitted, there would be an estimated 0.5 ppm increase in atmospheric CO2 by 2030, equivalent to ∼9% of United States total annual emissions.
The study recommends that 100% of federal MOG should be protected, including elevating the conservation status of Inventoried Roadless Areas. This would avoid substantial CO2 missions while allowing critically important carbon sequestration services.
Leader research: Dominic DellaSala, Wild Heritage
Contributing authors: Brendan Mackey (Griffith U), Patrick Norman (Griffith U), Carly Campbell (Griffith U), Patrick Comer (NatureServe), Cyril Kormos (Wild Heritage), Heather Keith (Griffith U), Brendan Rogers (Woodwell Climate Research)