Soil C storage following salvage logging and residue management in bark beetle-infested lodgepole pine forests

Authors: AVERA, BETHANY - COLORADO STATE UNIVERSITY; RHOADES, CHARLES - U.S. FOREST SERVICE (FS); CALDERON, FRANCISCO; COTRUFO, M - COLORADO STATE UNIVERSITY

Submitted to: Forest Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/16/2020
Publication Date: 9/15/2020
Citation: Avera, B.N., Rhoades, C., Calderon, F.J., Cotrufo, M.F. 2020. Soil C storage following salvage logging and residue management in bark beetle-infested lodgepole pine forests. Forest Ecology and Management. 472. Article e118251. https://doi.org/10.1016/j.foreco.2020.118251.
DOI: https://doi.org/10.1016/j.foreco.2020.118251

Interpretive Summary: Bark beetle infestations have had a profound effect in lodgepole pine forests across western North America. In addition, the tree mortality caused by the bark beetles can have a potentially significant effect on forest soils. We measured differences soil C stocks 6-7 years after salvage logging in beetle kill affected forests of northern Colorado. We compared logging treatments to uncut beetle-infested forests. Our results show that harvesting the dead residues did not reduce soil C stocks. Our data suggests that in these systems, the soil is more directly affected by root carbon inputs, and less so by C inputs coming from the above-ground residues. This has important implications for biomass harvesting in these forests. However, the long-term impacts of post-bark beetle management on C storage in these high-elevation ecosystems depend on forest recovery that may take decades.

Technical Abstract: Bark beetle outbreaks have altered carbon (C) dynamics in lodgepole pine (Pinus contorta) forests across western North America. The sensitivity of soil C to post-beetle management operations remains unknown in these forests. We quantified differences in O horizon and mineral soil horizon C stocks 6-7 years after salvage logging in lodgepole pine forests of northern Colorado and compared biomass retention or removal residue management to uncut beetle-infested forests. We evaluated the quantity and chemical composition of C in O horizon and in mineral soil organic matter (SOM) physical fractions to better understand how management impacts the stocks, distribution and quality of C with implications for soil C persistence. Post-harvest residue retention increased O horizon C storage compared to the other harvest treatment and unlogged stands. Salvage logging resulted in 3-8.5 Mg ha-1 more mineral soil C (0-10 cm), primarily as particulate organic matter, relative to uncut beetle-infested forests, but did not differ among residue management treatments. Salvage logging did not alter the chemical composition of the soil C fractions analyzed. Together the C:N ratios, Fourier-transform mid-infrared spectra, and 13C values analyses showed distinct C composition in the organic and mineral horizons suggesting that physical transfer or decomposition of C from the O horizon is not a significant source of particulate soil C in these mineral soils. Instead, we suggest that belowground inputs are the likely source of C into the mineral soils of these forests. Our finding that logging residue removal did not reduce post-harvest mineral soil C stocks has important implications for biomass harvesting in these forests. However, the long-term impacts of post-bark beetle management on C storage in these high-elevation ecosystems depend on understory dynamics, tree regeneration and overall forest recovery that occur over the course of decades. Our study suggests that greater understanding of post-disturbance and post-logging organic matter inputs and C dynamics in O horizon and mineral SOM fractions can help inform forest management decisions aimed at sustaining soil C stocks.