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

Authors: AVERA, BETHANY - Colorado State University; RHOADES, CHARLES - US Department Of Agriculture (USDA); Calderon, Francisco; COTRUFO, FRANCESCA - Colorado State University

Submitted to: Forest Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/17/2020
Publication Date: 9/15/2020
Publication URL: https://handle.nal.usda.gov/10113/6985886
Citation: Avera, B., Rhoades, C., Calderon, F.J., Cotrufo, F. 2020. Soil C storage following salvage logging and residue management in bark beetle-infested lodgepole pine forests. Forest Ecology and Management. 472:1-8. 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 on 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 beetleinfested 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.