Idaho forest growth response to post‐thinning energy biomass removal and complementary soil amendments

Abstract

Utilization of woody biomass for biofuel can help meet the need for renewable energy production. However, there is a concern biomass removal will deplete soil nutrients, having short-and long-term effects on tree growth. This study aimed to develop short-term indicators to assess the impacts of the first three years after small-diameter woody biomass removal on forest productivity to establish optimal biomass retention levels for mixed-conifer forests in the Inland Northwest region, and to evaluate the ability of soil amendments to compensate for potential adverse effects from biomass removal. We examined impacts of four biomass retention-level treatments at two study locations: full biomass removal (0x), full biomass retention (1x), double biomass retention (2x), and unthinned control. We combined biomass retention with four soil amendment treatments: biochar (B), fertilizer (F), fertilizer and biochar combined (FB), and an untreated control (C). We considered treatment effects on basal area and total stem volume growth for all trees per plot (plot trees) and for the six largest trees per plot (crop trees). Biomass removal had no effect on plot (P > 0.40) or crop tree growth (P > 0.65) compared to normal biomass retention. High biomass retention (2x) decreased plot tree growth as compared to normal biomass retention (1x) levels (P < 0.05) after three years. This growth difference was not explained by soil moisture, temperature, or nutrient uptake. While there were strong tree growth differences between study locations, patterns of biomass and amendment treatment responses did not differ. Fertilizer increased basal area growth and total volume growth (P < 0.10) as expected, because nitrogen is limiting in the region. Biochar had no effect on tree growth (P > 0.47). Initial findings after three years suggest removing small-diameter biomass for biofuel feedstocks is feasible in the Inland Northwest without negative impacts on tree growth.

Soil greenhouse gas, carbon content, and tree growth response to biochar amendment in western United States forests

“…Swift Creek soils were sandy skeletal, mixed, frigid Typic Haplustepts from the Totelake Series (Soil Survey Staff, ). UIEF soil was coarse‐silty, mixed, superactive, frigid Vitrandic Fragixeralfs (Santa Series) (Soil Survey Staff, ) and more information about its study sites and treatments can be found in Sherman, Page‐Dumroese, and Coleman (). The current study utilized the control and biochar only amended plots (across all thinning treatments) described in Sherman et al ().…”

“…UIEF soil was coarse‐silty, mixed, superactive, frigid Vitrandic Fragixeralfs (Santa Series) (Soil Survey Staff, ) and more information about its study sites and treatments can be found in Sherman, Page‐Dumroese, and Coleman (). The current study utilized the control and biochar only amended plots (across all thinning treatments) described in Sherman et al (). Purdue Creek soils consisted of a Threebear‐Norwidge Complex of medial over loamy, amorphic over mixed, superactive, frigid Oxyaquic Udivitrands (Threebear Series) and Alfic Udivitrands (Norwidge Series) (Soil Survey Staff, ).…”

“…Purdue Creek soils consisted of a Threebear‐Norwidge Complex of medial over loamy, amorphic over mixed, superactive, frigid Oxyaquic Udivitrands (Threebear Series) and Alfic Udivitrands (Norwidge Series) (Soil Survey Staff, ). The Pitwood site was ashy over loamy, amorphic over isotic, frigid Typic Udivitrands (Flewsie Series) and more details about the Pitwood study sites and treatments can be found in Sherman et al (). Umpqua soils were ashy‐pumiceous, glassy Xeric Vitricryands from the Lapine Series (Soil Survey Staff, ).…”

Forest soil respiration and exoenzyme activity in western North America following thinning, residue removal for biofuel production, and compensatory soil amendments

“…Sherman et al () report results of soil temperature and moisture collected at the field locations. In general, spring soil temperature is mild with high moisture, summer is hot and dry, and fall is cool with increasing moisture.…”

“…Clear cutting shifts soil microbial function from nutrient limited and ectomycorrhizal dominated toward carbon limited and saprobe dominated (Kyaschenko, Clemmensen, Hagenbo, Karltun, & Lindahl, ). Yet with thinning, soil microbial shifts are less definitive (Adamczyk, Adamczyk, Kukkola, Tamminen, & Smolander, ), which supports the idea that small‐diameter biomass removal from precommercial thinning will likely impact site conditions less than clear‐cut harvesting (Kabrick, Dwyer, Shifley, & O'Neil, ; Klockow, D'Amato, & Bradford, ; Sherman, Page‐Dumroese, & Coleman, ) because, with thinning, much of the overstory structure is retained and less biomass is removed.…”