Influence of Residue Management on Soil Chemical Properties and Nutrient Flux in Forests Harvested for Woody Biomass
Schroeder, A.. 2014.
Abstract
Altered soil solution chemistry and nutrient flux within forests harvested for
woody biomass may result from disturbance, slash removals, slash decomposition, and
mineralization. Because of the potential adverse effects of woody biomass harvest to soil
nutrient pools and overall soil quality, the Missouri Department of Conservation (MDC)
has developed Best Management Practices (BMPs) to retain coarse woody residues
associated with biomass harvesting to retain nutrient capital and sustain forest
productivity. However, these BMPs remain untested. To investigate the potential impacts
of woody biomass harvest and use of BMPs to mitigate deleterious effects, this study
examined soil nutrient concentrations and nutrient flux in Missouri Ozark forest soils
immediately following harvest to 1.5 years post-harvest. The eight treatments
investigated were Missouri's 1/3 harvest residue retention BMP for thinning and
commercial biomass harvests and alternative harvest scenarios. Chemical properties of
soils within the harvest treatments were quantified immediately after harvest and one year
post-harvest, and analysis of variance results are presented. Total organic carbon (TOC)
was the only dependent variable that was affected by harvest treatment (p-value =
0.0467); where TOC content for clearcut A (Missouri's BMP) and clearcut B (removal of
all biomass) were significantly greater than for clearcut C (alternative BMP). Changes in
nutrient flux were monitored using Plant Root Simulator (PRSTM) ion exchange
membrane probes provided by Western Ag Innovations. Nutrient flux dynamics differed
for the nutrients measured within harvest treatments and at two different depths. Results
indicate greater nutrient flux in the clearcut treatments compared to the intermediate thinning and control treatments for specific ionic species measured (NH4 , NO3-, P, K, S,
Ca, Mg, Mn, Al, Fe, Cu, Zn, and B).
Litter decomposition plays a major role in the cycling of energy and nutrients in
woodland ecosystems. The influence of woody biomass harvest scenarios were
investigated during a one year litterbag experiment in an oak-hickory forest of the
Missouri Ozarks. Total nitrogen (TN), total organic carbon (TOC), C:N ratio, and percent
mass loss of leaf litter material were analyzed and compared amongst eight harvest
treatments. Percent mass loss was positively correlated to total nitrogen. Treatment type
and decomposition time had a significant effect on TN (p = 0.0474 and p < 0.0001
respectively). When comparing the effect of treatment on TN, clearcut B (removal of all
biomass) was significantly lower than the control, intermediate A, clearcut A, (current
1/3 BMP) and clearcut C (alternative BMP). To semi-quantitatively assess how
decomposition processes vary in leaf litter material across different harvesting treatments, thinning and control treatments for specific ionic species measured (NH4 , NO3-, P, K, S,
Ca, Mg, Mn, Al, Fe, Cu, Zn, and B).
Litter decomposition plays a major role in the cycling of energy and nutrients in
woodland ecosystems. The influence of woody biomass harvest scenarios were
investigated during a one year litterbag experiment in an oak-hickory forest of the
Missouri Ozarks. Total nitrogen (TN), total organic carbon (TOC), C:N ratio, and percent
mass loss of leaf litter material were analyzed and compared amongst eight harvest
treatments. Percent mass loss was positively correlated to total nitrogen. Treatment type
and decomposition time had a significant effect on TN (p = 0.0474 and p < 0.0001
respectively). When comparing the effect of treatment on TN, clearcut B (removal of all
biomass) was significantly lower than the control, intermediate A, clearcut A, (current
1/3 BMP) and clearcut C (alternative BMP). To semi-quantitatively assess how
decomposition processes vary in leaf litter material across different harvesting treatments,
solid-state 13C nuclear magnetic resonance spectroscopy with cross-polarization and
magic-angle spinning (CPMAS-NMR) technique was applied to analyze the organic C
dynamics of mixed leaf litter. The type of harvest treatment had a significant effect on the
alkyl-C concentration (p = 0.0411), and on the aromatic-C concentration (p = 0.0071).
Significant decreases were seen in the total aliphatic C functional groups amongst
clearcut treatments compared to intermediate and control treatments. A significant
interactive effect of treatment type and decomposition time was found for the
concentrations of the alkyl-C, O-alkyl-C, and aromatic-C functional groups, indicating
that the change in concentration of these functional groups with decomposition time was significantly different among the different harvest treatments. This research will enhance our understanding of nutrient cycling in a forested
ecosystem following a woody biomass harvest, which will aid in maintaining sustainable
nutrient concentrations and long-term site productivity. To ensure long-term
sustainability and forest productivity, it is recommended to use the current Missouri
BMPs or the alternative BMP (retain tops of all cut trees ≥ 20 cm dbh; remove boles, tops
and limbs of all cut trees ≤ 20 cm dbh). Overall, the biomass guidelines supplement
existing forestry rules and guidelines, encourage forest health and productivity, and
enhance the full suite for ecological values. The current BMP and alternative BMP
provide an opportunity to suggest alternative harvesting techniques, besides the
traditional sawlog harvest, to high grading and damaging practices on the long-term
health of the forest ecosystem.
