Land management practices have strong potential to modify the biogeochemistry of forest soils, with
implications for the long-term sustainability and productivity of forestlands. The Long-Term Soil
Productivity (LTSP) program, a network of 62 sites across the USA and Canada, was initiated to address
concerns over possible losses of soil productivity due to soil disturbance from forest management.
Network sites employ an experimental design consisting of three harvest intensities (bole only, whole
tree, whole tree + forest floor removal) in combination with three soil compaction intensities (none,
intermediate, severe). Our purpose was to determine the impact of forest harvest intensity, soil compaction,
and their interaction on soil organic carbon (SOC) and total nitrogen (TN) storage, and on soil
microbial biomass C and N (MBC and MBN, respectively) in a Pinus taeda L. forest 15-years post-treatment
at the Groveton LTSP site in eastern Texas, USA. Soils were sampled (0–10 cm) five times during 2011–
2012, and we quantified SOC and TN by dry combustion, and MBC and MBN by chloroform fumigation
extraction. SOC and TN were both higher in the bole only treatment compared to the more severe harvest
treatments; however, while TN was significantly impacted by harvest and varied seasonally, SOC varied
only with season. MBC and MBN were impacted by harvest intensity and varied seasonally, and SMB-N
had a harvest by time interaction. Generally, both microbial indices decreased in the order: bole only
>whole tree > whole tree + forest floor. Temporal variations in MBN and TN were correlated with temperature.
Soil compaction and the harvest intensity soil compaction interaction had no effect on the
measured soil properties. Since N limits tree growth in forest ecosystems, and because soil microbial biomass
plays a key role in N mineralization, data suggest that harvest practices that minimize removal of
litter and slash will favor soil N retention, maintain the size of the soil microbial biomass pool, and maximize
the potential productivity of future rotations.
Land management practices have strong potential to modify the biogeochemistry of forest soils, withimplications for the long-term sustainability and productivity of forestlands. The Long-Term SoilProductivity (LTSP) program, a network of 62 sites across the USA and Canada, was initiated to addressconcerns over possible losses of soil productivity due to soil disturbance from forest management.Network sites employ an experimental design consisting of three harvest intensities (bole only, wholetree, whole tree + forest floor removal) in combination with three soil compaction intensities (none,intermediate, severe). Our purpose was to determine the impact of forest harvest intensity, soil compaction,and their interaction on soil organic carbon (SOC) and total nitrogen (TN) storage, and on soilmicrobial biomass C and N (MBC and MBN, respectively) in a Pinus taeda L. forest 15-years post-treatmentat the Groveton LTSP site in eastern Texas, USA. Soils were sampled (0–10 cm) five times during 2011–2012, and we quantified SOC and TN by dry combustion, and MBC and MBN by chloroform fumigationextraction. SOC and TN were both higher in the bole only treatment compared to the more severe harvesttreatments; however, while TN was significantly impacted by harvest and varied seasonally, SOC variedonly with season. MBC and MBN were impacted by harvest intensity and varied seasonally, and SMB-Nhad a harvest by time interaction. Generally, both microbial indices decreased in the order: bole only>whole tree > whole tree + forest floor. Temporal variations in MBN and TN were correlated with temperature.Soil compaction and the harvest intensity soil compaction interaction had no effect on themeasured soil properties. Since N limits tree growth in forest ecosystems, and because soil microbial biomassplays a key role in N mineralization, data suggest that harvest practices that minimize removal oflitter and slash will favor soil N retention, maintain the size of the soil microbial biomass pool, and maximizethe potential productivity of future rotations.
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