Impact of harvesting and logging slash on nitrogen and carbon dynamics in soils from upland spruce forests in northeastern Ontario

Abstract

The potential impact of timber harvesting in the boreal forest on aquatic ecosystem water quality and productivity depends in part on the production of nutrients within the soil of the harvested catchment. Nitrogen supplied by organic matter decomposition is of particular interest because of the important role that N plays in biotic processes in surface waters, and in forest nutrition in general. Logging slash quality and input to the forest floor has the potential to influence N availability after harvest on clearcut sites. Net production of organic and inorganic-N and microbial biomass C and N concentrations were determined during a 90-day laboratory incubation at constant temperature and moisture. Incubated soils included F horizon and shallow mineral soil horizons (0-5 cm) from unharvested and full-tree harvested (2 and 12 growing seasons since harvest) boreal forest sites at the Esker Lakes Research Area (ELRA), in northeastern Ontario, Canada. In an ancillary experiment, black spruce foliage was added to unharvested forest floor material after 30 days during a 90-day laboratory incubation to simulate the influence of logging slash from full-tree harvesting on C and N dynamics. Twelve-year old clearcut F horizon material released on average 75 and 5 times more NO À 3 -N and 3 and 2 times as much inorganic-N than soil collected from unharvested and 2-year-old clearcuts, respectively. This increase in NO À 3 -N accumulation during the incubation was accompanied by decreases in both exchangeable NH þ 4 -N and microbial biomass C and N levels. Net daily changes in microbial biomass N were significantly related to organic and inorganic-N accumulation or loss within the F horizon. Mineral soil release of inorganic-N was lower than release from the forest floor. Nitrate-nitrogen accumulation was lower, and NH þ 4 -N accumulation was higher in mineral soil from unharvested sites when compared to 12-year-old clearcuts. Calculated harvest response ratios indicated that incubated mineral soil from the 12-year-old clearcut sites released significantly greater amounts of NO À 3 -N than 2-year-old clearcuts. Incorporation of black spruce needles into F horizon material reduced the production of organic and inorganic-N and increased microbial biomass N. Laboratory incubations of F horizon and shallow mineral soil from 12-year-old clearcuts suggested that these boreal soils have the capacity for increased inorganic-N production compared to uncut stands several years after harvesting. This has the potential to increase N availability to growing boreal forest plantations and increase N leaching due to greater NO À 3 -N levels in the forest soil. r

The importance of catchment slope to soil water N and C concentrations in riparian zones: implications for riparian buffer width

“…In terms of NH 4 + and NO 3 -, the absence of a relationship is not surprising in that the annual riparian zone mineral soil water N concentrations for the extensive sites were extremely low in this boreal ecosystem when contrasted with other forest types (Van Miegroet et al 1992;Foster et al 2005). Low net mineralization potential, especially for NO 3 -, for the F horizon and 0-10 cm of mineral soil from unharvested stands at the ELRA has been reported by Hazlett et al (2007). Of significant note were forest floor percolate NH 4 + and NO 3 -concentrations and mineral soil water NO 3 -concentrations at sites with alder present that were as high or higher than concentrations determined in a N-rich tolerant sugar maple (Acer saccharum Marsh.)…”

“…Previous work has demonstrated that organic and mineral soils at the site have the potential to release N after harvest (Hazlett et al 2007); however, it is uncertain to what extent this N will be microbially immobilized or taken up by regenerating vegetation within clearcut areas and, therefore, what amount will move into the riparian buffers downslope. The ability of riparian forests and soils on shallow and steep slopes to modify soil water concentrations under increased inputs from cutover areas could be dissimilar to that which was observed for the unharvested forest.…”

“…Although this may apply for some forest ecosystems, it is unclear whether these processes play a significant role in nutrient-poor boreal forests with oligotrophic aquatic systems. Unharvested boreal forest soils have slow decomposition rates and low rates of inorganic-N production (Smith et al 2000;Hazlett et al 2007), and harvesting impacts on N production have been variable (Carmosini et al 2003;Hazlett et al 2007). In relation to nutrient movement from terrestrial to aquatic ecosystems, the application of buffer widths based on landscape slope implies that nutrient concentrations of drainage water in forest riparian zones will be correlated with catchment slope parameters.…”

Impacts and prognosis of natural resource development on water and wetlands in Canada’s boreal zone

“…The warm, mesic, and aerated conditions created from timber harvesting operations are ideal for microbial metabolism and their mineralization of organic matter. The rate and timing of decomposition is also constrained by the amount of organic material left following harvest and its quality (i.e., more easily degradable leaf or needle litter and fine roots vs. less easily degradable branches and stems) (Hazlett et al 2007). The amount and type of residue (slash) retained on the site will differ depending on timber harvest approach and whether whole tree (de-limbing at road, less residue in plot) or tree-length (delimbed where cut, more residue on plot) methods were used.…”

What are the Environmental Consequences of Using Silviculturally Effective Forest Vegetation Management Treatments?

“…Treatments that suppress vegetation for extended periods or cause extensive exposure of mineral soil and/or compaction or rutting will have longer-term (≥10 yrs) effects (Bormann and Likens 1979). However, since the relationship between a specific vegetation management treatment and the mineralization of a given element depends on many variables, it is difficult to determine how any given element will respond (Hazlett et al 2007).…”