The effect of boreal jack pine harvest residue retention on soil environment and processes

Abstract Forest residue left on the ground following harvesting (i.e., “slash”) plays an important role in moderating the physical and chemical environment of the soil for future forest growth. Leaving too little slash can leave the soil exposed to extreme fluctuations in soil conditions and fewer nutrients that may hinder future forest growth, while leaving too much slash makes it difficult for new trees to establish or increases fire hazard. This study investigated the impacts of blading and different loadings of slash (0, 15, 30 and 60 Mg ha−1 dry mass) on soil physical (temperature and moisture), chemical (soil solution) and biological (soil respiration and net ecosystem exchange) processes over 4 summers at a harvested jack pine stand within the Island Lake Biomass Harvest Experiment in northeastern Ontario. Soil temperature and moisture were highest in the bladed and lowest in the 60 Mg ha−1 slash loading. Soil solution chemistry was generally similar among the 0, 15 and 30 Mg ha−1 slash loadings. However, total organic carbon and potassium had higher concentrations at 60 Mg ha−1 treatment and lower concentrations in the bladed treatment, the opposite trend occurred for pH and nitrate. Over three years the concentrations of cations decreased and nitrogen species increased for bladed to 30 Mg ha−1 treatments. The 60 Mg ha−1 treatment had increases in some solutes over time suggesting there is a lag effect as needles and bark are incorporated into the soil. The soil respiration data showed that lowest rates of CO2 production occurred in the bladed treatment, but increased over time as the forest floor developed. CO2 production was highest in the 60 Mg ha−1 slash loading, with high rates of soil respiration in the first year, as fine debris from slash deposited onto the soil, however little photosynthesis occurred in these treatments. Thus retention of small to moderate amounts of slash seem to be sufficient for maintaining a suitable balance of soil conditions for a regenerating forest over the short term.