Soil respiration following alternative site preparation treatments in a boreal mixedwood forest

Abstract

The effects of experimental site preparation on CO2 evolution and on planted black spruce {Picea mariana (Mill.) B.S.P.) seedling growth were studied one year after the site preparation treatment, during the 1994 growing season (June-October) and again in May and June of 1995 on a boreal mixedwood site. Treatments included: uncut forest, cut forest without site preparation, cut and mixed where organic matter to a depth of 20 cm was mixed with mineral soil, and cut and screefed where the top organic layer was removed. Carbon dioxide evolution was determined once a month in the field by infra-red gas analyzer (IRGA) and by the soda-lime trap technique. Soil temperature and moisture contents were measured once a month during the 1994 growing season and for two months in 1995. Concentrations of organic matter, PO43-p and NH4+-N were also determined after treatment. Interactions of temperature, moisture and organic matter on CO2 evolution were studied under controlled laboratory conditions. Carbon dioxide evolution from the cut treatment plots was not significantly different from that of the uncut plots. Carbon dioxide evolution from the cut and mixed plots was significantly higher than from the cut and screefed plots. Evolution of CO2 varied seasonally. The IRGA proved to be a better method for determining CO2 evolution than the soda-lime technique due to its convenience and efficacy. Highly significant relationships among CO2 evolution, soil organic content, soil P and moisture contents were found. It was concluded that site preparation treatments had a significant effect on CO2 evolution by modifying the organic matter and moisture contents of the soils. Height of planted black spruce seedlings, however, did not vary significantly during the first two years after the treatments.