Forest soil respiration in eastern Ontario jack pine ecosystems

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Abstract
Forest soil respiration in situ was used as a comparative measure of the metabolic activity of substrate in eastern Ontario jack pine (Pinus banksiana Lamb.) ecosystems that had been exposed to various burning treatments, including wildfire. The five burning treatments consisted of a 1920 wildfire, experimental understorey burning (nonlethal to the overstorey) of this age-class in 1962 and 1963, a 1964 wildfire, and experimental burning of this age-class in 1977. Seasonal respiration trends were similar on all treatments. Carbon dioxide evolution increased in the spring (4000 mg .cntdot. m-2 .cntdot. d-1) in response to ambient warming (5000 mg .cntdot. m-2 .cntdot. d-1 in August) and decrease in late fall as seasonal temperatures declined (4000 mg .cntdot. m-2 .cntdot. d-1 in November). Precipitation and autumnal litter fall apparently acted as secondary modifiers of this general trend by affecting substrate moisture content and nutrient quality, respectively. Highest metabolic activities were measured on the 1963 understorey burning treatment followed in decreasing order by the 1920 wildfire, the 1964 wildfire, the 1962 experimental understorey burn, and the 1977 burn of the 1964 age-class. Multiple comparisons of overall seasonal respiration means revealed low rates (P < 0.01) on the latter two treatments compared with the 1963 treatment. Effects of understorey burning treatments on respiration activity appeared to depend on depth of burn and subsequent forest floor development. Stand-replacing fire, reoccurring during early stages of jack pine ecosystem development, significantly lowered metabolic activity of the site.