Mineral N availability for conifer growth following clearcutting: responsive versus non-responsive ecosystems

We compared mineral N concentrations, potential net mineralization rates and gross N mineralization rates in the forest floor of 4-year-old clearcut plots and adjacent mature forest stands, in three distinct coniferous ecosystems in British Columbia (coastal low elevation, coastal montane, interior montane). Our data showed that clearcutting has no effect on forest floor mineral N dynamics in some coniferous ecosystems, and significant effects in others. Among “responsive” sites, we noted contradictory effects of clearcutting on some of the measured N variables. Furthermore, the effects of clearcutting on potential net mineralization were not consistent with changes in gross production rates of mineral N. We discuss these observations in light of our knowledge of the ecology of each site, of the various sources and sinks of mineral N, and of the biotic and abiotic factors controlling mineral N dynamics. Our results suggest that generalizations cannot be made on the effects of clearcutting on mineral N supply to conifer seedlings, as these can lead to incorrect interpretations of ecosystem dynamics, with serious policy-relevant ramifications for the forest industry.