CHANGES IN O-HORIZON MASS, THICKNESS AND CARBON CONTENT FOLLOWING FIRE IN NORTHERN HARDWOOD FORESTS

This study examines temporal changes in the thickness, mass, and organ ic carbon content of the O horizon (forest floor) of eight forested pl ots in northern Michigan, USA. Each plot had experienced a recent burn (prescribed or accidental); burn dates ranged from 1798 to 1980. The climax forest in this region is mixed Pinus-Acer-Betula-Tsuga, whereas the fire successional species are predominantly Populus spp. and Betu la papyrifera. O horizon data were fit to logarithmic functions (chron ofunctions) that depicted rapid accumulations of mass and thickness in the first years after the fire, followed by decreasing rates of incre ase after almost-equal-to 100 years. Extension of the chronofunctions to almost-equal-to 5000 years allowed for a theoretical examination of forest floor conditions, e.g., steady state and time to steady state, after long periods without disturbance. The models predicted greater O horizon thicknesses and slightly lower mass for steady state conditi ons than have been reported for old-growth stands elsewhere. Steady st ate accumulations of litter in these mixed, temperate forests requires at least 200 and possibly > 1000 years, which is markedly longer than most other estimates. Although frequent disturbance by fire in these forests would likely preclude such values from being attained, these d ata provide theoretical maximum values for forest floor conditions in these ecosystems.