PARENT SESSION
Oral Session #87: Ecosystem Ecology.
Presiding: B. Currie
Thursday, August 8. 1:00 PM to 3:45 PM. Graham Meeting Room, TCC.
Post-fire plant species composition and fire severity determine nitrogen retention in upland black spruce forests.
Mack, Michelle*,1, Chapin, F. Stuart2, Schuur, Edward1, Valentine, David2, 1 University of Florida, Gainesville, Fl2 University of Alaska Fairbanks, Fairbanks, AK
ABSTRACT- Loss of nitrogen (N) during and after disturbance can limit primary productivity during succession and over ecosystem development. We used an ecosystem-scale 15N tracer experiment to examine the effects of fire on N retention and partitioning in two boreal black spruce (Picea mariana) forests near Fairbanks, Alaska, that burned in July 1999. In the year following fire, retention of the tracer applied to the surface of burned stands was reduced by 44-66% relative to unburned stands, primarily due to the absence of mosses and lichens from the burnt forest floor. In unburned stands, these growth forms accounted for 55-80% of 15N tracer retention. In burned stands, there was more total N and more 15N tracer found in mineral soil, with a greater proportion of the tracer in soil layers below the rooting zone. Within the burned treatments, the amount of tracer in deeper soil layers was negatively correlated with (1) amount of remaining forest floor, and (2) biomass of key graminoid species. Our results suggest that the effects of fire on the retention and partitioning of N in boreal black spruce forests depend upon fire severity and the consequent loss and growth of key plant functional types.
KEY WORDS: Nitrogen, Retention, Fire, Alaska