PARENT SESSION
OOS 5: Restoration Effects of Fire and Thinning Treatments on Mixed-Conifer Ecosystems.
Organized by: M North and J Innes
Monday, August 2, 8:00 AM to 11:30 AM, Meeting Room E 148.

Near term response of surface soil nitrogen cycling and pools to forest clearing and burning.

Erickson, Heather^*,1, ¹ Oregon State University, Corvallis, OR

ABSTRACT- Fire and tree thinning are increasingly being used in western forests to return stands to the more open conditions common prior to fire suppression. Understanding how these management strategies affect soils is crucial for attaining sustainability goals. I examined the effect of forest burning alone and burning in combination with two cutting treatments on surface soil C and N pools and additional N cycling processes as part of an on-going experiment in a spatially heterogeneous mixed-conifer forest at the Teakettle Experimental Forest in the Sierra Nevada Mountains of California. Surface soils (0-15 cm) were sampled across three patch types: closed canopy conifer (CC), Ceanothus cordulatus thickets (CECO), and sparsely vegetated open canopy (OC) areas for 2 years after experimental treatments began. Treatments included an understory burn (B), a light thin and a burn (BC), a more intense thin and a burn (BS), and an unburned, uncut control. The general pattern occurring across patch types was nearly a doubling of C and N pools with the BC and BS treatments and a slight (mean 10%) decrease in pools with the B treatment relative to controls. By the second year, treatment effects on N pools in the OC patches and the relatively high N CECO patches were not found. However in the CC patches, by the second year N pools remained 50% greater with the BC treatment and 20% less with the B only treatment, relative to control patches. The positive effect of the burning and cutting treatments on soil C and N may be due to incorporation of organic residues into the surface soils during harvesting. These results indicate that the marked increase in C and N pools from tree thinning and forest burning is likely to have the most lasting effect in the spatially dominant closed canopy conifer patches.

Key words: forest management, mixed-conifer, nitrogen cycling, carbon pools