Fuel Treatments Effectiveness at Savannah River Site

Project Description

A 12-month field study was conducted at Savannah River to characterize the forest floor depth and bulk density of the litter- and duff-fuelbed layers for a combination of forest types, stand age classes, and time since burning. A total of 388 depth and bulk density samples were collected from 97 Forest Inventory and Assessment sites at Savannah River. The data will be further analyzed to determine the factors that control the variation in depths and bulk density. This information is becoming increasingly important to fire managers as new fuel and fire management decision support systems come online.

Purpose and Scope

The forest floor fuelbed component can represent the bulk of the fuels that consume during wildland fires and therefore smoke emissions in the southern forests. It is therefore imperative the mass of this fuelbed component is accounted for when characterizing fuels.

Methods

Mean bulk density (tons/acre/inch) values associated with simple stand characteristics were extracted from field data collection to allow conversion of forest floor depth to forest floor mass.

The oven dry mass of the litter and duff collected for each sample was divided by the area of the sampling square (144 in2 ) divided by the average layer depth to determine bulk density.

Implementation

Bulk density sampling points were randomly selected from the Forest Inventory and Assessment sites established at Savannah River. Sites were selected and grouped based on stand type, stand age, and rough age as suggested by local land managers. A total of 97 FIA sites were visited and 388 bulk density samples collected.

Key Findings

Initial review of litter-depth data indicates average litter depth increased with stand age in the loblolly and slash pine and longleaf stands. Litter bulk density remained relatively constant across stand age

Stand age is the main factor contributing to duff bulk density variation across forest types

• Average litter depths ranged from 0.9 inch for upland hardwoods greater than 40 years in age without fire for over 10 years, to 1.6 inches on longleaf pine sites greater between 20 and 40 years in age and more than 3 years since fire.
• Average duff depth ranged from 0.4 inch on upland hardwood and pine and hardwood mix between 5 and 20 years in age with greater than 10 years since fire to 1.0 inch in pine and hardwood stands greater than 40 years in age and greater than 10 years since fire.
• Average litter bulk densities ranged from 1.5 t/ac/in for pine and hardwood mix between 5-20 years old without fire for over 10 years to 2.4 t/ac/in for loblolly and slash pine sites between 5 and 20 years in age and more than 3 years since fire.
• Average duff bulk densities ranged from 2.6 t/ac/in on upland hardwood mix between 5 and 20 years in age with greater than 10 years since fire to 9.0 t/ac/in for loblolly and slash pine greater than 40 years in age and 3 to 10 years since fire (table 5).

Project Deliverables

A total of 388 depth and bulk density samples were collected from 97 Forest Inventory and Assessment sites at Savannah River. The data was further analyzed to determine the factors that control the variation in depths and bulk density.