Document


Title

Sampling the moisture content of dead grass-like plants
Document Type: Guide / Handbook / Manual / Protocol
Author(s): Eric Miller
Publication Year: 2013

Cataloging Information

Keyword(s):
  • dead fuels
  • fuel moisture
  • grass
  • grass fuels
  • grasslike plants
  • moisture content
  • sampling
Region(s):
Record Maintained By:
Record Last Modified: January 17, 2019
FRAMES Record Number: 23209

Description

Grass is a prominent fuel type with fire behavior distinct from other carrier fuels, burning quickly and with sometimes surprising intensity. At its most specific level grass-like fuels include not just grass but also sedges and, more uncommonly, rushes. In Alaska grass-like fuels include tall grasses such as bluejoint (Calamagrostis) and wideleaf polargrass (Arctagrostis) or short grasses such as fescue. Tundra fires may be carried by tussockgrass (which is not a grass at all but a sedge). In terms of fuel models and fire behavior modelling live grass-like plants are grouped with forbs in the category of “Live Herbaceous” fuels. For the purposes of fuel moisture sampling the term grass refers to any grass-like plant. In Alaska, dead, overwintered grass is most susceptible to burning during the window between snow-melt and green-up or hardwood leaf-out. After green-up the high moisture content of new grass culms (>200%) tends to retard fire spread although dry underlying thatch or “skirts” of dead grass may be sufficient to carry fire. Unlike other areas of the continental U.S. senescense has little effect on fire behavior in Alaska. Senescense, or curing, marks a late season decline in foliar moisture. Below 30% moisture content foliage is considered dead. In Alaska grass may not reach a cured state before fire behavior is inhibited by declining day length, increasing time below the dew point temperature, and snow fall. Fire is primarily driven by dead grass conditions. During spring prescribed burn windows on military training ranges dead grass moisture content ranged between 7.4% - 15.8%. Probability of ignition was determined to be 50% at 12.4% moisture content in Alaska (Miller, unpublished data). The probability drops to 5% at about 22.5% moisture content. Since grass leaves are dead, moisture content is subject solely to atmospheric factors, including temperature, dew point, air pressure, wind speed, and solar insolation.

Online Link(s):
Link to this document (79.0 KB; pdf)
Citation:
Miller, Eric. 2013. Sampling the moisture content of dead grass-like plants. AWFCG Fire Research Development and Application Committee and Alaska Fire Science Consortium. 2 p.