Document


Title

In-site measurements of moss moisture
Document Type: Poster
Author(s): Sue A. Ferguson; Miriam L. Rorig; Andrew A. Bluhm; David V. Sandberg
Publication Year: 2000

Cataloging Information

Keyword(s):
  • fire ignition
  • Frostfire
  • fuel moisture
  • moss moisture
  • TDR - time domain reflectometry
Topic(s):
Region(s):
Record Maintained By:
Record Last Modified: August 16, 2019
FRAMES Record Number: 1982

Description

The moisture content of material on a forest floor can play a significant role in its potential for fire ignition and resulting severity, especially in boreal ecosystems that contain deep layers of moss. To better understand the effect of weather and permafrost on moss moisture, we fixed in place several time delay reflectometer (TDR) moisture sensors, at 5cm and 10 cm depths within the Frostfire experimental burn site. This allowed us to monitor the pattern of drying and wetting at each location over time. Spatial heterogeneity, structural bias, and variable porosity prevented proper sensor calibration. Therefore, we could not determine actual moisture content or compare the magnitude of values between sites. At times, however, manual moisture measurements were available from co-located sites. The volumetric and gravimetric samples compared favorably with the TDR sensor values and allowed modest calibration. Several interesting patterns in moss moisture were observed with the in-situ moisture sensors. For example, accelerated drying occurred shortly after the permafrost depleted. There was a strong diurnal pattern in moss moisture that was greatest at sites closest to the surface. Although diurnal patterns in moss moisture closely followed air humidity patterns, longer period drying trends in the moss were observed at times when the air humidity was rising, indicating a threshold dryness that retards the ability of moss to absorb new moisture. Also, rewetting after precipitation appeared to depend on the precipitation amount and rate, much like the rewetting characteristics of a dry sponge. At times, no increase in moss moisture was observed after a light precipitation event. Other times moisture increases were delayed by hours following sustained rainfall. At the time of the Frostfire ignition, the moss moisture was at its lowest for the season. More work is needed to determine if in-situ sensors can offer meaningful information from one season to the next. Also, more data are needed to determine if observed drying trends following permafrost depletion are common, whether a threshold of dryness that retards remoistening can be quantified, and whether diurnal changes in moisture are significant enough to alter the timing of planned ignitions. The promise of in-situ moisture sampling is encouraging and, in the future, may afford more accurate planning of prescribed burning and better prediction of wildfire potential.

Citation:
Ferguson, Sue A.; Rorig, Miriam L.; Bluhm, Andrew A.; Sandberg, David V. 2000. In-site measurements of moss moisture (poster). Fire Conference 2000: The First National Congress of Fire Ecology, Prevention, and Management.