You are here

Quantifying fuels and potential fire behavior in balsam woolly adelgid-impacted forests

The project seeks to develop methodology that allows rapid assessment of fuels and potential fire hazard in forests impacted by BWA.

The project seeks to develop methodology that allows rapid assessment of fuels and potential fire hazard in forests impacted by BWA to better protect and improve the health of western America’s high-elevation fir forests. Operational fire behavior models cannot utilize detail about forest structure or health and are thus inadequate for estimating fuel hazard and potential fire behavior in insect-impacted forests. Physics-based fire behavior models use fine-scale fuel and vegetation data and weather inputs to provide more realistic estimates of potential fire behavior.

Balsam woolly adelgid (BWA) is a non-native, sap sucking insect with the potential to cause widespread mortality of true firs. BWA feeds on tree boles and branches and their saliva causes a hormonal reaction which leads to xylem deformity and restriction of water transport, resulting in gradual tree desiccation and death (Balch 1952, Balch et al. 1964). BWA were first detected in southern Idaho in the 1980s and have likely been present in Utah since the mid-2000s (Davis et al. 2020). In this region (Region 4), mortality has been observed to occur within 1-3 years at the warmest and driest sites. The ecological sustainability of subalpine fir and other true fir host types is a primary concern in these areas as stands are highly susceptible to BWA-caused mortality and all age classes of trees are attacked, having implications for natural regeneration (Lowrey 2015). Spruce beetle and mountain pine beetle outbreaks have significantly impacted high elevation forests, such that subalpine fir is often the only conifer species remaining and has been identified by the Intermountain Adaptation Strategy for climate change as a species at risk (Littell et al. 2010). In 2019, Aerial detection surveys (ADS) recorded 350K acres of BWA-killed trees in Region 4 and estimates are expected to increase as detection methods improve as an additional 300K+ acres within BWA’s range is recorded simply as subalpine fir decline complex.

The tendency of true firs to retain dead green and red needles may increase fire behavior and fire severity. If BWA-killed trees with needles have much lower fuel moistures, flammability may significantly increase (Jolly et al 2012). Operational fire models (Behave Plus, FlamMap) cannot utilize within-stand vegetation and fuel detail, instead relying on stand-level metrics, with low sensitivity to fuel changes (Johnson et al. 2011, Noonan-Wright et al. 2014) and underprediction of crown fire occurrence and spread rates (Cruz and Alexander 2010). The ability of physics-based fire models such as the Wildland-Urban Interface Fire Dynamics Simulator (WFDS,) to account for these factors may provide greater insight into the effects of BWA-impacted stands on fire behavior (Parsons et al. 2017, 2018).

Airborne Laser Scanning (ALS; aerial lidar) coverage is becoming increasingly widespread across forested land and availability of ALS-derived data is becoming a growing priority for State and Federal agencies. ALS has been used to effectively quantify canopy fuel metrics but is less successful at measuring surface and ladder fuels, particularly in dense stands (Erdody & Moskal 2010), such as is common in fir-dominated forest types. Terrestrial laser scanners (TLS; i.e. ground-based lidar) are an emerging technology that can finely map both surface and canopy fuels and have the potential to greatly reduce field-based data collection times, while also producing high-resolution data (Loudermilk et al 2009, Chen et al 2016). However, stands with particularly thick canopies or high tree densities may in this instance reduce effectiveness of TLS scans in quantifying canopy fuels. While comparisons between field-collected fuels data and ALS-generated data exist (e.g. Bright et al. 2017), data collected using standard field protocols (e.g. common stand exams, Brown’s fuel transects) and TLS-generated data have not yet been compared, particularly in disturbed forest stands.

The project seeks to develop methodology that allows rapid assessment of fuels and potential fire hazard in forests impacted by BWA to better protect and improve the health of western America’s high-elevation fir forests. We will

  1. Compare canopy fuel metrics derived from standard field data procedures with metrics derived from a combination of terrestrial and aerial lidar
  2. Simulate fire behavior over a range of BWA severities using physics-based models (WFDS)
  3. Create a photo guide for a range of BWA severities to predict fire behavior under a range of weather scenarios

Several communities in Wasatch and Davis Counties, UT and Salt Lake City, as well as the ID communities of Adams, Valley, Bear, Caribou, Teton are looking for information regarding fire behavior and BWA. UT Dept. of Forestry, Fire and State Lands also has many requests from landowners. Therefore, we will create BMPs for fuel treatments in infested areas for use in Shared Stewardship efforts and new CFLRP projects in ID and UT. Improved fire behavior modeling would benefit both federal land managers in directing fuels treatments / funding for treatments to higher severity areas and would benefit private land owners in quantifying the need for treatment on private lands and protecting developed recreation infrastructure. Although the data for this project come from Region 4, we anticipate Regions 1, 2, and 6 also using the tool because no other alternative exists.

Modified: Apr 23, 2021

Select Publications & Products

For additional online publications please reference our alternative publications sites.