Fire Effects Monitoring Joint Base Lewis-McChord Annual Report 2019

Prescribed fire is the foundation to prairie management on Joint Base Lewis-McChord (JBLM), and prudent management necessitates understanding the variability of fire effects across weather and fuel conditions, as well as fire’s role in shaping prairie communities. Our objectives for fire effects monitoring on JBLM are to quantify burn-day fuel, soil, and weather conditions and build robust models describing their influence on burn temperatures and severity. We further aim to describe the relationship of fire intensity and severity with post-burn vegetation. Our focus has primarily been on open prairie units in priority habitat for streaked horned lark, Taylor’s checkerspot, and Mazama pocket gopher in Training Areas (TA) 14 and 15 and the Rainier Training Area (RTA).

We have collected data on 50 prescribed burns over four burn seasons from 2015 to 2018. Burn intensity and severity have had the strongest relationships with long-term precipitation patterns and time of year, peaking with the longest dry spells and in mid- to late-summer. We have found higher burn intensity to be associated with increases in cover of exotic annual forbs and decreased cover of exotic woody vegetation (i.e., Scotch broom) the following spring.

While fuel and thatch consumption is often a core objective of restoration burns, excessively high soil heating and severity may result in unwanted effects (e.g., insect or microorganism mortality and soil sterilization). This year we introduced a new decision-making tool which is a simple numerical index that combines precipitation patterns and time of year; these are essentially the fixed conditions that form a backdrop against which a variety of day-of-burn weather conditions may occur. In summer 2018, fire managers on JBLM used this index as a guide to assess whether day-to-day weather conditions were appropriate for certain burn units. In 2019, we recommend a more refined sliding scale of guideline conditions under which to burn prairie units where soil heating is undesirable, essentially aiming for increasingly lower-end day-of-burn weather conditions as the summer progresses without significant rainfall.