Physicochemical characteristics controlling the flammability of live Pinus banksiana needles in central Alberta, Canada

Background Few studies have focused on the integral assessment of live fuel flammability in the boreal forest. Aims We aimed to examine the flammability of living needles of jack pine (Pinus banksiana) as characterised by their form, moisture and chemical content at different ages and times of the year. Methods With a calorimeter and open flame, we estimated needle ignitability, consumption rate, maximum speed and amount of energy released. We measured their form, moisture and chemical content. Key results Needle form has a major effect on ignitability, whereas chemical composition primarily influences the amount and rate of energy release. Needles <1 year old are the least flammable; they are rounder and voluminous, with higher moisture and nitrogen content. Needles >= 1 year old are more flammable; they are drier, more curved, thinner, longer, and contain more carbon and terpenes. Needles release more energy during the early growing season, when starch and lipids are at their peak concentrations. Conclusions Moisture content is not the major factor affecting the flammability of jack pine live needles; physicochemical changes specific to age and month of collection are the most influential factors. Implications Assessing the multi-faceted properties of live fuels flammability will help to comprehend stand- and landscape-scale fire behaviour.