Effects of fire severity and season of burn on Betula glandulosa growth dynamics

Abstract

Betula glandulosa survives over a wide range of North American fire regimes by resprouting from the rhizome. Over-winter root carbohydrate reserves are important to sprout production and growth in the following spring. Nursery and field experiments were conducted to examine the effects of seasonal clipping and fire severity (lethal heat applied to different soil depths) on B. glandulosa sprouting and growth, and seasonal burning and clipping on over-winter root carbohydrate storage. Low fire severity increased sprout numbers, and low fire severity in spring caused a large increase in height growth and above-ground biomass production over a 2-year period. Mortality rates increased sharply with higher levels of fire severity. Over-winter total non-structural carbohydrate (TNC) concentrations in roots were significantly higher in plants burned immediately after leaf-flush than in mid-summer burned plants. None of the other seasonal burning or clipping treatments significantly influenced over-winter root TNC. Post-disturbance sprout growth reflected over-winter root TNC levels. B. glandulosa survives a wide range of fire frequencies by growing in plant communities that are most likely to burn in spring or autumn, and seldom burn in summer. This provides the greatest opportunity for maximum over-winter TNC storage. As well, high soil moisture after snowmelt ensures spring fires are almost always of low severity, which promotes increased sprout production, height growth and above-ground biomass.