Variability in Albedo Associated with Fire-Mediated Controls on Stand Density in Siberian Larch Forests

Abstract:

Fire is an integral component of boreal forests, and exerts strong control over ecosystem structure and function. The frequency and spatial extent of fire controls the age-class distribution of forests on the landscape. In addition, recent evidence from North American boreal forests has show that fire severity influences post-fire succession via impacts on seedling recruitment that manifest in mature ecosystems dominated by either deciduous or coniferous tree species. The effects of fire on ecosystem structure have important climate feedback implications; changes in forest density or leaf habit can influence surface net radiation by altering the snow-masking effects of vegetation.

Although Siberian larch forests occupy a more than 2.8 million km² of the boreal biome, and are the most prevalent forests in Russia, the influence of fire severity on succession and associated surface energy dynamics are less well understood in comparison to North American boreal forests. There is evidence suggesting that increased fire severity may lead to higher density of post-fire regrowth, but the influence of stand density on surface energy dynamics remains poorly quantified. Here, we quantify the effects of stand density on albedo across the Kolyma River basin using satellite-derived albedo and fire history in conjunction with maps and field observations of ecosystem structure. During snow-free periods albedo varies little with stand density. During periods of snow cover we find consistent negative correlations between multiple metrics of canopy cover and albedo. Albedo decreased with fire recovery over the forty-year fire record for the study area. However, the range of albedo observed within individual fire scars was similar to the magnitude of albedo recovery during the study period. This result indicates the importance of variability in post-fire regrowth within individual fire scars, potentially associated with fire severity, for understanding fire effects on surface energy dynamics in Siberian larch forests. In contrast to North American boreal forests, the effects of increasing fire severity on post-fire succession will decrease albedo in Siberian larch forests, acting as a positive feedback to climate.