Fires and climate change may alter Alaska’s forests

Climate change and more wildfires – the latter linked to the former – could eventually alter the composition of Alaskan forests, new modelling suggests.

Evergreen conifers would be replaced by deciduous broadleaf trees, say researchers led by the US Department of Energy’s Lawrence Berkeley National Laboratory, and that will have flow-on effects.

“Expansion of the deciduous broadleaf forests in a warmer climate may result in several ecological and climatic feedbacks that affect the carbon cycle of northern ecosystems,” says Zelalem Mekonnen, first author of a paper published in the journal Nature Plants.

Mekonnen and colleagues modelled four scenarios, from a zero increase in burn area up to a 150% increase by 2100. The scenarios were taken from published studies that accounted for factors such as warmer temperatures and increases in lightning strikes. {%recommended 9576%}

They predict that by the year 2100 the relative dominance of evergreen black spruce (Picea mariana) will decline by 25% and non-woody herbaceous plants such as moss and lichen will decline by 66%, while broadleaf deciduous trees, such as aspens, will nearly double in prevalence. 

Fires will play their part in change, the researchers say, because they deepen the active layer – the zone of soil that remains unfrozen – leading to an increase in soil nutrients, which favours deciduous plants.

The leaves of deciduous trees also decompose more rapidly, leading to faster carbon turnover, which determines the available nutrients in the ecosystem. “As you get more rapid turnover, you get more deciduous plants,” says co-author William Riley. “It’s a self-reinforcing mechanism.”

In addition, broadleaf deciduous trees are better at regenerating after a fire.

The researchers stress, however, that it is the combination of climate change and increased fire that will have the greatest impact on the likely deciduous dominance. 

Across the fire scenarios tested, that was projected to occur around the year 2058. If warming occurred without increased fire, or vice versa, the model found that evergreen conifers remained the dominant Alaskan tree type through the twenty-first century.