Ramona Heim, Institute of Landscape Ecology of the University of Münster in Germany, discusses her article: Arctic tundra ecosystems under fire – Alternative ecosystem states in a changing climate?
Fire events in the tundra are becoming increasingly frequent, garnering more media attention. These fires strongly reshape the landscape; however, our understanding of tundra vegetation recovery following these disturbances remains limited.
During my field work stays, I was struck by the strong contrast between the recovery rates of fire-affected areas in different ecosystems. In the wetlands of the Amur River region, signs of fire vanish within a couple of years. In the tundra, however, the impact of a fire can remain visible for decades. This longevity raises critical questions: Does tundra vegetation fully recover to its original composition after a fire? And how does this recovery interact with the rapidly changing climate of the Arctic? Answering these questions is challenging due to the slow growth rates of tundra vegetation. Lichens, for instance, can take up to a century or more to return to their pre-fire state.
Burnt areas persist in West Siberian forest tundra decades after burning. Here we see the difference between a burnt area near Tazovsky 28 years post-fire (upper) and an adjacent unburned control plot with typical lichen-dominated vegetation and a few shrubs (lower). Photos by Daniel Rieker.
Meta-Analysis: What Existing Data Tell Us
To address these questions, we conducted a small meta-analysis of existing datasets on vegetation recovery following tundra fires. Our findings indicate that grasses often dominate in the immediate aftermath of a fire (within approximately 20 years) but subsequently lose their dominance. Shrubs recover after 30 to 40 years and continue to grow beyond former cover values. Notably, lichens often fail to regain their previous abundance even after many decades.
Steps into the Unknown: Hypotheses
With our paper, we also explored whether fires could trigger ecosystem transitions from one stable state to another. We wondered whether this could be the case for tundra fires as in other ecosystems. One assumes that tundra fires would revegetate to original plant communities following a fire – if it were not for climate change. But climate change is driving better growth of vascular plants and more frequent fire events. We propose that post-fire tundra recovery, coupled with climate change, may not necessarily lead to pre-fire conditions. Our hypothesis, based on surveys and literature, suggests two climate-fire driven post-fire trajectories:
- Burnt areas might revegetate with more woody vegetation
- Grass might fill in and become more dominant after fire
These states would be stabilised by feedback mechanisms. For example, shrubs might benefit from longer growing seasons and deeper active soil layers, thus remaining dominant after a fire, whereas other plant groups (such as lichens – losers of climate change) could be out-competed. If fires occur at shorter intervals, preventing shrubs from establishing or re-establishing, grasses might become dominant. The quick buildup of dry leaf litter in graminoid tundra types helps promote their flammability compared to shrub-dominated areas. Grasses possess several competitive advantages in post-fire environments, including rapid regeneration from rhizomes or seedling establishment to quickly extend roots into newly accessible, nutrient-rich soil layers that were previously frozen. However, if climate change leads to increased Arctic moisture levels that in turn decrease fire frequency, grass-dominated ecosystems may transition towards greater woody dominance.
The Future: Addressing Uncertainties
Our understanding of tundra fires is geographically biased, with most studies focused on specific regions. The tundra is also not a uniform ecosystem but comprises various vegetation types, each responding differently to fire. Fire also plays a complex role in how trees spread into tundra areas, with both helpful and harmful effects. While a single fire can create good conditions for trees to grow, frequent fires combined with climate changes might stop forests from expanding in some places. To address uncertainties and broaden our understanding, future research should include other tundra regions and spatial scales beyond our study. More case studies, especially in underrepresented regions and ecosystem types, are essential to broaden the empirical basis for forecasts and potential fire management strategies.
