Why fire history matters: Understanding the linkages between vegetation, climate and people on multiple time scales

Background/Question/Methods

Fire history is an essential part of Earth system science, but that recognition was not the case in the early 1970s when Herb Wright and Bud Heinselman described the fire history of the Boundary Waters Canoe Area.  Subsequent paleofire studies led by students of Wright in the Midwest, Canada, New England, and western U.S. highlighted the importance of long-term fire information for understanding modern forests and their vulnerability to climate change.  Significant advances in paleofire research in the last 30 years have built on these early studies. Recent investigations at regional to global scales point to climate as the primary driver of fire activity, and studies at local scales highlight the importance of prehistoric humans in altering ignitions and fuels.  Among the outstanding questions are at what spatial-temporal scales do humans and climate jointly shape fire regimes and how can a long-term perspective best inform modern fire management. 

Results/Conclusions

The fire history of temperate rainforest ecosystems, where natural fires are infrequent and ignition-limited, is germane to understanding fire-climate-human linkages: (1) In the Pacific Northwest, paleoecologic records suggest that climate and postfire flammability trajectories help maintain old-growth Pseudotsuga-Tsuga rainforest.  Pre-Euroamerican fires were targeted not wholesale. (2) In Patagonia, paleofires in Nothofagus forest were also strongly influenced by increased summer insolation and ENSO variability in the late Holocene; human influences prior to European were minimal.  In both regions, humans may have modified natural fire regimes along ecotonal margins, but human-set fires reinforced climate-driven fire activity.  (3) In New Zealand, wildland fires were rare prior to the arrival of Maori, ~800 years ago. Deliberately set fires during a brief initial burning period transformed Nothofagus-Podocarpus forest to grassland and scrubland and unraveled watersheds. The rapid and lasting transformation of the forest was facilitated by the high flammability of early seral stages and the low fire tolerance of old-growth forest.  (4) Moorland in western Tasmania was probably also created and maintained by human-set fires, but multiple stable states, low nutrients, and climate were also important.   In summary, the confluence of human and climate drivers in shaping prehistoric fire regimes is evident at the landscape to subregional scale, but the feedbacks are complex.  While Herb Wright early on described the value of paleofire information in understanding modern ecosystems, discerning the extent to which past climate and land-use have altered fire regimes remains an area of active research.