TAS-1: Paleofire patterns

Title:  Reconstructing Holocene fire regimes in Tasmania

Investigators: Whitlock, Haberle, Fletcher

Students: Stahle (MSU Phd), Chin (ANU PhD)

Interns: Weingart, Fixico

Project Description

Objectives: Tasmania is an ideal area for WildFIRE PIRE to examine human and climate influences on wildfire activity because (a) a mosaic of fire sensitive vs. highly fire tolerant plant communities; (b) strong east-west contrasts in the history of European settlement and current land-use patterns; (c) long-lived (1000 years) trees with proven dendrochronological potential to yield annual-resolution tree-ring fire histories; (d) numerous small lakes with the potential for high resolution charcoal and pollen records, that can be tied to previous and ongoing paleoecological investigations; (e) previous research provides a broad understanding of vegetation responses to recent and past fire and climate variations and land-use history; and (f) Tasmania serves as one area of interest for our Australian colleagues and their work in other settings invites comparison and extend our reach.

High-resolution Holocene fire-history records are needed across Tasmania to identify the importance of climate, people, and geology in shaping Holocene fire regimes at regional and local scales.  Recent work in western Tasmania (Fletcher and Thomas, 2010; Fletcher et al., 2010) suggests that the arrival of humans during the LGM provided an ignition source that was independent of climate, and burning by humans during the glacial and Holocene periods facilitated the establishment of open moorland in regions that supported rainforest during previous interglacial periods. In contrast, fire-climate studies in Tasmania relate 20th century fire activity to ENSO variation; and declining precipitation over the last 50 years to the positive trend in SAM, implying a strong role for climate.

We will focus on the Holocene record of fire, vegetation, and climate change within the range of Athrotaxis cupressoides across western and interior Tasmania.  The presence of small lakes provides extraordinary research opportunities to reconstruct Athrotaxis history along (1) a longitudinal gradient from rainforest/moorland in the southwest to drier forest in the interior, (2) an elevational gradient from forest to alpine vegetation; and (3) a geologic gradient from highly infertile substrates in the southwest to more fertile settings in the interior. We will collect sediment cores from four or five lakes located across the current range of Athrotaxis to (1) reconstruct Holocene vegetation and fire patterns (2) gain a better understanding of postglacial Athrotaxis expansion and its relationship to fire; (3) compare long-term fire-vegetation patterns across physical gradients to identify times of synchrony and asynchrony in the response; and (4) gain insights on the relative importance of broad-scale (climate) controls versus more localized or temporally variable (human) controls in structuring past fire patterns.  This work will be undertaken by a PIRE PhD student (Stahle) working with the PIs.

Related Activities – Associated Funding

Australian Research Council Discovery Grant (Bowman, Veblen, Whitlock):  How has bushfire activity varied around the Southern Hemisphere over the last 10,000 years?  (2011-2015).  This five-year project was designed to complement the WildFIRE PIRE grant, with the joint goal of better understanding the past and present importance of fire in maintaining Athrotaxis.  The ARC Discovery grant supports the proposed study by providing logistical costs up to $42K to the project. 

Australian Research Council Discovery Indigenous Researchers Development Grant (Fletcher, Haberle): Tracking the response of the Australian climate to abrupt climate change (2011-2012).  This grant supports a related activity and shares field and analytical aspects that advance the goals of ARC and PIRE.  The ARC grant seeks to develop a high-resolution climate history of western Tasmania for the last 2000 years, using multiple paleoclimatic proxy (pollen, charcoal, isotopic, and sediment properties) preserved in cores from two lakes in the Athrotaxis range.  The cores collected in the ARC project clearly extend back to the glacial period, and the pre-2000 year sediments will also analyzed in the PIRE project discussed above. 

TAS-1/ARC also has direct linkages to other PIRE projects.  The Holocene records will provide critical information about the long-term controls of fire in Athrotaxis forest for comparison with dendroecological studies (PIRE TAS-2/ARC).  It will also be an important comparative for proposed charcoal research on dry sclerophyll forest on Flinders Island (PIRE TAS-3), and it closely relates to the study of fire and landscape feedbacks (PIRE TAS-4).

Expected Outcomes

High-resolution pollen, charcoal, and geochemistry records will be developed to reconstruct the vegetation, fire and climate history of western and central Tasmania for the past 10,000 years.  A better understanding will be gained about the controls of temporal and spatial variability in vegetation and fire activity at landscape and regional scales.  These empirical data will be critical in developing and testing models that consider fire-fuel-climate linkages on multiple time scales. Graduate students will lead publication efforts, and the data will be used in other synthetic activities.

Year 2 Update

The objective of this project is to reconstruct the Holocene fire and vegetation history of western Tasmania through an examination of charcoal, pollen, lithologic, and geochemical data from lake-sediment cores.  The research is jointly supported by a grant from the Australian Research Council to Bowman (Veblen and Whitlock are co-PIs on the ARC grant), as well as ongoing research by Haberle and students at Australian National University.  This year’s field work focused on collecting sediment cores from six lakes in Cradle Mountain National Park.  The Whitlock and Haberle teams worked together in the coring effort, which involved transporting rafts, coring gear, and other equipment over rugged terrain.  With the acquisition of these data, it is now clear that the project will be divided into four components, which represent the dissertation research of MSU PhD student Laurie Stahle: (1) a reconstruction of the Holocene fire and vegetation history, based on pollen and charcoal data from Wombat Pond and Lake Hansen; (2) a spatial analysis of fire history over the last 4000 years, based on charcoal records from Wombat Pond, Lake Hansen, Lake Lilla, Wilks Lake (research by ANU PhD student Chin), and other sites; (3) evaluation of the role of fire in maintaining Athrotaxis across its range, based on charcoal records from Lake Vera, Lake Osborne, and other sites (collaboration with Fletcher); (4) comparison of fire records from Cradle Mountain (Australia) and Yellowstone (U.S.) national parks.  Year 1 cores collected in Cradle Mountain National Park were examined in the field and at University of Tasmania.  They were shipped to University of Minnesota, and initial lithologic and geochemical (scanning XRF analyses) were performed.  Cores are currently being subsampled for pollen and charcoal analysis in the MSU Paleoecology Lab and samples are being submitted for AMS radiocarbon dating.   To date, charcoal analysis from Lake Vera has been completed and shows interesting trends that suggest a strong climate influence on past fire regimes.