TAS-4: Fire-landscape history

Title: Reconstructing landscape-scale patterns and ecological consequences of late-Holocene fire regimes in Tasmania

Investigators: Higuera, Veblen, Haberle, Bowman, Holz, Wood, Nichols

Students: Young (UIdaho)

Opportunities for intern participation: Possible opportunity for intern participation in fieldwork.

Project Description

Fire history in subalpine Athrotaxis forests is poorly documented across much of its range, yet fire is potentially a critical agent of mortality to these fire-sensitive species. Evaluating the impact of ongoing and projected environmental change in Athrotaxis forests requires basic knowledge of past fire activity and fire effects on vegetation and ecosystem processes including carbon and nitrogen cycling. This project capitalizes on the strong environmental gradients in central Tasmania, including vegetation, soil, hydrology and human land use, as well as watersheds that contain multiple small lakes and wetlands suitable for paleoecological investigation. Analysis of the landscape-scale variability in fire activity will help elucidate the role of biotic and abiotic controls on local fire activity. This information will aid efforts to interpret of charcoal-based fire-history records at larger spatial and longer temporal scales, providing an important link between tree-ring studies and charcoal-based Holocene reconstructions.

Numerous small lakes with the potential for high-resolution charcoal, pollen, and geochemical records exist in high-elevation regions of Cradle Mountain-Lake Saint Clair National Park and the surrounding region. This density of sites will allow for the reconstruction of fire history and variability at landscape scales, similar to studies underway in Yellowstone and Rocky Mountain National parks in the US.

We will work with Haberle and an ANU Ph.D. student (Chin) to examine spatial variability in past fire occurrence in a closely-spaced network of sediment cores and/or soil charcoal profiles. We anticipate developing records from approximately 10 sites, covering the last 1000-2000 years at each site. Environmental proxies to be analyzed include pollen, charcoal, XRF, and carbon and nitrogen isotopes (at selected sties). Chronologies will be developed with 210Pb or 137Cs profiles for recent decades to centuries, and ca. four 14C dates per core for deeper sediments (for a total of 40 14C dates). This estimate allows for potential development of soil-charcoal profiles, which would require more extensive dating than in sediment records. Site selection will be based on (1) basin size, as a proxy for source area of pollen and charcoal records, and (2) a suite of variables that relate to climate and past human activity, including elevation, aspect, soil type, and vegetation.

The goal of this work is to better understand the spatial and temporal pattern and impacts of fire over the past several millennia in a region that spans gradients in climate and human land use: How has past fire activity varied with elevation within subalpine forests? What do these patterns suggest about the relative importance of human and non-human controls in shaping fire history? Additionally, the closely spaced sites will help test assumptions of how sedimentary basins reflect past fire activity.

Related Activities – Associated Funding

ARC grant to Haberle: XXXXXXX

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 $42 k 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.

PIRE- and UIdaho-funded research in US Rocky Mountains: One UIdaho graduate student, Paul Dunnette, is undertaking complementary work in the US Rocky Mountain subalpine forests. This work is partially funded by Higuera’s start up funds and WildFIRE PIRE (PIRE US-2/NSF).

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).

Expected Outcomes

High-resolution pollen, charcoal, and biogeochemical records will be developed to reconstruct the fire history and ecological impacts in central Tasmania over the late Holocene. These patterns will be used to infer controls on the temporal and spatial variability in vegetation and fire activity at landscape and regional scales. These data will in turn be critical in developing conceptual models that look at fire-vegetation-climate linkages on multiple scales.

Year 2 Update

This project brings together an analysis of lakes and tree-ring records to better understand fire history in Athrotaxis region, and draws on co-support from the Australian Research Council grant to Bowman, Veblen, and Whitlock.  The objective is to work in a site that has the potential to compare lake-sediment records of fire and tree-ring records of fire, a collaborative activity that is not possible in most of the other PIRE projects.  Higuera, UI PhD student Young, Haberle, Holz, and Nichols, conducted fieldwork in Walls of Jerusalem National Park, Tasmania in May 2012.

Sites that had both numerous small ponds and live and dead Athrotaxis stands were deemed suitable for the project and selected for study.  During a 5-day trip sites were surveyed for paired tree-ring and sediment record collection and potential analysis focusing on understanding the fire and vegetation history of the Central Plateau region.  Sediment cores were collected with a D-section corer from nine sites. Cores ranged from 50-150 cm in length, and some showed evidence of past burning (i.e., macroscopic charcoal) and potential post-glacial origin (i.e., distinct transitions from organic to clay sediments).  Haberle and Nichols provided rafts, coring equipment, and other supplies for the coring operations.  Sediment cores were transported to Australian National University where they were described, subsampled and shipped to University of Idaho for further analysis.  Higuera and Young also spent a week at Australian National University teaching a course on software applications related to high-resolution charcoal analysis.