The legacy of mid‐Holocene fire on a Tasmanian montane landscape

Abstract

Aim To assess the long-term impacts of landscape fire on a mosaic of pyrophobic and pyrogenic woody montane vegetation.Location South-west Tasmania, Australia. MethodsWe undertook a high-resolution multiproxy palaeoecological analysis of sediments deposited in Lake Osborne (Hartz Mountains National Park, southern Tasmania), employing analyses of pollen, macroscopic and microscopic charcoal, organic and inorganic geochemistry and magnetic susceptibility.Results Sequential fires within the study catchment over the past 6500 years have resulted in the reduction of pyrophobic rain forest taxa and the establishment of pyrogenic Eucalyptus-dominated vegetation. The vegetation change was accompanied by soil erosion and nutrient losses. The rate of post-fire recovery of widespread rain forest taxa (Nothofagus cunninghamii and Eucryphia spp.) conforms to ecological models, as does the local extinction of fire-sensitive rain forest taxa (Nothofagus gunnii and Cupressaceae) following successive fires. Main conclusionsThe sedimentary analyses indicate that recurrent fires over several centuries caused a catchment-wide transition from pyrophobic rain forest to pyrophytic eucalypt-dominated vegetation. The fires within the lake catchment during the 6500-year long record appear to coincide with highfrequency El Niño events in the equatorial Pacific Ocean, signalling a potential threat to these highly endemic rain forests if El Niño intensity amplifies as predicted under future climate scenarios.

Low-resolution Australasian palaeoclimate records of the last 2000 years

“…These techniques, including reflectance spectroscopy (Saunders et al, 2012(Saunders et al, , 2013) and X-ray fluorescence (Fletcher et al, 2014), can be conducted at very high (< 1 mm) resolution, and are easily combined with other analyses for multiproxy studies.…”

European Impacts on Coastal Eastern Tasmania: Insight from a High-Resolution Palynological Analysis of a Salt-Marsh Core

“…However, at the regional scale, there are relatively few attempts to examine European impacts using palaeoecological proxies, due to the relatively low-resolution of existing Holocene reconstructions (Kershaw et al, 1994) that often attempt to provide insight into Holocene environments and/or focus on Aboriginal human-environment relationships (e.g., Colhoun and Shimeld, 2012;Ulm, 2013;Fletcher et al, 2014Fletcher et al, , 2015Rees et al, 2015;Mackenzie and Moss, in press for recent publications from Tasmania). Those records that do exist suggest that there is a great deal of regional variation in the timing and nature of ecosystem response to European settlement, with some alterations linked to obvious European impacts, such as land clearance (e.g., Moss et al, 2007), while other ecological alterations are linked to much more subtle changes in land management, particularly the imposition of new fire regimes (e.g., Fletcher et al, 2014). …”

Soil or fire: what causes treeless sedgelands in Tasmanian wet forests?

“…Such slow growth rates suggest that the rate of conversion of unburnt sedgelands to eucalypt forest over the hundreds of years assumed by Jackson is highly unrealistic, and is actually more likely to occur over millennia, thereby involving consideration of longer term climatic changes such as those that have occurred through the Holocene (e.g., Fletcher et al 2014a). This inference is supported by analysis of historical aerial photography showing that conversion of sedgelands to forest is extremely slow, and occurs through colonisation of woody pioneer plants (Leptospermum) that form shrublands close to the forest margins (Ellis 1985;Wood and Bowman 2012;Bowman et al 2013).…”

“…Furthermore, the soil nutrient capital of forests and sedgeland is reduced by fire through volatilisation and transport of ash (Harwood and Jackson 1975;Bowman and Jackson 1981), soil erosion (Wilson 1999;di Folco and Kirkpatrick 2013) and leaching (Bowman and Jackson 1981;Ellis and Graley 1983;Jackson 2000;Fletcher et al 2014a), and possibly clay eluviation (McIntosh et al 2005). These impacts are most pronounced on infertile, clay-deficient lithologies, such as quartzite, with much more limited effects on clay-rich soils such as those that develop on dolerite (Ellis and Graley 1983;Jackson 2000).…”