Modern pollen from small hollows reflects Athrotaxis cupressoides density across a wildfire gradient in subalpine forests of the Central Plateau, Tasmania, Australia

Abstract

Pollen assemblages from 50 small hollows were used to resolve fire-caused vegetation patterns in a ~2-km 2 subalpine landscape on the Central Plateau of Tasmania, Australia. Sites were characterized by varying abundance of the dominant tree species, Athrotaxis cupressoides, reflecting mortality from a wildfire that occurred 53 years prior to sampling. Sites were classified a priori based on fire-related Athrotaxis mortality as burned (100% standing dead), unburned (<5% standing dead), and mixed (intermediate proportions). Non-parametric analysis of variance and discriminant analysis were used to quantify the variability in key pollen taxa and pollen ratios among burn classifications. The ratio of Athrotaxis to Poaceae pollen was the clearest metric distinguishing among burn classifications. When discriminant analysis was informed with data from the eight most dominant pollen data, samples were classified with high accuracy (0.96-0.98). Macroscopic charcoal concentrations varied widely among sites, but median values were consistent with inferred fire patterns, increasing in abundance from unburned to burned sites. The results support the use of small hollows to resolve fine-scale vegetation patterns (e.g. within 100 m of a site). The discriminant analysis function was also applied to five late-Holocene pollen samples from the study area, to test the potential of these methods to classify samples with unknown group assignments. The posterior probability of assigned group membership ranged from 0.85 to 0.99, demonstrating the similarity of the fossil pollen to the calibration dataset. Our calibration dataset provides a means to classify fossil samples from the region in terms of Athrotaxis cover and fire-caused mortality. This approach could be applied to other regions to quantify disturbance-related vegetation patterns or spatial heterogeneity over Holocene timescales.

Forgotten impacts of European land‐use on riparian and savanna vegetation in northwest Australia

“…Aerial photography provides long‐term data on a broad geographic scale, but has limited temporal scope (usually late 20th century) and provides little detail on changes in understorey vegetation beneath the canopy where the impacts of savanna fire are presumably greatest. Palaeoecological data from small basins, such as the MP11A record, reveal vegetation changes at a small spatial scale over long time scales and are ideally placed to inform debates on vegetation structure (Mariani et al., ; Morris et al., ).…”

“…Surface sediment samples are routinely collected in palaeoecological research to calibrate pollen-vegetation relationships (Morris, Higuera, Haberle, & Whitlock, 2017). In the Kimberley Region, surface samples have been analysed to aid the interpretation of pollen records (Field, McGowan, Moss, & Marx, 2017;Proske, Heslop, & Haberle, 2014), but multi-site calibration has not been attempted.…”

Reconstructing Holocene fire records using dune footslope deposits at the Cooloola Sand Mass, Australia

“…In this study, we focus our analyses on larger macrocharcoal, which represents local (in situ) fire production originating within ca. 100 m of the dune soil profiles (e.g., Clark et al, 1998;Gavin et al, 2003;Higuera et al, 2005;Sanborn et al, 2006;Iglesias et al, 2015;Itter, et al, 2017;Leys et al, 2017;Morris et al, 2017). We analyzed charcoal >180 μm, because smaller fragments are more susceptible to eluviation processes (the vertical transport of particles through the soil profile), due to the homogenous (180-250 μm) and well-drained (600 mm/h) dune sands (Reeve et al, 1985).…”

Disturbance history and its influence on drought tolerance of interior Douglas-fir (Pseudotsuga menziesii var. glauca (Beisn.) Franco) in the Cariboo-Chilcotin region of British Columbia, Canada

“…Ecosystem change in the valleys of the Chilcotin and Fraser Rivers may parallel these alpine dynamics, though only fineresolution sediment core analysis could confirm the species shift (e.g. Morris et al, 2017).…”