Australian alpine SOC and vegetation dataset and metadata

Alpine soil organic carbon and vegetation composition dataset for 111 plots across 1000 m elevation within the Australian alps.
See methods below:
The study comprised 111 plots, ranging from 1256 to 2197 m in elevation, within the Australian Alps . The mean annual temperature (MAT) for the plots ranges from 3.4°C to 9.4°C, and mean annual precipitation (MAP) ranges from 953 mm to 1986 mm. In total, the plots host 398 plant species across 170 distinct genera. Sampling was conducted in 15 feldmark, 54 herbfields (including grasslands), 23 heaths, and 19 sub-alpine woodland plots. Sampling largely excluded wetland and sphagnum dominated communities (bogs and fens) but did include damp heaths and grasslands. Apart from feldmark, which is limited to high elevation regions, all vegetation types were sampled across the entire elevation gradient. Wherever feasible, sampling was clustered so that multiple vegetation types were sampled in proximity to each other to constrain variation resulting from local climatic variation. Plots were allocated to vegetation type in the field based on visual assessment of shrub, tree, herbaceous (both grasses and dicots) and bare soil cover. Sampling excluded any sites that were burned in the recent 2019-2020 fires. 75% of the sites occurred on granites or granodiorites, the remaining sites occurred across a range of lithology including sediments, tuffs, basalts, and pyroclastic rock. The sites spanned diverse topographies, with slopes ranging from 1 to 19.5° and a median value of about 7°, indicating generally mild inclines. Each plot consisted of a 20 m x 20 m quadrat. Ten 1 m² quadrats were arranged along two lines, each 5 m away from the mid-line of the 20 m x 20 m quadrat, with the 1 m² quadrats evenly spaced every 5 m (Supplementary Figure 2). Plots were established within zones of broadly contiguous vegetation structure and composition of the same vegetation type.
Field sampling was undertaken in December, January, February and March 2022 and January 2023. In each 1 m² quadrat, the cover of litter, bare ground, rock, cryptograms, and the foliage was visually estimated of herbaceous vegetation (grass & grass-like, forbs), shrubs and trees (including overhanging the quadrat) and a mean was taken of the ten quadrats. The sum of the foliage from the herbaceous vegetation and shrubs was defined as total vegetation cover for the plot and expressed as a fraction 0 - 1.0. Soil samples were collected from within each 20 m x 20 m quadrat under three different plant growth forms, termed patch types: herbaceous (graminoid or forb), shrub (woody sub-shrub or shrub), and tree. For shrub and tree patches, the sample was taken at the mid-point between the main stem and the outer edge of the canopy. For each patch type, eight separate soil samples were collected at each plot and pooled, with the sampling strategy designed to capture the spatial distribution of the patch type within the plot. When a certain patch type was underrepresented within the 20 m x 20 m quadrat, additional sampling was conducted within the larger 20 m x 50 m plot. If trees or shrubs were scarce within the 20 m x 50 m plot, additional samples were obtained from a single tree or shrub, sampling from opposing sides of the main stem. Surface vegetation and litter were removed prior to collecting a sample using a 10 cm deep core of 2 cm diameter. The samples were immediately stored in zip lock bags, kept in a cooler in the field, and transferred to cool storage (4 °C) within 10 hours. In total, samples were taken under 110 herb patches, 101 shrub patches, and 27 tree patches.
Laboratory analysis was carried out at the NSW Department of Climate Change, Energy, The Environment and Water, Soil & Water Environmental monitoring laboratory, at Yanco, NSW. All soil samples were dried at 40 ‎°C in a fan forced oven for 48 h. Charcoal, wood, root and other vegetative matter were removed from the soil, and the weight of each component was recorded. Samples were gently crushed using mortar and pestle to pass through 2 mm sieve. Sub-samples of approximately 8 g were finely ground (<100 μm) using a puck mill (Labtech ESSA Pty Ltd, Perth, WA, Australia) for use in the SOC MIR measurements. Ground samples were analysed for SOC using the high-temperature oxidative combustion (Rayment and Lyons, 2011, method code 7A5) with a Leco® Truemac CN elemental analyser (LECO Corporation, Saint Joseph, MI, USA). SWC was calculated as the difference in soil mass between soil dried to 105°C and the soil collected in field conditions, divided by the mass of the dry soil sample (Rayment & Lyons, 2010).