Century-scale environmental reconstruction by using stable carbon isotopes: just one method from the big bag of tricks

Abstract

Abstract/summaryThe field of 'historical ecology' is coming to maturity at a time when we, in Australia, are reflecting on our relationship with, and place in, the land. After an essentially ahistorical approach to land use we are now attempting to place land management into the context of environmental change since, and immediately preceding Western European settlement. This volume reflects an emerging concern that collectively, nonindigenous Australians have no 'environmental history'.One component of 'living in' rather than 'battling against' the land is developing a sense of our history. Without an oral narrative that is commonly shared, attempts to develop the story of environmental change have to be based on retrospective and reconstructive research. This volume captures part of this movement to develop an environmental narrative and context for our future relationship with the land.There are many methodological approaches to reconstructing a story of the past, from local knowledge and oral history to the high-tech and hard sciences. This paper reviews methods that apply stable carbon isotope techniques to reconstruct environmental change. Although well suited to environmental history, carbon isotope techniques remain under-utilised in the Australian context. Here I review applications to highlight the strengths, and limitations, of carbon isotope techniques in the reconstruction of century scale vegetation change. There have been two dominant applications of carbon 2 isotope techniques to environmental reconstruction. These applications fall broadly under either stable carbon isotope analysis of organic matter in soils and sediments, or alternatively, inferences of environmental states have been drawn from carbon isotope analysis of animal tissues and residues. The main strength of stable carbon isotope techniques is that they can be spatially precise while integrating a range environmental information into one isotopic signal. This integrative strength is at the same time one of the major limitations of carbon isotope techniques because floristic (taxonomic) resolution is low.

Diet of four rock‐dwelling macropods in the Australian monsoon tropics

“…Ratios of the stable isotopes 12 C and 13 C in plant tissues vary due to differential assimilation of the isotopes in different photosynthetic pathways (Witt 2002). In the Australian tropics, most grasses use the C 4 photosynthetic pathway which results in δ 13 C values of − 9 to − 17‰ (the standard notation for 13 C/ 12 C ratios is δ 13 C as per mil relative to the carbon isotopic ratio of the Pee Dee belemnite (PDB) standard (Peterson & Fry 1987) in units of parts per thousand, ‰) (Boutten et al .…”

Holocene boundary dynamics of a northern Australian monsoon rainforest patch inferred from isotopic analysis of carbon, (14C and δ13C) and nitrogen (δ15N) in soil organic matter

“…The effect of clay in carbon and nitrogen isotope fractionation dynamics of soil organic matter is poorly understood (Witt 2002; Krull & Skjemstad 2003). While it is possible that the higher clay content in the monsoon rainforest could confound the interpretation of the isotopic data, we suggest this is unlikely because such an effect is counter to the pattern reported by Bird et al .…”

“…2003). Tropical grasses typically have a C4 photosynthetic pathway that discriminates less strongly against 13 C than the C3 photosynthetic pathway in trees, shrubs and herbs (Witt 2002). The difference in fractionation between C3 and C4 pathways can be expressed as δ 13 C values, defined as the difference in the ratio of 13 C to 12 C in a sample compared with that in the Vienna‐PDB international standard (Peterson & Fry 1987).…”

Carbon isotope evidence for an abrupt reduction in grasses coincident with European settlement of Lake Eyre, South Australia

“…Isotopic evidence corroborating the aforementioned trends is relatively 10.1 191/0959683605hl861ra scant. While a significant decrease in C4 grass biomass in the middle part of the twentieth century is measured in sheep faeces from a shearing shed in northern New South Wales, isotopic results on sheep faeces from a neighbouring shearing shed in southwestern Queensland suggest minimal C4 grass uptake and biomass change over the same time period (Witt et al, 1996;Witt, 2002). These and other studies illustrate the derth of consistent and reliable evidence for short-term (century scale) vegetation change (Clark, 1990), particularly in the arid zone (reviewed by Lunt, 2002) and near Lake Eyre, South Australia.…”