Underpinning terroir with data: a quantitative analysis of biophysical variation in the Margaret River region of Western Australia

Abstract

Background and Aims The wine producers of Margaret River, as in many Australian wine regions, are interested in gaining a better understanding of the terroir of their region. Our aim was to determine whether the variation in soils and climate suggests that subdivision of the region may have merit. Methods and Results Clustering of digital map layers describing a range of climatic indices and soil properties of viticultural importance, using k-means, enabled exploration of regional scale patterns of spatial variation. These methods are the same as those that have been successfully used at within-vineyard scale in support of the development of Precision Viticulture. Whilst there is marked soil and climatic variation within the Margaret River geographical indication (GI), the results obtained from this analysis do not lend weight to previously proposed subdivisions of the Margaret River GI but rather, provide a guide for future targeted sensory analysis within the region. This was especially the case when the analysis was confined to just the 2.8% of the GI land area that is under vineyard. Conclusions Whilst the Margaret River GI shows marked biophysical variation, the data used in this analysis were not sufficiently strongly spatially structured at regional scale to indicate a basis for splitting the GI into subregions. However, some separation based solely on temperature and rainfall might form a useful basis for chemical and sensory analysis of wines and pursuit of understanding of the regional terroir. From both terroir and viticultural management perspectives, soil variation is likely of much greater importance at the within-vineyard and whole of property scales, than at regional scale. Significance of the Study This is one of the first studies which uses purely data driven methods to examine biophysical variation within a wine region. Aside from being free of the bias that is introduced by heuristics, or examination of historically delineated terroirs, the work highlights the importance of focussing solely on the land which is under vine in evaluating terroir, rather than all of the land within a GI.