Monitoring vegetation trends against objective baselines is fundamental to quantify the impacts of global change on plant biodiversity. Vegetation plot time series are a gold standard in vegetation monitoring, but such data are missing for many regions. Southern Patagonia is an example of a region strongly impacted by climate change but lacking time series data. Monitoring in this region could benefit from a comparison with vegetation survey data gathered between 1975 and 1979, as part of the multidisciplinary research program “Transecta botánica de la Patagonia austral” (hereafter Transecta). Published in 1985, it contains data on 668 vegetation plots, which were so far inaccessible to most researchers: Transecta has never been reprinted, nor fully digitized, and can only be found in specialized libraries. Here, we created a reproducible workflow, documenting how vegetation plot data from historical sources can be extracted and harmonized. The resulting open-access database we created fills a major regional gap and provides a needed baseline to assess the impacts of global change on southern Patagonia vegetation. By making these data available, we hope to inspire a new generation of vegetation scientists to resurvey the area and continue the legacy of the pioneer researchers who compiled Transecta.