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Data and code from: Pre-industrial land-use limits contemporary shrub encroachment in the French Alps

Nicoud, Baptiste1; Carrière, Florian1; Bayle, Arthur2; Devlieger, Christian3; Choler, Philippe1; Corona, Christophe1; Lavorel, Sandra1

Published Mar 23, 2026 on Dryad. https://doi.org/10.5061/dryad.wpzgmsc3t

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Abstract

Shrub encroachment has become a global phenomenon in recent decades. While global warming in the Arctic is often cited as the primary cause, human-managed mountain regions have experienced intense historical land-use that may also play a considerable role. Shrub encroachment has significant implications for biodiversity, carbon storage, and transformation of mountain landscapes. However, disentangling between the effects of present-day environmental conditions and historical land-use trajectories in explaining present-day shrubland distribution remains challenging. We use early 19th-century land registry records — rare historical sources documenting past land-use and vegetation cover — to assess whether these legacy conditions influence present-day shrub distribution. By combining these archive data with dendrochronological sampling and a diachronic analysis of shrub expansion based on historical aerial photographs, we provide a comprehensive analysis of shrub colonisation. Our results reveal an increase in shrub cover over the past two centuries, primarily driven by the expansion of common juniper (Juniperus communis). Dendrochronological analyses from never mown or ploughed plots indicate that shrub recruitment began around 1870, intensified until the 1970s, and then slowed slightly thereafter. While shrubs preferentially establish on steep, south-facing slopes and topographically rough terrain, their distribution remains highly heterogeneous and is strongly shaped by pre-industrial land-use patterns. Parcels that were ploughed or mown 200 years ago remain largely devoid of shrubs, even decades after mowing ceased. In contrast, surrounding areas — whether grazed or unused — have experienced shrub encroachment. We hypothesize that the low shrub density on former ploughed lands and hay meadows may reflect persistent legacy effects of dense, competitive herbaceous communities, which hinder the establishment of woody species. This study demonstrates that pre-industrial land-use continues to constrain both the distribution and recent dynamics of shrub expansion, highlighting the importance of accounting for land-use legacies when interpreting contemporary shrub encroachment.