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& Key message Despite variable dynamics of genetic diversification at the different altitudinal levels, strong gene flow tends to standardize larch genetic diversity: the larch forest distributed along the altitudinal gradient can be regarded as a single population. & Context While in forest tree species many studies focus on the structure of the genetic diversity at the natural range and at the forest stand levels, few studies have worked at intermediate levels like the landscape level. & Aims We tried to determine to what degree altitude variation can affect the genetic diversity and the local structure of the genetic diversity of European larch (Larix decidua Miller) at the landscape level. & Methods Using microsatellite markers, we determined the between-and within-plot genetic structure and the spatial genetic structure (SGS) of four altitudinal plots distributed between 1,350 and 2,300 m a.s.l. in a European larch forest located in the French Alps. & Results A homogenous neutral genetic structure was detected along this gradient. The intensity of the SGS was found to be stronger at 2,300 m and decreased at the 2,000-m plot. It was low or non-existent at the 1,700-and 1,350-m altitudinal levels. & Conclusion Our results suggest that the genetic structure observed at the landscape level in this European larch forest was only slightly affected by climatic variation, human activities, or historical events. However, the variation of intensity of the SGS within the altitudinal plots indicates the existence Contribution of the co-authors Maxime Nardin is the PhD student in charge of the study. Dr. Brigitte Musch supervised the writing of the article, then reviewed and commented on successive drafts of the paper. Dr. Yves Rousselle reviewed and commented on successive drafts of the paper. Vanina Guerin participated in cambium sampling and development of the genetic markers, supervised and organized the genotyping, and commented on successive drafts of the paper. Dr. Leopoldo Sanchez participated in the project and trial design and establishment, cambium sampling, and project coordination. Dr. Jean-Pierre Rossi participated in cambium sampling, designed and helped in performing the spatial genetic analysis (SGS), and reviewed and commented on successive drafts of the paper. Dr. Sophie Gerber supervised the development of the genetic markers and participated in cambium sampling, trial design and establishment, and project coordination. Sara Marin participated in the trial design and establishment, increment core and cambium sampling, and microdensity preparation and analysis process. Dr. Luc E. Pâques participated in the trial design and establishment and coordination of the research project, reviewed and commented on successive drafts of the paper, and co-supervised Maxime Nardin. Dr. Philippe Rozenberg led the project and trial design and establishment, participated in cambium sampling, reviewed and commented on successive drafts of the paper, coordinated the research project, and co-supervised Maxime Nar...

Tree-ring datasets are used in a variety of circumstances, including archeology, climatology, forest ecology, and wood technology. These data are based on microdensity profiles and consist of a set of tree-ring descriptors, such as ring width or early/latewood density, measured for a set of individual trees. Because successive rings correspond to successive years, the resulting dataset is a ring variables × trees × time datacube. Multivariate statistical analyses, such as principal component analysis, have been widely used for extracting worthwhile information from ring datasets, but they typically address two-way matrices, such as ring variables × trees or ring variables × time. Here, we explore the potential of the partial triadic analysis (PTA), a multivariate method dedicated to the analysis of three-way datasets, to apprehend the space-time structure of tree-ring datasets. We analyzed a set of 11 tree-ring descriptors measured in 149 georeferenced individuals of European larch (Larix decidua Miller) during the period of 1967–2007. The processing of densitometry profiles led to a set of ring descriptors for each tree and for each year from 1967–2007. The resulting three-way data table was subjected to two distinct analyses in order to explore i) the temporal evolution of spatial structures and ii) the spatial structure of temporal dynamics. We report the presence of a spatial structure common to the different years, highlighting the inter-individual variability of the ring descriptors at the stand scale. We found a temporal trajectory common to the trees that could be separated into a high and low frequency signal, corresponding to inter-annual variations possibly related to defoliation events and a long-term trend possibly related to climate change. We conclude that PTA is a powerful tool to unravel and hierarchize the different sources of variation within tree-ring datasets.