occurring at 8-10 year intervals, with an optimum at 1800 m altitude. Severe defoliation decreases the trees’ photosynthetic potential and growth, especially resulting into narrower ring width. We investigated annual-ring time series in order to reconstruct the history of LBM outbreaks between 1963 and 2007 along a larch altitudinal gradient ranging from 1350 to 2300 m, in the Briançon area of the Southeastern French Alps, A comparison of the annual-ring time series measured on the larch host trees with the annual variations in LBM population density estimated by branch samplings in a stand located a few kilometers apart revealed an excellent temporal coincidence between the occurrence of LBM outbreaks and the width of the rings. LBM outbreaks not only affected ring width but also other annual-ring variables, including traits related with sap conduction. Finally, the study of the annual-ring time series along the altitudinal gradient showed a recent altitudinal shift of LBM outbreaks from medium towards higher elevations, over 2000 m. We suggest that this altitudinal shift is a consequence of the variable effect of global warming at the different elevations. Longer and warmer summer improves larch life conditions at the top of the gradient while increased summer drought may have a harmful effect at the bottom. Winter warming is also expected to affect differently the timing of LBM egg hatch and that of larch bud flush, larvae being at present susceptible to emerge whereas no needles are available as food at the former optimal altitude. A better synchronization between larch and LBM may exist at higher elevations. Whether the larch ecosystem will be able to adapt at all points of its altitudinal distribution is still an open question.