Larix decidua altitudinal reciprocal transplant experiment in the French Alps. A preliminary analysis

The ongoing acceleration of climatic change makes it even more urgent to understand how tree seed sources (provenances) respond when growing in climates different from those they are naturally adapted to, either when planted on warmer or on colder sites than the climate that occur at their native distribution site. We evaluated four years of growth, bud phenology and survival of a Larix decidua clonal elevational reciprocal transplant trial in the French Alps, at Villard-St-Pancrace, close to Briançon (LN 44.9°; LE 6.65°). The experiment has four experimental sites, distributed along a north-faced Alpine steep-slope, at contrasting elevations: 2,400, 2,000, 1,700 and 1,350 m a.s.l. On each site, 4 sets of 30 clones were reciprocally planted, with each set originating from adult trees selected in natural forest plots at nearly the same elevations (2,300, 2,000, 1,700 and 1,350 m a.s.l). Results indicate that: (a) Plot populations have lower survival rates when relocated to environmental extremes within the mountain range, whether to colder sites at higher elevations or to warmer sites at lower elevations. (b) Growth also decreases when they are moved to colder (higher elevation) sites, although in general it increases when they are moved to warmer (lower elevation) sites. (c) Such growth pattern might be in part explained by the phenology of the leader bud elongation: by the end of spring, leader buds have already started to elongate at lower elevations, meanwhile they are still in full dormancy at the highest elevational site.