Studies of the altitudinal variations in the spruce morphology have shown a decrease in the height of trees of the same age at the highest mountain levels. Other alterations - such as the reduction in the trunk diameter, the length of the annual shoots, the number and size of the needles per shoot, as well as the fall in biomass or the delay in the bud break - would result from a weakening of the activity of the meristems (zones of cell division) linked to the decrease in heat with altitude.