Changes in the canopy structure of the Mediterranean shrub Lavandula stoechas after disturbance

This study attempts to show the dynamics of the canopy structure of the Med iterranean pioneer shrub Lavandula stoechas after man-made perturbation (i. e, grazing). The development of the vertical structure of the shrub was stu died by harvesting the canopy of plants of 2-6 yr old in horizontal layers. The supportive biomass of the canopy was concentrated near the base at all ages. Leaf biomass was evenly distributed all over the vertical profile in 2- and 3-yr old plants. In 4-yr old plants it presented a maximum near the top of the canopy. For 5-yr old plants a structural transition started wit h leaf profiles showing a bimodal distribution. Leaf biomass predominated n ear the base in 6-yr old plants, suggesting that the transition was complet ed. Three canopy stages in the growth processes of the plant were recognized af ter the first year of growth: in the first one (from 2 to 3 yr old) both le af and supportive biomass increased; in the second one (from 3 to 4 yr) lea f biomass remained stable and there was an increase in supportive biomass u ntil the plants reached a 'mature stage', in 4-yr old plants; finally, in 5 - and 6-yr old plants there was a decrease both in leaf and supportive biom ass and plant structure showed evidence of senescence. Early transitions fr om seedling to l-yr old plant and from this to 2- to 3-yr old plants were l ess obvious. The leaf/supportive biomass ratio always decreased with plant age, from 1.8 8 in seedlings to 0.01 in 6-yr old plants. Biomass density followed the pat tern of supportive biomass, with an increase from 1.7 g/dm(3) (2-yr old pla nts) to 2.4 g/dm(3) (4-yr old plants). Thereafter, biomass density decrease d to 0.6 g/dm3 (6-yr old plants).