BIOMASS DISTRIBUTION IN VEGETATIVE AND RE PRODUCTIVE-ORGANS OF THE EUROPEAN BEECH (FAGUS-SYLVATICA L), ACCORDING TO CROWN SECTOR AND TREE AGE

Resource allocation in plants can be estimated to study biomass distri bution in the various organs during an annual vegetative cycle. Fourte en beech trees were chosen on the Aigoual mountain (Cevennes, France, 44-degrees 20'N, 3-degrees 60'E, alt 1 400 m): 8 were very old trees ( 150 yr), and 6 were vigorous adult trees (100 yr old). The tree crown was divided into upper and lower sectors. Beech produces long (L) and short (C) annual shoots, which are vegetative (V) or both vegetative a nd floriferous. Shoots of each type located on first-order axes in the ramification were analysed to describe the distribution of dry matter among various vegetative and reproductive functions. In each tree, 40 terminal buds were chosen at random: 20 on the upper part of the crow n and 20 on the lower sector; approximately half seemed floriferous. D uring April these buds were enclosed in situ in gauze bags permeable t o pollen and light. The 640 shoots produced from these buds were colle cted during the following November; of these only 524 were in good con dition and were analysed. After desiccation, shoot length (V2L) was me asured and shoot organs were weighed. leaves and stipules (V1), axes ( V2P), buds (V3), female production (R1) and male inflorescences (R2). Development strategies vary according to tree age, tree sector and sho ot type. Vegetative functions are favoured in long shoots of the young est trees particularly in the upper sector (except V1). In short shoot s, biomass is also more important in the upper crown sector. There was no biomass difference in hermaphrodite shoots according to the sector . But the age effect is considerable: female acquisitions are much gre ater in old trees (p < 0.001), whereas male acquisitions tend to be a little lower (p < 0.05). There are great differences in vegetative bio mass according to shoot type, but, in hermaphrodite shoots there are f ew differences in reproductive functions according to age and sector. Biomass allocation (% of the shoot biomass) is often different accordi ng to tree age: (i) female allocation in hermaphrodite shoots is much greater in the oldest trees, whereas it is the opposite for vegetative functions, and (ii) vegetative long-shoot allocation is greatest for the V1 function in old trees, whereas vegetative short shoot allocatio n is very high for the V1 function whatever the age (this confirms the ir essential role in exploiting the environment). There are significan t positive biomass correlations in vegetative functions, above all in long shoots. Concerning biomass allocations, correlations among vegeta tive functions vary according to age and shoot type. Generally, there is a negative correlation between female allocation and the various ve getative allocations. All these results show. (i) a partial developmen t of each shoot type, (ii) a synergy between vegetative functions in h ermaphrodite shoots (biomass and allocations), whereas a strong compet ition appears for allocations principally between female and vegetativ e functions, and (iii) a tree age effect: in 100 yr-old trees, vegetat ive development is still very important, principally at the upper part of the crown. In very old trees, vegetative development tends to beco me stable and female function is preponderant