INTRODUCCIÓNEn varias comarcas de la depresión prelitoralcatalana se ha venido observando desde principios de la década de los años setenta, una progresiva transformación de la ocupación del suelo . El abandono de tierras de labor ha sido el elemento de mayor significación yen la actualidad los campos abandonados ocupan una parte no despreciable del territorio de dichas comarcas, espe_ cialmente en el Valles Occidental .
Inula viscosa is a shrub that colonize abandoned arable lands and becomes the most conspicous species of this kind of habitat in some parts of Catalunya. The individuals of this species are composed of several cohorts of branches which grow up from the stumps every year.
The changes and tranference of biomass between the components : alive biomass, dead biomass, current growth and shed meterial were estimated in a field of 6 years from 1975 to 1978. The dead biomass component increased from 300 g.m.-% to 1000 g.m. ~2 but, conversely, the alive biomass com ponent decreased from 700 g.m.~ % to 250 g.m. The current growth chaged from 227 g.m. year'l in 1976 to 139 g.m . year~l in 1978. The biomass and current growth in a younger field (2 years old ) were 534 g.m." % and 492 g.m.~ 2 y~ � respectively.
The data suggested the following model of development : these populations attain a rough ly constant level of biomass within the 2-3 years of colonization, reach maturity when they are 6-7 and become declining at ages of around 8-10 years. The biomass composition of individuals during the transition to the declining stage showed a dramatic chage and only some of the younger cohorts of branches persisted alive. The causes which induced the decline are unknown and several candidates are discussed briefly.
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