In Europe, the management of semi-natural grasslands is changing steadily in extent and intensity. These changes represent a serious threat to one of the most species-rich habitats in Europe; therefore, the related shifts in species composition should be assessed by means of sound scientific. We describe a new methodology aimed at: (i) quantifying the temporal changes in vascular plant species composition of semi-natural grasslands; (ii) identifying the environmental and management variables that drive patterns of change. Our approach consists of a diachronic analysis based on historical phytosociological data associated with detailed vegetation maps. To describe and test our methodology, in 2013 we re-visited 24 historical plots of Bromus erectus grasslands that were first sampled in 1982. To designate the new sampling sites, we combined the topographic and typological information available for the historical plots with the spatial information of the associated map. The degree of change in species composition was calculated through ordination techniques; multivariate distances were used in a regression analysis to identify the environmental variables responsible for patterns of compositional change. Our worked example demonstrated that species composition has changed significantly in the last 30 years, with patterns that have been substantially influenced by topography and landscape structure. Gospodarjenje s pol naravnimi travišči se v Evropi spreminja po obsegu in po intenzivnosti. Spremembe predstavljajo resno grožnjo enim vrstno najbolj bogatih habitatov v Evropi, zato je potrebno ocenjevati spremembe v vrstni sestavi z znanstveno metodo. Opisujemo novo metodologijo, ki stremi h (i) kvantifikaciji časovnih sprememb v vrstni sestavi pol naravnih travišč ter (ii) opredelitvi dejavnikov okolja in gospodarjenja, ki vodijo v spremembe. Naš pristop temelji na diakronični analizi historičnih fitocenoloških podatkov v povezavi z natančnimi vegetacijskimi kartami. Za opis in preverjanje metodologije smo leta 2013 ponovno obiskali 24 starejših ploskev travišč z vrsto Bromus erectus, mi smo jih prvič vzorčili leta 1982. Za izbiro novih vzorčnih mest smo kombinirali topografske in tipološke informacije, ki so na voljo za starejše ploskve, s prostorskimi informacijami na povezani karti. Stopnjo sprememb vrstne sestave smo izračunali z ordinacijskimi metodami; uporabili smo multivariatne razdalje v regresijski analizi za opredelitev okoljskih dejavnikov odgovornih za vzorec sprememb vrstne sestave. Z našim primerom smo pokazali, da se je vrstna sestava v zadnjih 30 letih značilno spremenila, na vzorec sprememb pa sta bistveno vplivala topografija in krajinska sestava.