HERB LAYER VEGETATION OF SOUTH SWEDISH BEECH AND OAK FORESTS - EFFECTS OF MANAGEMENT AND SOIL ACIDITY DURING ONE DECADE

Effects of forest management and soil acidity on herb layer vegetation were studied after 10 years on 190 permanent plots in south Swedish b eech (Fagus sylvatica) and oak (Quercus robur) forests. Species richne ss generally increased with management intensity, mainly due to establ ishment of ruderal species from the seed bank. Species richness of the typical forest flora was unaffected by management. Moderate managemen t of oak stands favoured several species which are commonly found in s emi-natural pastures. Classification and ordination of the data showed that the main floristic gradient within Swedish beech and oak forest vegetation is related to soil acidity. Species richness of the typical forest flora was strongly positively correlated with soil pH in beech forests, but this correlation was weaker in oak forests. The number o f herbaceous plants with a broader habitat range increased with pH onl y in the oak forest plots. Long term changes in the forest environment , which may affect the vegetation, are the decline of grazing 150-50 y ears ago and soil acidification mainly caused by atmospheric pollutant s during the last 50 years. In the one-decade perspective of this stud y, however, we did not find a general vend towards a more acid-toleran t flora. Neither could we find a general decrease of pasture species i n currently ungrazed oak stands. The results indicate that most typica l forest plants are well adapted to and partly depend on occurrence of canopy gaps and soil disturbance. If canopy thinning is followed by p eriods of canopy closure the characteristic shade tolerant flora of Sw edish beech and oak forests may be able to persist as long as soil che mical limits of existence are not exceeded.