During the last 50 years several changes has occurred in the flora of Oslofjord region. The Crambe maritima populations in the Oslofjord region have increased in size and number, the Eryngium maritimum populations seem stabile, but some populations have disappeared and the Mertensia maritima populations are declining in the region. Parallel environmental changes include increases in temperature and the amounts of nitrogen in the soil and decreased grazing pressure. Such environmental changes might influence habitats and plant life.I preformed germination experiments to test the effect of temperature, light, GA3 and seed coat on germination. Growth experiments were also conducted to study the effect of nitrogen, grazing and three different temperature scenarios (I: 20 °C 10 °C; II: 25 °C 15 °C; III: 30 °C 20 °C) on growth and biomass production of these species under controlled conditions.The germination of C. maritima seeds was enhanced by lower night temperatures, light and removal of the seed coat. There was little germination of M. maritima seeds, and no variables were found to significantly enhance the germination of these seeds. Different simulated grazing treatments on C. maritima had an effect on the morphology of the leaves, but no effect on biomass. The plants that had 25 % of their laminas cut away had shorter laminas and smaller lamina area, than the controls and the plants where 100 % of the laminas were cut away.Nitrogen strongly affected the biomass production of E. maritimum. Plants also had higher biomass when the temperature was 25 °C during the day and 15 °C during the night. Under optimal temperatures, higher nitrogen levels had a positive effect on biomass production. In similar experiments on C. maritima plants were also found to have higher biomass when the temperature was 25 °C during the day and 15 °C during the night and added nitrogen had no effect on biomass production. Higher temperatures and lower grazing pressure might contribute to the observed increase in the C. maritima populations. The E. maritimum populations are declining in the region, while my results show that the growing conditions should be better with higher temperature and more nitrogen. Low seed quality may contribute to the decline of Mertensia maritima populations in the Oslofjord region.