Glossy buckthorn (Rhamnus frangula) is a shrub or small tree which is a native of Eurasia, introduced to North America about the mid-nineteenth century. Escaped from cultivation, Rhamnus frangula is rapidly becoming a serious pest in certain kinds of wetland habitats and has been in the Cedarburg Bog for at least the last thirty years. Glossy buckthorn is most dense in the string bog, the most unique vegetation type in the Bog. Since 1968, the string bog population of Rhamnus frangula has been growing logarithmically at a rate which doubles the population size in less than 4 years. Individual shoots also grow (accumulate woody biomass) logarithmically. The rate of growth of woody dry weight decreases, however, at 11 - 12 years of age, the age at which shoots attain the height of the string bog canopy. As they reach the canopy, shoots become more branched, allocate less biomass to wood, and allocate more biomass to leaves and probably to fruits. The estimated rate of accumulation of R. frangula woody biomass density has also been logarithmic, with a present density of 610 g/m2. If the current rate of woody biomass accumulation continues as expected, by 1993 the woody strings of the string bog will contain 2.2 kg/m2 of R. frangula wood. Light intensity in the strings will decrease markedly as shading by R. frangula increases. At present, there appears to be no hope of controlling the spread of glossy buckthorn on a Bog-wide basis, although it could be removed and then excluded from certain selected areas. A long term research project is required to document the effect of R. frangula on the native vegetation. Its effect on the string bog is expected to be catastrophic.
Reinartz, J.A. and J. Kline. 1988. Glossy buckthorn (Rhamnus frangula), a threat to the vegetation of the Cedarburg Bog. 21(2): 20-35.