Leaf phenology and seasonal carbon gain in the invasive plant, Bunias orientalis L.

In two potentially competing herbaceous plants, the invasive Bunias orienta lis L. (Brassicaceae) and the native Picris hieracioides L. (Asteraceae), s easonal changes in leaf CO2 gas exchange and plant growth were studied over an entire growing season from February 1998 to December 1998 in two experi mental fields. The study was motivated by the hypothesis that pre-adaptive phenological displacement of alien species relative to the native flora may be an important reason for the observed expansion of B. orientalis in cent ral Europe. We quantified the importance of phenological differences for an nual carbon gain in both species by estimating total leaf carbon gain from the results of leaf CO2 exchange and changes in plant leaf area. Bunias ori entalis achieved almost half of its annual carbon gain in the time between early September and December, when competition for light by other species, like P. hieracioides, is low. Our quantitative approach corroborates the no tion that the phenological shift of a relatively poor competitor, such as B . orientalis, could be of great importance for the success as an invasive s pecies.