Case Study :
Ecological Research on European Buckthorn (Rhamnus cathartica)
Dr. Liam Heneghan, Professor of Environmental Science at DePaul University
Rhamnus cathartica in the Chicago Wilderness
R. cathartica, described as a small tree or shrub, is a dominant invader in woodlands throughout the residual woodlands of northeastern Illinois. The control of R cathartica is the typical prelude to restoration of these woodlands (Gourley et al. 1984.; Boudreau et al. 1992). It is clear that R cathartica has a substantial impact on the light regimes of the woodlands that it invades, and that the extended seasonal longevity of R. cathartica leaves gives it the advantage of exploiting high light levels early in the season prior to canopy leaf-out (Harrington et al. 1989). Thus the physical removal of the shrub (typically mechanical removal of the aboveground portion followed by chemical treatment (Archibold et al. 1997)) is undertaken to restore light gradients in invaded habitat. Such management may thereby positively affect understory plant diversity (Knight et al. 2005). However, it is also obvious that there is a chronic problem with reinvasion by R. cathartica which impedes restoration (Heneghan, personal observation). It is important to consider the possibility, therefore, that R. cathartica invasion imposes a persistent impact on soil physical and biological properties in a manner observed for a variety of other invasive shrubs (Ehrenfeld 1997; Ehrenfeld et al. 2001; Kourtev et al. 2002; Ehrenfeld 2003; Rice et al. 2004). If this is the case, managed woodlands may retain modified ecosystem properties that constrain the success of subsequent restoration. That is, an invasion may shift the ecosystem into a relative persistent modified state that is not easily repaired in the absence of specialized intervention (Suding et al. 2004)
Rhamnus cathartica and the modification of soil ecosystems properties
We review the results of a number of recent replicated observations and experimental studies that demonstrate that R. cathartica is indeed associated with significant modifications to a variety of ecosystem properties in an urban woodland. I discuss several of these impacts, and conclude with a summary of the implications for future management.
To read more, click the link below to view the entire article in a pdf document.
Liam
Heneghan
Biography
Liam Heneghan is an ecosystem ecologist currently working at DePaul University where he is a Professor in the Environmental Science Program. His research has included studies on the impact of acid rain on soil foodwebs in Europe, and on inter-biome comparisons of decomposition and nutrient dynamics in forested ecosystems in North American and in the tropics. Recently, Heneghan and his students at DePaul have been examining the impacts of invasive species on nutrient cycling and soil organisms in Midwestern woodlands. Heneghan is co-director of DePaul University ' s Institute for Nature and Culture and is co-chair of the Science Team with Chicago Wilderness .