PARENT SESSION
Oral Session #62: Vegetation change: Succession, recovery, facilitation. Presiding: S. Franklin.
Thursday, August 9, 2001. 8:00 AM to 12:00 PM. Hall of Ideas G.
Acer platanoides invasion in the Northern Rocky Mountains—facilitation of exotic seedlings by overstory conspecifics.
REINHART, KURT1, MAESTRE, FERNANDO2, CALLAWAY, RAGAN1, 1 2
ABSTRACT- Positive interactions between plant species are known to be important in structuring plant communities. Our observations suggest that conspecific facilitation may promote the spread of Acer platanoides. We monitored the demography of Acer seedlings at 6-m intervals radiating from a patch of mature conspecific trees established in Pseudotsuga-dominated forest. Seedling densities were much greater in and near the parental patch. Recruitment and survival of Acer seedlings also appeared to vary with distance from the parental patch. Leaf water potentials were significantly lower for seedlings outside the parental patch than inside the patch, and fluorimeter measurements (Fv/Fm at predawn and midday and 
F/F'm at midday) demonstrated that seedlings within the parental patch were less photoinhibited than seedlings outside of the patch. Experiments at other sites suggest A. platanoides seedlings have enhanced growth when located beneath conspecifics, while Populus trichocarpa and Pinus ponderosa seedlings have increased growth when beneath Populus. Our results suggest that A. platanoides seedlings are physiologically more stressed outside the parental patch and that the invasion of Acer into western forests may be enhanced by an overstory of conspecifics.
KEY WORDS: conspecific facilitation, positive interactions, Acer platanoides, biological invasion