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.
Primary succession in coastal sand dunes: is there facilitation?
Martinez, Luisa1, 1
ABSTRACT- An understanding of natural successional processes is needed to restore and preserve coastal sand dunes which, worldwide, are usually severely degraded ecosystems. Facilitation is predicted to occur in dunes as these ecosystems have the harsh physical conditions common during primary succession. I tested for the existence of facilitation in tropical coastal sand dunes by analyzing: spatial relationships and associations of early and late colonizers; by measuring environmental amelioration; and by monitoring seedling survival. In the Gulf of Mexico, a relatively small area (31% of a large mobile dune) was covered by the nurse shrub (Chamaecrista chamaecristoides), however the occurrence of both seedlings and adults of late colonizers (Trachypogon plumosus, Triplasis purpurea, Schizachyrium scoparium and Pectis saturejoides) was positively associated with this shrub. The density and frequency of these species were higher beneath the shrub than out in the open, while the mean distance to the closest shrub was always significantly smaller than expected by chance. Midday temperatures, wind speed and sand accretion were significantly reduced beneath the shade of shrubs, although soil conditions (water and nutrients) were not significantly altered. Seasonal fluctuations did not modify these results. Experimentally introduced seedlings only survived and established successfully beneath the shrubs. With few exceptions, previous studies suggest that similar trends are present in temperate sand dunes. These results suggest facilitation as an important natural process for regeneration in coastal dune environments.
KEY WORDS: facilitation, succession, coastal sand dunes, Gulf of Mexico