PARENT SESSION
Oral Session #88: Wetland Ecology.
Presiding: K. Ewel
Thursday, August 8. 1:00 PM to 3:45 PM. Gila Meeting Room, TCC.

Regional spatial patterns of seed banks of bald cypress swamps at the northern extreme of the Mississippi Alluvial Valley.

MIDDLETON, BETH^*,1, ¹ National Wetlands Research Center, USGS, Lafayette, LA

ABSTRACT- The geographic boundaries of the species of baldcypress swamp in the northern extreme of the Mississippi Embayment are likely maintained by a combination of dispersal and physiological limitations, the configuration of the watershed, and anthropogenic disturbance. This study examined the role of dispersal by examining directional trends of deposition as indicated by the regional distribution of the species in seed banks across the Cache River watershed, Illinois. Geostastical analysis indicated that most species had distribution patterns that fit anisotropic models with the directions of the principal axes to the southeast (135-159^o). Forces that underlie directional patterns in distribution can sometimes be identified at approximately 45^o angles to the anisotropic principal axis. Similarly, dispersal routes along the Cache River for the majority of aquatically dispersed species of baldcypress swamps are predominantly east/west with the flow of the water. The spatially structured variance (C/(C_o + C) described by the anisotropic models over the distances examined were 26-67%. Kriged maps of species distribution showed that species had higher densities of seeds in the seed banks in the northern or central portions of the Cache River watershed, than in the southern part, except for Xanthium strumarium. Fragmentation of species distribution in the seed bank was apparent for all species examined including Ammannia auriculata, A. coccinea, Cephalanthus occidentalis, Cyperus erythrorhizos, Nyssa aquatica, and Taxodium distichum, Penthorum sedoides, and X. strumarium. Because the boundary is likely to be maintained at least in part by the direction of the flow of dispersal in the watershed, it is likely that the regeneration and establishment of the species of baldcypress swamps upstream of current locations will be limited in the event of global climate change.

KEY WORDS: boundary dynamics, regeneration dynamics, spatial ecology, baldcypress swamp