Disturbance and regeneration of swamp forests in Nicaragua: Evidence from ecology and paleoecology.

In October 1988, Hurricane Joan struck the Caribbean Coast of Nicaragua, severely damaging 100,000 hectares (ha) of tropical swamp forest. In the following dry season, 90,000 ha of the hurricane-damaged swamp forest burned and most trees were killed. In 1992, I began studying the regeneration of these severely damaged swamps, located just to the west of Bluefields, Nicaragua. My research included: (1) natural history of the relatively unknown swamps; (2) interactions between a common palm, Raphia taedigera Mart. (Arecaceae) and the pioneering fern, Blechnum serrulatum Rich. (Pteridophyta-Blechnaceae); (3) autecology of seeds and seedlings of hardwood trees; and (4) swamp paleoecology. I censused R. taedigera populations and studied the effects of R. taedigera and artificial shade on B. serrulatum to determine if R. taedigera is likely to exclude B. serrulatum over time. The R. taedigera palms were growing rapidly, and B. serrulatum showed many signs of being shade-intolerant. Thus it appears that the larger R. taedigera palms will eventually shade out the ferns. However, when B. serrulatum no longer inhibits colonization by tree seedlings, the hardwood species will still face the difficulties of germinating and establishing in a seasonally flooded environment. To understand their responses and tolerances to flooding, I subjected both seeds and seedlings to various treatments to simulate flooding. Germination and survival varied among species. However, the same species that germinated in water could also survive submersion as seedlings and proved flood tolerant, whereas other species failed in both regards and were flood intolerant. To explore the role of disturbance in the past, I conducted paleoecological studies by examining the fossil pollen of a 5.0 m sediment core from a lagoon at the center of the swamp. The pollen spectrum changed radically at about 8,000 years before present (BP), indicating the formation of the swamp as sea levels rose due to melting of polar ice. At 3300 BP, X-rays revealed a sand layer indicative of a hurricane. Shortly after this prehistoric hurricane, there were charcoal fragments and abundant B. serrulatum spores. Forest regeneration was set back by repeated fires after the hurricane. Future regeneration therefore probably requires a combination of lack of fires, growth of R. taedigera palms, and colonization by flood-tolerant hardwood species.Ph.D.Biological SciencesBotanyEarth SciencesEcologyPaleoecologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/130857/2/9811211.pd