The spatial and temporal vegetative dynamics at Mentor Marsh between 1796 and 2000 A.D. are assessed in a landscape history of the region, an ecological synthesis detailing the effect of change in environmental stress within the marsh basin, and a preliminary model using fuzzy logic. A conceptual model or methodology is developed to guide the application of the Gleasonian individualistic concept of vegetative dynamics in the analyses of vegetative-landscape systems. The ecological synthesis links the individualistic concept of vegetative change to ecological system dynamics over time and space by using information identified in the landscape history of the site. The model utilizes fuzzy rule-based modeling to further distill the results of the landscape history and ecological synthesis to produce a more concise and predictive means of addressing vegetative change at Mentor Marsh and to suggest future site research and conservation and restoration strategies.
The landscape history of the Mentor Marsh area provides information on changing land use paradigms between 1796 and 2000 A.D. Land use paradigms shifted from movement between hunt and harvest during Native American use of the area to individual property ownership and control established during the beginning of European American settlement. A more recent shift in land use paradigms in the area is characterized by ecosystem management, which emphasizes conservation of natural areas and sustainable land use practices. Population density between 1796 and 2000 A.D is estimated to have increased from 0.25 to 980 persons per square mile in Lake County, where Mentor Marsh is located. The landscape history shows the linkage between agricultural, commercial, and industrial development in the area and changes in the spatial and temporal distribution of vegetative communities at Mentor Marsh. Four environmental stresses were identified in the research of the landscape history: flood stress, salt stress, fire disturbance, and shade stress.
The ecological synthesis shows the influence of both long-term climate change and anthropogenic modifications to hydrologic control points on flood stress, which has affected the vegetative dynamics of the site. Analysis of the long-term record of average annual Lake Erie water levels and annual precipitation for the region, including 5-year running averages, shows a pattern of climate change characterized by extended periods of high flood stress and low flood stress affecting the spatial and temporal distribution of wetland plant community types within the marsh basin. Beach accretion, owing to the development of Fairport Harbor in the early to mid-1800s, dammed the stream that drained the eastern basin in 1796. This caused increased flood stress in the eastern basin. Development of Mentor Harbor in the western basin in the 1920s caused the greatest loss in open marsh habitat during the period of study. Activities associated with commercial and industrial development in the watershed of Mentor Marsh led to catastrophic salt intrusions into the marsh basin between 1959 and the late 1970s causing dramatic vegetative change throughout the marsh basin including the loss of large areas of swamp forest followed by the invasion of Phragmites australis (Cav.) Steudel. Water salinity varied from oligosaline (500 to 5,000 mg/L) to hypersaline (40,000 mg/L and above) conditions between 1969 and 1997. Criteria for assessing water salinity hazard for the marsh basin were developed and applied, revealing the spatial and temporal distribution of water salinity within the marsh basin in relation to plant species salt tolerance. The results show salt pollution was adequate to cause the shifts in wetland plant community type that occurred during this time period. Fire disturbance has been a major factor in recent years. The historical record shows no indication that fire disturbance played a role in the vegetative dynamics at Mentor Marsh until Phragmites became the dominant wetland plant within the marsh basin in the 1970s. Since 1979, nine major fires have occurred, with an average return interval of approximately 3 years. Analysis of plant species tolerance to fire disturbance show that frequent and intense fires favor the proliferation of Phragmites and hamper the recovery of remnant swamp forest along ecotone areas within the marsh basin. Shade stress is discussed as the primary mechanism facilitating the expansion of swamp forest into Phragmites dominated areas.
A preliminary model of vegetative dynamics at Mentor Marsh used fuzzy rule-based modeling techniques to represent the interaction between changes in the four environmental stresses and change in percent cover of wetland plant community types between 1796 and 2000 A.D. The model was constructed to predict shifts in wetland plant community type in response to changing environmental site conditions. Predicted values of wetland plant community type percent cover were useful to derive the dominant wetland plant community type and changes in its relative abundance in response to changes in flood stress, salt stress, fire disturbance, and shade stress. Future refinements to increase the models predictive capabilities are suggested including its linkage to a comprehensive GIS for the site for assessing spatial distribution of wetland plant community types over time. Future research to facilitate model refinement are also suggested, including comprehensive hydrologic monitoring and soil salinity mapping.
Implications of this research for decision-makers and managers for Mentor Marsh are discussed including suggestions for future research, site monitoring, and restoration strategies. Fire control strategies, monitoring and control of salt pollution sources, groundwater and surface water monitoring programs, and restoration of historically importance features of the marsh are discussed including restoration strategies for swamp forest, additional wetland areas, and stream channels.