Recovery status of a cypress (Taxodium distichum)-water tupelo (Nyssa aquatica) wetland seven years after harvest disturbance
Zaebst, Thomas Winter
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Research documenting the functional changes of wetlands in response to harvest disturbance has often been limited to initial-response time frames of one or two years. A cypress (Taxodium distichum L. Rich.)-water tupelo ~ aQuatica L.) swamp located in the Mobile-T ensaw River Delta of Southwestern Alabama was harvested in the fall of 1986. Harvest treatments included: c1earcutting the entire study area with helicopter log removal, or with an added simulated rubber-tired skidder transport, or with herbicide control of all regenerating vegetation. An adjacent nondisturbed stand served as a reference area. Remeasurement of the area was initiated seven years after harvest. The helicopter logged and skidder simulation treatments have produced stands of comparable diameter, height, density, and basal area. ~ aqyatica was dominant in the skidder simulation treatment~ ~ tica, ~ nigra, and Fraxinus caroliniana dominated the helicopter treatment. Overstory biomass was less in the helicopter logged areas (20,981 kg/ha) than in the skidder simulation treatment (30,533 kglha). Lowerstory trees in both treatments were of comparable diameter and height, however, the helicopter treatment contained a greater density, basal area, and biomass ofFraxinus caroliniana. The rutting and mounding associated with the skidder simulation treatment favored a greater diversity of both diversity of both lowerstory and herbaceous species. Groundflora biomass was greatest in the herbicide controlled treatment (13,127 kg/ha), comparable in both the helicopter logged and skidder simulation treatments (5128 kg/ha; 5648 kglha, respectively), and least in the reference area (1495 kglha). Sediment accumulation reflected these differences in groundflora biomass; 104 mm in the herbicide controlled treatment, 79 mm and 63 mm in the helicopter logged and skidder simulation treatments, respectively, and 37 mm in the reference area. Three gradients were identified in the study areas via the tests of Latin squares, rows, and columns which actually corresponded to gradients of hydrology and! or sediment deposition. Square two was wetter than squares one or three because square two had fewer residual pullboat runs, which facilitate greater water movement. The rows are indicative of the distance from the main river channel; rows nearer the river are slightly higher in elevation, less inundated, and favor the less flood tolerant species. The columns reflect the sediment trapping patterns of the vegetation and the subsequent effects of site hydrology and nutritional status.
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