Management of shallow impoundments to provide emergent and submergent vegetation for waterfowl

Abstract

Effects of partial drawdowns, drawdown timing, and tilling on vegetation and seed production for waterfowl were tested in ponds at the Lewisville Aquatic Ecosystem Research Facility in north-central Texas. Vegetation lists, percent cover (PC), and above-ground biomass (AGB) revealed partial drawdowns produced a typical zonation of wetland plants: submergent macrophytes in deep-flooded zones; cattail (7ypha sp.), black willow (Salix nigra), and sedges in shallow-flooded zones; forbs in moist zones adjacent to water; and, grasses in upper, drier zones. Seed production of grasses, sedges, and forbs generally reflected vegetation present in each soil-moisture zone. Taxon richness of emergent plants was highest in dewatered zones. Drawdown timing did not affect taxon richness of emergent plants within dewatered zones, but forb and sedge PC and AGB, and grass AGB, were highest during 1993 spring drawdown. The majority of grasses and forbs had higher seed production during 1992 late-summer/early-fall drawdown, whereas sedges produced more seeds during spring drawdown. Black willow occurred most frequently and cattail was first recorded during spring drawdown. Most submergent macrophytes were unaffected by drawdown timing. Soil disturbance with rototilling created diversity in ponds by increasing taxon richness of emergent plants, encouraging annuals, and discouraging perennials. PC, AGB, and seed production of forbs and grasses generally increased and decreased, respectively, with tilling, whereas sedges were not affected. Cattail and black willow occurred most frequently in tilled areas. Most submergent macrophytes were not affected by tilling, except southern naiad (Najas guadalupensis), with higher PC in tilled plots. Waterfowl visiting ponds utilized regions according to water depth and plant communities. Gadwall (Anas strepera) and American wigeon (A. americans) were most often observed within deep zones supporting submergent vegetation. Although data were not statistically significant, blue-winged teal (A. discors) and green-winged teal (A. crecca) occurred most often in shallow zones supporting emergent vegetation and seeds. Therefore, partial drawdowns, variations in drawdown timing, and soil disturbance, were effective in providing a variety of vegetation and seeds for a diversity of migrant and wintering waterfowl.