A review of cattle grazing effects on lake margin vegetation with observations from dune lakes in Northland, New Zealand. 

C C Tanner 

1992 

 

 

Article in journal 

Lake margin vegetation has become incrasingly valued as a habitat for wildlife and as a moderator of sediment and nutrient inputs from surrounding catchments. This has encouraged action to exclude livestock from lake shorelines. Cattle grazing effects are reviewed in relation to natural grazing of lake margin vegetation. Direc consumption and trampling of plant biomass by livestock affects the structure, diversity, productivity, succession and nutrient dynamics of plant communities. In addition, livestock grazing may affect lake marginal vegetation and water quality by pugging and erosion of lakeshores, nutrient addition, bacterial contamination and promotion of weed invasion. Agricultural modifcation of surrounding catchemtns also causes many indirect effects such as increased nutrient runoff and changed hydrological regimes. However, low levels of grazing can result in benefical changes in lake margin vegetation by reducing comination by tall rank species and incrasing plant and habitat diversity. Observations of cattle grazing impacts on the lake margin vegeation of Northland dune lakes howed a graded range of effects dependant largely on grazing pressure. Ungrazed, agriculturally undeveloped shorelines were characterised by <i>Leptospermum scoparium</i> growing to the wetted margin, grading into an inshore zone of mixed sedges. At sites subject to heavy grazing pressure inshore sedge communities were absent, leaving only a remnant outer zone of emergent <i>E. sphacelatea</i> inwater too deep to graze. Sites with light to moderate grzing pressure wre associated with more open inshore sedge zones showing an incrased diversity and abundance of short shallow-water species including <i>Myriophyllum, Potamogeton, Lilaeopsis, Juncus</i> and <i>Triglochin spp</i>., and in some areas the endangered species <i>Hydatella inconspicua</i>. It is concluded that although heavy grazing of lakeshores is clearly detrimental to marginal vegetation, low levels of grazing may be an appropriate management tool in areas of some lakes to promote more diverse inshore habitgats for plants and wildlife 

 

Biogeophysical--grazing effects--aquatic plants--native vegetation--endangered plants--lake management--wildlife management--dune lakes--northland, NZ.