| Description: |
Human impacts have degraded riverine environments worldwide. In south‐eastern Australia, livestock grazing and non‐native Salix spp. (Willow) infestations throughout riverine environments commonly degrade instream conditions on which instream plants rely. However, the effects of livestock grazing and Salix spp. infestations on instream plants remain uncertain. We investigated the responses of two submerged and two emergent instream plant species to different levels and combinations of simulated grazing and shading. In a glasshouse experiment, we tested the response of Cycnogeton procerum, Juncus usitatus , Schoenoplectus tabernaemontani , and Vallisneria australis to combinations of clipping (simulated grazing) and shading (low (30%) and high (90%)) over a 14‐week period. Plant length, above‐ and below‐ground biomass, and vegetative output were measured in response to the different treatments. Most plants recovered in length following clipping, except V. australis , while shading either had minimal effects or increased plant length. Clipping reduced biomass for all species, while shading produced varying effects on above‐ and below‐ground biomass. S. tabernaemontani and V. australis tended to have reduced rates of new leaf/stem production under clipped or high shade conditions. The combined effects of clipping and high shade on J. usitatus led to plant death. Our results show that clipping and shading can change the growth characteristics of instream plants, leading to general declines in plant fitness and in some cases, plant death. Although some species may tolerate clipping and low shading, the long‐term effects of grazing, high shading, and combinations of the two are likely deleterious. Our study provides support for restoration efforts involving livestock exclusion and non‐native Salix spp. removal from waterways. |