Effects of dams and geomorphic context on riparian forests of the Elwha River, Washington

Abstract

Abstract. Understanding how dams affect the shifting habitat mosaic of river bottomlands is key for protecting the many ecological functions and related goods and services that riparian forests provide and for informing approaches to riparian ecosystem restoration. We examined the downstream effects of two large dams on patterns of forest composition, structure, and dynamics within different geomorphic contexts and compared them to upstream reference conditions along the Elwha River, Washington, USA. Patterns of riparian vegetation in river segments downstream of the dams were driven largely by channel and bottomland geomorphic responses to a dramatically reduced sediment supply. The river segment upstream of both dams was the most geomorphically dynamic, whereas the segment between the dams was the least dynamic due to substantial channel armoring, and the segment downstream of both dams was intermediate due to some local sediment supply. These geomorphic differences were linked to altered characteristics of the shifting habitat mosaic, including older forest age structure and fewer young Populus balsamifera subsp. trichocarpa stands in the relatively static segment between the dams compared to more extensive early-successional forests (dominated by Alnus rubra and Salix spp.) and pioneer seedling recruitment upstream of the dams. Species composition of later-successional forest communities varied among river segments as well, with greater Pseudotsuga menziesii and Tsuga heterophylla abundance upstream of both dams, Acer spp. abundance between the dams, and P. balsamifera subsp. trichocarpa and Thuja plicata abundance below both dams. Riparian forest responses to the recent removal of the two dams on the Elwha River will depend largely on channel and geomorphic adjustments to the release, transport, and deposition of the large volume of sediment formerly stored in the reservoirs, together with changes in large wood dynamics.

Thirty years after Balbina Dam: Diversity and floristic composition of the downstream floodplain forest, Central Amazon, Brazil

“…On one hand, the predictable monomodal flood pulse of the Abacate River and the periodic flooding of its forest at high elevations allowed the establishment of plants with morphological, physiological, and phenological adaptations to flooding (Junk et al, 1989; FIGURE 7 Fisher's alpha diversity in the two areas of Uatumã Sustainable Development Reserve. Thus, the construction of the dam in Uatumã area may have altered the lateral connectivity of the river stretch downstream, reducing seed migration, an important phenomenon that contributes to high habitat diversity in floodplains (Shafroth, Perry, Rose, & Braatne, 2016;Ward & Stanford, 1995;Ward, Tockner, & Schiemer, 1999). SA, adults; SB, saplings; and SC, seedlings.…”

Coastal habitat and biological community response to dam removal on the Elwha River

“…, Shafroth et al. ). The lack of sediment delivery to the coast contributed to altered sediment transport (Miller et al.…”

“…The two dams on the Elwha River had large impacts on downstream habitats because sediment, habitat-forming LWD, and nutrients were sequestered behind the dams , Shafroth et al 2016. The lack of sediment delivery to the coast contributed to altered sediment transport ) and erosion of coastal beaches (Warrick et al 2009).…”

Functional coordination between leaf traits and biomass allocation and growth of four herbaceous species in a newly established reservoir riparian ecosystem in China

“…The original plant communities have been gradually replaced by those dominated by perennial and annual herbaceous species (Fan et al., ; Wang et al., ; Ye, Zhang, Deng, & Zhang, ). Therefore, the detailed knowledge of the eco‐physiological processes underlying their dominance is critical to understanding the community assembly mechanism of this riparian ecosystem, as well as improving restoration practices (Fraaije, Braak, Verduyn, Verhoeven, & Soons, ; Garssen, Baattrup‐Pedersen, Voesenek, Verhoeven, & Soons, ; Shafroth, Perry, Rose, & Braatne, ).…”

“…The original plant communities have been gradually replaced by those dominated by perennial and annual herbaceous species Wang et al, 2012;Ye, Zhang, Deng, & Zhang, 2013). Therefore, the detailed knowledge of the eco-physiological processes underlying their dominance is critical to understanding the community assembly mechanism of this riparian ecosystem, as well as improving restoration practices (Fraaije, Braak, Verduyn, Verhoeven, & Soons, 2015;Garssen, Baattrup-Pedersen, Voesenek, Verhoeven, & Soons, 2015;Shafroth, Perry, Rose, & Braatne, 2016). Jie, Fan, Xie, Zhang, and Xiong (2012) have measured the leaf traits of 42 species in the riparian zone of the Three Gorge Reservoir Area (TGRA) and found that these traits were restricted to the lower-investment and faster-return end of the global leaf spectrum, which are typical characteristics of fast-growing species (Wright et al, 2004).…”