The influence of hydrological regimes on sex ratios and spatial segregation of the sexes in two dioecious riparian shrub species in northern Sweden

Abstract

River management practices have altered the hydrological regimes of many rivers and also altered the availability of regeneration niches for riparian species. We investigated the impact of changed hydrological regimes on the sex ratios and the Spatial Segregation of the Sexes (SSS) in the dioecious species Salix myrsinifolia Salisb.-phylicifolia L. and S. lapponum L.by studying the free-flowing Vindel River and the regulated Ume River in northern Sweden.We surveyed sex ratios of these species in 12 river reaches on the Vindel River and in 17 reaches on the Ume River. In addition we surveyed the sex and location above mean river stage of 1002 individuals across both river systems to investigate the SSS of both species.Cuttings were collected from male and female individuals of S. myrsinifolia-phylicifolia from both rivers and subjected to four different water table regimes in a greenhouse experiment to investigate growth response between the sexes. We found an M/F sex ratio in both river systems similar to the regional norm of 0.62 for S. myrsinifolia-phylicifolia and of 0.42 for S.lapponum. We found no evidence of SSS in either the free-flowing Vindel River or the regulated Ume River. In the greenhouse experiment, hydrological regime had a significant effect on shoot and root dry weight and on root length. Significantly higher shoot dry weights were found in females than in males and significantly different shoot and root dry weights were found between cuttings taken from the two rivers. We concluded that changed hydrological regimes are likely to alter dimensions of the regeneration niche and therefore to influence sex ratios and SSS at an early successional stage, making it difficult to find clear spatial patterns once these species reach maturity and can be sexed.2

Hydrologic linkages between a climate oscillation, river flows, growth, and wood Δ13C of male and female cottonwood trees

“…; Ueno, Suyama & Seiwa ; Hughes et al . ). The prior studies are fairly consistent in indicating that males are more prevalent in higher and drier positions and better adapted to drought, while females are often more abundant and display superior performance in lower and wetter environments (Hultine et al .…”

Projected changes in plant species richness and extent of riparian vegetation belts as a result of climate‐driven hydrological change along the Vindel River in Sweden

“…, 2008), with important intraspecific variation among populations (De Carvalho et al. , 2008) or between sexes (Hughes et al. , 2010; Nielsen et al.…”

Responses of riparian guilds to flow alterations in a Mediterranean stream

“…; Polzin & Rood ; Lytle & Merritt ; Birken & Cooper ; DeWine & Cooper ; Hughes et al. ; Merritt & Poff ). Nevertheless, species‐based knowledge reveals only part of the ecological consequences of flow alterations; moreover, because of the large number of plant species along rivers around the world, it is impossible to assess the impacts on all species.…”